pediatric perfusion gerald mikesell, ccp childrens national medical center washington dc

Pediatric Perfusion

Gerald Mikesell, CCPChildrens National Medical Center

Washington DC

Fundamental Goals of CPB

To facilitate a surgical intervention Provide a motionless field Provide a bloodless field Supply adequate substrate for the

metabolism of all tissues Remove unwanted byproducts of

metabolism Minimize the deleterious effects of

bypass

The Cardiovascular Perfusionist

The perfusionist controls the patients blood flow, blood pressure, and gas exchange as well as monitoring and delivering anticoagulation and protective heart medications

Differences Between Adult and Pediatric

Cardiopulmonary Bypass

Major differences exist between adult and pediatric cardiopulmonary bypass (CPB), stemming from anatomic, metabolic, and physiologic differences in these 2 groups of patients.

Cardiopulmonary BypassGeneralized inflammatory reaction

Capillary Leak Cardiac dysfunction Organ dysfunction/MSOF Mortality

CPB Deleterious Effects Coagulopathy

Systemic heparinization Hemodilution of factors Platelet dysfunction/ consumption Coagulation factor consumption

Cellular destruction/Hemolysis Mechanical stress

Inflammatory Activation Mechanical stress Non-endothelial exposure Complement activation Cytokine and leukocyte activation White cell activation

Effects of CPB

All the discussed effects of bypass are related to exposure to our circuits and the mechanical devices used to allow bypass to procede Total bypass time continually emerges as a

risk factor for morbidity and mortality Optimal outcome is benefited by surgeons

operating accurately and rapidly, using efficient sequencing of repair

Bypass Management

No perfect means to measure level of support

Normal monitoring: EKG, NIRS, Saturations and Pressures are designed for non-bypass monitoring

With bypass, loss of normal physiologic homeostatic control, loss of pulsatility, change of oxygen supply, hemodilution

Venous Saturation Measurement Though looked to as a standard of

perfusion adequacy, there are limitations Cooling causes left shift of oxyhemoglobin

dissociation curve Cooling causes increase of pH

Alkaline blood also causes left shift of oxyhemoglobin curve

Fetal Hemoglobin in neonates Left shift of curve

Lower levels of 2,3DPG in bank blood also cause left shift

Therefore, as temperature of blood drops, venous saturation will rise but brain and tissues are still warm and not receiving the O2 needed to meet metabolic demand

Venous Saturation Measurements Left Heart Return and collateral steal

Dangerous to assume all flow pumped into patient is going where planned. Colleteral development with some lesions can steal up to 50% of flow and return directly to venous return

Collaterals to pulmonary veins to LA across unrepaired ASD,VSD to venous cannula

Differental return flow from SVC vs IVC Warm brain uses lots of O2 and SVC with low

sat but Systemic blood colder, IVC with higher sat, blood mixes in venous line and sat monitor reading appears fine

Bypass Management

We do things to exert control of the patient on CPB and work to maintain a margin of safety for the patient even if all parameters aren’t perfectly controlled. The important decisions that we can control:

TemperaturepHHematocritPerfusion flow

Temperature

Advantage: Reduce Metabolic Rate

Tissue preservation Myocardial preservation Allows flow variation to improve surgical

access Flexibility in cannulation

Decreased inflammatory response to CPB

Decreases Complement activation and release of vaso-active substance

Decreases white cell activation

Temperature

Disadvantages: Prolongs bypass Increases probability of post-operative

bleeding Possible prolonged post-operative

recovery Especially in adults

Use of Hypothermia

Effect on Central Nervous System The effect of hypothermia on the nervous

system is multifactorial. In addition to decreasing the metabolic rate, hypothermia has been demonstrated to decrease the release of glutamate, which is involved in CNS injury during CPB.

A negative effect of hypothermia on brain function is the loss of autoregulation at extreme temperatures, which makes the blood flow highly dependent on extracorporal perfusion.

Techniques of Hypothermia

Currently, two surgical techniques commonly used in congenital heart surgery, namely,

Deep hypothermic circulatory arrest (DHCA)

Hypothermic low-flow bypass (HLFB)

Deep Hypothermic Circulatory Arrest

DHCA provides excellent surgical exposure by eliminating the need for multiple cannulas within the surgical field. Normally use arterial cannula and a single venous cannula in the right atrium.

Surgical technique Initiate the cooling phase prior to

institution of CPB by simple cooling of the operating room environment and begin surface cooling the patient

After systemic heparinization and cannulation, initiate CPB.

Monitor body temperature via esophageal, tympanic, and rectal routes.

Have also seen less edema.

Deep Hypothermic Circulatory Arrest

Disadvantages:Time constraints on the surgical team.

Must be highly organized with the repair and efficient with technique. Precise and accurate repairs must be completed in limited time.

Deep Hypothermic Circulatory Arrest

Late 1980’s study out of Boston Childrens looking at DHCA vs low flow in arterial switch patients Both groups with deep hypothermia and

hematocrit of 20% One group had circulatory arrest, the other

group a low flow of 50 mL/kg/min Patients have now been followed for 20+ years

CA patients had lower verbal and development scores until age 4. Caught up with developmental scores by age 4 and by age 8 caught up with verbal.

Both groups were below mean controls. If longer periods of arrest are anticipated, may

be advantageous to apply ancillary procedures such as intermittent reperfusion.

Deep Hypothermic Circulatory Arrest

Mechanical Problems Arterial cannula misplacement can occur. If the

cannula inadvertently slips beyond the takeoff of the right innominate artery, preferential perfusion to the left side of the brain can be observed.

Presence of any anomalous systemic-to-pulmonary shunts can lead to shunting of blood away from the systemic circulation, through the pulmonary circuit, and then through the venous cannula returning to the CPB circuit.

Thus, the systemic perfusion is shunted away from the body in a futile circuit back to the CPB circuit. Anatomic lesions where such shunting can occur include an unrecognized patent ductus arteriosus and large aortopulmonary collaterals as found in pulmonary atresia.

Effect of pH

pH and pCO2 have strong systemic and cerebral vasodilatory effects

Effects are opposite with pulmonary circulation Shift in pH or pCO2 can cause a marked

shift in blood flow between pulmonary and systemic beds

A-P collaterals or systemic to pulmonary shunts (B-T shunt for example) need to be considered

Effect of pH

Perfusionist important to acid-base control during CPB Flow rate Dilution Hypothermia

As temperature drops, pH of H2O increases

Effect of pH

Alpha Stat vs pH Stat: First studies in the 1980s Alpha Stat

Maintains optimal intracellular enzyme activity

Maintains cerebral auto-regulation and the coupling of flow and metabolism at low temperatures

In adults, showed improved cognitive outcome

Possibly related to reduced number of micro-emboli

pH Stat: Loss of cerebral auto-regulation as

temperature drops Cerebral flow is pressure dependent, could

cause “luxuriant” flow with the potential for increased micro-emboli

Effects of pH

Boston Childrens Hospital did multiple studies, both clinical and animal, in the late 1980’s Alpha stat patients had worse

developmental outcome during cooling than pH stat. There was strong correlation during cooling of pCO2 and developmental outcome

The circulatory attest time of 35-60 minutes had no impact

With alpha stat patients, there were 19 cases of choreoathetosis in 4 years/ With pH stat, there were none

In lab studies with piglets, found that cerebral micro-circulation was better in pH stat piglets vs alpha stat

Effect of pH

In 1990’s Boston Childrens completed two randomized clinical studies which both showed better outcomes with pH stat pH stat had lower mortality (p=0.058) pH stat, with continuous EEG monitoring

during surgery and 48 hours post bypass, show lower rate of post-op seizures

pH stat: First EEG activity returned faster after circulatory arrest

pH stat: Decreased post-op acidosis (p=0.02) pH stat: Decreased post-op hypotension

(p=0.05)

Effect of pH

Boston pH vs Alpha stat clinical studies (Cont)

pH stat: Shorter mechanical ventilation time and ICU stay (p=0.01)

pH stat: in d-TGA sub-group, higher cardiac index with lower inotrope requirement

pH stat: A trend to better developmental scores at 1 yr of age

Effect of pH

Boston study: Conclusion was pH stat:

Suppresses cerebral metabolism and lengthens safe duration of DHCA for a given temperature and hematocrit

Improves oxygen availability by counteracting the oxy-hemoglobin curve’s leftward shift with dropping temperatureVery important in early cooling period

when blood is cold but brain still warm

Improved developmental outcome

pO2 and Bypass Historically feeling that hyperoxia was

responsible for microemboli associated mobidity post CPB A problem with bubble oxygenators, especially

without arterial filters Two studies in piglets at Boston Childrens

in 1999 looked at this issue Compared bubble oxygenator vs membrane

oxygenator with arterial filter Compared normoxia with hyperoxia and DHCA Compared free radical production Compared histological injury of normoxic vs

hyperoxic

pO2 and Bypass

Study Results: At cold temperatures there was increased

microemboli with bubble oxygenator vs membrane oxygenator with filter

As temperature was dropping, there were more microemboli with normoxia vs hyperoxia

Reasoned that nitrogen was less soluble in the blood than oxygen as the temperature dropped

Looking at histological injury, there was significantly more injury in the brains of normoxic animals vs hyperoxic animals after 120 minutes of arrest at 15 deg C

An interesting observation was that temperture gradient both cooling and warming had no effect on microemboi

Bypass and Optimal Flow

The standard bypass flow target has always been 2.4 L/min/m²

Must weigh all the options: Normal may be as much as 3.5-4 L/min/m² Hemodilution can add up to 3-4 times greater

flow demand to meet O2 demand Add aorto-pulmonary collaterals with 50% of

pump flow returning directly to the pump. Leaves an effective flow of 1.2 L/min/m²

Potential for hypoxic injury

Bypass and Optimal Flow

Flow considerations for bypass: What is the metabloic demand for different temperatures Normal thermia

Mild hypothermia: temperature greater than 30ºC

Moderate hypothermia: temperature 25-28º C

Deep hypothermia: temperature less than 18ºC

CPB Flows

• 2.4 -3.0 l/m2 at 37o

• 1.6 l/ m2 at 28o

• 1.2 – 1.6 l/m2 at 25o

• 1.0 – 1.6 l/m2 at 20o

• 0.5 – 1.0 l/m2 at 15o

Hemodilution

Decreased concentration of cells & solids in the blood RBC’s, WBC’s, Platelets, Plasma

Proteins, Clotting factors, Lytes (Ca,Mg)

Is hemodilution bad? May allow better perfusion as

temperature drops Causes a drop in O2 delivery

blood volumeprime volume

Adult

blood volumeprime volume

Pediatric

blood volumeprime volume

Infant

Prime Volumes

30% of blood volume

23% of total volume

Hct 35% 27%

50% of blood volume

33% of total volume

Hct 35% 23%

176% of blood volume

63% of total volume

Hct 40% 14%

Hemodilution

On bypass and before cooling, O2 demand still high flow not compensated Thought to be related to drop in perfusion

pressure Perfusion pressure change in direct proportion

to change of viscosity with hemodilution If hemodilution not on bypass, body compensates by

increasing cardiac output

Hemodilution vs Cerebral Protection

1996 study by Shinoka et al, in JTCVS. Working with piglets looked at 3 levels of hematocrit, 10,20 and 30%; went on bypass and cooled to 15ºC and arrested for 60 minutes. Low hematocrit piglets had worse neurological

outcome, both physiologically and histologically.

Lowest hematocrit piglets showed hypoxic stress during cooling and before arrest

Hemodilution vs Cerebral Protection

2001 Study by Sakamoto et al looked at the interaction of hematocrit (20 and 30%), pH (alpha stat vs pH stat) and temperature on the neurological impact of piglets Lower hematocrit, more alkaline pH and

longer circulatory arrest were predictive of neurological damage

Hematocrit: 30% showed distinct advantage to neuroprotection vs 20%

pH stat was more neuro-protective with lower histological injury vs alpha stat

A temperature of 15ºC was more neuro-protective than a temperature of 25ºC

Study looked at circulatory arrest times of 60, 80 and 100 min

Hemodilution vs Cerebral Protection

2001 a companion study by Duebener et al looked at microcirculation (capillary blood flow) and at tissue oxygenation with hematocrits of 30% vs 10%. 30% was associated with improved re-

perfusion (functional capillary density) vs 10% There was no evidence of capillary plugging or

white cell activation with the higher viscosity level of the 30% hematocrit

Hemodilution vs Cerebral Protection

2002 Study by Jonas et al, JTCVS. The Influence of Hemodilution on Outcome After Hypothermic CPB: Results of a Randomized Trial in Infants 147 patients randomized to a hematocrit of 21

(74) or 27 (73) Hematocrit 21: post-operative serum lactate

was higher, cardiac index was lower and had greater total body water at POD1.

Blood product usage was the same for both groups

Baley Scales of Infant Development: at 1 year the high hematocrit group had higher Psycomotor Development Index (low hct group was 2 SD below normal populations) , there was no difference in Mental Development Index

Showed that a hemodilution practice thought to be safe was associated with adverse perioperative and developmental outcomes in infants

Hemodilution and Bypass

Hemoconcentration During bypass

Conventional

Modified Ultrafiltration

MUF

Hemodilution and Hemoconcentration

Conventional Removes free water, dissolved ion and small

molecules Remove byproducts of bypass and excess volume,

i.e. cardioplegia after delivery Maximize hematocrit before termination of bypass We like to come off with hct of 30-35 or even 35-40

with single ventricle repairs

Modified Ultra-Filtration (MUF) Hemoconcentration of patients circulating

blood volume along with remaining volume in circuit

Improvement with CO and blood pressure Disadvantages are the need to maintain

heparinization and cannulation for extended time and…

Complexity of circuit and risk of air around arterial cannula

Myocardial Protection Strategies

Myocardial Protection The term "myocardial protection" refers to

strategies and methodologies used either to attenuate or to prevent postischemic myocardial dysfunction that occurs during and after heart surgery.

Principles of Myocardial Protection The main principles of myocardial protection

are the reduction of metabolic activity by

hypothermia the therapeutic arrest of the contractile

apparatus and all electrical activity of the myocytes by administering cardioplegic solution (e.g. depolarizing of the membrane potential by high potassium crystalloid or blood cardioplegia)

CARDIOPLEGIC TECHNIQUES

Cardioplegic solutions contain a variety of chemical agents that are designed to

arrest the heart rapidly in diastole, create a quiescent operating field, and provide reliable protection against

ischemia/reperfusion injury. There are two types of cardioplegic

solutions: crystalloid cardioplegia

extracellular intracellular

blood cardioplegia. These solutions are administered most

frequently under hypothermic conditions.

CARDIOPLEGIA DELIVERY SYSTEM

Purpose = arrest and preservation

Two types of delivery crystalloid cardioplegia: no

blood added blood cardioplegia: blood is

mixed with crystalloid) proposed advantages: oxygen,

buffers, proteins

Cardioplegia Delivery

Antegrade

Retrograde

Directly to coronary

Cases CNMCCardioplegia Delivery

2-3o CConducer Recirculation System

Plegisol (Oxygenated)First dose 20 ml/kgFollowing doses10 ml/kgAbove 50 kg 1000 mlWith 500 ml second dose

Blood Cardioplegia at CNMC

Use a modified Plegisol recipe. Potassium is added with a high K and low K formulation. Cardioplegia is delivered 4:1 blood:crystalloid.

High K: 20 mEq/LLow K: 10 mEq/L

First dose is high K then switch to low K for redosing

Hemodilution and Prime

1985 study by Haneda et al, compared crystalloid prime vs blood and plasma prime in pediatrics Crystalloid prime patients had a +63 mL/kg

fluid balance vs + 16 mL/kg with blood/plasma

Blood/plasma prime group had a lower mortality and 50% reduction in ICU time compared with the crystalloid group

There is a general consensus that prime for children should not include lactate or dextrose. Hyperglycemia is associated with a worse neurological outcome.

Prime used at Childrens National Medical Center

Circuit primed with Plasma-lyte A, excess drained off

Packed Cells between 3-7 da old Try to maximize 2,3-DPG and have lower K+ Units are leuco-depleted in the blood bank Primary unit of RBC is divided, half for

perfusion for prime and half for anesthesia to use post bypass so donor exposure can be reduced

FFP: Same donor as RBC when possible We use some of the unit in the prime, add

some to the circuit while rewarming and any remaining goes to anesthesia post CPB.

If using clear prime, will add 100-300 mL 25% Albumin

CNMC Prime

Cefazolin: 25 mg/kg, (1 gm maximum dose)

Lasix: 0.25 mg/kg Feel a loop diuretic is helpful to maintain renal

function Mannitol 25%: 0.5 gm/kg (12.5 gm

maximum dose) Potent osmotic diuretic with free radical

scavenger properties Add to prime, some also give a second dose on

release of cross clamp Heparin Sodium Bicarbonate 84% Solumedrol: 30 mg/kg

Patients ˂ 1 week and DHCA patients

CNMC Bypass

Magnesium Sulfate: 50 mg/kg (1 gm maximum) Given immediately after cross clamp release Has significantly reduced incidence of

junctional ectopic tachycardia ( JET) Calcium Gluconate: 500 mg-1 gm

Given 5 minutes after release of cross clamp

Current PrimesCNMC

250-300 Neonates

300-400Infants

400-600 Toddlers

Blood product use for CPB

Hemodilution from pump prime

Volume expansion Treatment of iatrogenic

or concomitant coagulopathies

Surgical blood loss

Descending order of

incidence

PRBC Transfusion

Hematocrit On CPB < 27% Post CPB < 27% This is patient dependent: size and

lesion Oxygenation

SVO2 < 65% at maximal flow on bypass Hemodynamics

Acute blood loss

FFP Transfusion

Coagulopathies Obvious non surgical bleeding

Long pump runs Hemodilution Preexisting conditions

Heparin resistance Inadequate ACT despite 2X normal

Heparin Dose “Fast” easy source of ATIII

Platelet Transfusion Triggers

Coagulopathies Obvious non surgical bleeding

Long pump runs Hemodilution Preexisting conditions DHCA patients

Low platelet count < 70,000

How do we achieve low prime circuits

Get mind set Look at circuit as separate

components Be willing to use different

venders Must modify perfusion

techniques Must be adaptable Constantly update equipment &

techniques

Our goal with bypass is reduce the surface area of exposure of the patient’s blood to our circuits. We can accomplish this goal through our selection of circuit components and cannulae and the use of techniques such as bio-passive circuit coatings to attenuate the response of our patients to bypass

Tubing 2/32" I.D. 0.6ml/ft.

3/32" I.D. 1.8ml/ft.

1/8" I.D. 3.5ml/revolution(2.5 ml/ft.)

5/32" I.D. 5ml/revolution(3.7 ml/ft.)

3/16" I.D. 7ml/revolution(5 ml/ft.)

1/4" I.D. 13ml/revolution(9.65 ml/ft.)

5/16" I.D. 18ml/revolution(13.5 ml/ft.)

3/8" I.D. 27ml/revolution(21.71 ml/ft.)

7/16" I.D. 38ml/revolution(28.5 ml/ft.)

1/2" I.D. 45ml/revolution(38.61 ml/ft.)

5/8" I.D. 65ml/revolution(55.77 ml/ft.)

Arterial Lines

3/16” 1200 ml/min

1/4” 2500 ml/min

3/8” 7000 ml/min

Venous Lines

3/16” 600 ml/min

1/4” 1500 ml/min

5/16” 2200 ml/min

3/8” 4000 ml/min

1/2” >7000 ml/min

A-V LOOPSCNMC

Flows 0-1 L/min 3/16 x 1/4

Flows 1 – 1.5 L/min 1/4 x 1/4

Flows 1.5 – 2.5 L/min 1/4 x 3/8

Flows 2.5 – 4.0 L/min 3/8 x 3/8

Flows > 4.0 L/min 3/8 x 1/2

Oxygenators

New Oxygenators specific for infants and pediatrics Reduced volume Arterial flilters incorporated in design

Reduces prime of circuit (??) Improved flow dynamics

Reduced pressure drop Improved reservoir design with improved

drainage and volume handling VAVD capable

Most common

Maquet

Terumo

Medtronic

Sorin

Medos

VENOUS RESERVOIR

Two types of venous reservoirs hardshell venous

reservoir “open” system

collapsible bag venous reservoir

“closed” system

VENOUS RESERVOIRSHARDSHELL VS. BAG

Arterial Blood Gas Control

Blender and Gas Flowmeter Carbon Dioxide Anesthesia - Forane

Arterial Blood Gas ControlAnesthesia: Forane

CDI500

On-line arterial blood gas, hemoglobin/hematocrit, K+ and venous saturation

Cannula Selection

Arterial Important component of the circuit as it’s a

point of narrowing in the pressurized limb of the bypass circuit

A point of increased flow velocity and potential high sheer stress and increased hemolysis

Want largest cannula possible for expected flow but not large enough to obstruct vessel lumen preventing retrograde flow around the cannula

Other factors include: thin wall, tolerate temperature variations without kinking or stressing aorta when cold

Ease of insertion

VENOUS CANNULA Two types of venous cannulation

procedures right atrial cannulation

single RA cannula: through the RA appendage; tip in body of the RA

cavo-atrial cannula (or two-stage cannula): through the RA appendage; tip in the IVC and “basket” in the body of the RA

used when the heart IS NOT going to be opened

vena caval cannulation one cannula through the RA appendage into

the IVC a second cannula through the RA wall into

the SVC used when the heart IS going to be opened

a tie encircling the IVC and SVC is secured

Cannula Selection

Venous Essential for surgeon to have a cannulation

plan based on the defect to allow for optimal venous return and perfusion of the entire body throughout the procedure

Cannulation must not interfere with appropriate sequencing of operative steps

A balance of a size large enough to meet flow demands and small enough to be accommodated with a particular defect

Right angle vs straight Develop flow tables for cannulas ( and for each

surgeon)

Cannulas

Venous Drain blood

from the body 2 stage Bicaval Femoral Arterial

Return blood to the body

Aortic Femoral

THE SUCTION SYSTEM Purpose = evacuate shed blood Usually ¼” I.D. tubing Requires an occluded roller pump This blood directed to the

cardiotomy reservoir filters any fluid to 19-35 microns open system: cardiotomy integral with

venous reservoir closed system: cardiotomy is separate

from venous reservoir blood, priming fluids, blood components

VENT (or sump) SYSTEM Purpose = evacuate LV blood

sources of LV blood right atrium escaping the venous

cannula bronchial venous blood non-coronary collateral blood

Usually ¼” I.D. tubing Usually requires an occluded

roller pump requires a negative pressure

relief valve This blood directed to the

cardiotomy reservoir

SAFETY SYSTEMS

Reservoir level detection Air bubble detection

(arterial line) Arterial line pressure

Safety Systems

Flow Meter: Distal to all shunts to give more accurate flow delivery to the patient

Safety Systems

Level and air sensors

Safety Systems

Arterial line pressure

Cardioplegia delivery pressure

Pressure Monitoring

Cardiopulmonary bypass…

Do you ever wonder….How does it affect your patient?