波形分析在机械通气的应用

环路分析在机械通气中的应用武警医学院附属医院呼吸科刘阳CriticalinassessingtheMechanicallyVentilatedPatient机械通气目的提供足够的肺泡通气量（VA）在安全的供氧浓度下达到适宜的动脉氧分压胸腔压升高的情况下避免发生气压病人舒适合适的呼吸肌负担良好的人机同步

进行波形分析的必要性Patient–ventilatordyssynchronyimposesanadditionalburdenontherespiratorysystemandmayincreasethemorbidityofcriticallyillpatients.ThilleAW,RodriguezP,CabelloB,etal.

IntensiveCareMed,2006.32(10):p.1515-22.Ignoranceoftheseissuesmaypreventtheventilatorfromachievingitsgoalsandmaycausepatientharm.GeorgopoulosD,PrinianakisG,andKondiliE.IntensiveCareMed,2006.32(1):p.34-47.

Inspectionofpressure,flowandvolumewaveformsrepresentsavaluabletoolforthephysiciantorecognizeandtaketheappropriateactiontoimprovepatient–ventilatorsynchrony

Eumorfia

Kondili,Nektaria

XirouchakiandDimitris

Georgopoulos.Curr

Opin

Crit Care13:84–89.NilsestuenJOandHargettKD.RespirCare,2005.50(2):p.202-34;discussion232-4. PressureversusTimeInspirationExpirationPaw(cmH2O)Time(sec)}TIPeakInspiratoryPressurePIPPEEPTE Pressure-VolumeLoopControlledAssistedSpontaneousVol(ml)Paw(cmH2O)I:InspirationE:ExpirationIEEEIIFlow-VolumeLoopVolume(ml)PEFRFRCInspirationExpirationFlow(L/min)PIFRVTMechanicalMonitoringAirwayPressuresStaticorPlateauPressure静态顺应性和平台压Separatesresistancefromelasticrecoil吸气末测量Shouldbekept<35cmH2OtoavoidvolutraumaAllowscomputationofstaticcompliance,whichdecreasesasthelungsbecomestiffStaticcompliance=静态顺应性Staticcompliance=定容模式下压力、流速、容量-时间曲线简图NormalCrsisapproximately100mL/cmH2Ointherangeofusualoperationallungvolume.通气模式为定容thepressureintheventilatorcircuit("inspiratoryplateaupressure")equalstheamountofpressureneededtodistendthelungsandchestwallbytheamountoftidalvolumejustdelivered因此静态顺应性可以表示为Crs=潮气量/(气道平台压-PEEPi).Staticcompliance=StaticcomplianceCrs,st=肺纤维化的P-V曲线阻力R=P/flowPinPoutflowRPinPoutflowPIPPplat阻力OppositiontoairflowbynonelasticforcesNormally2-5cmH2O/L/sec气道分泌物增多或者气道痉挛时会显著增加对于评价支气管扩张剂的效果十分有用Raw=

Paw(cmH2O)NormalNormalPPlat(NormalCompliance)IncreasedPIP}IncreasedPTA(increasedAirwayResistance)NormalPIPPPlatHighRawPIPPPlatIncreasedAirwayResistanceMeasuredVolumesTidalVolume潮气量5-7mL/kgIBWVT=VA+VDVD=1mL/lbIBWMechanicaltidalvolumevarieswithdiseaseprocess定容量模式下设定VT与呼出VT的差值为漏气量leak:ETTcuffleak PneumothoraxTubingdisconnection 随着气道顺应性的下降，在PCV模式下，VT将出现显著下降MeasuredVolumesMinuteVentilation(VE)分钟通气量VTxf4-8L/minuteVEof6L/minassociatedwithaPaCO2of40mmHgHighPaCO2withahighVEindicatesincreaseddeadspaceorincreasedmetabolism自主呼吸时（T-管实验）VE>10L/min常常提示撤机失败VE,VA,andPaCO2

FlowversusTimeTheflow-timecurvecanbeusedtodetect:WaveformshapeTypeofbreathingPresenceofAuto-PEEP(IntrinsicPEEP)Patient’sresponsetobronchodilatorsAdequacyofinspiratorytimeinpressurecontrolventilationPresenceandrateofcontinuousairleaks判断流速波形Inspiratoryflowpatternscanvarybasedontheflowwaveformsettingorthesetbreathtypeasillustrated减速波呼气流速波形在下一个吸气相开始之前呼气流速突然回到0,这是由于小气道在呼气时过早地关闭,使部分气体阻滞在肺泡内而引起Auto-PEEP(PEEPi)存在不同类型呼吸下，五种类型的流速-时间曲线评估支气管扩张剂的反应effectofinspiratorytimeinpressurecontrolonflowdeliverytothepatient.maybedesirableinsomecases患者对支气管扩张剂的反应性BeforeTime(sec)Flow(L/min)PEFRAfterLongTEHigherPEFRShorterTE漏气对吸呼切换的影响：漏气会导致吸气流速下降缓慢，达不到预设的切换标准（setterminationthreshold）吸气峰流量Tinsp45%15%Thresholdcannotbereachedtheperiodofmechanicalinflationmustmatchtheperiodofneuralinspiratorytime(thedurationofinspiratoryeffort),andtheperiodofmechanicalinactivitymustmatchtheneuralexpiratorytimeWhiletheventilatorwasstillpumpinggasintothepatient,hisexpiratorymuscleswererecruited,causingabumpintheairway-pressurecurve.Thattheflowneverreturnedtozerothroughoutexpirationreflectedthepresenceofauto–positiveend-expiratorypressure.AutoPEEP吸呼切换延迟Delayedterminationpresent患者呼气肌开始活动时，呼吸机的吸气过程还未完成，因此发生亚临床的人机对抗。Notethereisalsoasmallairwaypressurespikeneartheendofmechanicalinflation,whichcoincideswiththepatient’sneuralexpiratoryactivity.切换延迟CycleCriteria?吸气预置流速不足Flow

(L/min)Time(sec)NormalAbnormalActiveInspirationorAsynchronyPatient’seffort吸气预置流速不足或者患者主动吸气(SIMV)/volume-limited/pressuresupportapproach“doublebreathing”assistvolumecontrol恒定流速患者持续吸气，气道压力下降，在呼气阀打开时，发生doublebreathingAirTrappingInspirationExpirationNormalPatientTime(sec)Flow(L/min)AirTrappingAuto-PEEP}PRESSURE-TIMECURVESBreathtypedeliveredtothepatientWorkrequiredtotriggerthebreathBreathtiming(inspirationvsexhalation)PressurewaveformshapeAdequacyofinspirationAdequacyofinspiratoryplateauAdequacyofinspiratoryflowResultsandadequacyofastaticmechanicsmaneuverAdequacyoftheRiseTimesettingBreathtypedeliveredtothepatientBreathtypedeliveredtothepatientCMV,withauto-flowonMeasuringStaticMechanics

illustratesastablestaticpressureplateaumeasurementthatdifferentiatesthepressurecausedbyflowthroughthebreathingcircuitandthepressuresrequiredtoinflatethelungs.Thepressure-timecurvecanbeusedtoverifythestabilityoftheplateauwhencalculatingstaticcomplianceandresistance.C代表不稳定的气道平台压力，常见原因为漏气或者患者出现自主吸气AssessingRiseTime吸气斜率ChiumelloD,PelosiP,CrociM,etal.,Eur.Respir.J.,2001.18(1):p.107-114.Atherisetopressuremaybetooslow.Bidealwaveform恰当的斜率设置CArisetimethatistoofast流速不足AdequateFlowInadequateFlowPaw

(cmH2O)Time(sec)InadequateFlow预置流速不足Thedished-outappearanceoftheairwaypressurewaveformillustratesthechangesfromthepassivebreathwhenflowdoesnotmeetpatientdemand.Progressiveincreasesinpatienteffortduringbreaths2and3werecreatedbymanuallyliftingthetestlungTriggeringdifficultyandunnecessarypatientwork触发困难第三次为患者触发的通气，虽然患者触发了呼吸机，但是P-T曲线呈下凹型，显示了预制流速不足

第一次呼吸患者未达到触发阈值，但是启动了按需阀，为时间触发；Thesensitivitysettingis–4cmH2O.第二次患者仍打开了按需阀，启动了自主呼吸，自主呼吸末，时间触发了一次同步间歇指令通气吸气时的作功大小吸气做功主要由吸气负压大小和持续时间长短决定，吸气负压越大和持续时间越长，吸气功越大，反之亦然

人机不同步HewasbeingmechanicallyventilatedandarterialbloodgaseswereacceptableonventilatorsettingsofSIMV12/min,VT850ml,PEEP5cmH2OandFiO20.40.Hethenbecamecombative,requiringsedationandrestraints.TheendtidalCO2hadincreasedfrom42mmHgto48mmHgandarterialoxygensaturationhaddecreasedfrom98%to94%.Hisheartrateincreasedfrom80to110andhisbloodpressureincreasedfrom140/80to180/100.Thephysicianincreasedtheinspiratoryflowrateandventilatorsensitivity.Thepatientimmediatelybecamecalmerandallvitalsignsreturnedtobaselinevalues.无效触发Further,ifthepeakflowrateoftheventilatorisinadequate,thentheinspiratoryflowwillbe"scooped"inwards,andthepatientappearstobefightingtheventilator.Ifthenumberoftriggeringepisodesisgreaterthanthenumberofbreaths,thepatientisasynchronouswiththeventilator.Loops–agoodthingallroundP-VloopF-Vloop肺通气功能测定

一、肺容积(lungvolume)

（一）基本肺容积(basallungvolume)

1.潮气量(TidalVolume,VT)

2.补吸气量(InspiratoryReserveVolume,IRV)

3.补呼气量(ExpiratoryReserveVolume,ERV)

4.残气量(ResidualVolumeRV)（二）基本肺容量(basallungcapacity)

1.深吸气量(InspiratoryCapacityIC)

2.功能残气量(FunctionResidualCapacityFRC)

3.肺活量(VitalCapacityVC)

4.肺总量(TotalLungCapacityTLC)静态P-V环横轴为压力有正压(机械通气)、负压(自主呼吸)之分,纵轴是容积(潮气量Vt),此环说明压力与容积的关系.一般分为静态P-V、动态P-V曲线，上图为静态P-V环，因为P-V主要反映呼吸系统顺应性情况，因此需要去除阻力的影响，而静态静态P-V曲线是在流速为0的时候测量的，可以满足此要求。但是在临床中，这是无法达到的，因此可以尽量模仿理想状态的静态环，一般认为流速<9L/min，可以消除呼吸系统由于阻力成分造成的压力变化，称之为”quasi-static”[10].HarrisRS.RespirCare,2005.50(1):p.78-98;discussion98-9动态PV环ForthisreasonthePVloopdoesnotgiveanaccuratepictureofthecourseofcompliance.Thegreatertheinspiratorybreathinggasflowthegreatertheadditionalpressuregradientandthusthedegreeofinaccuracy.DynamicPVloops的局限性随着流速的增加，PVloop显著右移，而且流速越大，由阻力带来的压力变化越大，因此越不可信，因此临床上常规描记的动态P-V环可信性较差、临床指导意义不大通气区间Volume(ml)Pressure(cmH2O)WithlittleornochangeinVTPawrisesNormalAbnormal临床应用中，潮气量通常根据理想体重来设置，以保证通气量及使VT＞VTD。利用机控呼吸下的压力-容量环可以有助于选择一个合适的肌控呼吸潮气量。事实机上，因为早期流速、环路顺应性、漏气等原因还需要一些额外的容量，新型呼吸机对于这些因素有一定补偿功能。Pressure-VolumeLoopsHighResistance阻力升高

容量控制通气时，容量恒定，压力依据阻力和顺应性而变化当阻力增加时，PIP上升（A-B），PVloops变宽。该种PVloop，称为滞后steepnessofloopremainsunchangedPressure-VolumeLoops3、HighandLowCompliance——顺应性容量控制通气时，顺应性增加，输出lowerPIP；顺应性降低，输出higherPIPYellowforHighComplianceDecreasedcompliance正常人和ARDS患者PV曲线P-VloopsinARDSaregionoflowcomplianceatlowlungvolume—alowerinflectionpointaregionwithasteeperslopeshowinghighercompliancearegionwithaflatterslope(poorlycompliant)PEEPandPVloopHypotheticalrespiratorysystempressure-volumecurvesforapatientwithARDSshowingaflatterthannormalrelationship(decreasedrespiratorysystemcompliance,Crs=VT/ΔP1).WithadditionofPEEP,ashifttoamorecompliantcurvemayoccursuchthatCrs=VT/(ΔP2-PEEP)increases.ThechangeincompliancemayrepresentrecruitmentofpoorlyventilatedornonventilatedlungunitswithapplicationofPEEPandmaybecorrelatedwithimprovedoxygenationandgasexchange.AirTrappingInspirationExpirationVolume(ml)Flow(L/min)流速未回到基线NormalAbnormalIncreasedRawPressure(cmH2O)HigherPTANormalSlopeVol(mL)LowerSlope气道阻力升高InspirationExpirationVolume(ml)Flow(L/min)DecreasedPEFRNormalAbnormal“Scoopedout”patternP-Vloop“Scoopedout”pattern呼吸功

A:ResistiveWork

B:ElasticWorkPressure(cmH2O)Volume(ml)BA触发灵敏度的设置不当Volume(mL)Paw(cmH2O)IncreasedWOB预置吸气流速不足Paw(cmH2O)V