麻醉知覺，深度監測儀

AEPMonitor麻醉知覺/深度監測儀(AuditoryEvokedPotential)台大醫學系六年級全以祖Contents1、前言2、AEPMonitor的理論及臨床應用3、AEPv.s.BIS4、WHYAEP？有人說：麻醉醫師的工作流程非常類似〝Pilot〞不同的是--pilot已有非常精確及〝直接〞且〝即時〞的自動導航系統、全球衛星定位系統…etc.。--pilot有非常嚴格的工作時間限制。然而--麻醉醫師只有一些輔助儀器〝間接〞且〝非即時〞來提供病患麻醉深度/知覺的判斷。--麻醉醫師常overtime。有人說：麻醉是一種Science更是一種Art如何在安全、品質、成本間取得最佳的Result，仍是最主要的目標？各位麻醉醫師在過去的經驗中，是否仍有一些有待挑戰的Subject呢？例如：1、在Induction時，提供的劑量是否夠或不夠？可否intubation了或再等一下？2、多種藥物的交互作用下，對麻醉深度的影響到底為何？3、在maintenance期，血壓亦或心跳升高，是否深度不夠，亦或其他原因呢？4、在reversing期，如何判斷病患意識已開始恢復，可被喚醒了？5、在maintenance期，何時可減量麻醉氣體，以提早reversepatient？各位麻醉醫師在過去的經驗中，是否仍有一些有待挑戰的Subject呢？例如：6、如何在OB或TrumaCases中，更能掌握病患麻醉深度呢？7、如何在低溫Open-Heart中，更能掌握病患麻醉深度呢？8、做Low-Flow時，能否告知麻醉深度，以便更能掌握呢？9、目前麻醉環境中，是否就是缺少一個〝直接且即時〞告知麻醉深度的設備呢？2.AEPMonitor理論及臨床應用ThepatientThepatienthas2worries:1:Willhesleepduringtheoperation?2.Willhewakeupaftertheoperation?BasicbasicbasicbasicbasicThehearingisthelastsensethatleavesandthefirstthatreturnsduringanaesthesia.AEPisjustthebrainresponsetoaclickstimulithroughthehearingnerveAEPisaveryweakelectricalsignalwrappedintheEEGbackgroundactvity.Let’slookathowtinytinythissignalis.TheimplicationsofundersedationPatientremainsimmobilizedbutfeelspainAlthoughitisoccursinonly0.1%-0.2%ofallsurgeries,23millionsurgeriesareperformedintheU.S.eachyearResultingin35,000casesofsurgicalawarenessTheimplicationsofoversedationToavoidthepossibilityofsurgicalawarenesstoomuchhypnoticsandanalgesicsmaybeadministeredThepatient’srecoverytimeisextended:higherroomcostMoredrugsthannecessaryareused:higherdrugcostWhymonitorsleep?Itisimportanttothinkaboutthis.BurstSuppressionWelookatspikes3,5uV.Incontrast:AnawakePaamplitudeistypically0.7uV.And,anasleepamplitudeistypically0.4uVECGsignalhasapprox.400xamplitudethantheAEPsignals.EEGsignalhasapprox.40xamplitudethantheAEPsignal400x40xExtractingtheevokedresponseBeforeA-Lineittooktoolongto”detectandpresent”(extract)thisweaksignal,becauseitrequiresadvancedsignalprocessing1click128clicks256clicks1024clicks100msclickBut,letsmakethismorevisibleLet’sseewhathappenswhenwesendaclickthroughtheear.Adeviationinthepositioningoftheelectrodesupto2cmdoesnothavesignificantinfluenceontheARX-index.ToMonitorSomeprefertowaitwiththeheadphonesuntilelectrodesareconnected2TheauditoryPathwayFIGURE35–10Schematicofauditoryneuralpathway.TheBAEPisinitiatedbystimulationofthecochleawithabroadbandclickstimulusgivenviaanearinsertintheexternalauditorycanal.NeuralgeneratorsoftheBAEPpeaksareshown.AuditoryEvokedPotentialsClassLatency(MS)BestResponseSourceEraValueCochlear01-4SP(DC)CM(AC);AP(N1)HaircellsVIII?**Fast2-12P6-SN10BrainstemVIII***Middle12-50P35Brainstem,Midbrain,CortexI**??Slow50-300200-800N90-P180-N250CortexII(awake)CortexIII(asleep)**?*Late260-600DC-shiftP300,p350,CNVCortexIV(eventrelated)?AcousticnerveandbrainstemMedialgeniculateandprimaryauditorycortexFrontalcortexandassociationareasWhatdoestheAEPLookLike?+0.1µV100msecPaNbPalatencyPaamplitudeAnd,thisiswhathappensAcousticnerveandbrainstemMedialgeniculateandprimaryauditorycortexFrontalcortexandassociationareasAmericanEncephalographySocietyCriteriaforRetrochochlearDysfunction1.Abscencrofallwaves2.AbsenceofallwavesfollowingwaveIorII3.IncreaseofI-Vinterpeakinterval4.DecreaseofV/Iamplituderatio5.InterauralI-VintervalasymmetryPaNbAnd,oftheoppositeduringawakeningNN11NN117NoNoPoPoNaNaPaPaNbNbPP11PP7NoNoPoPoNaNaPaPaNbNbPP11PPPatient-RelatedFactors1.Age2.Temperature3.DrugEffects-Barbiturates,Benzodiazepines-Fentanyl-Ketamine,N2O-Isoflurane-Halothane,EnfluraneDesflurane1.5%PaNb3%6%TheAEPduringAnaesthesiaWithkindpermissionfromDrChristineThornton,NorthwickPark,London,UK.Pre-intubation100ms0.1µV+PaNbPost-intubationEffectofintubationontheAEPWithkindpermissionfromDrChristineThornton,NorthwickPark,London,UK.TheEffectofMidazolamontheAEP010050Time(ms)AwakeNbLossofeyelashresponseWithkindpermissionfromDrChristineThornton,NorthwickPark,London,UK.TheeffectofpropofolontheAEP010050ResponsetocommandNoresponsetocommandNbTime(ms)WithkindpermissionfromDrChristineThornton,NorthwickPark,London,UK.ConclusionsGradedchangeswithdepthofanaesthesiaSimilarchangesfordifferentanaestheticsShowsresponsetonoxiousstimulationAEPindicateslevelofconsciousnessTechnologyhasbeenstudiedsinceearly1980’sAEPsignalprocessing?Howcanitbesofast?Newelementstoversion1.5ismarkedwithorgange12345678...........239...256MTA256sweepsMTA18sweepsMovingtimeAveragingandARXARX-model257Indexcalculation?AEPwindow=20-80msxixi+1Indexcalculation?mv0,1mv0,2mv0,3mv0,4Total3,7xfactor=100IndexcalculationSo,thenyouhavearealcurve,theindexishighAnd,analmostflatcurvegivesalowindex=93=16WhatitisAAIistypicallyhigherthan60whenthepatientisawakeanddecreaseswhenthepatientisanaesthetised;lossofconsciousnesstypicallyoccurswhentheAAIisbelow30TheclickdetectionisachievedbyestimatingtheSignaltoNoiseRatio(SNR).TheSNRisdefinedastheratiobetweenthemeasuredsignalandthenoise.TheSNRthresholdis1.45;thismeansthatwhentheSNRisabove1.45,thequalityoftheAEPissatisfactory.OntheotherhandiftheSNRisbelow1.45,thesignalqualityislow,andafurtheraveragingoftheAEPiscarriedout.Yetifthisdoesnotimprovethe