physiology of pain

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http://ccn.aacnjournals.orgPublished online 2008 American Association of Critical-Care NursesCrit Care Nurse. 2008;28: 38-49

Jennifer E. Helms and Claudia P. Barone Physiology and Treatment of Pain

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38 CRITICALCARENURSE Vol 28, No. 6, DECEMBER 2008 http://ccn.aacnjournals.org

understand the principles of painmanagement.

The pain experience can be func-tionally divided into acute and chronictypes. Acute and chronic pain are dueto different physiological mechanismsand thus require different treatments.In addition, children, adults, and eld-erly persons have both subtle andsharp differences in the perception ofpain. Much of the nursing literatureon pain is focused on common inter-ventions but does not explain thephysiological mechanisms of pain andthe vastly different types of pain thatpatients may have. Thus, in this article,we review theories of pain and examinethe physiology of pain, with emphasison the types of pain and their mani-festations. To provide the best possiblecare for patients experiencing pain,nurses must understand the physiol-ogy of pain, the different types of painand their varied manifestations, thediversity of patients responses, andthe rationale for choices of pain con-trol methods.

Evolution of Pain TheoriesAs early as 1644, Descartes pro-

posed a theory of pain, that a straight-line channel of pain exists from skinto brain.7 During the 19th century,von Frey theorized that pain pathwaysmove from specialized receptors in

Clinical Article

PRIME POINTS

Learn about how pain isunique for each person.

Do patients withchronic pain exhibit objec-tive physiological indica-tions expected of patientswith pain, such as pallor,sweating, tachycardia, andfacial grimacing?

Is there a difference inhow women and menexperience pain ?

How do children experi-ence pain and how shouldthey be treated if they can-not verbalize their painexperience?

Do elderly patientsexperience pain differentlycompared with youngerpersons or do they justrespond more slowly topain?

This article has been designated for CE credit.A closed-book, multiple-choice examinationfollows this article, which tests your knowledgeof the following objectives:

1. Describe the different types of pain 2. Recognize the diversity of patients

responses to pain3. Understand the physiology of pain

CEContinuing Education

Physiology and Treatment of Pain

Jennifer E. Helms, RN, PhDClaudia P. Barone, RN, EdD, LNC, CPC, CCNS-BC, APN

Pain often occurs in criti-cal care patients and isone of the most clinicallychallenging problemsfor critical care nurses.

Pain and discomfort in these patientscan be due to surgical and posttrau-matic wounds, invasive monitoringdevices, prolonged immobilization,mechanical ventilation, and routinenursing procedures such as suction-ing and dressing changes.1-5 In addi-tion, patients may have a preexistingchronic pain condition, complicat-ing the assessment and treatment ofacute pain. Pain is a problem in crit-ical care that has not been adequatelyaddressed.6 Strategies for changingpain management practices includeproviding documentation, imple-menting pain guidelines, using algo-rithms, and increasing education inpain management for acute andcritical care nurses.6 A review ofpain physiology is essential to fully


http://ccn.aacnjournals.org CRITICALCARENURSE Vol 28, No. 6, DECEMBER 2008 39

body tissues to a pain center in thebrain. The focus of this theory, knownas the specificity theory, is specializedperipheral receptors rather than a cen-tral mechanism of pain in the brain.However, although receptors are spe-cialized, a focus on peripheral receptorsdoes not explain how an amputee canfeel pain in the amputated limb (aphenomenon known as phantom limbpain) when the peripheral receptorsno longer exist.

According to the pattern theory ofpain proposed in the late 19th century,pain is the result of stimulation of cer-tain nerve impulses that form a patternand are then combined and dumpedinto the spinal cord as a lump sum ofpain, a process called central summa-tion.7 This theory can better accountfor the phantom limb phenomenon,because the focus is on what occurs inthe brain rather than on peripheralreceptors. However, the theory doesnot account for other factors in painperception, such as the effect of place-bos on pain.

In 1965, Melzack and Wall8 pub-lished the well-known gate control the-ory of pain, the theory most familiarto nurses. According to this theory, amechanism in the brain acts as a gateto increase or decrease the flow of nerveimpulses from the peripheral fibers tothe CNS. An open gate allows theflow of nerve impulses, and the braincan perceive pain. A closed gate does

not allow flow of nerve impulses,decreasing the perception of pain(Figure 1). Although the gate control

theory has been widely accepted sincethe 1970s, it leaves unanswered ques-tions, including chronic pain issues,sex-based differences, stress effects, andthe effects of previous pain experiences.

In 1999, Melzack and Wall10 pre-sented a newer theory of pain, consis-tent with the idea of gate control, thataddresses some of these unansweredquestions. This new and improvedtheory, the neuromatrix theory, saysthat each person has a geneticallybuilt-in network of neurons called the

Jennifer E. Helms is an associate professor of nursing at Arkansas Tech University, Russell -ville, Arkansas.

Claudia P. Barone is professor and dean, College of Nursing, University of Arkansas forMedical Sciences, and a registered nurse II at University Hospital, PRN, Little Rock,Arkansas.Corresponding author: Jennifer E. Helms, RN, PhD, Associate Professor of Nursing, Arkansas Tech University,Dean Hall, 402 W O St, Russellville, AR 72801 (e-mail: [email protected]).

To purchase electronic or print reprints, contact The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656.Phone, (800) 809-2273 or (949) 362-2050 (ext 532); fax, (949) 362-2049; e-mail, [email protected].

Authors

Figure 1 The gate control theory of pain.Reprinted from Ignatavicius and Workman,9(p67) with permission. Copyright Elsevier 2006.

Brain

Spinal cord

GateclosedGate

open Substantiagelatinosa

Small-diameterfibers

Pain sensationSmall-diameter fibers


body-self neuromatrix. Just as eachperson is unique in physical appear-ance, each persons matrix of neuronsis unique and is affected by all facetsof the persons physical, psychological,and cognitive makeup, as well as hisor her experience. Thus, the painexperience does not reflect a simpleone-to-one relationship between tis-sue damage and pain.

Pathways of PainNociceptors, or pain receptors,

are free nerve endings that respond topainful stimuli. Nociceptors are foundthroughout all tissues except the brain,and they transmit information to thebrain. They are stimulated by biologi-cal, electrical, thermal, mechanical,and chemical stimuli. Pain perceptionoccurs when these stimuli are trans-mitted to the spinal cord and then tothe central areas of the brain. Painimpulses travel to the dorsal horn ofthe spine, where they synapse withdorsal horn neurons in the substantiagelatinosa and then ascend to thebrain. The basic sensation of painoccurs at the thalamus. It continues tothe limbic system (emotional center)and the cerebral cortex, where pain isperceived and interpreted (Figure 2).

Two types of fibers are involved inpain transmission. The large A deltafibers produce sharp well-defined pain,called fast pain or first pain, typi-cally stimulated by a cut, an electricalshock, or a physical blow. Transmissionthrough the A fibers is so fast that thebodys reflexes can actually respondfaster than the pain stimulus, resultingin retraction of the affected body parteven before the person perceives thepain. After this first pain, the smallerC fibers transmit dull burning or achingsensations, known as second pain.The C fibers transmit pain more

slowly than the A fibers do becausethe C fibers are smaller and lack amyelin sheath. The C fibers are theones that produce constant pain.

According to the gate controltheory, stimulation of the fibers thattransmit nonpainful stimuli can blockpain impulses at the gate in the dorsalhorn. For example, if touch receptors(A beta fibers) are stimulated, theydominate and close the gate. This abil-ity to block pain impulses is the reasona person is prone to immediately graband massage the foot when he or shestubs a toe. The touch blocks the trans-mission and duration of pain impulses.This capacity has implications for theuse of touch and massage for somepatients in pain.

Regulators of PainChemical substances that modu-

late the transmission of pain arereleased into the extracellular tissuewhen tissue damage occurs. Theyactivate the pain receptors by irritat-ing nerve endings. These chemicalmediators include histamine, sub-stance P, bradykinin, acetylcholine,leukotrienes, and prostaglandins.The mediators can produce otherreactions at the site of injury, suchas vasoconstriction, vasodilatation,or altered capillary permeability.For example, prostaglandins induceinflammation and potentiate otherinflammatory mediators. Aspirin,nonsteroidal anti-inflammatorymedications, and the new COX-2


Figure 2 Pathways of pain.Reprinted from Copstead and Banasik,11(p1174) with permission. Copyright Elsevier 2005.

Primary sensory cortex Location of pain

Limbic forebrain Emotional reactionto pain

ThalamusAxons projectto other areasof brain

Cortical association area Interpretation of pain

Dorsal hornAnterolateral

tract

Brainstem

Spinal cord

NociceptorsNoxious stimulus

(may be chemical,thermal, or mechanical)

Release ofsubstance PPeripheraltransmissionPeripheral activity Vasodilation Edema Hyperalgesia Release of

chemicals



inhibitors block cyclooxygenase 2,the enzyme needed for prostaglandinsynthesis, thus reducing pain.12,13 Con-sequently, these medications are oftenprescribed for painful conditions dueto inflammation.

The body also has a built-inchemical mechanism to manage pain.Fibers in the dorsal horn, brain stem,and peripheral tissues release neuro-modulators, known as endogenousopioids, that inhibit the action ofneurons that transmit pain impulses.14

-Endorphins and dynorphins are thetypes of natural opioidlike substancesreleased, and they are responsible forpain relief. Endorphins are the modu-lators that allow an athlete to continuean athletic event after sustaining aninjury. Endorphin levels vary fromperson to person, so different personsexperience different levels of pain.

This endogenous opioid mecha-nism may play an important role inthe placebo effect. A placebo is aninactive substance or treatment usedfor comparison with real treatmentin controlled studies to determine the

efficacy of the treatment under study.Despite the lack of any intrinsic value,placebos can and do produce an anal-gesic response in many persons.15

Placebo analgesia can affect nocicep-tive mechanisms in the cortex of thebrain and descending pathways of thespinal cord.16-19 Matre et al20 found thatexpectations about pain and analgesiacan modify pain perception by alter-ing pain mechanisms in the spinalcord. For example, psychological fac-tors such as the threat of pain andexpectations about analgesia modifyspinal pain transmission, therebymodifying pain.

Acute and Chronic PainAcute Pain

Acute pain serves a biologic pur-pose by providing a warning that ill-ness or injury has occurred. The painis usually confined to the affected areaand is limited over time. Acute painstimulates the sympathetic nervoussystem, resulting in fight or flightresponse symptoms, includingincreased heart and respiratory rates,

sweating, dilated pupils, restlessness,and apprehension.

Types of acute pain includesomatic, visceral, and referred9 (seeTable). Somatic pain is superficial,coming from the skin or subcuta-neous tissues; visceral pain originatesin the internal organs and the liningsof the body cavities. Referred pain isfelt in an area distant from the site ofthe stimulus; it occurs because thearea of referred pain is supplied bythe same spinal segment as the site ofthe stimulus21 (Figure 3). Referredpain often occurs with visceral pain.Examples include shoulder pain frommyocardial infarction, back painfrom pancreatitis, and right shoulderpain from gallbladder disease.

Chronic PainChronic pain is prolonged pain,

persisting beyond the expected normalhealing time.23 This characterizationwas previously the official definitionof chronic pain according to the Inter-national Association for the Study ofPain. The term chronic is still widely

Table Physiologic sources of pain

Physiologic structure

Nociceptive painSomatic painClutaneous or superfi-

cial: skin and subcuta-neous tissues

Deep somatic: bone,muscle blood vessels,connective tissues

Visceral painOrgans and the linings

of the body cavities

Neuropathic painNerve fibers, spinal

cord, and central nervous system

Characterictics of pain

Sharp, burningDull, aching, cramping

Poorly localizedDiffuse, deep cramping or

splitting, sharp, stabbing

Poorly localizedShooting, burning, fiery,

shocklike, sharp, painfulnumbness

Sources of acutepostoperative pain

Incisional pain, pain at insertionsites of tubes and drains,wound complications,orthopaedic procedures, skele-tal muscle spasms

Chest tubes, abdominal tubesand drains, bladder distentionor spasms, intestinal distention

Phantom limb pain, postmastec-tomy pain, nerve compression

Sources of chronic pain syndromes

Bony metastases, osteoarthritis andrheumatoid arthritis, low back pain,peripheral vascular disease

Pancreatitis, liver metastases, colitis,appendicitis

HIV-related pain, diabetic neuropathy,postherpetic neuralgia, chemotherapy-induced neuropathies, cancer-relatednerve injury, radiculopathies

Reprinted from Ignatavicius and Workman,9(p67) with permission. Copyright Elsevier 2006.


used, although many pain experts nowthink that all forms of chronic painare variations of the same phenome-non and should be labeled specifically,such as neuropathic pain.23 Chronicpain can be continuous (eg, arthritis)or intermittent (eg, migraines).Chronic pain is poorly understoodand is more complex and difficult tomanage than is acute pain. Under-standing chronic pain requires recog-nizing that the nervous system is nothardwired. If it were hardwired, eachnoxious stimulus, such as a needlestick, would elicit exactly the samenervous system response at the sameintensity every time. But pain is muchmore complex, involving affective andcognitive traits of the person whoexperiences it. Melzack and Wall8

showed that repeated stimulation ofC fibers results in progressive buildupof electrical response in the CNS, aphenomenon called windup, some-what analogous to the effect of wind-ing up a childs windup toy. The morethe toy is wound up, the faster andlonger the toy will run. This persistent

stimulation of peripheral nerves windsup the CNS, leading to intensifiedstimulation of nerve fibers that isreferred to as nonnociceptive pain.The concept of windup is crucial tounderstanding chronic pain.24 Windupis the reason pain can continue longafter the expected recovery time foran injury or a pain-initiating event.

Patients with chronic pain maynot have the behaviors associatedwith acute pain.12 Additionally,autonomic nervous system responses(eg, nausea, vomiting, pallor, sweat-ing) decrease with prolonged pain.The bodys fight-or-flight reaction,which normally occurs with acutepain, does not occur because thesympathetic nervous system hasadapted to persistent pain impulses.Understanding chronic pain, there-fore, requires listening to the per-sons description of it, becauseexpected physical symptoms maynot be present. Unfortunately,because of the lack of objective evi-dence of pain, many patients whoreport chronic pain are viewed as

hypochondriacs and malingerers byhealth care professionals.

Some evidence indicates thatchronic pain and depression sharethe same physiological pathway.25,26

Tricyclic antidepressants and selectiveserotonin reuptake inhibitors havebeen used successfully for relief ofmany chronic pain syndromes suchas neuropathic pain, low back pain,and fibromyalgia. These medicationsblock the reuptake of neurotransmitterssuch as epinephrine and norepineph-rine, thereby altering neurotransmis-sion along pain pathways.27 Patientsshould be educated that the onset ofanalgesia with these medications dif-fers from the onset of the antidepres-sant effect; analgesia will occur soonerthan the expected antidepressant effectwill. Some patients prescribed anantidepressant as therapy for painmay misunderstand the purpose ofthe drug and assume that their com-plaints of pain are viewed as an indi-cation of depression or hypochondria.Health care professionals thereforeshould explain to patients that anti-depressants, in lay terms, help blockpain impulses.

Special Types of PainNeuropathic Pain

Chronic, often intractable paindue to injury to the peripheral nervesis known as neuropathic pain.According to Devor and Seltzer,28

this pain is a paradox. Injury toperipheral nerves should deadensensation, much as cutting a tele-phone wire leaves the phone linedead, but the opposite occurs inneuropathic pain. Injury to theperipheral nerves can cause sponta-neous paresthesias, numbness, painwith movement, tenderness of apartly denervated body part, and


Figure 3 Sites of referred pain.Reprinted from Huether and McCance,22(p333) with permission. Copyright Elsevier 2004.

Liver

Smallintestine

KidneyKidney

OvaryStomachPancreas

Heart

Lung and diaphragm

Appendix

A B

Ureter

Bladder

Colon

Liver



treatment is universally effective.Usually combinations of various treat-ments have the best results. However,treatments typically only reduce thepain, rather than eliminating it, sopatients should be warned that reliefprobably will not be complete. Treat-ment includes pharmacotherapy,transcutaneous electrical nerve stimu-lation, and neurosurgery. Antidepres-sants, antiepileptics, antiarrhythmics,local anesthetics, analgesics, and awide variety of other medications havebeen used for central pain, all withvarying success. Neurosurgical proce-dures, such as cordotomy (interrupt-ing the pathways that carry painthrough the spinal cord) and thalam-otomy (destroying cells in the thala-mus), may be tried in patients withcentral pain that do not respond toother treatments, but even these meas-ures have had only limited success.36

Differences in PopulationsSex-Based Differences

An abundance of research hasindicated sex-based differences inthe experience of pain. Women reportpain with greater frequency thanmen do37-41 and have lower thresh-olds and tolerance to painful stim-uli.42-45 Differences also exist in thetypes of painful conditions that areprevalent in women and men. Forexample, headaches occur in bothsexes, but women experience moretension headaches and migraineswith aura, whereas men report morecluster headaches and migraineswithout aura.46 Musculoskeletalconditions (eg, fibromyalgia) andautoimmune diseases are reportedmuch more often by women thanby men.

The reason for these sex-baseddifferences is a matter of debate.

pain that is electric shocklike, burn-ing, shooting, or tingling.

Abnormally amplified signals inthe CNS due to windup result in cen-tral sensitization, which is an increasedsensitivity of spinal neurons. Centralsensitization causes allodynia (painfrom a stimulus that does not normallyproduce pain, such as touch) andhyperalgesia (a heightened painresponse to a stimulus that is painful).Transcutaneous electrical nerve stim-ulation is used as an adjuvant therapyfor some patients with neuropathicpain.29 With this technique, stimulat-ing the large-diameter nerve fiberscloses the gate in the spinal cord dor-sal horns. The mainstay of treatmentfor neuropathic pain, however, ispharmacotherapy with antiepilepticsand antidepressants. Antiepilepticdrugs inhibit discharges on damagednerves, and antidepressants enhancedorsal horn inhibition (ie, they helpclose the gate). The tricyclic antide-pressants, despite their poor side effectprofile, are more effective in treatingneuropathic pain than are the newerserotonin selective reuptake inhibitors.

Phantom PainAfter amputation of a limb, a

patient may experience painful sensa-tions in the missing limb. As many as70% of amputees report this phantomlimb pain,30 usually within the firstweek after amputation.31 Painful sen-sations, which are typically intermittent,are described as shooting, stabbing,pricking, squeezing, throbbing, andburning. The missing limb may feeltwisted or cramped. Often preampu-tation pain and phantom pain aresimilar.32,33 Most patients report adecrease in the degree and incidenceof phantom pain in months to yearsafter the amputation. Although several

theories have been proposed toexplain the pathophysiology of phan-tom pain, the exact etiology remainsunknown. The origin of phantompain is thought to be in the CNS andmay be a somatosensory memorythat involves complex neural interac-tions in the brain.34

Treatment for phantom pain ischallenging and often unsuccessful. Nomedications are specifically indicatedfor phantom pain, but anticonvulsants(carbamazapine), antidepressants(clomipramine, doxepin), -blockers,and opioids have been used success-fully to relieve phantom pain in somepatients. Transcutaneous electricalnerve stimulation and sympatheticblocks have had limited success.35

Central PainCentral pain is a form of chronic

pain caused by a lesion or dysfunctionin the CNS. Causative lesions includeinfarction, hemorrhage, abscess,degeneration, tumors, and traumaticinjury in the brain or spinal cord. Forexample, stroke, multiple sclerosis,and spinal cord injury can all result incentral pain.36 The term thalamic painis often used synonymously with cen-tral pain, although thalamic pain isspecifically caused by lesions in thethalamus. The intensity of the painranges from mild to excruciating, butthe pain is constant and irritating,causing the patient much suffering.Patients with central pain often reportburning, aching, lancing (cutting),pricking, lacerating, and pressingsensations. The location of the paindepends on the lesion involved; thepain may occur in an entire half ofthe body or in only a small area, suchas a hand.

The specific mechanisms of centralpain are poorly understood, and no


Potential mechanisms in pain includesex hormones, differences in the brainand spinal cord in men and women,genetics, sociocultural roles, stress,and neuroactive agents.41,43,45 Interest-ingly, researchers have found that brainactivity in men and women differsduring a pain experience. Silvermanet al47 used positron emission tomog-raphy to examine brain activationpatterns in healthy men and womenwho were not in pain and comparedthe patterns with those of men andwomen experiencing a painful condi-tion. The brain patterns of the menand women experiencing pain dif-fered significantly, but no sex-baseddifferences were detected in the con-trol group. This finding suggests thatpain is processed differently depend-ing on sex.

Pain in ChildrenUntil the 1970s, pain in children

was ignored in health care research.48

The common assumption was thatchildren did not experience pain tothe extent that adults do, because ofthe immature nervous system, or thatchildren would not remember the pain.Consequently, children were oftenundermedicated or not medicated atall for pain. This practice continueduntil the late 1980s, when changesbegan to occur in pain managementin infants and children as a result ofresearch, consumer demands, andlegislation to promote developmentof drugs for these patients. Substantialevidence now indicates not only thatchildren experience pain but that thepain experience may have long-termadverse consequences.

The misperception that infantshave immature nervous systems andtherefore do not feel pain is still com-mon. All nerve pathways necessary

for pain transmission and perceptionare present and functioning by 24weeks gestation.48 Research49-54 in bothanimal models and human newbornsconfirms that a lack of analgesia forpain causes rewiring in the nervepathways involved in the transmissionof pain. Consequently, an infant orchild who experiences pain once willhave greater pain perception duringlater painful experiences. For example,Taddio et al54 found that babies whodid not receive analgesia or anesthe-sia during circumcision later hadgreater behavioral and physiologicaldisturbances during immunization.Furthermore, a lack of adequate post-operative analgesia in children canincrease morbidity. In a study byAnand and Hickey,49 compared withpostoperative infants who receivedhigh-dose opioid analgesia, postoper-ative infants who did not had a signif-icantly higher risk for death.

Another common myth is thatchildren do not experience chronicpain. Indeed, children do experiencechronic pain syndromes, such as com-plex regional pain syndrome, as wellas acute forms of pain related to chronicconditions such as sickle cell anemia.55-57

They also experience various forms ofrecurrent pain, most commonlyheadache, abdominal pain, back pain,chest pain, and limb pain.48,56,58

Pain in the ElderlyThe effects of aging on pain sensa-

tion, perception, and behavior are notwell established.59 Findings from stud-ies on pain in human aging are con-flicting, partly because of inconsistentresearch methods and ambiguousresearch definitions of pain.60 Somenotable consistencies have been found,however. Compared with youngeradults, elderly persons rely more on

second pain (C fiber) than on first pain(A fiber). This difference means thatolder adults are more likely to describea painful injury or stimulus as burning(slower C fiber second pain) ratherthan as sharp or pricking (faster A fiberfirst pain).61,62 Another well-documentedfinding in the elderly is a slowerresponse time to pain.58,59,63

No evidence exists that pain inten-sity lessens with age. Pain as a sensoryprocess does not mimic other senses,such as hearing and sight, which grad-ually diminish with normal aging.56

Altered reactions to painful eventsmay be due to loss of communicationsskills, cognitive abilities, or the failureof basic reflexes due to aging. Addi-tionally, pain in the elderly may bemanifested as something other thanpain, such as delirium. Referredpain may be atypical in the elderly,as in silent (painless) myocardialinfarction. Although this lack ofreferred pain is a clinical problem,no definitive evidence exists of therelationship between age and silentmyocardial infarction.

Assessment and Treatmentof Pain

Pain management in criticallyill patients can be challenging. Fora variety of reasons, critically illpatients may be unable to verbalize,or they may not fully communicatethe nature of their pain. Patients andhealth care providers may assumethat treatment with opioid analgesicscan lead to addiction. Despite effortsto relieve pain, harmful physiologi-cal effects can ensue, includinginadequate sleep, exhaustion, dis-orientation, anxiety, tachycardia,increased myocardial oxygen demand,immunosuppression, and increasedcatabolism.64-67 Recognition of pain

44 CRITICALCARENURSE Vol 28, No. 6, DECEMBER 2008 http://ccn.aacnjournals.org by on June 4, 2009 ccn.aacnjournals.orgDownloaded from


in critically illpatients is crucial.Painful stimulican be triggeredby a variety ofconditions ortreatments, suchas incisions,drains, ischemia,inflammation,edema, andindwelling inva-sive and nonin-vasive catheters,and by a patientsprevious experi-ences withpainful stimuli.

AssessmentPain is an

important prob-lem in criticalcare, and the assessment of painshould be a priority. The Joint Com-mission67 developed a pain assess-ment and management programthat hospitals must implement tofulfill accreditation requirements.Unfortunately, even with pain assess-ment guidelines and mandates inplace, clinicians often underratepain.68,69 Critically ill patients self-reports of pain can be inaccurate orinconclusive because of endotrachealintubation, use of sedatives, or anunconscious state. As a result, healthcare providers must rely on sensory,physiological, and behavioralparameters to assess the presenceof painful stimuli. These parametersinclude increases in heart rate andblood pressure, anxiety, and difficultyin providing mechanical ventilation.

Pain scales can be used to deter-mine the degree of pain a patient isexperiencing. Two commonly used

scales are the numeric rating scaleand the FACES scale. Scores on thenumeric rating scale range from 0to 10, with 10 being the worst painever experienced and 0 being nopain sensation at all. The difficultywith using this scale is that criticallyill patients often cannot speakbecause of endotracheal intubation.The second pain scale is the FACESpain-rating scale,70 which may bemore useful in critical care. Thisscale includes 6 faces with indica-tions of increasing pain intensity(Figure 4); a patient points to theappropriate face to indicate thepatients pain level.

Some patients cannot provide aself-report because they are sedatedor have cognitive impairment. Assess-ment of these patients requires useof a tool that relies on evidence ofpain behaviors. The Behavioral PainScale71 was developed for use in

critically ill patients and is used toevaluate behaviors that may indicatepain, including facial expression,upper limb movement, and ventila-tor compliance. Use of the scale islimited to patients who can demon-strate the behaviors being assessed.72

TreatmentOnce pain has been assessed,

interventions directed toward painrelief must be implemented. Painmanagement can be divided intopharmacological and nonpharmaco-logical interventions. In a study byGelinas et al,73 nonpharmacologicalinterventions were used in 22% of thepain episodes evaluated. A variety ofcomfort-producing measures wereimplemented, including endotrachealtube suctioning, repositioning in bed,massage, oral care, and reassurance.Other nonpharmacological measuresfor critically ill patients include

Figure 4 Wong-Baker FACES Pain Rating Scale.Reprinted from Hockenberry MJ, Wilson D, Winkelstein ML.70 Wongs Essentials of Pediatric Nursing. 7th ed. St Louis, MO, 2005, p 1259.Used with permission. Copyright, Mosby.

Brief word instructions: Point to each face using the words to describe the pain intensity. Ask the child tochoose face that best describes own pain and record the appropriate number.

Original instructions: Explain to the person that each face is for a person who feels happy because he hasno pain (hurt) or sad because he has some or a lot of pain. Face 0 is very happy because he doesnt hurtat all. Face 1 hurts just a little bit. Face 2 hurts a little more. Face 3 hurts even more. Face 4 hurts awhole lot. Face 5 hurts as much as you can imagine, although you dont have to be crying to feel this bad.Ask the person to choose the face that best describes how he is feeling.

Rating scale is recommended for persons age 3 years and older.Download FACES scale

April 2005

NO HURT

0 1 2 3 4 5

0 2 4 6 8 10

HURTSLITTLE BIT

HURTSLITTLE MORE

HURTSEVEN MORE

HURTSWHOLE LOT

HURTSWORST

Alternatecoding


application of heat or cold, massage,therapeutic touch, guided imagery,and relaxation techniques.

Principles of pharmacologicalmanagement begin with preemptiveanalgesia (before the pain begins) oras soon as possible after the painbegins. Preemptive analgesia not onlyreduces the pain response but alsocan reduce the chance of long-termsequelae. As previously described,painful experiences can imprint them-selves on the nervous system.54,74,75

Preemptive analgesia can preventnoxious signals from reaching theCNS, thereby reducing the chancethat spinal neurons will becomesensitized and lead to heightenedpain responses (hyperalgesia) or painexperiences from typically painlesssensations (allodynia).76 Continuouspain management is essential. Recentevidence77 suggests that durationand efficacy of analgesic interven-tion, rather than just timing, may bethe most important factors for treat-ing pain and preventing hyperalge-sia after surgical intervention.

For acute pain episodes, anal-gesics should be administered intra-venously for the quickest onset ofaction. Importantly, not only theonset of action but also the expectedduration of action of pain medica-tions must be understood so thatthe medication schedule can maxi-mize pain control efforts.78 Around-the-clock dosing is appropriate forcritically ill patients. Such dosing

helps prevent pain and maintain apain rating that is satisfactory ortolerable to the patient and helpsprevent the physiological changesdue to poor pain management.Despite efforts to relieve pain, harm-ful physiological effects can ensue,including inadequate sleep, exhaus-tion, disorientation, anxiety, tachy-cardia, increased myocardial oxygendemand, immunosuppression, andincreased catabolism.64-66 Expectationsof patients regarding pain can radicallychange the strength of pain responsesin the spine. Research79 has shown thatpain relief, to a large degree, dependson what the patient expects from apain relief intervention. More recentresearch80 confirmed the converse ofthis phenomenon, that antianalgesicexpectations can dramatically reducethe effect of analgesic treatments byblocking the action of the drugs. Inother words, if a patient expects littleor no pain relief from an analgesic ora pain relief measure, then the actionof that drug or measure can be blockedin the spine, and the drug or measurewill be ineffective.

Pain can be a severe and frequentsymptom in intensive care unit patients.Many patients report dissatisfactionwith inconsistent pain relief and theinability to acquire restful sleep as aresult of painful stimuli. Pain controlin intensive care unit patients shouldencompass use of a variety of pain-relieving approaches. These may includeoptions such as traditional opioidsand nonopioid analgesics as well asnarcotics and synthetic narcotics. Inaddition, the use of nonsteroidal anti-inflammatory drugs in certain circum-stances may augment a patientsresponse to pain and provide relief.Personal beliefs of each patient andthe patients family should also be

considered useful when deemedappropriate. These beliefs mightinclude prayer, meditation, relaxationtechniques, and acupuncture.

ConclusionThe experience of pain is unique

for each person and encompasses apersons physical, psychological, cog-nitive, and emotional network. Thefirst step in effectively dealing withpain is determining the specific typeof pain a patient is experiencing.Acute pain and chronic pain have dif-ferent manifestations. A patient withchronic pain will not have objectivephysiological indications expected ofpatients with pain, such as pallor,sweating, tachycardia, and facial gri-macing. Additionally, differences insex and age may play a role in a patientspain experience. Women and mencan experience pain differently becauseof mechanisms not yet understood.Children do experience pain andshould be treated accordingly eventhough they may not be able to ver-bally express their pain experience.Elderly patients may describe theirpain differently than younger personsdo and often respond more slowly topain. This difference in description ofpain does not mean that elderlypatients experience less pain. Painshould be treated promptly and ade-quately in all patients. To provide thebest care for patients in pain, nursesmust be alert to the different typesand manifestations of pain and thedifferences of each patient that con-tribute to the pain experience. CCN


eLettersNow that youve read the article, create or con-tribute to an online discussion about this topicusing eLetters. Just visit http://ccn.aacnjournals.org and click Respond to This Article in eitherthe full-text or PDF view of the article.

dtmoreTo learn more about pain management,read Validation of the Critical-Care PainObservation Tool in Adult Patients byCline Glinas et al in the American Journalof Critical Care, 2006;15:420-427.Available at www.ajcconline.org.



Financial DisclosuresNone reported.

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http://ccn.aacnjournals.org CRITICALCARENURSE Vol 28, No. 6, DECEMBER 2008 49 by on June 4, 2009 ccn.aacnjournals.orgDownloaded from

CE Test Test ID C0863: Physiology and Treatment of PainLearning objectives: 1. Describe the different types of pain 2. Recognize the diversity of patients responses to pain 3. Understand the physiology of pain

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Objective 1 was met Objective 2 was met Objective 3 was met Content was relevant to my

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for this content The level of difficulty of this test was: easy medium difficult

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Test answers: Mark only one box for your answer to each question. You may photocopy this form.

1. Which of the following statements is correct about acute and chronic pain?a. Acute and chronic pain have different physiological mechanisms.b. Treatments for acute and chronic pain are the same.c. Children and adults share the same perceptions of acute and chronic pain.d. Physiologic indicators of acute and chronic pain are identical.

2. Which of the following pain theories includes the process of centralsummation?a. Gate control theory c. Neuromatrix theoryb. Specificity theory d. Pattern theory

4. Where is pain interpreted?a. Substantia gelatinosa c. Cerebral cortexb. Nociceptors d. Limbic forebrain

4. Surgical patients exhibit malignant hyperthermia when exposed towhich classes of drugs? a. Neuromuscular blocking agents and volatile inhalation agentsb. Neuromuscular blocking agents and antibioticsc. Antibiotics and sedating agentsd. Steroids and antibiotics

5. Compared with A fibers, which one of the following is correct about C fibers?a. C fibers are largerb. C fibers have a myelin sheathc. C fibers produce fast pain.d. C fibers produce constant pain

6. What modulator allows an athlete to continue an athletic event aftersustaining an injury?a. Leukotrienes c. Prostaglandinsb. Endorphins d. Bradykinin

7. Which of the following statements is correct about visceral pain? a. Visceral pain is superficialb. Visceral pain is described as sharp and burningc. Visceral pain is poorly localizedd. Visceral pain is described as painful numbness.

8. Which of the following is a source of neuropathic pain?a. Bladder distentionb. Incisional painc. Phantom limb paind. Skeletal muscle spasms

9. What is the reason pain can continue long after the expected recoverytime for an injury?a. Windupb. Open gatec. Body-self neuromatrixd. Somatosensory memory

10. Compared with men, which is correct about the pain experience in women?a. Women experience more migraines with aurab. Women have a higher pain threshold.c. Women report pain less frequentlyd. Women have a higher pain tolerance

11. Which of the following statements is correct about pain in children?a. Children do not experience chronic painb. Inadequate postoperative analgesia in children can increase morbidityc. Children do not experience pain to the same extent as adultsd. Children do not feel pain because of an immature nervous system

12. Which of the following statements is correct about pain in olderadults?a. Older adults rely more on first pain than second painb. Pain intensity lessens with agingc. Older adults have a faster response time to paind. Pain may be manifested as delirium

13. Which of the following terms describes pain from a stimulus thatdoes not normally produce pain?a. Hypesthesia c. Hyperesthesiab. Allodynia d. Hyperalgesia

Test ID: C0863 Form expires: December 1, 2010 Contact hours: 1.5 Fee: AACN members, $0; nonmembers, $11 Passing score: 10 correct (77%) Category: A Synergy CERP A Test writer: Denise Hayes, RN, MSN, CRNP

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