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NEGATIVE PRESSURE WOUND THERAPY

Wound Vac System

JASSIN M. JOURIA MD

Dr. Jassin M. Jouria is a practicing Emergency Medicine physician, professor of academic medicine, and medical author. He graduated from Ross University School of Medicine and has completed his clinical clerkship training in various teaching hospitals throughout New York, including King’s County Hospital Center and Brookdale Medical Center, among others. Dr. Jouria has passed all USMLE medical board exams, and has served as a test prep tutor and instructor for Kaplan. He has developed several medical courses and curricula for a variety of educational institutions. Dr. Jouria has also served on multiple levels in the academic field including faculty member and Department Chair. Dr. Jouria continues to serve as a Subject Matter Expert for several continuing education organizations covering multiple basic medical sciences. He has also developed several continuing medical education courses covering various topics in clinical medicine. Recently, Dr. Jouria has been contracted by the University of Miami/Jackson Memorial Hospital’s Department of Surgery to develop an e-module training series for trauma patient management. Dr. Jouria is currently authoring an academic textbook on Human Anatomy & Physiology.

ABSTRACT

Vacuum-assisted drainage has been used in surgical applications for many

years, but only recently has this concept been applied to healing. Known as

negative pressure wound therapy, the use of vacuum-assisted drainage to

reduce edema and increase blood flow has proven beneficial for many

patients with different types of wounds and injuries. Some wounds treated

with a vacuum-assisted drainage have healed in less than half the standard

time, a strategy that has been beneficial to both patients and medical

clinicians alike.


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Policy Statement

This activity has been planned and implemented in accordance with the

policies of NurseCe4Less.com and the continuing nursing education

requirements of the American Nurses Credentialing Center's Commission on

Accreditation for registered nurses. It is the policy of NurseCe4Less.com to

ensure objectivity, transparency, and best practice in clinical education for

all continuing nursing education (CNE) activities.

Continuing Education Credit Designation

This educational activity is credited for 3.5 hours. Nurses may only claim

credit commensurate with the credit awarded for completion of this course

activity.

Statement of Learning Need

Clinicians require special education and training of the wound types and

complications associated with the different wounds, as well as the benefits of

negative pressure wound therapy to promote healing. The basic concepts of

wound therapy, of wound cleaning, exudate, granulation tissue and dressing

management, are necessary continuing competency requirements for

clinicians involved in acute and chronic wound care at all levels of hospital

and outpatient care.

Course Purpose

To provide health clinicians with knowledge about wound types, wound care,

and the application and benefits of negative pressure wound therapy.


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Target Audience

Advanced Practice Registered Nurses and Registered Nurses

(Interdisciplinary Health Team Members, including Vocational Nurses and

Medical Assistants may obtain a Certificate of Completion)

Course Author & Planning Team Conflict of Interest Disclosures

Jassin M. Jouria, MD, William S. Cook, PhD, Douglas Lawrence, MA

Susan DePasquale, MSN, FPMHNP-BC – all have no disclosures

Acknowledgement of Commercial Support

There is no commercial support for this course.

Please take time to complete a self-assessment of knowledge, on page 4, sample questions before reading the article.

Opportunity to complete a self-assessment of knowledge learned will be provided at the end of the course.


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1. With negative pressure wound vacuum systems,

a. suction should be intermittent, never constant. b. the patient should not be able to feel the suction. c. suction may be constant or intermittent. d. the suction system is, by definition, uncomfortable.

2. True or False: In comparison to traditional forms of wound

bandages, which may require dressing changes every 2 to 3 days, negative pressure dressings are typically changed every day.

a. True b. False

3. Negative pressure wound therapy with irrigation

a. promotes granulation tissue formation. b. can treat traumatic wounds but not necrotizing fasciitis. c. is designed to be used on a constant basis. d. is used in lieu of surgical debridement.

4. A coating of protective ointment or ______________ dressing

may be applied to the skin to shield and protect it.

a. hydrocolloid b. saline c. bacitracin d. polyhexanide

5. The filler material used in negative pressure wound therapy

systems

a. is placed over the drain system. b. is cut to fit over the periwound skin. c. consists of hydrocolloid or foam. d. is placed in the wound bed.


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Introduction

Negative pressure wound therapy is used to improve the rate of healing of

wounds. Negative pressure wound therapy will help a wound heal at a faster

rate than those using traditional therapy. It may reduce hospital stays,

reduce incidences of surgical site infections, and healthcare costs. Before

applying a negative pressure wound vacuum system, it is essential for health

clinicians to first understand the recommended technique for varied types of

wounds, and which wounds are most likely to respond to negative pressure

therapy. Some negative pressure systems for wound healing have added

components that may make applying the type of product a bit more

complicated. For example, some negative pressure systems that use

instillation require separate tubing and administration of prescribed solutions

to the wound. The mechanisms of use, such as whether to apply intermittent

or continuous pressure or the most appropriate type of filler material to use

are also important aspects of negative pressure administration. Specific

situations that call for some of these systems may require additional clinical

training on how to correctly apply and use the negative pressure system,

and to understand which type of system is appropriate for use with different

wounds.

Negative Pressure Wound Therapy Models

Despite some of the differences in NPWT models available by manufacturers,

most negative pressure systems have many of the same components. This

often includes foam or filler material that is placed in the wound bed, a

covering that protects the filler and that is attached to the rest of the system

through a tubing set, and then a machine that provides gentle suction from

the wound through the connected tubing. There is typically a canister or

container also connected to the system, which collects excess fluid and

drainage that the suction has pulled from the wound.


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Variations arise in relation to the wound type. A patient with an infected

venous stasis ulcer may need negative pressure wound therapy (NPWT) with

instillation of antibiotic solution, while another individual preparing for skin

flap transfer may need negative pressure with low, continuous suction.

A person using the system, whether a health clinician who offers patient care

or a patient and family who are managing a wound, must routinely check the

system to ensure that it is working properly, is turned on, and has no tubing

kinks or disconnection. Because the system provides constant or intermittent

suction, depending on the physician’s orders, the patient often feels the

suction as a type of pulling sensation. It should not be painful or

uncomfortable; the suction is typically set at a low enough level that it can

pull off excess fluid and stimulate new growth of tissue without being too

strong. Most people who use negative pressure therapy must keep the

system in place 24 hours a day, unless the dressing is being changed.39

Patients typically benefit more from ongoing and continued use of the

system, rather than sporadic use.

Application of the system is typically done at a health facility, even if the

patient will be using it at home. Once the system has been set up and

turned on, it will remain in place to work until dressing changes are made

and overall wound healing is measured and evaluated. In comparison to

traditional forms of wound bandages, which may require dressing changes at

least once a day, negative pressure dressings are typically changed every 2

to 3 days.39 In between time, the system continues to work by drawing out

and collecting fluid and stimulating tissue repair.

The negative pressure system is used until the edges of the wound are

brought closer together, the wound bed has healed to the point that there is


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little to no exudate from the wound, edema is under control, and granulation

tissue has filled in. The system does not stay in place until scar formation at

the wound site; rather, it can be discontinued once the expected wound bed

healing and repair have been accomplished.

Use of NPWT does not necessarily relegate a person to bed; in fact, most

patients who use an NPWT system connected to their wound site can

continue to be active. As discussed, in addition to the filler material placed in

the wound, some negative pressure systems also have irrigation techniques

in place that involve instilling solution, allowing for a dwell time, and then

removing the solution through suction where it is collected in a canister. For

example, one type of therapy may apply an antibiotic compound to kill

bacteria before removing the solution from the surface of the wound.

Some of the more commonly used solutions for instillation include those that

are generally used for topical skin cleansing, and may include saline or

antimicrobial formulas that contain silver, bacitracin or polyhexanide.40-42

There may be some other agents that can be instilled into the wound that

have purposes beyond infection control. Some chemotherapeutic agents can

be used as part of wound instillation, as well as anti-inflammatory solutions,

growth factors, and nutritional mixtures designed for supporting the health

and nutrition of the skin and mucous membranes.65-67 With an instillation

system in place, solution travels through the filler material so that it reaches

and can penetrate the wound bed. The solution is allowed to dwell for a

specified period of time and then the suction from the pump removes it and

deposits the remainder, along with any other exudate or wound drainage,

into the collection canister.


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Studies have shown that NPWT with instillation is successful in promoting

more active tissue healing and faster granulation tissue formation. One case

series by Brinkert, et al., presented in the International Wound Journal

evaluated the use of negative pressure wound therapy systems with

instillation of saline into the wounds of 131 patients.18 The system that was

used in all of the cases involved irrigating and soaking the wound with

saline, followed by removal of the solution through the negative pressure

system; the system was set up with tubing that included a solution delivery

line as well as a suction tube to use for both irrigation and suction of solution

from the wound. The wounds were irrigated with saline through the system,

the saline was left to soak on the wound for approximately 10 minutes, and

then the saline was removed from the wound via suction. An open-cell foam

filler was used with the irrigation system and remained in place throughout

the process.

The case series showed that in 98% of the cases the patients who

underwent negative pressure wound therapy with irrigation had healed

complex wounds when the process was used for a period of treatment and

when combined with surgical debridement.18 The system is not designed to

be used on a constant basis as part of wound treatment and is instead

designed to be adjunctive therapy, but when utilized for a set period of time,

the regular irrigation of the wound promotes granulation tissue formation.18

The system described was used in wounds caused from a variety of

mechanisms, including diabetic foot ulcers, traumatic wounds, and

necrotizing fasciitis.

Part of setting up the negative-pressure system also involves preparing the

wound bed before adding any of the materials. Prior to system placement,

the wound must be cleaned, with any necrotic tissue or debris removed.


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Remember that debridement is the process of removing necrotic tissue and

slough through one of several methods, including mechanical, surgical, or

enzymatic processes. Debridement is often performed on chronic wounds or

burns where there may be a larger amount of exudate and when the wound

has been open for a longer period, producing more dead skin and necrotic

tissue.35

The skin surrounding the wound should be clean and dry to ensure that the

outer dressing of the system will adhere. The clinician should note any areas

of periwound skin irritation or breakdown, which is more likely to occur with

long-term use of the system. A coating of protective ointment or

hydrocolloid dressing may be applied to the skin to shield and protect it.

With a standard system (including those that do not involve instillation of

saline), the protective coating is applied after wound cleansing,

debridement, if necessary, and wound measurement. This final step is

performed routinely to determine how well the system is working, if the

wound is decreasing in size, and if new healthy tissue is forming.

Prior to applying the system, the orders for its use must be reviewed. The

prescribing clinician must provide instructions not only about when to start

the negative pressure system, but also other details about its settings and

what materials, such as filler material, instillation solutions, or dressing

overlays, should be included. The type of filler material applied to the wound

bed, including foam, cotton gauze or polyester should be specified, including

the negative pressure setting (the amount of suction) and whether the

suction is continuous or intermittent, and how often dressing changes should

be done.39-41 It is extremely important to follow the guidelines given for use

of the negative pressure system to ensure that the patient is protected from

harm and that it is working in a safe and efficient manner.


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Filler Material

The filler material is made up of a predesigned substance that is placed in

the wound to evenly distribute the negative pressure suction. The material

used as the filler is fitted into the wound itself, where it works at a cellular

level to impact the cells and the blood vessels within the tissue to promote

new growth and to establish healing. The filler material describes a type of

dressing that is placed directly on the wound bed. The type of material may

vary, depending on the system used, but most types of filler consist of a

kind of foam or gauze that can be cut and shaped to the wound. Prior to

applying the negative pressure system, the size of the wound bed is

measured and the filler material is cut to fit. The actual wound bed may be

irregularly shaped, which may necessitate tracing the approximate outline

before cutting. Once prepared, the filler is placed in the wound bed before

being covered with a drain that is connected to the negative pressure device.

Not all wounds involve development of a significant amount of granulation

tissue; this occurrence is most closely associated with secondary intention of

healing and is more often seen with chronic wounds. When negative

pressure is used in an acute wound or a situation where granulation tissue is

not anticipated, use of filler material may need to be adjusted. For example,

in an acute wound that does not necessarily need longer term vacuum-

assisted therapy and no granulation tissue formation, the clinician would still

use filler material as part of treatment, but may place a non-adherent

dressing between the filler and the wound bed.6 This layer acts as a barrier

to reduce excess tissue growth within the wound bed where it is not

necessary, but the wound still derives the benefits of the negative pressure

system through evacuation of excess fluid and control of bacterial growth.

Alternatively, in a chronic wound where granulation tissue formation is

desirable, the filler material is placed directly into the wound bed against the


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tissue where new tissue growth is expected, as the filler’s mechanical forces

against this tissue is what stimulates new granulation tissue.

Prior to application of the filler material, the bed of the wound may need

debridement or cleaning to remove dead tissue or debris. The patient may

need pain medication prior to debridement or even when changing the

dressing of the negative pressure system. If slough is present within the

wound bed, it should be removed prior to placing filler material for the

vacuum on top. If eschar has developed, the filler material may be placed

around it, depending on whether the healthcare provider has ordered for

eschar to remain in place. If eschar must be removed prior to negative

pressure therapy, it is often softened first to facilitate easier removal and

then can be debrided, such as through surgical debridement.

The wound bed must be assessed before applying the filler material.

Although wound inspection should be a routine part of care for any patient

with a wound, inspecting the wound prior to applying the filler material will

help to better determine the state of the lesion and to understand how much

filler is necessary. A significant amount of drainage from the site indicates

the supplemental need for negative pressure to remove excess fluid.

The size of the wound bed should be measured, including the diameter of

the wound as well as its depth. These measurements may already be

determined as part of routine wound care; for example, a patient in long-

term care who has developed a pressure ulcer may have routine wound

measurements, including diameter and depth of the wound to determine its

stage, as part of treatment to establish whether therapeutic practices are

adequate and if the wound is actually healing.


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Part of the assessment of a wound such as a pressure ulcer that will be

managed with negative pressure therapy is understanding the depth of the

wound. This often involves measurement of total depth from the location of

the skin surface to the wound bed below. Some pressure ulcers may show

obvious depth and are staged in a relatively straightforward manner because

the depth of tissue involvement is apparent. Alternatively, wounds that are

very moist with exudate and those that contain a significant amount of

eschar or necrotic tissue may be difficult to measure. Many health clinicians

measure diameter or circumference of wounds and note major

characteristics, but measurement of wound depth is not always performed.

However, wound depth is an important clinical indication to understand and

identify the most appropriate type and amount of filler to use.

When tunneling is present, the clinician can measure the depth and extent of

the tunnel by using a moistened, cotton-tipped applicator. After moistening

the end of the applicator with saline or sterile water, the soft tip is gently

inserted into the tunneling at the deepest part. The length can then be

measured using a ruler or line gauge.21,48 It should be noted that any other

object besides a moist, cotton-tipped applicator, including its wooden tip,

should never be inserted into a wound bed or tunnel for measurement;

doing so could cause significant tissue injury, prevent wound healing, and

causing severe pain for the patient.

After wound measurement is complete and the results have been

documented, the filler should be placed in the wound bed. The filler material

is applied as one of the earliest steps in using the system. The clinician cuts

the filler material to the size and shape of the wound bed. This is typically

done using sterile scissors over an open tray or table and not directly over

the wound, to reduce the risk of dropping small fibers directly into the


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wound. If a wound bed has exposed blood vessels or very deep structures

such as bone or tendons that are visible, they should first be covered with a

contact layer dressing before adding the filler.

Once the filler material is the right size and shape, it is inserted into the

wound so that it fits directly onto the wound bed, packing the material in as

needed so that the filler comes into contact with the entire wound bed and

its edges.39-41 The filler should fit inside of the wound bed and should not

extend over the lip of the wound to cover intact skin beyond its borders. If

tunneling is present, the filler may need to be packed into tight areas. If

more than one piece of filler is used, the number of pieces applied should be

documented so that when dressing changes occur, there are no foreign

objects left in the wound bed.

There is a balance to the appropriate amount of filler to pack into a wound.

While a certain amount is needed to fill the space, packing too much filler

into the wound is detrimental toward healing. If there is too much filler, it

will be too thick for the negative pressure from the system to reach the base

of the wound bed, and the system will not work properly. Excess fluid and

drainage can then build up in the wound bed and obstruct the filler but will

not necessarily be removed through the vacuum system.

Filler material is placed as a means of evenly distributing the pressure from

the suction device across the wound bed. In this way, there is not one area

of the wound that receives more negative pressure while another area is

neglected. The type of filler used depends on the patient’s wound and the

negative pressure system being used. There are various forms of filler

material, although different types may be ordered for specific types of

wounds because of their characteristics and effects on the process of wound


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healing. For example, polyurethane foam is a type of filler that repels water

and may promote more rapid granulation tissue formation, which is

appropriate for wounds that have had a lot of tissue removed through

debridement or that are slow to heal.42

Various characteristics of filler materials, such as whether they absorb

moisture, have great flexibility, repel excess fluid, or are infused with

antimicrobial solutions are all factors in deciding about the most appropriate

type of filler to use. Because of the various characteristics of filler materials

available, it is extremely important to select the most appropriate type to

best enhance the wound healing process.

Foam Dressing

One of the more common types of filler material used with negative pressure

therapy is foam sponge. Of the foam types, there are two main kinds that

are often used, depending on the wound circumstances. These foam types

are generally referred to as black foam and white foam. Foam dressings may

be an option because they are relatively easy to apply to the wound bed and

they are flexible and can be cut or altered to match the shape of the wound.

Foam dressings were discovered several decades ago for use in wounds

when it was determined that they act as a type of sponge to control

moisture in the wound bed, making them particularly beneficial in cases

where wounds produce heavy exudate. Foam fillers control moisture in the

wound bed and are semi-permeable so they can prevent bacteria or other

microorganisms from penetrating the wound bed.43 They are useful for

wounds where excess drainage is a challenge, and they work together with

the negative pressure of the wound vacuum system to maintain healthy

amounts of moisture in the wound without keeping it too moist or letting it


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become too dry. This concept is important, as a wound that is too dry will

heal more slowly, while a wound that remains too wet will develop tissue

breakdown and skin maceration.

The thickness of the foam material also acts as insulation for the wound bed,

in addition to protecting it from exposure to potentially infectious

microorganisms. The protection of the foam in the wound bed can regulate

the temperature of the wound tissue, maintaining appropriate circulation to

the wound bed and preventing fluctuations in temperature. When dressing

changes are needed, the experience can be uncomfortable and even painful

for the patient, even though negative pressure systems require fewer

dressing changes when compared to traditional gauze. When foam is used as

a filler, the material is less likely to adhere to the wound bed, thereby

decreasing tissue damage that can occur when it is pulled away.

Foam fillers can be used in all types of wounds where negative pressure

therapy is employed. Some wounds may produce a small amount of

exudate, while others may drain much more; foam filler materials are

appropriate for wounds that produce either small or large amounts of

exudate, as they can soak up and then trap the excess fluid within their

layers before it is removed through negative pressure suction. The foam

may have several layers with different characteristics: the layer that is

placed against the wound bed may be porous and absorbent to pull fluid

from the wound, while the external foam layers are non-adherent and allow

fluid to pass through.43

The black foam is made of polyurethane and is structured with small, open

pores that range in size from 400 to 600 µm. The creators of the V.A.C.

system refer to their product of black foam dressing as GranuFoam. It is so


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named because it plays an important role in the growth of granulation tissue

in the wound bed. It has a sponge-like consistency that is flexible and allows

for the contours of the wound bed while maintaining consistent coverage

over all areas. It does not adhere to the wound and because it is made of

polyurethane, it will not shed small fibers or leave behind strands in the

wound bed.

When considering the type of foam filler to use, black foam may be a

possibility in some cases because the layer placed against the wound bed

absorbs moisture but the outer layer is hydrophobic and it repels water and

fluid. This is beneficial in instances of heavily draining wounds because the

foam is less likely to become saturated with exudate. The VAC GranuFoam

Silver is another type of dressing that consists of polyurethane black foam

that is combined with silver particles for its antimicrobial effects.64,65 The

benefit of this particular type of dressing is that it has the foam properties

that make microdeformations in the wound bed to support tissue formation

as well as moisture control, but it also can be used in infected wounds or in

situations where the risk of infection is higher. The two types of foam

dressings have very similar clinical outcomes.

The Avance brand of foam dressing for negative pressure therapy contains a

green foam that is similar in structure to the black foam dressing used as

filler material. It is made of polyurethane but is thought to be stronger than

typical black foam products, so it does not tear easily during dressing

changes. As with black foam, green foam promotes growth of granulation

tissue in the wound bed and controls moisture from exudate. The

manufacturers also promote the product because its green color may be

easier to use and to visualize the wound when compared to black foam.50


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White foam is another filler type that may also be used for drainage control

from wounds with exudate. The white foam has a structure that is denser

than the black foam, giving it greater strength and flexibility.49 It is a

polyvinyl alcohol product, which is a synthetic material consisting of very

closely packed molecules. The same material is often used in certain fabrics

and textiles for its strength and elasticity. Because of its higher levels of

strength, white foam needs to be used at higher pressure levels when

compared to polyurethane foam types.64-66 This type of filler may be found

under the brand name of VAC WhiteFoam.

When compared to black foam, white foam is hydrophilic and the filler may

be impregnated with saline or other solutions for tissue growth. The white

foam is non-adherent to the wound bed and will not stick to the new

granulation tissue when it is removed during dressing changes. Because of

this, its use is often associated with less pain for the patient, particularly

during dressing changes. The newly formed tissue is also not likely to grow

into the filler, which is sometimes an issue with some materials that are

packed into the wound bed. Because of its structure, white foam can be

easily formed and shaped to pack into the wound cavity or areas of

tunneling. Studies have also shown that white foam is beneficial when used

among patients with wounds that require skin grafts, as it may promote

graft survival.49

Some other types of foam dressings that have also been successfully used

for wound treatment and that are available on the market include RENASYS-

F foam, which is a type of black foam; and Hydrofera Blue Foam, which

contains antibiotic agents that are designed to manage drug-resistant

organisms such as MRSA or vancomycin-resistant enterococcus (VRE).65 The

use of these particular types of foam has been shown to be beneficial for a


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variety of wound types, including those that were otherwise resistant to

healing, and in particular, they are valuable for wounds that produce very

large amounts of exudate. Health clinicians who prescribe NPWT must

remain familiar with the various types of foam available when prescribing

orders for specific kinds of wounds.

A type of foam wound filler that has recently developed by Acelity known as

VAC Veriflo Cleanse Choice was recently studied for its effects on wounds

that produce large amounts of exudate. The review was published in the

International Wound Journal. This particular dressing is designed to be used

with negative pressure therapy; it is made up of a type of foam that has

extra pores to facilitate better removal of fluid and debris from the wound

bed. The review discussed the use of the dressing combined with

intermittent saline instillation. It showed that when used among patients in

the designated facility, the heavy exudate released from the wounds and

most of the slough present was controlled and removed. Use of this

particular type of system was suggested to be possibly helpful as an

adjunctive measure to control fluid and moisture in some hard-to-heal

wounds as well as those that contain significant amounts of exudate and

debris.

Wound debridement is often necessary prior to beginning negative pressure

therapy, in order to best remove slough or eschar that has formed in the

wound bed, although there are many people who do not tolerate the

debridement process. Review of this particular type of foam with negative

pressure therapy suggests that it could be also be used in those cases where

debridement is not available or when it is not tolerated.53


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Foam dressings are available in a number of designs, and they may be large

or small in size, with varying degrees of thickness. A larger foam pad can be

cut down to a smaller size to fit into the wound bed. A deep wound that

requires more filler can be packed with a thicker style of foam sponge. Some

fillers are designed as cavity dressings in that they are thick and pliable and

can be packed into deep wounds when setting up the negative pressure

system. Once the foam is in place, it is held in position by the external seal

of the wound vacuum; foam fillers and dressings are non-adherent, so they

need another item to cover them and hold them in place.

While there are some foams used as wound dressings that have adhesive

edges, when foam is used as a filler for negative pressure, it should be kept

as the filler cavity material, not as an external dressing. The foam dressing

may be available with the wound vacuum system or it may be used as a

separate entity, where it can be removed and replaced with dressing

changes.

Open-weave Cotton Gauze

Cotton gauze is another type of filler that may be appropriate for some

wounds. It has been found to be beneficial because it is adaptable to the size

and shape of the wound, it is economical, and it is easy to use. The term

open-weave describes a loosely woven type of fabric that is often known for

its use with bandages. The fabric of the dressing is lightly woven together

through a system in which some of the fibers are paired and crossed before

intersecting them with perpendicular thread strands. In this manner, the

fibers are loosely joined but still have adequate strength to fulfill their

purposes.67,78 This open-weave cotton gauze is often used in medicine for

various functions as a dressing and wound covering.


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The Chariker-Jeter system of application is most commonly associated with

open-weave cotton gauze filler. This system was first developed in 1989 as a

method of managing wound exudate using a combination of gauze filler and

continuous suction.69 The technique involves the insertion of gauze into the

wound bed, followed by the application of the remainder of the negative

pressure system. The gauze is pre-moistened with saline and is impregnated

with an antimicrobial substance. Once the gauze is placed, it is covered with

the drain from the negative pressure system, followed by another layer of

gauze over the drain in order to fill the wound. Finally, the entire structure is

covered with an occlusive dressing to create a seal.68

Use of gauze may be simpler than some other forms of filler material. For

instance, when compared to foam filler, gauze often does not need to be cut

or sized to fit the wound bed. This can be beneficial in some situations where

wounds are asymmetrical, very large, or are located in areas where body

contours make it difficult to connect the negative pressure system.

One case review published in the journal Eplasty discussed the use of cotton

gauze as filler material for NPWT when treating injuries resulting from land

mine explosions in soldiers. These particular types of wounds result in

traumatic injuries that involve damage to bone and soft tissues in the

affected area. They are also at higher risk of contamination because of

exposure to debris, and so are at greater risk of developing infections. The

review was of three cases of traumatic injuries from land mines in which the

patients’ wounds were treated with negative pressure therapy using cotton

gauze as filler. In one case, the wound had large amounts of exudate

present already, so the gauze was not moistened prior to insertion. In all

three cases, the patients were prepared for skin grafting and ultimately

healed of their injuries using the system. The gauze provided effective


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control of exudate from the wounds, and because the injuries were

extremely irregular in shape, the gauze could be easily packed into the

wound beds because it is lighter and more flexible when compared to foam

filler. Because these wounds were extensive and covered very large body

areas, it was simpler to lay the pieces of gauze into the wounds to use as

filler instead of trying to cut foam or resize it in some way to fit the contours

and irregular shapes of the wounds.68

Use of gauze primarily involves moistening the filler prior to application to

the wound bed; in some cases, the gauze may be pre-moistened with a

particular solution as part of its original design for use with certain kinds of

wounds. Note that gauze is not always pre-moistened; where wounds

produce large amounts of exudate, sterile cotton gauze may be placed

directly in the wound bed and since it is dry to begin with, it may

immediately begin to absorb excess exudate. The decision of whether to

moisten the gauze prior to insertion depends on the patient’s condition and

the composition of the wound. The gauze is layered in the wound bed where

it surrounds the tubing for the negative pressure system. The entire

structure is then covered with a transparent dressing to seal the system.

The amount of negative pressure used with cotton gauze is somewhat lower

when compared to that used with foam filler. This is because the foam is

usually thicker and requires more suction to collapse into the wound bed

when negative pressure is applied. Alternatively, cotton gauze is much more

lightweight and does not require as much suction for it to fold and collapse

into the wound as it starts to work. Gauze may be a filler of choice in cases

where the wound does not need to develop much granulation tissue.

While granulation tissue formation is preferable in many wounds that are

healing through secondary intention, it is not the goal in all cases.


22

Foam filler is known to promote granulation tissue development to the point

that there is sometimes a risk of the new tissue growing into the foam and

causing significant pain with dressing changes when the foam is removed.

The tissue that develops under the foam filler is more likely to be denser and

to produce thicker scarring when compared to gauze filler.69 Because of this,

gauze is preferable as a filler material for some types of wounds, such as

when treating an area that is being prepared for a skin graft, so that too

much granulation tissue does not form in the wound bed.

Some studies have shown that gauze filler provides the same rate and type

of healing when compared to foam filler materials.42 A review by Tuncel, et

al., published in the journal Wounds evaluated the use of gauze with NPWT

to promote wound closure among subjects with various types of chronic

wounds that required delayed closure using the Chariker-Jeter system of

placing gauze into the wound bed. The patients underwent wound irrigation

and debridement and had dressing changes every 24 to 48 hours. Overall,

the reduction in the size of the wounds was significant when this gauze-

based system was used. Subjects also had improvements in granulation

tissue formation and wound exudate was well controlled and minimized.78 Of

note, the subjects in the study also received antibiotic therapy and their

dressing changes were performed more often (every 1 to 2 days) when

compared to standard dressing changes associated with NPWT, which is

approximately every 2 to 3 days.

In addition to the positive outcomes associated with gauze-based filler used

in this study, the patients also reported greater pain control associated with

use of the negative pressure system and during dressing changes as

evidenced by minimal use of analgesics. Overall, gauze filler is also

associated with a decrease in costs for the patients when compared to foam


23

filler. The study reported a cost of gauze filler as being over 50 percent less

than the same amount needed for polyurethane foam filler.78 The many

results attained with this study show that gauze is sometimes preferable to

foam filler in negative pressure wound management, depending on the

wound type and stage of healing. There are obvious differences between

gauze and other types of filler materials, but gauze has its own benefits and

advantages.

Non-woven Polyester

Although polyurethane and cotton gauze are more commonly used as fillers

with the wound vacuum system, polyester blends are becoming increasingly

popular for use as a type of filler material for the wound bed. Non-woven

polyester is a specific type of fabric that makes up the dressing that can be

used as filler. It is considered non-woven because of how the threads of the

fabric are combined. Woven fabric is made up of threads that are intertwined

at right angles and pushed close together throughout the length of the yarn

or thread.

Woven materials are generally stronger overall when compared to non-

woven items; however, with non-woven materials, such as gauze used for

dressings, the fibers are held together through heat or chemical

compression. While the final product may not be as strong as tightly woven

material, non-woven items are typically more economical and there may be

less risk of the fibers splitting or shredding with regular use.45 Additionally,

non-woven products may be just as much or more absorbent when

compared to woven items.

The polyester used in non-woven filler materials is made up of strong fibers.

When considering items created from polyester, such as clothing or linens, it


24

is understood that these products are typically durable, they do not stretch

out of shape, they are easy to wash and dry, and they are not prone to

wrinkling. Polyester is also naturally hydrophobic as well, so it resists and

repels water and fluid, preventing maceration of nearby skin when it is used

as a wound dressing. When all of these characteristics are included in the

filler material for a wound dressing, it creates a dressing that is stable and

resilient that can be packed into a wound bed and fixed in place without

adhering to the fragile growth of new tissue and without releasing lint or

small fibers into the wound bed.

One form of non-woven polyester that may be an option for use with NPWT

is BioDome manufactured by ConvaTec. It was developed specifically for its

pore size, which are less likely to collapse under very low negative pressure

levels, and are less likely to lead to ingrowth of granulation tissue that is

sometimes seen with foam filler materials. This allows for greater removal of

exudate while simultaneously promoting tissue growth. A similar product,

the BioDome Easy Release facilitates even easier removal of filler material

without damaging any of the newly growing tissue and preventing growth of

granulation tissue into the fibers of the filler.90-93

Many of the non-woven polyester fillers available have been created with

silicone elastomer, which is a synthetic material similar to rubber that coats

some of the layers of the dressing. This creates a dressing that is softer and

more gentle toward the affected skin. A previous case study published in

Ostomy Wound Management reviewed the use of non-woven polyester and

low-pressure NPWT as preparation for placement of split-thickness skin graft

in three patients. Non-woven polyester was used as filler material because it

was less likely to adhere to the wound bed. In all three cases, not only did

the size of the wounds studied reduce by 60 percent during the time of


25

negative pressure use, but the patients also had decreased pain with

dressing changes over time and there was little to no trauma with dressing

changes.93 One of the greatest benefits of NPWT is that it is less likely to

adhere to the wound tissue, making dressing changes less painful and

traumatic for the patient.

Non-woven polyester filler has been shown in some research to be just as

protective of the wound bed and beneficial for growth of new, healthy tissue

when compared to other kinds of filling materials used with negative

pressure systems. A study by Losi, et al., in the Journal of Materials Science:

Materials in Medicine compared the use of non-woven polyester dressings

with cotton gauze and with open-weave polyurethane fillers in vacuum-

assisted closure technology. The silicone-coated polyester dressings were

used with negative pressure therapy on sheep that had been inflicted with

wounds for the purposes of the study.44 The animals were treated with

negative pressure therapy at a pressure of -125 mmHg pressure for 16

days; some of the wounds were given the polyester filler, while others were

treated with gauze or polyurethane.

At the end of a 16-day period, researchers reported that those wounds that

had used the non-woven polyester filler showed a significant decrease in the

size of the wound, greater rates of epithelialization and vascular agenesis,

and greater amounts of collagen deposition when compared to wounds that

used gauze or polyurethane.44 While the use of this specific type of filler

showed promise when the study was conducted on sheep and not

necessarily on humans, it does suggest that this particular kind of filler

material plays an important role in wound healing.


26

Air-tight Seal

Once the filler material has been placed in the wound, it is covered with a

drape and then sealed with a pad that contains the tubing leading to the

vacuum pump. This seal provides an air-tight setting within the wound,

which is needed for the suction to be fully effective. This seal is required as

part of the system: without a secure seal, the system cannot produce a

vacuum effect. The wound healing takes place when the suction has a

mechanical effect on the wound bed, but without an effective seal, suction is

inadequate, and the filler material and the outer dressing may separate from

the wound. Consider that once the vacuum pressure is started, the filler

material and drape within the wound collapses slightly; this indicates that

the negative pressure is working and there is suction being applied to the

wound bed. Normally, the outer seal permits this slight collapse and keeps

all of the elements in place. If the seal is not air-tight though, the rest of the

components are unable to achieve this collapse, rendering much of the

system ineffective.

Once filler material has been placed in a wound, an occlusive dressing is cut

to size and placed over the filler material and the wound bed; in some kits,

this is referred to as the Layer 1 drape.41,62 The dressing has an adhesive on

one side so that it will be secured directly to the area. This occlusive

dressing should provide a tight seal over the entire wound bed. To attach

the rest of the system, a small hole can be cut into the occlusive dressing

and the vacuum tubing pad is connected at this site for the negative

pressure to draw suction from the wound through the vacuum system. Once

the pad has been placed, the entire system should be air tight since the

connection of the vacuum tubing seals the only hole created for entry.62


27

Despite maintaining a tight seal over the site of the wound, the drape is

actually a semi-permeable layer that allows for some exchange of oxygen

and moisture in the skin surrounding the wound bed.66 The outer layer is

usually made up of a polyurethane material that has a hypoallergenic

adhesive to allow it to hold on to the surface but that won’t irritate the skin.

It is transparent so that the clinician can visualize the wound and the filler

underneath, which is important in case of complications or difficulties. For

example, without a transparent layer covering the system, bleeding within

the wound could occur and might not be noticed in the filler material until

damage is significant. The actual type and variety of transparent dressing

that is used varies with the different systems available, but the main

purposes of this layer are to seal the wound and support the position of the

rest of the negative pressure system.

The outer occlusive dressing also has the added benefit of keeping the

wound tissue warm and preventing its drying out. While excess fluid and

drainage should be removed from the wound bed, the goal overall is not to

completely dry out the tissue. Ideally, the wound should remain warm and

the environment moist, and the seal acts as a cover that keeps heat and

some amount of moisture in the wound bed. The covering is protective

against outside fluids from entering the wound and is waterproof. In addition

to regulating and maintaining moisture and temperature within the wound,

the outer dressing prevents debris and other fragments from entering the

site and contaminating the wound.

The type of dressing used to seal in the wound bed typically does not change

with different types of filler material. In other words, the same type of

occlusive dressing is used whether the filler material is foam or gauze, as it

will have the same effects. When setting up the system, the wound dressing


28

material, including the filler and the sealing drape may already be pre-

packaged into one set and the items are used together, however, some

facilities may separate the products if they use more or less for different

wounds. For instance, an extensive burn wound may require more filler

material than can be found in a single package; additionally, a single

occlusive drape may not be enough to cover the wound, so more packages

of just these drapes are needed.

The KCI Wound VAC system has a product known as the Sensa T.R.A.C.

(Therapeutic Regulated Accurate Care) pad that provides a seal over the

drape and filler material.51,65 This pad is able to monitor the amount of

pressure applied at the wound site while the system is in use. It also

eliminates the need to insert the tubing directly into the foam filler. If

adjustments need to be made, the system can automatically make the

changes based on the sensations from the pad. The pad also acts as an air-

tight seal to close off and hold in the filler material and keep it in place.

When a patient’s wound is in a location where it is difficult to create an

airtight seal, such as in areas where there are many contours or folds of

skin, it may be necessary to add more filler material or to use foam that is

specially formulated for locations that are difficult to seal. Some contours of

the body make it challenging to close because the outer surface is not flat. If

the patient is obese, there may be large areas of adipose tissue and folds of

skin that must be managed as well. If a wound has too many contours and

filler material cannot adequately reach all margins within the wound, it may

need further packing to fully close off the wound bed. In cases where the

dressing overlay is unable to produce an adequate seal because of the

location or the contours of the wound, another system beyond vacuum-

assisted closure may be needed instead.


29

Vacuum Pump

The suction applied through the negative pressure system evacuates the

excess fluid and drainage that comes from the wound. During the healing

phase, the wound produces exudate, which is created by the body as a

response to tissue damage. While a certain amount of exudate is normal and

the goal of wound treatment is to keep the wound moist, too much exudate

impedes the healing process. The vacuum pump removes excess fluid from

the wound bed so that the wound is not overly moist, however, it does not

remove so much fluid that the wound bed becomes dry.

The vacuum pump is a small machine connected to the system that provides

the negative pressure suction through use of an air pump. It may run on a

battery or it may need to be connected to a power source, although with

battery power, the device is much more portable for the active patient. The

pump is relatively lightweight, which further increases its portability and

ease of use, even if the patient is not ambulatory. The actual size of the

pump may vary depending on the manufacturer, although most pumps are

small and weigh only a few ounces.

One company, Kalypto Medical, Inc., has developed the NPD 1000, which is

a pocket-sized vacuum pump that runs on AA batteries.65 Although the

system has no suction canister, it could be ideal for some patients who are

ambulatory and active and who have wounds with minimal exudate and

drainage. Any exudate that is collected from the wound is stored in the

dressing. Other systems are also being developed that improve portability

for patients with minimal items to transport and may include carrying cases

to maintain portability as well as discretion. Some portable models are

designed to be disposable; they can be used for the duration of wound

healing and then the vacuum pump is discarded.


30

Some dressings available with portable systems are designed to replace the

canister for fluid collection; the exudate from the wound is collected by a

special dressing that has a high moisture vapor transmission rate (MVTR).

The MVTR describes how much water or fluid is evaporated through an item.

A dressing with a high MVTR allows extra moisture to be absorbed and then

evaporated through the dressing, but the area underneath remains moist.

Some disposable negative pressure systems utilize these dressings, and

when the therapy is complete, the dressing and the system are discarded,

because the dressing has replaced the need for a canister. A downside of

using this particular type of system is that it is not as easy to measure

wound exudate when compared to a collection container; however, if a

wound is not producing very heavy exudate, this type of dressing may be

appropriate.69-72

The vacuum pump is connected to the wound through tubing that is inserted

into the filler material in the wound bed and secured with a dressing that

provides an air-tight seal. The tubing may vary in length to provide the

patient with the ability to move and travel when the machine is in place or if

a portable system is being used. The diameter of the tube may also vary,

depending on the system used and whether the patient has significant

drainage or particulate exudate. The tubing not only delivers the negative

pressure from the vacuum pump to the wound bed, but it also collects

drainage back toward the collection canister through the force of suction.

The connective tubing is more than just a channel for carrying fluids from

the wound to a collection container. The end of the structure that lies in the

wound bed can determine if there are changes in the amount of pressure in

the wound; in some systems, the tubing can also monitor the amount of

negative pressure delivered.65


31

The fluid collected from the wound exits the wound bed and is carried

through the tubing by the force of the pump to be gathered in a suction

canister. Depending on the model of the pump, the canister may hold

anywhere from 300 to 1000 milliliters of fluid.63 Obviously, the larger the

size of the collection container, the more difficult it is for the system to be

portable for the patient. The tubing has a one-way valve that prevents fluid

drawn from the wound from returning back through the tubing toward the

wound bed.

Prior to the portable vacuum systems that are available today, the patient

receiving negative pressure therapy used to be connected to wall suction in

the inpatient hospital room or long-term care center. While this system still

provided suction needed for wound evacuation, the exact levels of pressure

were sometimes difficult to control and maintain, there was more noise

associated with system use, and it was often inconvenient, as the patient

had to remain in one place. With the development of small pumps that are

now portable, there are fewer issues with suction and noise and the systems

are easier for the patient to use. The pumps used today are much more

specific with settings to the particular orders given for negative pressure

levels.65,91-94

The vacuum pump and collection unit allow the caregiver to monitor the type

and amount of exudate suctioned from the wound. There are various types

of exudate that may be produced. The appearance of the drainage can

indicate if the wound is healing normally or if there are potential

complications involved. Drainage from a healing wound that is not infected is

typically serous drainage and appears clear and thin. Drainage may appear

red or pink in color.


32

Sanguineous drainage is red because it contains blood. Serosanguineous

drainage is clear drainage that has a small amount of blood in it, so it may

be tinged pink. Both serosanguineous and sanguineous drainage indicate

that some amount of bleeding is present within the wound bed, whether it is

over-bleeding from tissue damage or whether bleeding is occurring at the

capillary level. The presence of blood within exudate typically means that

some amount of damage has occurred to the blood vessels in the wound.

An infected wound often produces purulent drainage, which is thick and may

have a bad odor. Unlike serous drainage, it is not clear, but may be white,

brown, yellow, or green in color. Seropurulent drainage is a combination of

serous and pus-filled drainage; it is thin in consistency but is discolored and

has an abnormal odor. Neither type of drainage is desirable from a wound

and indicates the presence of infection.7 The wound vacuum system is

designed to remove all types of drainage that may come from a wound.

Through the system, the healthcare provider can monitor the type of

exudate produced, as well as how much of it is being removed within a span

of time.

To set up the vacuum pump for the system, the filler is placed in the wound

bed and the area over the wound is sealed, with tubing connected directly to

the pump. Prior to turning the vacuum on, any clamps in the tubing should

be open and the tubing should be in a position so that it does not place

pressure on the skin. Prolonged time spent with such pressure can

contribute to pressure ulcer development at the site and yet another wound.

The tubing carries fluid, debris, and air from the wound. When the pump is

able to sense the transfer of fluid and exudate from the wound bed and

manage the pressure delivered to the wound, it is more likely that healing

times will be faster and the rate of recovery will be quicker.65


33

The sensitivity of the system allows for small shifts in pressure delivery, so

that the wound is not simply receiving a set amount of pressure whether it

needs it or not. Instead, the ability to sense how much negative pressure

the wound needs is one great benefit of the vacuum system and will

reinforce the changes needed to make pressure adjustments to keep up.

Many of the vacuum systems available have a plastic canister or collection

container to allow for drainage accumulated from the wound. After the

system has been started, the filler and the seal should collapse into the

wound slightly from the suction of the negative pressure. The setting, as

ordered, should be set up as soon as the system is started; the vacuum

should reach the appropriate setting just after starting and the clinician can

verify that the desired amount of suction is happening by reading the

settings on the monitor of the machine. A dial on the vacuum pump allows

for an increase or decrease in the amount of pressure. The suction canister

is often connected to the pump or is right next to the machine where both

the pressure settings and the amount of output may be monitored at the

same time.

Most collection systems have alarms in place that will send a signal if there

is a sudden or significant increase in fluid collected in the container or when

it becomes full, which could occur if there is considerable blood loss of if the

wound has high output of exudate. The alarm may also be set to signal if

there is a blockage in the drainage tubing, which could occur if large clots or

debris are pulled from the wound bed. If a patient is using the system at

home, he/she should be taught prior to use about how to address alarms,

how to change the suction canister, and when to contact the provider if

there is excess blood loss through the system.


34

In addition to the traditional methods of using the vacuum pump as part of

NPWT, there may be some techniques that allow caregivers to treat larger

wounds or more than one wound at a time using the same system. The KCI

Wound VAC system has a method of treating more than one wound at a time

using negative pressure through a technique known as bridging. When a

patient has two wounds that are relatively close together, they can be

treated with the same vacuum system and the same tubing. Each wound is

packed with the appropriate filler material and then a drape is placed

between the wounds. A strip of foam is then placed over the top of this

drape to connect the foam filler between both wounds. Once all of the foams

are touching, the tubing for the pump is placed in the center and the

vacuum can draw suction from both wounds at the same time.51-54

The vacuum system is not placed directly over intact skin, and a drape must

be placed first on the skin to act as a barrier between it and the negative

pressure system. This system is beneficial in situations where the patient

has more than one wound but with similar circumstances; for example, a

person may have more than one venous stasis ulcer in the lower leg. The

bridging technique could be used to treat both ulcers, as long as neither

wound has developed complications, and use only one vacuum system for

both. Pressures used with this technique are often higher than average use

with one wound, as the vacuum system is needed for pulling fluid off of the

wounds and treating more than one wound at a time.

A similar technique that may be used with wounds in the same region is the

application of a Y-connector to the tubing leading from the dressings to the

vacuum pump. If two wounds are relatively close together, they can each be

packed with filler material, covered with a seal, and their tubing brought

together to converge at the connector before it is connected to the vacuum


35

pump. This system has the benefit of drawing suction from more than one

wound at a time, but the patient does not require a drape applied over intact

skin. Both wounds require the same settings on the vacuum pump, since

they are both draining into the same suction container.39

Negative Pressure And Tissue Healing

At the core of vacuum-assisted therapy is negative pressure applied to the

wound to aid in healing of tissue. The system is devised to provide a set

amount of suction when all elements, including the filler material and the

overlay to seal the wound, are in place. As discussed, the pressure is drawn

through the vacuum pump that is attached to the dressing, and the amount

of pressure withdrawn can be set according to the pump’s specifications and

the health clinician’s orders.

Pressure is normally described as a force against an object or item. When

pressure is applied against the skin, for instance, it may be directed from

another entity from the nearby environment. Even the surrounding air,

though it cannot be felt most of the time, has weight. Atmospheric pressure

is the amount of pressure within the air in the earth’s atmosphere, which is

a layer of gas surrounding the surface of the earth.55 Negative pressure is a

level that is below the normal atmospheric pressure that each individual

experiences; it is also known as sub-atmospheric pressure. This negative

pressure has the effect of a vacuum or suction that can be set and modified

to different levels depending on patient use.

A pressure of -125 mmHg (also denoted as a negative pressure of 125

mmHg) is a default pressure setting and may already be established in the

vacuum pump on some models when setting up the system. This standard

setting is based on the results of various clinical studies that have shown


36

that it provides the greatest benefits in the wound bed versus other pressure

levels. The pioneering work performed by Morykwas, et al., in 1997 and

published in the Annals of Plastic Surgery showed that pressure, when

applied at settings of -125 mmHg, increased the blood supply by fourfold

when the system was administered to the wounds in pigs used for the

research. While this is the most common setting used for negative pressure

therapy, the actual settings prescribed can vary significantly.60-64

In fact, the amount of pressure prescribed may be determined in part by the

type of tissue involved; for example, there are some tissue types that react

differently to the mechanical forces of the negative pressure system, and so

may need different amounts of pressure. Actual prescribed pressure

amounts may range from -50 to -175 mmHg, although this can vary

between facilities and particular negative pressure models.60-64 The amount

of pressure to apply is always recommended by the prescribing clinician

when starting out. It is important to note how the patient responds to the

system and the pressure overall. Too high of settings can be painful at the

wound site; alternatively, pressure that is not high enough may render the

system ineffective.

There is evidence that differences in pressure can affect the rate and extent

of wound healing for some wounds. Although standard pressures of -125

mmHg have been shown to be beneficial in the literature and in clinical

practice, lower amounts of pressure may also be used with negative

pressure and may also be beneficial in promoting wound healing. One study

conducted by Lavery, et al., in the Journal of Diabetes Science and

Technology considered the use of low negative pressure and gauze dressings

for the treatment of diabetic foot wounds. The study involved using a

negative pressure system set at 80 mmHg along with gauze dressing to


37

treat the wounds over a period of four weeks. Dressing changes were

performed three times a week. By the end of the study, 43 percent of the

subjects experienced greater than 50 percent reduction in wound area since

the start of the program.52 Although the study did not compare the use of

low pressure suction with other negative pressure systems, a reduction of

this volume with use of low pressure over four weeks suggests that not all

negative pressure systems must use the standard -125 mmHg suction that

is commonly prescribed to achieve healing results.

It may be that wounds should be treated on a case-by-case basis to

determine the extent of tissue healing that can occur with lower amounts of

pressure and the appropriate amount of pressure to use will depend on the

wound’s response. Some smaller devices are not necessarily equipped to

provide pressure settings above a certain level. For instance, when lower

pressures are ordered, the patient may be able to use a system that is

designed for low negative pressures. Alternatively, many systems can handle

the dispensation of high or low pressures and the prescribed levels can be

titrated up or down without requiring a change in the actual machine. It

should be noted that prior to applying the negative pressure of the vacuum

system, the patient’s wound should have undergone the coagulation stage to

the point that it is not actively bleeding. To apply this system to a bleeding

wound that does not show evidence of initial clot formation puts the patient

at risk of significant bleeding as well as delayed healing time.

When the device is started, the initial negative pressure may give the

appearance of a vacuum effect on the dressing and the filler. The material in

the wound bed and the overlying sealant may shrink or collapse slightly with

the negative pressure, but this is a normal response to the suction. In fact,

this appearance is desirable and demonstrates that the system is working;


38

the dressing should provide a seal over the wound and should not appear

loose or slack as if it were coming off. When foam filler is used, the suction

from the vacuum system decreases the size of the foam slightly while it

exerts a pulling force on the wound bed. This results in the

macrodeformation effects of the wound’s edges being drawn and contracting

in toward the center.

The amount of macrodeformation that occurs during this process is affected

by the filler used and the size of its pores, as well as the amount of suction

applied.6 The appearance of the collapsed structures in the wound should

come into view soon after starting the negative pressure. If there is little to

no response at the site of the dressing, the system should be checked to

ensure that the proper amount of suction is being applied and that there is

nothing blocking the suction and preventing it from working.

Even without its application through negative pressure therapy, suction is

sometimes applied to wounds or other types of lesions to remove excess

fluid and drainage. Within many inpatient care settings, suction devices and

canisters are available at the bedside to remove fluids manually, such as

with suctioning excess oral secretions or for assistance with procedures,

such as through tracheostomy suctioning. The application of suction allows

the health clinician to clear and remove secretions, blood, mucus, or pus.

This suction or vacuum effect is similarly applied with the negative pressure

system in which the vacuum is applied to a gentler degree and the suction is

spread across the area of the wound. The mild negative pressure not only

removes exudate and fluid, but it also acts as a mechanical force to

stimulate microscopic changes in the wound tissue, as described as

microdeformations that promote tissue healing and granulation tissue

formation.


39

Prior to initiation of therapy, the clinician must assess the wound to

determine whether the injury would tolerate the negative pressure. In cases

where there is tissue ischemia in or near the wound, pressure should be

applied at a lower amount, as higher negative pressure can worsen

ischemia.42 The standard setting of -125 mmHg has been shown to

maximize blood flow and contribute to tissue perfusion; however, when

negative pressure is especially high, it can impact vascular resistance and

may influence the amount of blood perfused. As a result, an area that is

already compromised in terms of adequate oxygenation could further

deteriorate when high pressures affect circulation. If a wound has such

severely compromised blood flow and there is risk of necrosis because of

critical ischemia, an alternative for wound healing besides negative pressure

should be used.

The health clinician not only determines the amount of negative pressure

that is applied with the system, but also whether the system will work on a

continuous or intermittent basis. There are various explanations as to why a

patient would require one mode over the other. Depending on the type and

condition of the wound as well as the patient’s tolerance for the negative

pressure system, the pressure may need to be set to provide constant

suction. Alternatively, there are cases where intermittent suction is a better

alternative, such as when there is more granulation tissue expected to fill in

the base of the wound. The suction mechanism used could also be changed,

depending on how the patient responds. Periods of suction that are

interspersed with breaks may affect tissue oxygenation and circulation in the

wound. In some cases, the settings could be changed to improve these

effects. For example, instead of intermittent suction at a higher level of

pressure, continuous suction at a low but constant pressure may be a more


40

effective alternative. There have been proven benefits and disadvantages of

each mode of operation.

Constant Mode of Negative Pressure

While suction can be applied at either a continuous or an intermittent rate,

the constant mode of negative pressure is a standard application and is

more commonly used. With continuous therapy, the set amount of negative

pressure is delivered on an uninterrupted basis. After the initial application

of the negative pressure system, the suction settings may start at constant

suction for a specified period. Eventually, the health clinician may change

the settings so that the system works on an intermittent basis, although in

many cases, the patient uses the system with ongoing and continuous gentle

suction.

When the system is first introduced, the tissues within the wound bed

collapse slightly and are pulled downward and the external layer of occlusive

dressing creates an airtight seal on the wound bed. One of the reasons why

constant suction is frequently administered is that once the therapy has

started and the wound has reached this state, it remains so with the

continued application of negative pressure, rather than fluctuating back and

forth with intermittent pressure. The constant suction supports and

maintains the external seal, thereby improving the conditions of the wound

and the rate at which the healing occurs.

Alternatively, a patient may need intermittent suction for a period and then

the situation must be re-evaluated after 1 to 2 days to determine if it is

efficient or if changes need to be made. For example, after initial application

of NPWT on an intermittent basis, the provider may recheck the settings and


41

evaluate the results after 48 hours and decide to change to constant suction

at a lower amount of pressure.

While intermittent therapy may be used in many cases, some patients are

better candidates for constant negative pressure therapy. A patient should

use constant therapy when he otherwise cannot tolerate intermittent

suction, such as if the suction causes pain whenever it starts and stops. The

episodic pattern of intermittent therapy may cause too much discomfort, and

this may correspondingly depend on whether further complications are

present, such as infection, as well as the location of the wound and the

patient’s overall pain tolerance. In unstable wounds, constant negative

pressure is preferable over an intermittent mode. The constant, mild pull of

the suction is able to work normally and consistently without the alternating

give and take of the intermittent setting. The intermittent mode causes

slight movement of the tissues when the system is on and then off again; for

very fragile wounds, this movement might be enough to damage some

tissues or cause bleeding.94-96

Constant therapy is also typically more appropriate in cases where there is a

large amount of wound exudate. The continuous mode can remove excess

fluid and exudate from the wound without being interrupted and may be

used for a period of time until the amount of exudate has tapered off.

Alternatively, if intermittent suction is used with a high-output wound, it

may not be able to manage the excess production and fluid can build up in

the wound bed, retaining moisture and saturating the filler material.

Similarly, when there is a high risk of bleeding, continuous negative pressure

is preferable over intermittent therapy.


42

The tissue movement that occurs with intermittent delivery could damage

the very fragile blood vessels as they are newly forming. If excess bleeding

has already occurred, the continuous mode should be used instead of

intermittent in order to absorb blood. The constant negative pressure

unceasingly removes the blood and exudate in a manner that it can be

transported to the suction container and there is little chance of backflow of

fluid into the wound, which is a potential risk associated with intermittent

therapy.

PICO

One type of negative pressure system that may be utilized in certain cases

and that only provides constant suction is PICO, which is intended for single

use and is a disposable system. PICO was developed by Smith & Nephew as

a disposable device that does not use a canister for fluid collection. The

system is indicated for a variety of wound types including surgical incisions,

acute wounds, chronic ulcers, partial thickness burns, flaps, and skin grafts.

Patients who are ambulatory would most benefit from this type of system

because it is disposable and small. There is no fluid collection chamber

because the dressing that comes with the system is designed to have a high

moisture vapor transmission rate in which excess exudate is rapidly

absorbed into the dressing and then evaporated.98

Because PICO is compact and disposable, it is used on a continuous basis,

instead of utilizing an intermittent mode. Because of its size and purposes,

PICO has also been shown to decrease the need for some nursing care and

the associated costs. Not only does the system work without the required

changes in the collection container, but because it does not use intermittent

settings, it may not need to be as closely monitored and the patient may be

more comfortable with its use. Clearly, continuous use of negative pressure


43

has its place in vacuum-assisted wound healing. Because this mode is used

so frequently, there are specific machines and systems available that only

provide this setting.

Intermittent Use of Negative Pressure

Some research has shown that intermittent use of negative pressure

produces the same benefits on growth of granulation tissue and wound

healing when compared to continuous use, particularly when moderate cycle

times are used.6 In fact, intermittent use of negative pressure therapy may

have some advantages over continuous use. Use of intermittent mode is

thought to improve granulation tissue formation and superior healing

because it stimulates the growth of new cells in a way that is unlike that of

the continuous mode of NPWT. Intermittent use of negative pressure is also

associated with up to 40 percent more granulation tissue formation in the

wound bed when compared to continuous mode.97 It is understood that

negative pressure system applies a type of mechanical stimulation to the

cells, however, when the pressure is delivered in an intermittent, rather than

constant fashion, there is greater stretching of cells, and increased

production of fibroblasts and collagen.97

Negative pressure that is delivered on an intermittent basis may improve the

rate at which new blood vessels form in the wound, thereby increasing the

growth of blood vessels and delivery of oxygen and nutrients to the wound

tissue. Recall that in order for capillary sprouting to occur, some of the

tissue experiences a slight amount of hypoperfusion and hypoxia, followed

by rapid hyperperfusion and concentrated blood flow to the area when the

negative pressure is stopped. During intermittent therapy, the vacuum pump

may exert negative pressure for a specified period of time. While it is

working, it may initially contribute to the hypoperfusion in the tissues that


44

has been discussed. Once the machine enters into the episodic period of

rest, the pressure is stopped briefly and increased blood flow and

hyperperfusion of blood fills the area.

Another benefit of using intermittent therapy is that instillation of solution

can be used with this mode. The machine may be set to instill a prescribed

chemical solution, such as antibiotic mixture or cleansing agents, where it is

administered into the wound bed and then given a period of time known as a

dwell time. During the dwell time, the solution infuses the matter in the

wound to penetrate the granulation tissue matrix. With intermittent therapy,

the negative pressure system would be off for a set period to allow for the

dwell time. Once the machine cycles through to start the next episode, the

solution is removed from the wound through suction, along with wound

debris and exudate.

A case series published in the journal Therapeutics and Risk Management,

investigated the use of intermittent NPWT with instillation in the treatment

of wound infections following surgical hip replacement. In the cases

reviewed, subjects each had infections that had developed in their surgical

incisions that they had been treating through various methods to prevent

further tissue loss. The subjects then had treatment with NPWT applied

intermittently with instillation of antibiotic solutions and in both cases, the

subjects’ wounds formed new granulation tissue, their infections were

cleared, and after the therapy was discontinued, they showed no evidence of

recurrence after one year or more of follow-up.94

The settings for intermittent mode of negative pressure delivery vary

depending on the wound being treated and the healthcare provider’s orders.

An example of an order for intermittent delivery might be 5 minutes of


45

pressure, where the predetermined amount is applied continuously for that

period, followed by 2 minutes with no pressure.95 This provides a rest period

in between periods of negative pressure and suction. The time in between

gives a brief interval for the affected tissue and allows for a short recovery

before the suction starts again. The settings of “5 minutes on and 2 minutes

off” is often seen as a standard recommendation in many treatment

situations, but the appropriate settings can be variable.

Some patients complain of sleep disruption when the intermittent settings

are used at night. The repeated stopping and starting of the suction with the

system may be disturbing when the individual falls asleep when there is no

pressure but is then awakened when the intermittent pressure system starts

up again. The discomfort occurs because the cycle causes changes in the

size of the filler material during the cycling periods. When the suction stops

during intermittent cycling, foam filler that has been contracted may then

expand slightly until the negative pressure cycle begins again. The patient

may be more likely to experience some pain during this expansion when the

filler pulls on the new and healing tissue in the wound bed.

Intermittent therapy may also require more nursing care and associated

caregiver attention to monitor the system and ensure that an airtight seal is

maintained, to confirm that there is no backflow of fluid during the “off”

period, and to maintain patient comfort if the intermittent setting is hurting.

The caregiver may need to change the settings from intermittent to constant

pressure for a period prior to any procedures or dressing changes to better

ensure patient comfort.96


46

Benefits Of Vacuum-assisted Wound Closure

There are various benefits associated with vacuum-assisted wound closure,

including an increased rate of healing and decreased risks of complications,

including infection. When a patient uses this type of wound treatment

system, he/she may be able to move from an acute care setting into one

that is outpatient, or he may use the system at home, requiring much less

direct nursing care through dressing changes and wound management.

Negative pressure systems are also often associated with fewer

complications when they are used appropriately, and patients who use these

treatment systems are much less likely to have to contend with costly or

painful procedures to further manage complications. For instance, a wound

that develops an infection typically needs antibiotic medication and possibly

more frequent dressing changes to keep the wound bed clean and free of

debris. A significant infection may need surgical debridement or instillation

of a drainage tube to remove pus from the site, which is costly, painful, and

time consuming for the patient, and further extends the overall healing

process of the wound itself. Some of the benefits that have been shown to

be associated with vacuum-assisted closure include a faster rate of healing

and decreased risk of infection.

Faster Healing

Negative pressure wound therapy has been shown to improve rates of

healing in both acute and chronic wounds by improving tissue growth, even

when complications have developed. Although tissue debridement and

dressing changes are still required with this form of treatment, they are

typically performed much less often when compared to other forms of wound

care. Many people with chronic wounds or with burns and who have

traditional wound dressings require frequent care for dressing changes, pain


47

control, and management of wound complications. This treatment results in

shorter hospital stays and reduced cost.

Vascular Endothelial Growth Factor

As discussed, granulation tissue formation is a critical component of wound

healing and one of the steps that must be completed before the final step of

scar formation. The negative pressure system is thought to induce a faster

rate of healing by more rapid stimulation of the production of cells needed to

form granulation tissue, including connective tissues and new blood vessels.

Negative pressure therapy is believed to promote the production of a specific

type of protein in the wound bed known as vascular endothelial growth

factor (VEGF). This is released into the wound bed from platelets initially

after the wound has developed. It is responsible for the growth and

development of new blood vessels, which is beneficial in cases where the

circulatory system has been damaged, such as within a wound bed. The

microdeformations that occur with mechanical stimulation to tissues from

the negative pressure system are thought to stimulate production of VEGF

and ultimately new blood vessels at the healing site.

Reduced Healthcare Costs

This faster rate of wound healing associated with negative pressure has an

economic impact on the healthcare provided for the patient overall. Faster

healing times decrease healthcare costs by reducing the amount of nursing

care needed for wound care and dressing changes, and they decrease the

time of hospitalization for some patients if they can be discharged from an

inpatient facility with a wound vacuum system to use at home. This is

particularly beneficial when the patient is ambulatory and active and can use

a portable system to be able to maintain activity levels while still treating


48

the wound. Some locations have noted that there is an increased cost of

using negative pressure systems overall when compared to traditional

wound dressings; however, these increased costs may be offset by a faster

rate of healing and decreased time needed for caregiving activities.

Pain Control

Dressing changes can be extremely painful for some patients, and the

presence of a wound dressing can impact activity levels if the dressing is

bulky. The negative pressure system may be more comfortable for some

patients, decreasing pain associated with frequent dressing changes and

increasing the rate at which they can return to normal activity levels.

Surgical Site Healing

Negative pressure therapy that is used over surgical sites also has been

shown to improve healing rates and decrease complications associated with

surgery. Surgical incisions are typically considered to be those that heal by

primary intention in that they are planned incisions and are closed with

sutures or staples. Although this is the objective, the patient who undergoes

surgery must still undergo a period of time where the incision is healing;

surgical sites may also develop complications of infection or hematoma that

could delay wound healing. These closed surgical incisions benefit from

negative pressure therapy.

A study performed by Karlakki, et al., and published in Bone & Joint

Research evaluated the benefits of using incisional negative pressure

therapy on surgical incisions following hip and knee arthroplasties. The study

aimed to determine the negative pressure effects on several factors related

to this particular type of wound and its healing process, including control of

exudate, length of stay, and potential for complications. It showed that the


49

study group that used negative pressure had significantly lower amounts of

wound exudate when the system was applied to their surgical sites. There

was also a reduction in overall length of stay for patients because their

wounds healed more quickly. There were reduced numbers of dressing

changes needed, and better wound outcomes overall for those patients who

used the system.72

Lower Risk of Infection

Infection is a potential complication associated with any wound, although

there are some situations in which there is a greater risk of infection, such

as when the wound is already contaminated or if the patient has a chronic

health condition that affects his/her ability to fight off infection. The risk of

infection can be lowered when using NPWT through several factors. For

example, traditional gauze dressings require frequent changes when the

materials used dry out or become soiled with exudate. In addition, NPWT

improves blood supply to the wound site, and has been effective in fighting

the presence of biofilm in the wound site, and surgical site infections.

Less Frequent Dressing Changes

Negative pressure therapy requires far less frequent dressing changes, and

the system may need to be changed every 2 to 3 days, in contrast to

standard dressing changes that might occur every 8 to 12 hours.6 Dressing

changes can cause some tissue trauma, which could further introduce

microorganisms into the wound and increase infection risk, particularly when

dressing changes are performed frequently. By reducing the number of

dressing changes needed with NPWT, the system maintains a seal in the

wound bed for longer periods, potentially reducing the risk of exposure to

infectious organisms.


50

Improved Blood Supply to Wound

It is thought that a reduction in the potential for infection found among

users of negative pressure therapy may also come from the system’s

abilities to improve blood supply, promote granulation tissue growth and

angiogenesis in the wound bed, and improve lymphatic drainage and control

edema.

The increase in blood supply to the affected site can improve the rate at

which the body sends anti-inflammatory and immune system cells to the site

to fight or control numbers of microorganisms. Additionally, lymph channels

needed for circulation of lymph fluid are often close by. The lymph fluid also

contains white blood cells, which are needed to fight infection. The negative

pressure system reduces edema and fluid buildup at the wound site, which

improves blood flow as well, as the skin and surrounding tissues have

greater mobility when they are not constrained by too much extracellular

fluid.72,73

Biofilm in the Wound Site

As noted, biofilm may develop and be present within the wound bed, which

can contribute to infection development. The open wound is often available

as a space where microorganisms can congregate and colonization can

occur. Biofilm can be particularly difficult to control since many of these

microorganisms are resistant to antibiotic solutions. Studies have shown,

though, that NPWT can improve healing when biofilm is present if the

system is applied early. Further, early application of NPWT can also prevent

biofilm formation, and has been shown to inhibit growth of biofilm that

contains S. aureus in some clinical research studies.80,96


51

Incisional Negative Pressure Wound Therapy

In acute wounds such as surgical incisions, there is a risk of infection

because the wound itself represents a break in the skin’s barrier to the rest

of the body. In fact, the World Union of Wound Healing Societies reported

that 346 hospitals in the United States showed that surgical site infections

were the most common reason for readmission.69 Incisional negative

pressure therapy has been associated with a reduction in wound infections.

When vacuum pressure is used with surgical procedures, it is referred to as

incisional negative pressure therapy.

Surgical site infections (SSIs) are associated with prolonged hospitalization

and increased time and money needed for treatment. In addition to reducing

the overall length of stay and time for wound healing of infections, incisional

negative pressure therapy may reduce instances of SSI that can develop in

the wound bed following an operative procedure. An SSI is an infection that

develops at the site of an operative procedure where a wound was created

for the purposes of surgery. The SSI can range from being superficial and

affecting the skin and soft tissue to a deep infection that impacts the

underlying fascia, bone, and organs. The condition causes pain, purulent

drainage, odor, fever, and tenderness at the surgical site.69 Additionally,

many SSIs develop as healthcare-acquired infections, in which the patient

contracted it while receiving care in a hospital or healthcare facility.

There is evidence that use of incisional negative pressure wound therapy can

reduce instances of SSIs and can lower the risk of infection overall. A review

published by Acosta, et al., in the British Journal of Surgery evaluated the

use of negative pressure therapy among patients who had vascular surgery.

The review discussed the benefits of incisional negative pressure therapy on

surgical sites, particularly when patients have had vascular surgery in


52

common areas such as the groin or with fasciotomy wounds as being able to

actively treat the wound while simultaneously managing exudate and fluid

levels, requiring fewer dressing changes, and decreasing overall length of

hospital stay.70

Another study published by Chaboyer, et al., in the journal Healthcare

evaluated the use of negative pressure therapy as a preventive measure

against development of SSI in the incisions of obese women who had

undergone elective Cesarean sections. The study was a pilot study

undertaken to determine whether a larger clinical trial could be conducted to

study this particularly topic. Although the sample size in this trial was small,

the overall trend showed that women who used negative pressure therapy at

their incision sites were less likely to develop SSIs.71 Because this was a

small pilot trial to begin with, more research is needed to observe the effects

of incisional negative pressure therapy for this particular group of patients.

However, these early results may show some promise for use in certain

populations at risk, including overweight or obese patients similar to those

studied.

Given this evidence, a consensus statement was released from the World

Union of Wound Healing Societies recommending the use of negative

pressure therapy for patients with closed surgical incisions who are at

increased risk of developing surgical site infections or who have risk factors

that could lead to prolongation of wound healing at the surgical site.69

Other Risks of Infection

There are many other groups of people who are at risk of infection

development when wounds are present. Negative pressure wound therapy

has been successful in managing infection, reducing biofilm, and even


53

preventing excess colonization that can lead to infection symptoms in a

variety of situations. Regardless of whether a wound is acute or chronic and

many other underlying factors that may be present, NPWT is clearly

successful in controlling pathogen growth and maintaining a healthy wound

environment.

Contraindications Of Negative Pressure Wound Therapy

Despite the many benefits associated with negative pressure wound therapy,

the system is not devised for use on all kinds of wounds. Some complex

wounds that have developed complications will not benefit from vacuum-

assisted closure, and the process may actually cause further problems. Prior

to initiating negative pressure therapy, the healthcare provider must have a

solid understanding of the complexities of the wound and be familiar with

the patient’s overall health condition to avoid introducing new obstacles with

use of the system.

The U.S. Food and Drug Administration has issued a list of wound types and

conditions for which negative pressure wound therapy is contraindicated and

should not be used, including cases of malignancy in the wound, untreated

osteomyelitis, cases where there is necrotic tissue with eschar present; and

wounds with exposed nerves, organs, vessels, or an anastomotic site.11

Further, the FDA lists guidelines for healthcare providers to use when

assessing the underlying condition of patients with wounds before applying

negative pressure therapy, to ensure that affected patients do not meet any

of the conditions where this type of treatment could cause complications.

Various patient risk factors make use of negative pressure wound therapy

difficult and susceptible to complications, even if they do not have the

specific wound type listed as being contraindicated. For example, a patient


54

with a history of bleeding disorder may not have a wound type that is

contraindicated for vacuum-assisted closure, but the patient’s bleeding

tendencies must be considered before prescribing this particular type of

treatment. Other considerations include such conditions as patients taking

anticoagulant medications, those who have blood vessel abnormalities, such

as particularly friable vessels or blood vessel infections; patients who will be

undergoing certain medical procedures such as MRI or use of a hyperbaric

chamber; and those who have circumferential wounds where application of a

negative pressure system might be overly constricting to tissue and could

possibly contribute to tissue ischemia.11

While not necessarily contraindicated, there are some situations in which

negative pressure therapy is not the most appropriate type of treatment for

some wounds. Despite its common use and proven benefits for many

different wound types, some people are not able to tolerate the negative

pressure system and the presence of the suction is uncomfortable.

Additionally, unlike a wound that is covered with a traditional gauze

dressing, a wound vacuum is a system that utilizes mechanical pressure and

the patient may not be able to accept being connected to the unit on a

continuous basis. In situations where long-term use of the system is in

place, such as for slow-to-heal wounds, skin irritation and odor have

occurred because of the extended use of the outer occlusive dressing, the

ongoing use of filler material and dressings in the wound bed, and the

collection of drainage from the site.

Although there are known contraindications to negative pressure therapy

use, any patient who has a health condition or clinical situation that could

potentially cause difficulties should be cautiously monitored with system use

or alternative methods of treatment should be explored. Negative pressure


55

therapy requires frequent monitoring of the system, the wound, and the

patient’s health. Continued vigilance with system use, combined with

avoiding negative pressure with known contraindications can go a long way

toward reducing or eliminating complications.

Malignancy

Malignant wounds are painful conditions that are thought to affect up to 5

percent of patients with cancer, and up to 10 percent of patients with

metastatic disease.12 Some patients with cancer can develop malignant

wounds when cancerous cells grow out of control and enter the blood or

lymphatic vessels and eventually reach the skin. The cancerous cells can

cause tissue ischemia by preventing normal blood flow, eventually leading to

necrosis of the skin and subcutaneous tissues. Malignant wounds are

sometimes referred to as fungating wounds; they can develop anywhere on

the body.

The wound develops in a method similar to a tumor that has erupted in the

skin and it may produce exudate or it may bleed. Some fungating wounds

have a strong odor and are quite painful for affected patients. They can be

extremely difficult to manage because they not only are made up of wound

tissue that needs to heal, but they also consist of cancerous cells as well.

Ultimately, treatment of a malignant wound requires a comprehensive

system of managing the underlying cancer as well as controlling pain and

undesirable symptoms associated with the wound at the skin surface.

The most common types of cancer that contribute to malignant wounds

include breast cancer, melanoma, lung cancer, and colorectal cancer.12 The

wound can develop as a result of the primary site of cancer, or it may occur

as a result of metastasis. For example, a patient with breast carcinoma could


56

develop a malignant wound on the surface of the breast if the cancerous

cells migrate to the skin surface. Alternatively, the same patient with

metastatic breast cancer that has spread to the lymph nodes could develop a

malignant wound in the axilla or another area where the lymph nodes are

close to the surface of the skin. If the cancerous cells are able to penetrate

the cardiovascular or lymphatic systems, they could travel to any number of

locations throughout the body to form malignant wounds.

Initially, malignant wounds can have variations in appearance and

characteristics. The skin surrounding the wound site may appear red and

inflamed but may remain intact for a time, forming a nodule at the area of

growth. There may be alterations in skin pigmentation, with skin color

changing to red, purple, brown, or black in appearance. Eventually,

ulceration develops and the skin surface is broken, revealing the open

wound. Malignant wounds tend to produce large amounts of exudate, they

can be quite painful, and they often have a very strong odor, all of which is

not only physically uncomfortable for the affected patient, but also

contributes to poor quality of life and potential depression.

The main goals of care of malignant wounds are to control exudate and odor

while promoting quality of life for the patient. Treatment of the underlying

cancer is also often ongoing in these cases, with many patients also

requiring medication, chemotherapy, or surgery while concurrently treating

their wounds. Although malignant or fungating wounds produce exudate that

needs to be controlled, applying a negative pressure treatment system to

any malignant wound for control of exudate and healing is contraindicated.

It is thought that application of vacuum pressure on this type of wound could

potentially encourage tumor growth, thus worsening the patient’s condition.


57

Because negative pressure wound therapy promotes angiogenesis during the

wound healing process, the new blood vessels formed could stimulate the

spread of cancerous cells and the patient’s condition could worsen.

Ideally, VEGF would contribute to new blood vessel formation to allow for

greater circulation to the wounded area and the promotion of healing at the

damaged site. However, too much VEGF and subsequent blood vessel

development can also contribute to disease development. For instance,

tumors can grow in size and progress when they have more blood vessels

available to them. VEGF is linked with the development of angiogenesis and

spread of some cancer cells through new blood vessels, including cells of

colorectal cancer.13

A study by Tanaka, et al., in the European Journal of Plastic Surgery

investigated the effects of negative pressure wound therapy on the growth

of new blood vessels within the wound bed by applying the therapy to

rabbits with wounds that were created specifically for the purposes of the

study. The study found that application of NPWT accelerated vasculogenesis,

or the generation of new blood vessels, by promoting expression of certain

types of VEGF in the wound bed.16 This suggests that the one of the

mechanisms by which negative pressure therapy promotes wound healing is

through the stimulation of VEGF. However, if NPWT is used when cancer is

present, it may support the growth of VEGF as well as new blood vessels

that will provide blood supply to the tumor, thereby sustaining it and

supporting its further growth and metastasis.

Normally, vacuum-assisted therapy is ideal for establishing a healthy wound

bed and promoting the growth of new blood vessels for wound healing, but

research has shown that too much of the therapy and too many new blood

vessels could cause proliferation of cancerous cells to the area, thereby


58

increasing the risk of new tumor growth or the spread of the cancerous

tissue.

Negative-pressure therapy could also be associated with some other wound

complications when malignancy is present. Any patient who has been

diagnosed with cancer is at risk for infection or further illness because the

immune system has already been compromised. When a fungating wound

develops, there is greater likelihood of complications because the body is

already using much of its resources and energy to control the cancer, and

there may be less focus on healing of the wound.

Cancerous wounds often must be treated very carefully, taking into

consideration the patient’s overall state of health because of the malignancy.

A case report by Andrades, et al., published in Case Reports in Clinical

Medicine presented a situation in which a patient with who had surgery for

soft-tissue sarcoma in the lower extremity developed complications and

tumor recurrence following negative pressure wound therapy. The initial

margins of the surgical wound were shown to be clear and without any

evidence of cancerous cells. The patient was set up to receive NPWT, but

after approximately two weeks, he experienced an increase in wound

exudate and increased pain at the site. A follow-up biopsy showed

recurrence of the cancer cells and the patient ultimately had to have lower

extremity amputation.9

With negative pressure therapy, there is the potential for an increase in

wound complications during healing and the wound may not necessarily

respond in the traditional manner. It should be noted that not all patients

with malignancy who use negative pressure wound therapy develop tumor

recurrence or even any complications associated with use of the system. In


59

fact, there have been some cases where NPWT has been carefully used

among certain patients with cancer in that it improved their quality of life.

One study published in the journal Palliative Medicine used negative

pressure therapy on six patients who were in metastatic stages of cancer

and who were all receiving palliative care only. The negative pressure

therapy in these situations did not cure the wounds and all of the patients

used the systems within weeks to months before death. However, all six

patients reported a decrease in wound odor and a decrease in overall

amount of exudate from their wounds; there were no instances of bleeding

or increased pain reported from the patients. Additionally, they all needed

fewer dressing changes for their wounds, which resulted in greater comfort

and improved quality of life during their final days.10

While this review represents the successful use of NPWT in several cases

where malignancy was present, note that all of the patients were at the

stage of receiving palliative care only and not active treatment. The negative

pressure system did help with control of exudate and wound odor, which was

beneficial for all involved and improved quality of life, but there was no

discussion of its impact on the size and healing rate of the wounds.

Consequently, NPWT could be considered on a case-by-case basis when

malignancy is present, as it may improve the patient’s comfort and life

value, but it could also contribute to clinical deterioration. In cases where

patients are actively trying to control their cancer, negative pressure is then

inappropriate and contraindicated.

Osteomyelitis

Although somewhat uncommon, osteomyelitis is a condition that occurs

when there is an infection in a bone, and it can develop as a severe

complication of a wound when an infection spreads to the deep, underlying


60

structures. Osteomyelitis most often occurs among people who are

immunocompromised, including older adults and children, as well as adults

with cancer, HIV infection, alcoholism, or those with chronic diseases that

have weakened the immune system. When these conditions are present and

the patient also has a chronic wound, he/she may be at greater risk of

complications as well.

The bones are normally impervious to infection, which is why osteomyelitis is

relatively rare. Bones can become infected when microorganisms are spread

through the bloodstream and collect and proliferate in the bone tissue.

Osteomyelitis most often develops when microorganisms from nearby

infected tissue or open wounds invade the bone tissue and multiply. Some

patients who have systemic infections in the bloodstream can also develop

osteomyelitis when the organisms travel through circulation to infect

particular areas. Additionally, some patients who already have deep wounds

that affect the skin, subcutaneous tissue, and underlying fascia may also

develop osteomyelitis if infectious organisms travel to the bones under the

wounded site. An example of this may be when a patient sustains a third-

degree burn that is slow to heal and has impacted the epidermis and dermis,

and the subcutaneous fat. Infectious organisms could invade the wound,

causing an infection, but if the organisms then spread into the nearby bone,

the affected patient could also develop osteomyelitis.

The most common organism associated with osteomyelitis is S. aureus,

although the infection can develop because of infiltration of a variety of

types of bacteria or fungi, and often, more than one organism is present in

the wound.14,15 In children, the condition typically develops in the bones of

the extremities, while in adults, osteomyelitis is more commonly seen in the

bones of the pelvis or the spine.14 Note that the condition could occur in any


61

of the bones of the body and some areas are more prominently affected than

others, such as the vertebrae.

When the infection develops, it can block normal blood flow to the affected

bone, eventually causing ischemia and tissue death. Osteomyelitis can be

considered acute or chronic. Among children, the infection is typically acute

and short-lived with appropriate treatment. Adults may have acute or

chronic infections; acute infection causes symptoms of pain and swelling at

the site, but over time when the infection becomes chronic, there may be

few symptoms at all, despite the residual bacteria.15 Some people with

chronic osteomyelitis experience occasional pain at the infection site that is

unresolved by pain medication; diminished use and tenderness in the

affected area are also common.

Most cases of osteomyelitis are treated with antibiotics that are specific for

the infectious agent. The wound may initially need to be cultured to identify

the organism causing the infection. In acute cases, short-term, intravenous

antibiotics are prescribed and are usually effective. Chronic osteomyelitis

may require long-term administration of antibiotics and possibly surgery to

remove damaged bone or muscle and to debride necrotic tissue.15 When a

wound is present that extends from the infected bone to the surface of the

skin, the patient also needs routine wound care through regular dressing

changes and possibly the application of topical antibiotics to the wound.

When osteomyelitis has developed because of wound infection, treatment is

still necessary, but negative pressure wound therapy is contraindicated in

cases where osteomyelitis is present and not well-managed. In some cases

where osteomyelitis has developed within a wound, negative pressure

therapy may be used when there is already treatment onboard. In other


62

words, untreated osteomyelitis is contraindicated with NPWT, but if the

condition is being managed, negative pressure therapy may be considered.

Untreated osteomyelitis can cause serious and life-threatening complications

if the infection spreads to another area or to a different bone. Some patients

can develop sepsis following osteomyelitis when it has not been well-

managed, and if enough necrotic tissue develops at the affected site, the

bone must be removed through amputation. Negative pressure therapy

should not be used when untreated osteomyelitis is present since applying

the filler material and the dressing over the site of the deep infection may

obstruct recovery. The system may draw exudate and fluid from the upper

layers of tissue but the deep infection remains and may actually continue

long enough to cause an abscess.41,42

A case study presented by Stanger, et al., in the International Wound

Journal reviewed a case of a patient who had a venous insufficiency ulcer of

the lower leg that had developed because of chronic osteomyelitis. The

patient was prescribed negative pressure wound therapy as treatment but

the wound tissue became necrotic and the anterior tibial artery was

perforated. The wound was cultured and the patient had a further infection

with Helcococcus kunzii bacteria. The study authors could not determine

whether the negative pressure wound therapy contributed to the tissue

necrosis and arterial bleed, but they speculate that because the system

removes air and fluid from the wound bed, it could have precipitated the

growth of H. kunzii, which is an anaerobic bacterium.17

Negative pressure wound therapy cannot control the spread of infectious

organisms when osteomyelitis is present. Further, because the system does

not reach into the affected bone, it cannot control the severe infection that


63

lies deep within the bone matrix or keep it from spreading to contaminate

other areas. A severe bone infection due to untreated osteomyelitis requires

management first through removal of necrotic tissue and cleansing of the

infected bone, which often involves surgical debridement of the intraosseous

infection, followed by administration of antibiotics. Some patients also need

orthopedic surgery for bone fixation to help the bone heal while recovering

from the infection. All of these processes must first be done before

implementing NPWT.

Wound treatment when underlying osteomyelitis is present may involve

surgical debridement of necrotic tissue from the wound bed, as well as some

other surgical interventions that can promote granulation tissue

development and wound healing, such as with placement of a skin graft in

severe cases. When osteomyelitis infection is in the underlying bone, the

surgical treatment of the wound may occur in conjunction with treatment of

the bone infection. When this happens, wound treatment through instillation

therapy or silver-impregnated dressings, as well as with negative pressure

wound therapy is appropriate. As long as the osteomyelitis is being managed

in some method, vacuum therapy could be used to simultaneously treat the

wound.

In contrast to untreated osteomyelitis, when a bone infection has developed

and there is an associated wound but the overall condition is being treated

through antibiotics and debridement, negative pressure wound therapy could

be an option for wound treatment if the system is closely monitored and

carefully managed. An example case report of this situation was published in

the Chinese Journal of Traumatology, which described a case of a man who

had suffered a clenched fist injury and developed subsequent osteomyelitis

in the affected bone and joint. A clenched fist injury is sometimes referred to


64

as a reverse bite injury, in which an individual who punches another person

in the mouth using a closed fist suffers a bite or injury to his hand from the

teeth of the victim. In the case report, the subject not only had

osteomyelitis, but also septic arthritis of the joint closest to his injury. The

individual’s wound was treated with negative pressure wound therapy, but it

was combined with antibiotic treatment and surgical revision. The patient

was able to recover from his infection through antibiotics and the wound was

fully healed after negative pressure therapy.19

An outcome such as this is not always the case when osteomyelitis is

present near the wound. Each situation in which a person presents with a

wound that is badly infected and where the infection has spread to the bone

must be managed according to the current situation, considering all factors

about the etiology of the wound, the patient’s health status, and any other

complications that have occurred alongside the condition. When

osteomyelitis is being controlled and the patient has received treatment,

negative pressure wound therapy could be appropriate for a nearby wound.

Alternatively, if osteomyelitis is part of a larger infection and is not being

managed, negative pressure therapy is contraindicated and other methods

of wound treatment should be considered instead.

Non-enteric and Unexplored Fistulas

There are some cases where a wound is so complex that fistula development

appears. A fistula is described as an abnormal opening or passageway

between two structures. Fistulas may be external, such as when there is a

path that develops between an organ and the skin; or they could be internal,

such as when a fistula develops between two organs.20 Fistulae development

is a complication that may be more likely to follow surgery, although these

abnormal passageways can occur as part of a number of circumstances,


65

including following cancer treatment; with severe infection, such as

pancreatitis, or as a result of trauma. They are associated with a high level

of morbidity and mortality for the affected patient.

Often, when a fistula occurs near a wound, it is the result of an infection or

an uncontrolled disease process. The infection can spread from one area to

another, causing damage and necrosis that ultimately breaks down some of

the tissue, leaving a path of a fistula. Excess fluid within a wound bed can

also contribute to fistula formation; if the wound is not properly suctioned

and exudate is not controlled, the excess fluid can increase pressure within

the wound bed with nowhere to go.

Trauma to the skin or underlying tissues near the wound can lead to tissue

breakdown and necrosis, causing fistula formation. Some wounds develop

tunneling or sinus tracts near the edge of the wound margins. These are

somewhat similar to fistulae in that they cause an abnormal passageway

extending from the wound. They are often located under the skin, tunneling

through subcutaneous tissues and causing damage, and ultimately leading

to serious infection or abscess formation.20,21

Fistulae often produce an excessive amount of fluid from the affected site;

often, the drainage must be contained through very frequent dressing

changes with gauze covering or even with pouching as is sometimes seen

with ostomies. Patients with wounds that have developed fistulas need

frequent wound management, including numerous dressing changes,

medications and application of topical antibiotics, and possibly drain

insertion to remove excess fluid. Grafting is also needed in some complex

cases where fistulae have developed; the graft may be applied over the


66

wound site, but the fistula is sometimes left exposed so that it can continue

to drain and be dealt with.20

Negative pressure therapy may be used in some wounds where fistulas have

occurred. The presence of a fistula alone is not a contraindication toward

using negative pressure therapy. In fact, some studies have shown that

NPWT works very well in healing of wounds with fistulae and other complex

configurations. For example, a case study by Trevino, et al., published in the

journal Wounds reported on the success of changing an enterocutaneous

fistula associated with a large open wound into one that could be controlled

with a drainage system while the original wound was treated with NPWT.100

In many cases, if the fistula could be isolated from the original wound, it

may be treated separately from the wound itself.97

A fistula that is classified as enteric involves communication between a

portion of the intestinal tract and another area of the body, including any of

the internal organs, the bones, or the skin. As an example, an

enterocutaneous fistula describes a condition in which a fistula has

developed between some point in the gastrointestinal tract and the surface

of the skin. In contrast, a non-enteric fistula is a specific type of abnormality

in which there is communication between two areas, but the gastrointestinal

system is not involved.

Fistulae are more likely to occur in situations where there are complications

with the wound, including cases of wound dehiscence or where there is

already infection or abscess. The main forms of treatment for these types of

complications involve controlling drainage output, maintaining the patient’s

hydration status, controlling wound odor, and preventing further

complications. When present, they may need to have packing or filler


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material placed directly in the channel and are then covered with an external

wound dressing. Other factors related to wound care, including wound

debridement and dressing changes, take place regularly as well to ensure

appropriate healing.

An unexplored fistula is one that cannot be visualized or checked; its actual

extent and endpoints are unknown. This particular type of fistula is also

contraindicated for negative pressure wound therapy. Normally when a

fistula develops, the healthcare provider must first explore the wound to

determine the extent and severity of the abnormality. After the extent of

tissue involvement has been determined, treatment processes can be

started. However, when the degree of tissue involvement cannot be

determined, it is unknown how much material is needed to pack the wound

bed.

If the NPWT system were used and filler material placed into the channel of

the fistula without knowing how deep or long the fistula is, it may be too

difficult to perform dressing changes and there is a risk of materials being

left behind in the wound. Additionally, the filler material of the negative

pressure system makes contact with the edge of the wound bed where

healing needs to occur to mechanically impact the tissues and promote

growth of granulation tissue as well as angiogenesis. If a fistula is large and

undetermined, the filler material may not contact the base of the wound.

The fistula is considered as a blind tunnel in which it is not safe to attempt to

pack filler material into the passage.

If the fistula can be isolated from the rest of the wound, NPWT can be

implemented to treat just the wound itself and not the fistula. To segregate

the fistula from the rest of the wound, the provider covers the entrance of


68

the fistula with a dressing such as petroleum gauze and then packs the rest

of the wound bed with filler for the negative-pressure device. The opening of

the fistula is not covered with filler. The rest of the system is put in place

with an adherent dressing covering the entire wound but with a hole cut at

the site of the fistula opening. An ostomy bag or collection container can

then be secured to the site of the fistula to collect the drainage and output

while the rest of the wound receives the negative pressure therapy.20

Necrotic Tissue with Eschar

Because of the damage and disruption to the skin when a wound occurs, the

healing process often produces a certain amount of drainage and exudate

and there is an increased risk of tissue necrosis when wounds take longer to

heal. Necrotic tissue describes tissue that is dead because of a lack of

oxygen, typically because of absent circulation to the affected site. The skin

and tissue in the wound bed may also die because of infection; when

microorganisms infect a certain area, the tissue can become necrotic

because pathogens damage the skin to the point that it causes cell death.

When tissue necrosis occurs due to a lack of oxygen, an area may first

become ischemic, in that there is reduced blood flow, but it still has the

potential for viability.

When tissue becomes necrotic, it cannot be recovered. When present in the

wound bed, necrotic tissue can contribute to infection and inflammation; its

occurrence usually signifies an underlying issue that has caused tissue

death, including chronic disease that affects circulation, tissue injury, or

excess pressure, such as with development of pressure ulcers. When

necrosis is present, the wound cannot fully heal. Thus, it is essential that the

wound remains cleared of necrotic tissue and that steps are taken to prevent

its development or recurrence.


69

As discussed, eschar describes dead tissue that is found within a wound;

eschar is typically present in full-thickness wounds and is not the same as a

scab, which is actually a crusty layer of dried and coagulated blood and fluid,

although it may have a similar appearance. It is often thick and tough and

may appear brown or black in color. When present within a pressure ulcer,

eschar makes wound staging difficult because it is sometimes impossible to

determine how deep the necrotic tissue extends. Eschar is a type of necrotic

tissue that is often removed as part of debridement. Slough is the thick,

yellow substance that is made up of pus, and it, too is a type of necrotic

tissue that must be removed in order for the wound to heal properly.

When present, necrotic tissue prevents the growth of new granulation tissue

and angiogenesis that are essential to healing. It also blocks the work of the

negative pressure system so that the wound cannot drain properly and

bacteria and biofilm remain in place and are difficult to remove. Because

necrotic tissue such as eschar is made up of components of connective

tissue, it eventually becomes hard and dry, which prevents the negative

pressure system from working properly. If an antimicrobial solution is added

to filler material, eschar acts as a barrier to the medication reaching the

wound bed.

Prior to starting negative pressure therapy, the wound bed should be

cleaned and devitalized tissue removed. Debridement is necessary if there is

necrotic tissue present, and the system cannot be used if debridement has

not first cleared the area. As noted, there are several different methods of

debridement available that are successful in removing eschar and slough to

clean the wound bed and expose the healing tissue underneath. If the

necrotic tissue remains, but vacuum therapy is applied anyway, the effects

of the system may not be effective.


70

The eschar itself, being dry and tough, can prevent successful contact

between the filler material and the wound bed for granulation tissue to fill in.

Its presence also prevents an adequate seal from being formed over the site

and the entire system may be either inefficient or completely futile. The

suction from the negative pressure cannot reach the damaged areas under

the eschar to exert its effects and to induce wound healing. Similarly, when

excess slough is present in the wound bed, the negative pressure system is

not effective. Slough develops as a type of necrotic tissue in the wound; it is

not always as firmly connected to the wound bed when compared to eschar,

but it typically requires debridement for thorough removal.

Slough is made up of various components that contribute to its appearance

and constitution, including leukocytes, collagen, and fibrin. It is often creamy

yellow or gray in appearance, although it should not be confused with new

granulation tissue. Slough is stringy and slimy in consistency; the tissue

itself is separating from the normal tissue found in the wound bed. When

slough coats part of the wound bed, it can cover areas of the wound that

need oxygen and moisture control for healing. An area covered by slough is

more prone to infection and it may develop more exudate and odor.79,80

Excess slough may also be associated with an increase in biofilm formation.

Recall that biofilm is a collection of microorganisms and extracellular

materials such as proteins and polysaccharides that can attach to the

surfaces of tissues in the wound bed. Biofilm can be difficult to remove

because as it develops, it is encased in a protective covering of extracellular

material. Because the slough covers parts of the wound that need to heal, it

creates a barrier and increases the amount of surface area where

microorganisms can adhere and proliferate to create an infection.


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There is some evidence that the greater length of time that biofilm is

present, it becomes more difficult to fully remove.81 Therefore, because

slough can be associated with biofilm formation and has the propensity to

contribute to wound infection, it should be removed through debridement as

soon as possible and prior to starting NPWT.

An article by Percival, et al., published in the Journal of Wound Care

described chronic wounds as essentially being persistently stuck in the

inflammatory phase of healing, and that they remain in this stage because of

issues with the normal cellular phases of healing. This persistent state of

inflammation not only prevents a wound from healing within a normal

timeframe, but also increases the amount of necrotic tissue formed that can

contribute to poor wound oxygenation as well as infection. When managing

slough that has formed in the wound bed, the authors recommended a

process known as desloughing, which is a type of debridement that involves

removing slough through a mechanism of debridement using wound cleanser

combined with mechanical debridement that removes excess necrotic tissue

and slough as well as many of the microorganisms they may be harboring.8o

The article further described slough as a type of biofilm, in that it contains

microorganisms that can develop into infection and that these organisms

have the potential to separate from the slough and proliferate in the

surrounding tissues as well as within the wound dressing and the periwound

area.80

Debridement of slough must be performed to remove the excess from the

wound bed first so that the area will be cleared and the filler material can

come into contact with tissue. Despite routine dressing changes that cleanse

the wound of debris, slough can still develop in the wound bed while the

vacuum system is in use. If slough is noted during a dressing change when


72

the system is off for a period, the necrotic tissue should first be removed

through debridement before applying the next dressing.35 Based on the

increased potential for infection associated with excess slough, it is

important that the wound needs to be cleansed and debrided prior to

application of NPWT in order for the system to be accurate and effective,

without any other barriers in place.

Blood Vessels, Organs, Nerves, and Anastomotic Site

Some wounds are so complex and extensive that underlying structures are

visible in the wound bed. Some very deep wounds expose the organs

underneath the damaged tissue, whether because of traumatic injury or due

to further tissue breakdown over time. Open exposure to blood vessels and

nerves can cause bleeding and significant pain for the affected patient.

Surgical wounds may uncover areas of internal repair, including anastomosis

sites. All of these kinds of occurrences require intervention and healing, but

treatment through NPWT is not always indicated.

The suction applied through NPWT is an essential component of the vacuum

system; without the suction effect, the system cannot clear excess moisture

and fluid from the wound nor stimulate the growth of new and healthy tissue

in the wound bed. As integral as suction is to the system, it must be well

regulated and used in specific areas to be effective and to avoid harm to the

tissues. Suction must only be used in situations where the tissue is strong

enough to withstand the pressure. Very fragile tissue can easily bleed and

could sustain even more damage than the original wound if the negative

pressure from the suction continuously draws on it. For instance, if the

negative pressure system comes into direct contact with blood vessels, it

could tear the fragile covering of the vessel and cause bleeding. With larger

vessels, blood loss can be severe and life-threatening.


73

Very deep wounds could potentially expose some internal organs, not only

increasing the risk of infection, but also direct organ damage. The filler

material of the negative pressure system should never be placed directly

into contact with internal organs, as the connection with the suction can

cause fistula formation near the organ and perpetuate problems with wound

healing.77,97 Placing the system so that it is in contact with anastomotic sites

can also be damaging, as the negative pressure may destroy the tissue

designed to be surgically connected.

Although direct contact with organs and blood vessels is not recommended,

there may be some cases where clinicians may use vacuum-assisted closure

in wounds that are large enough that the system comes within close

proximity to one of these structures. When this is the case, it is

recommended that a barrier be placed next to the structure before applying

the filler material and the rest of the wound care system. A dressing made of

oil emulsion or petroleum gauze is advised to act as a barrier so that the

system is not in direct contact with exposed organs or other delicate

structures.6

A study by Wang, et al., published in Wounds evaluated the use of negative

pressure therapy among subjects with complex abdominal wounds. In cases

where subjects had such deep openings in the abdomen that the intestinal

tract was visible, the authors recommended the use of porous hydrocolloid

dressings impregnated with silver ions and placed directly over the intestine

before applying the negative pressure. Another system proposed was the

use of several layers of paraffin gauze placed under the foam filler.98 In

either case, there is a barricade of a dressing in between the organ or

exposed tissue and the negative pressure system so that further damage will

not occur.


74

While some wounds produce heavy exudate and large amounts of fluid

output, the vacuum system is not designed to accommodate significant

blood loss that could occur if the system comes directly into contact with

blood vessels and causes bleeding. Of note, most collection systems with the

vacuum pump have alarms in place that will notify the healthcare provider of

an increase in fluid output. In cases of severe wound bleeding because of

inappropriate placement of the system, it should self-alarm with blood loss,

however, avoiding applying the system to exposed blood vessels in the first

place will significantly reduce the risk of errors.

Summary

Application of the negative pressure wound therapy system is typically done

at a health facility. Once the system has been set up and turned on, it will

remain in place to work until dressing changes are made and overall wound

healing is measured and evaluated. In comparison to traditional forms of

wound bandages, which may require dressing changes at least once a day,

negative pressure dressings are typically changed every 2 to 3 days. In

between time, the system continues to work by drawing out and collecting

fluid and stimulating tissue repair. Over time, the wound heals and the

system can be discontinued.

Use of NPWT does not necessarily relegate a person to bed; in fact, most

patients who use the NPWT system connected to their wound site can

continue to be active and may actually heal at a faster rate than those using

traditional therapy. In addition to the filler material placed in the wound,

some negative pressure systems also have irrigation techniques in place that

involve instilling solution, allowing for a dwell time, and then removing the

solution through suction where it is collected in a canister.


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The increase in use of negative pressure devices for vacuum-assisted wound

closure has transformed wound care, bringing a mode of treatment

availability to even some of the most complex wounds. The system has

helped many people to successfully complete the wound healing process,

whether their wounds are acute surgical incisions or chronic wounds that are

slow to heal. Negative pressure therapy has many proven benefits for wound

care and can reduce the time and energy required for wound healing. When

compared to some traditional forms of wound care, vacuum-assisted closure

continues to promote faster healing and improve overall outcomes.

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1. With negative pressure wound vacuum systems,

a. suction should be intermittent, never constant. b. the patient should not be able to feel the suction. c. suction may be constant or intermittent. d. the suction system is, by definition, uncomfortable.



a. True b. False


a. promotes granulation tissue formation. b. can treat traumatic wounds but not necrotizing fasciitis. c. is designed to be used on a constant basis. d. is used in lieu of surgical debridement.

4. A coating of protective ointment or ______________ dressing

may be applied to the skin to shield and protect it.

a. hydrocolloid b. saline c. bacitracin d. polyhexanide


systems

a. is placed over the drain system. b. is cut to fit over the periwound skin. c. consists of hydrocolloid or foam. d. is placed in the wound bed.

6. The development of a significant amount of granulation tissue is

a. seen in all wounds. b. most closely associated with primary intention of healing. c. is more often seen with chronic wounds. d. is more often seen with acute wounds.


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7. True or False: A significant amount of drainage exuding from a wound site indicates that negative pressure is not further needed.

a. True b. False

8. Prior to negative pressure therapy, eschar that has developed

a. must be removed prior to negative pressure therapy. b. may remain and filler material may be placed around it. c. must remain and filler material placed directly on it. d. should not be debrided but should be allowed to slough on its own.

9. If a wound has a significant amount of eschar or necrotic tissue, it

may be more difficult to measure

a. wound depth. b. the circumference of the wound. c. the diameter of the wound. d. All of the above

10. If a wound bed has exposed blood vessels or very deep

structures such as bone or tendons that are visible,

a. they should first be covered with a contact layer dressing before adding the filler.

b. a greater amount of filler material will be needed. c. filler material may be placed directly on these structures within the

wound bed. d. filler material may not be used.

11. There are two main kinds of foam types used as filler material

with negative pressure wound therapy, generally referred to as

a. green foam and white foam. b. thick or thin foam. c. porous or non-porous foam. d. black foam and white foam.


78

12. Foam fillers control moisture in the wound bed and are _______________ so they can prevent bacteria or other microorganisms from penetrating the wound bed.

a. impermeable b. dense c. semi-permeable d. porous

13. True or False: A wound that is too dry will heal more slowly,

while a wound that remains too moist will have tissue breakdown and skin maceration.

a. True b. False

14. Because of its higher levels of strength, _____ foam needs to be

used at higher pressure levels, compared to polyurethane foam types, when it is used for wound treatment.

a. black b. green c. open-weave d. white

15. Use of cotton gauze in treating wounds may be simpler than

foam filler because gauze

a. does not need to be cut or sized to fit the wound bed. b. uses higher negative pressure. c. creates more granulation tissue in the wound site. d. does not require a covering.

16. Use of polyester as a filler material in wound treatment is

a. not recommended. b. useful because it is naturally hydrophobic. c. difficult to use because it may release small fibers into the wound. d. simpler because it stretches its shape to fit the wound bed.


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17. Once filler material has been placed in a wound, an occlusive dressing is placed over the filler and the wound bed. This dressing

a. is transparent so clinicians may see the wound and filler material. b. is an airtight layer. c. must be removed before negative pressure wound therapy may

begin. d. All of the above

18. Which of the following is characteristic of a dressing with a high

moisture vapor transmission rate (MVTR)?

a. Moisture is evaporated through the dressing to dry the wound site. b. The high-MVTR dressings are reusable. c. Measuring wound exudate with a high MVTR dressing is difficult. d. A canister is used to collect heavy exudate.

19. True or False: Drainage from a healing wound that is not

infected is typically serous drainage and appears translucent with a pink tinge.

a. True b. False

20. Negative pressure is a level that is

a. measured at -125 mmHg or below. b. below the normal atmospheric pressure. c. equal or greater than the Earth’s atmospheric pressure. d. a measure of pain to a wound site.

21. The amount of negative pressure prescribed for wound

treatment

a. varies between care facilities and negative pressure models. b. can be painful at the wound site if set too high. c. will be ineffective if set too low. d. All of the above


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22. Negative pressure wound therapy is thought to promote the production of a specific type of protein in the wound bed known as

a. vascular endothelial growth factor (VEGF). b. extracellular proteins and polysaccharides (biofilm). c. collagen. d. fibrin.

23. Which of the following conditions is NOT contraindicated for the

use of negative pressure wound therapy?

a. Malignancy in the wound b. Untreated osteomyelitis c. Necrotic tissue with eschar present. d. A history of a bleeding disorder

24. True or False: Malignant wounds are sometimes referred to as

fungating wounds; they can develop anywhere on the body.

a. True b. False

25. Which of the following must be performed when a patient has a

severe bone infection due to untreated osteomyelitis BEFORE negative pressure wound treatment may be administered?

a. Removal of necrotic tissue b. Administration of antibiotics c. Cleansing of the infected bone d. All of the above


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CORRECT ANSWERS: 1. With negative pressure wound vacuum systems,

c. suction may be constant or intermittent. “Because the system provides constant or intermittent suction, depending on the physician’s orders, the patient often feels the suction as a type of pulling sensation. It should not be painful or uncomfortable; the suction is typically set at a low enough level that it can pull off excess fluid and stimulate new growth of tissue without being too strong.”



b. False “In comparison to traditional forms of wound bandages, which may require dressing changes at least once a day, negative pressure dressings are typically changed every 2 to 3 days.”


a. promotes granulation tissue formation. “The case series showed that in 98% of the cases, the patients who underwent negative pressure wound therapy with irrigation had healed complex wounds when the process was used for a period of treatment and when combined with surgical debridement. The system is not designed to be used on a constant basis as part of wound treatment and is instead designed to be adjunctive therapy, but when utilized for a set period of time, the regular irrigation of the wound promotes granulation tissue formation. The system described was used in wounds caused from a variety of mechanisms, including diabetic foot ulcers, traumatic wounds, and necrotizing fasciitis.”


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4. A coating of protective ointment or ______________ dressing may be applied to the skin to shield and protect it.

a. hydrocolloid “A coating of protective ointment or hydrocolloid dressing may be applied to the skin to shield and protect it. With a standard system (including those that do not involve instillation of saline), the protective coating is applied after wound cleansing, debridement, if necessary, and wound measurement.”


systems

d. is placed in the wound bed. “The filler material ... used as the filler is fitted into the wound itself, where it works at a cellular level to impact the cells and the blood vessels within the tissue to promote new growth and to establish healing.... The type of material may vary, depending on the system used, but most types of filler consist of a kind of foam or gauze .... Once prepared, the filler is placed in the wound bed before being covered with a drain that is connected to the negative pressure device.”

6. The development of a significant amount of granulation tissue is

c. is more often seen with chronic wounds. “Not all wounds involve development of a significant amount of granulation tissue; this occurrence is most closely associated with secondary intention of healing and is more often seen with chronic wounds. When negative pressure is used in an acute wound or a situation where granulation tissue is not anticipated, use of filler material may need to be adjusted.”

7. True or False: A significant amount of drainage exuding from a

wound site indicates that negative pressure is not further needed.

b. False “A significant amount of drainage from the site indicates the supplemental need for negative pressure to remove excess fluid.”


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8. Prior to negative pressure therapy, eschar that has developed

b. may remain and filler material may be placed around it. “Prior to application of the filler material, the bed of the wound may need debridement or cleaning to remove dead tissue or debris. The patient may need pain medication prior to debridement or even when changing the dressing of the negative pressure system. If slough is present within the wound bed, it should be removed prior to placing filler material for the vacuum on top. If eschar has developed, the filler material may be placed around it, depending on whether the healthcare provider has ordered for eschar to remain in place. If eschar must be removed prior to negative pressure therapy, it is often softened first to facilitate easier removal and then can be debrided, such as through surgical debridement.”

9. If a wound has a significant amount of eschar or necrotic tissue, it

may be more difficult to measure

a. wound depth. “Part of the assessment of a wound ... is understanding the depth of the wound. This often involves measurement of total depth from the location of the skin surface to the wound bed below.... wounds that are very moist with exudate and those that contain a significant amount of eschar or necrotic tissue may be difficult to measure. Many health clinicians measure diameter or circumference of wounds and note major characteristics, but measurement of wound depth is not always performed.”

10. If a wound bed has exposed blood vessels or very deep

structures such as bone or tendons that are visible,

a. they should first be covered with a contact layer dressing before adding the filler. “If a wound bed has exposed blood vessels or very deep structures such as bone or tendons that are visible, they should first be covered with a contact layer dressing before adding the filler.”


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11. There are two main kinds of foam types used as filler material with negative pressure wound therapy, generally referred to as

d. black foam and white foam. “One of the more common types of filler material used with negative pressure therapy is foam sponge. Of the foam types, there are two main kinds that are often used, depending on the wound circumstances. These foam types are generally referred to as black foam and white foam.”

12. Foam fillers control moisture in the wound bed and are

_______________ so they can prevent bacteria or other microorganisms from penetrating the wound bed.

c. semi-permeable “Foam fillers control moisture in the wound bed and are semi-permeable so they can prevent bacteria or other microorganisms from penetrating the wound bed.”

13. True or False: A wound that is too dry will heal more slowly,

while a wound that remains too moist will have tissue breakdown and skin maceration.

a. True “...a wound that is too dry will heal more slowly, while a wound that remains too wet will develop tissue breakdown and skin maceration.”

14. Because of its higher levels of strength, _____ foam needs to be

used at higher pressure levels, compared to polyurethane foam types, when it is used for wound treatment.

d. white “Because of its higher levels of strength, white foam needs to be used at higher pressure levels when compared to polyurethane foam types.”


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15. Use of cotton gauze in treating wounds may be simpler than foam filler because gauze

a. does not need to be cut or sized to fit the wound bed. “Use of gauze may be simpler than some other forms of filler material. For instance, when compared to foam filler, gauze often does not need to be cut or sized to fit the wound bed.... The amount of negative pressure used with cotton gauze is somewhat lower when compared to that used with foam filler.... Gauze may be a filler of choice in cases where the wound does not need to develop much granulation tissue.”

16. Use of polyester as a filler material in wound treatment is

b. useful because it is naturally hydrophobic. “The polyester used in non-woven filler materials is made up of strong fibers. When considering items created from polyester, ... these products are typically durable, they do not stretch out of shape.... Polyester is also naturally hydrophobic as well, so it resists and repels water and fluid, preventing maceration of nearby skin when it is used as a wound dressing.... [I]t creates a dressing that is stable and resilient that can be packed into a wound bed and fixed in place without adhering to the fragile growth of new tissue and without releasing lint or small fibers into the wound bed.”

17. Once filler material has been placed in a wound, an occlusive

dressing is placed over the filler and the wound bed. This dressing

a. is transparent so clinicians may see the wound and filler material. “Once filler material has been placed in a wound, an occlusive dressing is cut to size and placed over the filler material and the wound bed; in some kits, this is referred to as the Layer 1 drape.... Despite maintaining a tight seal over the site of the wound, the drape is actually a semi-permeable layer that allows for some exchange of oxygen and moisture in the skin surrounding the wound bed.... It is transparent so that the clinician can visualize the wound and the filler underneath, which is important in case of complications or difficulties....”


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18. Which of the following is characteristic of a dressing with a high moisture vapor transmission rate (MVTR)?

c. Measuring wound exudate with a high MVTR dressing is difficult. “The MVTR describes how much water or fluid is evaporated through an item. A dressing with a high MVTR allows extra moisture to be absorbed and then evaporated through the dressing, but the area underneath remains moist. Some disposable negative pressure systems utilize these dressings, and when the therapy is complete, the dressing and the system are discarded, because the dressing has replaced the need for a canister. A downside of using this particular type of system is that it is not as easy to measure wound exudate when compared to a collection container; however, if a wound is not producing very heavy exudate, this type of dressing may be appropriate.”

19. True or False: Drainage from a healing wound that is not

infected is typically serous drainage and appears translucent with a pink tinge.

b. False “Drainage from a healing wound that is not infected is typically serous drainage and appears clear and thin. Drainage may appear red or pink in color. Sanguineous drainage is red because it contains blood. Serosanguineous drainage is clear drainage that has a small amount of blood in it, so it may be tinged pink. Both serosanguineous and sanguineous drainage indicate that some amount of bleeding is present within the wound bed, whether it is over-bleeding from tissue damage or whether bleeding is occurring at the capillary level. The presence of blood within exudate typically means that some amount of damage has occurred to the blood vessels in the wound.”

20. Negative pressure is a level that is

b. below the normal atmospheric pressure. “Negative pressure is a level that is below the normal atmospheric pressure.... This negative pressure has the effect of a vacuum or suction that can be set and modified to different levels depending on patient use.”


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21. The amount of negative pressure prescribed for wound treatment

a. varies between care facilities and negative pressure models. b. can be painful at the wound site if set too high. c. will be ineffective if set too low. d. All of the above [correct answer]

“Actual prescribed pressure amounts ... vary between facilities and particular negative pressure models. The amount of pressure to apply is always recommended by the prescribing provider when starting out.... Too high of settings can be painful at the wound site; alternatively, pressure that is not high enough may render the system ineffective.”

22. Negative pressure wound therapy is thought to promote the

production of a specific type of protein in the wound bed known as

a. vascular endothelial growth factor (VEGF). “Negative pressure therapy is thought to promote the production of a specific type of protein in the wound bed known as vascular endothelial growth factor (VEGF).”

23. Which of the following conditions is NOT contraindicated for the

use of negative pressure wound therapy?

d. A history of a bleeding disorder “The U.S. Food and Drug Administration has issued a list of wound types and conditions for which negative pressure wound therapy is contraindicated and should not be used, including cases of malignancy in the wound, untreated osteomyelitis, cases where there is necrotic tissue with eschar present.... [A] patient with a history of bleeding disorder may not have a wound type that is contraindicated for vacuum-assisted closure, but the patient’s bleeding tendencies must be considered before prescribing this particular type of treatment.”


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24. True or False: Malignant wounds are sometimes referred to as fungating wounds; they can develop anywhere on the body.

a. True “Malignant wounds are sometimes referred to as fungating wounds; they can develop anywhere on the body.”

25. Which of the following must be performed when a patient has a

severe bone infection due to untreated osteomyelitis BEFORE negative pressure wound treatment may be administered?

a. Removal of necrotic tissue b. Administration of antibiotics c. Cleansing of the infected bone d. All of the above [correct answer]

“A severe bone infection due to untreated osteomyelitis requires management first through removal of necrotic tissue and cleansing of the infected bone, which often involves surgical debridement of the intraosseous infection, followed by administration of antibiotics. Some patients also need orthopedic surgery for bone fixation to help the bone heal while recovering from the infection. All of these processes must first be done before implementing NPWT.”


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References Section

The References below include published works and in-text citations of published works that are intended as helpful material for your further reading. [References are for a multi-part series on Wound Vac Therapy]. 1. Tiwari, V. (2012). Burn wound: how it differs from other wounds?

Indian J Plast Surg. 45(2): 364-373. 2. Burn Injury. (n.d.). Electrical burns. Retrieved online at

http://burninjuryguide.com/types-burns/electrical-burns/ 3. Rowan, M., et al. (2015). Burn wound healing and treatment: review

and advancements. Crit Care, 19: 243. 4. UW Health. (n.d.). Burn center frequently asked questions. Retrieved

online at http://www.uwhealth.org/burn-center/burn-center-frequently-asked-questions/29616

5. Teng, S. (2016). Use of negative pressure wound therapy in burn patients. International Wound Journal 13(S3): 15-18.

6. Huang, C., et al. (2014). Effect of negative pressure wound therapy on wound healing. Current Problems in Surgery 51(7): 301-331. Retrieved online at http://www.currprobsurg.com/article/S0011-3840(14)00084-7/fulltext

7. Morgan, N. (n.d.). Wound exudate types. Retrieved online at https://woundcareadvisor.com/blog/wound-exudate-types/

8. Dealey, C. (2012). The care of wounds: a guide for nurses (4th ed.). Oxford, UK: John Wiley & Sons, Ltd.

9. Andrades, P., et al (2014). Tumor recurrence after negative pressure wound therapy: an alert call. Case Reports in Clinical Medicine 3(6).

10. Riot, S., et al. (2015). Is the use of negative pressure wound therapy for a malignant wound legitimate in a palliative context? “The concept of NPWT ad vitam”: a case series. Palliat Med. 29(5): 470-473.

11. Henderson, V., et al (2010). NPWT in everyday practice. Retrieved online at http://www.woundsinternational.com/media/issues/375/files/content_9720.pdf

12. Seaman, S. (2014). Providing appropriate care to patients living with malignant wounds. Today’s Wound Clinic 8(9). Retrieved online at http://www.todayswoundclinic.com/articles/providing-appropriate-care-patients-living-malignant-wounds

13. Kubek, E., et al. (2013). Negative-pressure wound therapy and the emerging role of incisional negative pressure wound therapy as prophylaxis against surgical site infections. In Méndez-Vilas, A. (Ed.). Microbial Pathogens and Strategies for Combating Them: Science, Technology and Education. Badajoz, Spain: Formatex Research Center


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14. Lalani, T. (2017). Overview of osteomyelitis in adults. UpToDate. Retrieved online at https://www.uptodate.com/contents/overview-of-osteomyelitis-in-adults?source=search_result&search=osteomyelitis&selectedTitle=1~150.

15. Schmitt, S. (2017). Osteomyelitis. Retrieved online at https://www.merckmanuals.com/professional/musculoskeletal-and-connective-tissue-disorders/infections-of-joints-and-bones/osteomyelitis

16. Tanaka, T., et al. (2016). Negative pressure wound therapy induces early wound healing by increased and accelerated expression of vascular endothelial growth factor receptors. Eur J Plast Surg. 39: 247-256.

17. Stanger, K., et al (2015). Management of chronic osteomyelitis of the tibia with life-threatening complications under negative pressure wound therapy and isolation of Helcococcus kunzii. International Wound Journal 12(4): 445-446.

18. Brinkert, D., et al (2013). Negative pressure wound therapy with saline instillation: 131 patient case series. International Wound Journal 10(s1): 56-60.

19. Miroslav, K. (2016). Clenched fist injury complicated by septic arthritis and osteomyelitis treated with negative pressure wound therapy: one case report. Chinese Journal of Traumatology 19(3): 176-178.

20. Stein, S. (2017). Overview of enteric fistulas. UpToDate. Retrieved online at https://www.uptodate.com/contents/overview-of-enteric-fistulas?source=search_result&search=fistula%20management&selectedTitle=1~150.

21. Wound Source. (2017). Tunneling wounds or sinus tracts. Retrieved online at http://www.woundsource.com/patientcondition/tunneling-wounds-or-sinus-tracts

22. Demidova-Rice, T. (2012). Acute and impaired wound healing: pathophysiology and current methods for drug delivery, part 1: normal and chronic wounds: biology, causes, and approaches to care. Adv Skin Wound Care 25(7): 304-314.

23. Wound Source. (2016). The four stages of wound healing. Retrieved online at http://www.woundsource.com/blog/four-stages-wound-healing

24. Wound Source. (2017). Venous insufficiency ulcers. Retrieved online at http://www.woundsource.com/patientcondition/venous-insufficiency-ulcers

25. Tidy, C. (2016). Diabetes, foot care and foot ulcers. Retrieved online at https://patient.info/health/diabetes-foot-care-and-foot-ulcers

26. National Pressure Ulcer Advisory Panel. (n.d.). NPUAP pressure injury stages. Retrieved online at


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http://www.npuap.org/resources/educational-and-clinical-resources/npuap-pressure-injury-stages/

27. Wound Consultants, Inc. (n.d.). Pressure ulcer staging. Retrieved online at http://woundconsultant.com/sitebuilder/staging.pdf

28. Kroshinsky, D. and Strazzula, L. (2017). Pressure ulcers. Retrieved online at http://www.merckmanuals.com/professional/dermatologic-disorders/pressure-ulcers/pressure-ulcers

29. Srivastava, R. (2014). A non-randomized, controlled clinical trial of an innovative device for negative pressure wound therapy of pressure ulcers in traumatic paraplegia patients. Int Wound J. DOI: 10.1111/iwj.12309.

30. Zhang, J., et al. (2014). Effectiveness and safety of negative-pressure wound therapy for diabetic foot ulcers: a meta-analysis. Plastic and Reconstructive Surgery 134(1): 141-151.

31. Kucharzewski, M., et al. (2014). The application of negative pressure wound therapy in the treatment of chronic venous leg ulceration: authors experience. BioMed Research International (2014). Article ID 297230, 5 pages. Retrieved online at https://www.hindawi.com/journals/bmri/2014/297230/

32. Morey, J. (2014). Assessment and treatment of lower extremity ulcers. Retrieved online at http://www.wi-don-council.org/wp-content/uploads/2014/09/Judy-Assessment-and-Treatment-of-Lower-Extremity-UlcersUlcers.ppt.pdf

33. Federman, D., et al. (2016). Wound healing society 2014 update on guidelines for arterial ulcers. Wound Repair and Regeneration 24(1): 127-135.

34. Association for the Advancement of Wound Care (AAWC) Guideline of Pressure Ulcer Guidelines (2010). Malvern, PA: Association for the Advancement of Wound Care (AAWC).

35. Bazarov, I., Vartivarian, M., Reyzelman, A. (2014). Laser debridement: can it have an impact for chronic wounds? Podiatry Today 27(5). Retrieved online at http://www.podiatrytoday.com/laser-debridement-can-it-have-impact-chronic-wounds

36. Sardina, D. (2010). Ask the treatment expert: defining the tissue types seen in pressure ulcers. McKnight’s. Retrieved online at http://www.mcknights.com/news/ask-the-treatment-expert-defining-the-tissue-types-seen-in-pressure-ulcers/article/179985/

37. Advanced Tissue. (2014). What is the appropriate treatment of black heels? Retrieved online at https://www.advancedtissue.com/appropriate-treatment-black-heels/

38. Acapsil (n.d.). What is primary intention, secondary intention and tertiary intention healing? Retrieved online at http://acapsil.com/en-gb/2016/11/19/what-is-primary-intention-secondary-intention-and-tertiary-intention-healing/


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39. KCI. (2010). V.A.C. therapy patient information booklet. Dublin, Ireland: KCI Medical, Ltd.

40. Rock, R. (2014). Guidelines for safe negative-pressure wound therapy. Retrieved online at https://woundcareadvisor.com/guidelines-for-safe-negative-pressure-wound-therapy/

41. Ellies, G. (2016). How to apply vacuum-assisted closure therapy. Nursing Standard, 30, 27, 36-39.

42. Hasan, M., Teo, R., Nather, A. (2015). Negative-pressure wound therapy for management of diabetic foot wounds: a review of the mechanism of action, clinical applications, and recent developments. Diabet Foot Ankle, 6. DOI: 10.3402/DFA.V6.27618

43. Advanced Tissue. (2014). Your guide to foam dressings. Retrieved online at https://www.advancedtissue.com/guide-foam-dressings/

44. Losi, P., et al (2012). Silicone-coated non-woven polyester dressing enhances reepithelialisation in a sheep model of dermal wounds. Journal of Materials Science: Materials in Medicine 23(9): 2235-2243.

45. Quality Logo Products. (2017). Polypropylene, polyester, and nylon: guide to materials. Retrieved online at https://www.qualitylogoproducts.com/promo-university/guide-to-materials.htm

46. Nunan, R., Harding, K., Martin, P. (2014). Clinical challenges of chronic wounds: searching for an optimal animal model to recapitulate their complexity. Disease Models & Mechanisms 7: 1205-1213. Retrieved online at http://dmm.biologists.org/content/7/11/1205

47. Zhao, G., et al. (2013). Biofilms and inflammation in chronic wounds. Adv Wound Care (New Rochelle) 2(7): 389-399.

48. Brown, C. (2016). Measuring the depth of a wound. Skin Deep Sept/Oct 2016. Retrieved online at https://www.advancedtissue.com/wp-content/uploads/2013/04/Sept-Oct-16-Newsletter1.pdf

49. Technology update: Understanding foam dressings. (n.d.). Wounds International 1(2). Retrieved online at http://www.wintjournal.com/media/journals/_/274/files/technology-update-understanding-foam-dressings.pdf

50. MöInlycke Health Care. (2017). Avance Foam dressing kit with transparent film. Retrieved online at http://www.molnlycke.us/advanced-wound-care-systems/npwt-system/avance-foam-dressing-kit/#confirm

51. KCI. (2013). Frequently asked questions about V.A.C.® therapy. Retrieved online at http://www.kci-medical.sg/SG-ENG/vacfaqs#

52. Lavery, L., et al (2014). Negative pressure wound therapy with low pressure and gauze dressings to treat diabetic foot wounds. Journal of Diabetes Science and Technology 8(2): 346-349.


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53. Téot, L., et al (2017). Novel foam dressing using negative pressure wound therapy with instillation to remove thick exudate. International Wound Journal. DOI: 10.1111/iwj.12719

54. Campbell, B. (2012). The science behind negative pressure wound therapy. Pullman, WA: Washington State University

55. Rao, J. (2013). Atmospheric pressure: definition & facts. Retrieved from https://www.livescience.com/39315-atmospheric-pressure.html

56. Daigle, P., et al (2013). How mechanical deformations contribute to the effectiveness of negative-pressure wound therapy. Wound Repair and Regeneration (2013).

57. Wound Source.com. (n.d.). Edema. Retrieved online at http://www.woundsource.com/patientcondition/edema

58. Owens, B. (2013). Silver makes antibiotics thousands of times more effective. Nature. Retrieved online at https://www.nature.com/news/silver-makes-antibiotics-thousands-of-times-more-effective-1.13232

59. Park, J., et al. (2013). Evaluation of an antimicrobial silver foam dressing. Wounds 25(6): 153-159. Retrieved online at http://www.woundsresearch.com/article/evaluation-antimicrobial-silver-foam-dressing

60. Patmo, A., et al (2014). The effect of vacuum-assisted closure on the bacterial load and type of bacteria: a systematic review. Adv Wound Care (New Rochelle) 3(5): 383-389.

61. Malmsjö, M., et al (2014). Use of bacteria- and fungus-binding mesh in negative pressure wound therapy provides significant granulation tissue without tissue ingrowth. Eplasty 14: e3.

62. Berlowitz, D. (2017). Clinical staging and management of pressure-induced skin and soft tissue injury. UpToDate. Retrieved online at https://www.uptodate.com/contents/clinical-staging-and-management-of-pressure-induced-skin-and-soft-tissue-injury?source=search_result&search=essentials%20of%20negative%20pressure&selectedTitle=3~150.

63. Wound Educators.com. (2015). Modalities utilized in wound healing: negative pressure wound therapy. Retrieved online at http://woundeducators.com/npwt/

64. Evans, K. (2017). Overview of treatment of chronic wounds. UpToDate. Retrieved online at https://www.uptodate.com/contents/overview-of-treatment-of-chronic-wounds?source=search_result&search=vaccuum%20assisted%20closure&selectedTitle=2~46.

65. Lower Extremity Review. (2010). Kalypto NPWT system. Retrieved online at http://lermagazine.com/products/kalypto-npwt-system


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66. Armstrong, D. and Meyr, A. (2017). Basic principles of wound management. UpToDate. Retrieved online at https://www.uptodate.com/contents/basic-principles-of-wound-management?source=search_result&search=wound%20care&selectedTitle=1~150.

67. Cannon, J.W. and Rasmussen, T.E. (2017). Severe extremity injury in the adult patient. UpToDate. Retrieved online at https://www.uptodate.com/contents/severe-extremity-injury-in-the-adult-patient?source=search_result&search=lower%20limb%20trauma&selectedTitle=1~150.

68. Sandoz, H. (2014). Negative pressure wound therapy: clinical utility. Chronic Wound Care Management and Research 2015:2, 71-79.

69. World Union of Wound Healing Societies (WUWHS) Consensus Document (2016). Closed surgical incision management: Understanding the role of NPWT. Wounds International.

70. Acosta, S., et al (2016). Negative-pressure wound therapy for prevention and treatment of surgical-site infections after vascular surgery. BJS 104(2): e75-e84.

71. Chaboyer, W., et al (2014). Negative pressure wound therapy on surgical site infections in women undergoing elective caesarean sections: a pilot RCT. Healthcare 2(4): 417-428

72. Karlakki, S., et al. (2016). Incisional negative pressure wound therapy dressings (iNPWTd) in routine primary hip and knee arthroplasties. Bone Joint Res 5(8): 328-337.

73. Gestring, M. (2017). Negative pressure wound therapy. UpToDate. Retrieved online at https://www.uptodate.com/contents/negative-pressure-wound-therapy?source=search_result&search=negative%20wound%20vac&selectedTitle=1~150.

74. University of Michigan School of Medicine (2012). Surgical wound classifications. Retrieved online at http://www.med.umich.edu/surgery/mast/r_surgwoundclass.html.

75. Webster, J. (2014). Negative pressure wound therapy for skin grafts and surgical wounds healing by primary intention. Cochrane Database of Systematic Reviews. DOI: 10.1002/14651858.CD009261.pub3

76. Sibaja, P., et al. (2017). Management of the open abdomen using negative pressure wound therapy with instillation in severe abdominal sepsis. Int J Surg Case Rep. 30: 26.-30.

77. Novak, A., et al. (2014). The evidence-based principles of negative pressure wound therapy in trauma & orthopedics. Open Orthop J. 8: 168-177.

78. Tuncel, U., et al. (2012). Clinical experience with the use of gauze-based negative pressure wound therapy. Wounds 24(8). Retrieved


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online at http://www.woundsresearch.com/article/clinical-experience-use-gauze-based-negative-pressure-wound-therapy

79. Swanson, T., et al (2014). Slough: what is it? How do we manage it? Retrieved online at http://www.woundinfection-institute.com/wp-content/uploads/2014/11/Slough_AWMA_2014.pdf

80. Percival, S. (2015). Slough and biofilm: removal of barriers to wound healing by desloughing. Journal of Wound Care 24(11).

81. Halim, A., et al. (2012). Wound bed preparation from a clinical perspective. Indian J Plast Surg. 45(2): 193-202.

82. Miller, J. (2015). Managing your soft tissue injury. Retrieved online at http://physioworks.com.au/treatments-1/what-are-the-phases-of-a-soft-tissue-injury.

83. Rezzadeh, K., et al. (2015). The use of negative pressure wound therapy in severe open lower extremity fractures: identifying the association between length of therapy and surgical outcomes. Journal of Surgical Research 199(2): 726-731.

84. Wound Care Center. (n.d.). Dehisced wounds. Retrieved online at http://www.woundcarecenters.org/article/wound-types/dehisced-wounds

85. Ko, Y. and Jung, S. (2014). Vacuum-assisted closure versus conventional treatment for postlaparotomy wound dehiscence. Ann Surg Treat Res. 87(5): 260-264.

86. Granick, M. and Teot, L. (2012). Surgical wound healing and management (2nd ed.). Boca Raton, FL: CRC Press.

87. Ma, Z., et al. (2016). Negative pressure wound therapy promotes vessel destabilization and maturation at various stages of wound healing and thus influences wound prognosis. Exp Ther Med. 11(4): 1307-1317.

88. Stechmiller, J. (2012). Biofilms and wound infection: assessment and treatment. University of Florida College of Nursing: National Pressure Ulcer Advisory Panel.

89. Phillips, P., et al. (2013). The effect of negative pressure wound therapy with periodic instillation using antimicrobial solutions on Pseudomonas aeruginosa biofilm on porcine skin explants. International Wound Journal Dec; 10 Suppl 1: 48-55.

90. Kim, et al. (2015). Negative pressure wound therapy with instillation: review of evidence and recommendations. Malvern, PA: HMP Communications, LLC.

91. Krasner, D., et al. (2012). Chronic wound care 5. Malvern, PA: HMP Communications, LLC.

92. Soylemez, M., et al (2016). Intermittent negative pressure wound therapy with instillation for the treatment of persistent periprosthetic hip infections: a report of two cases. Therapeutics and Clinical Risk Management 2016(12): 161-166.


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93. Bryant, R. and Nix, D. (2012). Acute & chronic wounds: current management concepts (4th ed.). St. Louis, MO: Elsevier Mosby

94. Rock, R. (2014). Getting positive results with negative pressure wound therapy: the story behind NPWT. Retrieved online at http://www.clevelandclinicmeded.com/live/courses/WOCN/pre-syllabus/100314_1330_Montague_Positive%20results%20with%20negative%20pressure.pdf

95. Smith & Nephew. (n.d.). PICO. Retrieved online at http://www.smith-nephew.com/key-products/advanced-wound-management/pico/

96. Tongtong, L., et al. (2016). Early application of negative pressure wound therapy to acute wounds contaminated with Staphylococcus aureus: An effective approach to preventing biofilm formation. Exp Ther Med. 11(3): 769-776.

97. Trevino, C., et al (2014). Conversion of an enterocutaneous fistula associated with an open abdominal wound into a drain-controlled enterocutaneous fistula. Wounds 26(2). Retrieved online at http://www.woundsresearch.com/article/conversion-enterocutaneous-fistula-associated-open-abdominal-wound-drain-controlled-enterocu

98. Wang, Z., et al (2017). Negative pressure wound therapy for patients with complex abdominal wounds. Wounds 29(7). Retrieved online at http://www.woundsresearch.com/wang

99. Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edition. Susan Standring, Ed. Chapter 73. Elsevier.

100. Franklin, S. (2013). Techy medicine for wounds: meet NPWT. Retrieved online at http://www.vmdtechnology.com/techy-medicine-wounds-npwt-1/

101. Cheong, Y., et al. (2013). Negative pressure wound therapy for inguinal lymphatic complications in critically ill patients. J Korean Surg Soc 85(3): 134-138. Retrieved online at https://openi.nlm.nih.gov/detailedresult.php?img=PMC3764365_jkss-85-134-g001&req=4

102. Medline. (2017). PICO negative pressure wound therapy. Smith & Nephew. Retrieved online at http://www.medline.com/product/PICO-Negative-Pressure-Wound-Therapy-by-Smith-Nephew/Z05-PF54450

103. Mount Nittany Health. (2016). Staff ed: cleaning and dressing pressure ulcers. Retrieved online at https://www.mountnittany.org/articles/healthsheets/6672


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