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Mechanisms of postoperative pain

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Mechanisms of postoperative pain

    Mechanisms of postoperative pain

    ChineseMedicalJournal2007;120(22):1949-19501949 Editorial

    Mechanismsofpostoperativepain

    舰物n

    广1r1hepracticeofmodemanaesthesiologyhasextended 1intoperioperativemedicine.Duetoeexpertisein

    analgesicdrugpharmacologyandperipheralnerve blocking.anaesthesiologistshavepioneeredintlle managementofacutepostoperativepain.Efiective postoperativeanalgesiareducestlleincidenceof postoperativechronicpain,improvesthefunctioningof organsfollowingsurgeryandshortensthehospitalstay.1,2 Althoughavarietyofanalgesictechniquesand preventativeapproachesareattlledisposalofmodem aneasthesiologists.includingPatientcontrolledepidural analgesia(PCEA).patientcontrolledintravenous analgesia,multimodalanalgesiaandpreemptyanalgesia.

    Despitethisarrayofstrategies.tllesepredominantly opioidbasedtechniquesarestilllimitedbyside.effects suchasvomiting,nausea,itchingandurinaryretention. Tooptimizefurthertllemanagementofacute

    postoperativepain,basicmechanismsofpostoperative painmustbeexploredandnewtreatmentsmustcontinue tObedeveloped.

    Theaetiologyofpostoperativepainmaybedifferentfrom antigeninducedinflammation.formalininJectionand

    capsaicininjection.Therefore,postoperativepainhasa differentpharmacologyofanalgesiacomparedwitll sustainedpain.Forexample.aloughspinalN.mev.

    DaspartatereceptorantagonistsaRenuatehyper- sensitivityinpersistentpain;theseantagonistsarenot effectiveinincisionalpain.Surprisingly.intrathecal administrationofnon.N.mev.D.aspartatereceptor

    antagonistsandneurokininlreceptorantagonistsare

    effective.Further,hypersensitivityafterincisionalsurgery issuppressedbyintraecalcVclOOxVgenase.1butnotby

    cyclooxygenase.2inhibitors.Theseobservationssuggest tllatmechanismsofhypersensitivityafterincisiondiffer fromtlloseafterinflammatoryorperipheralnerveinjury. Tissueinjuryleadstotwochangesineresponsiveness

    ofthenociceptivesystemperipheralsensitizationand

    centralsensitization.Peripheralsensitizationinvolvese

    primaryafferentfibresandischaracterizedbylowering ofresponsethreshold,anincreaseinresponsemagnitude tosuprathresholdstimuli,anincreaseinspontaneous activityandanincreaseinreceptivefieldsize.C:entral sensitizationischaracterizedbyenhancedresponsesof paintransmissionneuronsinthecentralnervoussystem. Peripheralsensitizationleadstoprimaryhyperalgesiaand centralsensitizationleadstosecondaryhyperalgesia. Primaryhyperalgesiaisrestrictedtoesiteofiniuryand

    ischaracterizedbvhvperalgesiatobOmechanicaland

    tllermalstimuli.whereassecondaryhyperalgesiais observedinundamagedskinadjacenttotheinjuredarea andischaracterizedbyhyperalgesiatomechanicalbut nottothermalstimuli.

    Theidealpreventativestrategiesforacutepain managementfollowingsurgeryaretosuppressthe developmentofboperipheralandcentralsensitization. whichinvolvesbotlltlleprimaryafferentnociceptorsand spinaldorsalhomneurons.Moststudiesofpostoperative painarefocusingontheseaspects.Asfaras

    anaesthesiologistsareconcemed,particularinterestis focusedonspinalmechanismsandpharmacologybecause neuraxial,spinalandepiduralanalgesiaaremore effectiveforpostoperativepain.Itiscleartllatcentral sensitizationiscloselyassociatedwithneurosynaptic plasticity,whichisdependentonpresynaptic neurotransmittersandpostsynapticreceptors.Recent studieshavedemonstratedtllatdifferentialalterationsin metabolicglutamatereceptorsubtypesandcyclooxy. genaselexpressionsinthespinalcord,inresponseto surgicalincision.wereinvolvedinealteredpain

    processingandrestorationofnormalsynapticactivity. However,itisstillunclearwhethertlleneuro廿ansmitters

    correlatedwitllpainprocessingareinvolvedintlle mechanismsofpostoperativepainandreleasedduring postoperativeperiod.

    InthisissueofeChineseMedicalJouma1.Wangetal

    reportaninterestingstudyonthereleaseof

    neurotransmittersduringpostoperativepain.Thisstudy showsthattlleexcitatoryaminoacidsincludingaspartate andglutamatereleasedareincreasedintlleearlyphase aftersurgeryandretureedtothelevelofbaselineonday 1aftereincision.However,ereleaseofglycine,

anterinhibitoryaminoacid.peakedonday1aftere

    incisionandreturnedtotllebaselineonday2afterthe incision.ThereleasepaRemofaminoacidsinincisional painisdifferentfrominflammatorypain:differentpains relyondifferentneurotransmittersandreceptorssystem. Intestingbehaviour,thecumulativepainscoreincreased at3hoursaftereincision.graduallydeclinedovertwo daysaftertlleincisionandreturnedtoebaselineon

    thirddayaftertlleincision.Thereleaselevelsof excitatoryaminoacidsdidnotparalleltllepain behaviouralchanges:evreturnedtobaselineonday1

    aftertheincision.inspiteofehighlevelofcumulative

    painscore.Itindicatesateexcitatoryaminoacidsare

    possiblyinvolvedinespinalsensitizationintheearly

    Correspondenceto:Dr.YUEYun,DepartmentofAnesthesiology, BeijingChaoyangHospital,CapitalMedicalUniversity,Bei"ing 100020,China(Email:yueyun@hotmail.com)

l950ChinMedJ2007;120(22):1949J950

    phaseafterSUrgeryanddonotplayanimportantrolein themaintenanceofhyperalgesia.Furtherstudyisrequired tounderstandhowtosuppresstheexcessreleaseof excitatoryaminoacidsandadiustthereleaseofinhibitory aminoacids.Similarly,furtherstudyalsocanbedoneto investigatethemechanismsofhowacutepOstOperat1ve paincanleadtochronicpain.

    Abetterunderstandingofthetemporalandspatialpattem ofneurotransmitterreleasefollowingsurgerywillhelp elucidatethemechanismsofpostsurgicalpainanddirect treatmentatthesetargetstoachievemaximumanalgesia

pOstOperatiVely.

    REFERENCES

    BrennanTJ,ZahnPK,PogatzkiZahnEM.Mechanismsof

    incisionalpain.AnesthesiolClinNorthAmerica2005;23: 2

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    WuCL,SapirsteinA,HerbertR,RowlingsonAJ,Michaels RK.PetrovicMA.eta1.EfieCtofpostoperativeepidural analgesiaonmorbidityandmortalityafterlungresectionin Medicarepatients.JClinAnesth2006:l8:5l5520.

    WuC,BoustanyL,LiangH,BrennanTJ.Nervegrowth factorexpressionafterplantarincisionintherat. Anesthesiology2007:l07:l28l35.

    DolanS,KellyJGMonteiroAM,NolanAM.Differential expressionofcentralmetabotropicglutamatereceptor (mGluR)subtypesinaclinicalmodelofpostsurgicalpain.

    Pain2004;ll0:369377.

    WangY,YueShiL'WuAS,FengCS,NiC.Spinalrelease oftheaminoacidswithatimecoupeinaratmodelof postoperativepain.ChinMedJ2007:120:l9691974.

    (ReceivedOctober9.2007)

    EditedbyCHENLirnin

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