机械通气的呼吸力学基础(修改)

机械通气的呼吸力学基础,空军总医院呼吸科张波,主要内容,重要的呼吸力学指标呼吸力学指标测定的方法和意义呼吸力学曲线的分析新的通气模式,WhataretheNewAdvancements,RespiratoryMechanicsCompliance,Resistance&auto-PEEP”UndertheinstructionofrespiratorymechanicstoapplyindividualizedventilationLungprotectionstrategy,正压通气与负压通气的比较,VolumeChange,GasFlow,PressureDifference,自主呼吸,VolumeChange,Time,GasFlow,PressureDifference,机械通气,重要的呼吸力学指标,压力阻力容量峰压力吸气阻力吸气潮气量平台压力呼气阻力呼气潮气量平均气道压力弹性阻力可压缩气量胸膜腔内压力呼气末肺容积autoPEEP,重要的呼吸力学指标,顺应性静态顺应性动态顺应性呼吸系统顺应性肺顺应性（C=V/P，正常肺0.2-0.3L/cmH2O）胸壁顺应性（C=V/Ppl，正常0.2L/cmH2O）流速呼吸功P-V曲线P0.1,呼吸力学三要素,压力（P）、阻力（R）、流速（V）P=RV流速对时间积分得到容量压力和流速为可控因素控制压力时阻力改变可导致容量降低（VT=TiV）控制流速时阻力增大可导致压力增高,time,Pressure,PEEP,PIP,Pplat,AlveolarDistending(recoil)Pressuredifference(Pdis),Flow-ResistivePressuredifference(Pres),Pressurecomponents,dP=RxFlow+dV/Cst,不同通气方式下在不同部位测得压力的含义,测压部位和通气方式所克服的阻力PV曲线的斜率自主呼吸时的食道内压肺吸气和呼气阻力肺顺应性机械通气时的食道内压胸壁的吸气和呼气阻力胸壁顺应性自主呼吸时隆突上气管整个呼吸装置（气管插管、整个呼吸设备的顺应性插管内压力呼吸管路、呼吸机）阻力机械通气时隆突上气管肺和胸壁的吸气和呼气阻力呼吸系统的顺应性插管内压力自主呼吸时气道开口处呼吸管路和呼吸机的吸气和呼吸管路的顺应性（Y型管接口处）呼气阻力、机械通气时气道开口处肺和胸壁阻力加气管插管阻力呼吸系统顺应性,压力监测部位,流速监测部位,床旁监测气道压力的意义,峰压力增高而平台压无改变气道阻力增高（分泌物堵塞、气管痉挛）峰压力与平台压同时增高提示肺或胸壁扩张受限明显腹胀肺不张气胸肺水肿、ARDS、肺炎autoPEEP人-机对抗气道峰压降低（管路漏气、气囊漏气）,肺（气道）阻力与顺应性的改变都可导致气道压力的改变,通过气道压力的改变可以推测病变的性质和部位,Paw(cmH2O),NormalPPlat(NormalCompliance),IncreasedPIP,IncreasedPTA(increasedAirwayResistance),IncreasedAirwayResistance,DECREASEDCOMPLIANCE,Time(sec),Paw(cmH2O),NormalPPlat(NormalCompliance),IncreasedPPlat(DecreasedCompliance),Normal,PIP,RespiratoryMechanics,Aspressurerisesordecreasesinpatientsonmechanicalventilation,itisimportanttoknowwhyHighpressurecanresultfromeitherstiffnessofthelung/thoraxorresistancetoflowCausesofstiffnessorresistancetoflowandthereforetreatmentaredifferent,Resistance,气道阻力的计算公式和意义,RI=（PIPPpla）/吸气末流速RE=（PplaPEEP）/最大呼气流速气管插管产生的阻力在总的呼吸阻力中占很大比例，与管腔内径关系最大，流速和气管插管长度也对阻力有一定的影响改变吸入气体的性质，如氦-氧混合气也可减低吸气阻力，减少呼吸功。在COPD和哮喘患者采用高压力和高流速通气时肺泡内压不会有很大的升高,气道阻力,大气道以湍流为主，占总阻力的80%小气道以层流为主，占总阻力的20%正常人气道阻力为1cmH2O/L/S哮喘和COPD患者气道阻力为5-10cmH2O/L/S8号气管插管阻力为5cmH2O/L/S7号气管插管阻力为8cmH2O/L/S气管插管时气道阻力相当于中度哮喘发作,AirwayResistanceCalculations,VolumeChange=PressureDifferencexComplianceoftheBalloon,C=,DV,DP,compliance,StaticMechanicsConcepts,MeasurementsaretypicallydisplayedascomplianceandresistanceCompliance-measuresthestiffnessofthelungStaticNoflowdynamicflowandresistance,肺顺应性监测的意义,静态顺应性（Cs）反映肺和胸壁的弹性（弹性阻力）特征,排除了气道阻力成分动态顺应性（Cd）反映气道的阻力（非弹性阻力）和呼吸系统弹性（弹性阻力）特征，气道阻力可明显影响Cd的水平顺应性的动态变化趋势更有意义,StaticMechanicsCalculations,Compliance=VolumePressureorCompliance=mlcmH20Resistance=PressureFloworResistance=cmH20/L/SEC,顺应性测定要求,Thegoldstandardformeasuringcomplianceandresistanceutilizesavolumebreathdeliveredwithasquarewaveflowandadequateplateau,ComplianceCalculations,VTE500cc,10cmH20,区分肺顺应性和胸壁顺应性的意义,CRS=（CLCW）/（CL+CW）胸壁顺应性相对稳定时，CRS的动态变化可代表肺的顺应性改变评价PEEP对血流动力学的影响,Crs=Vt/dPdist(aw)Ccw=Vt/dPdist(pl)CL=Vt/Pdist(aw-pl),机械通气时气体分布,机械通气时气体在肺内分布特点,自主呼吸时吸入气体主要进入肺的下垂区域和肺周边胸膜下部位机械通气时气体主要分布在肺非下垂区和大气道内在ARDS时，病变分布以双侧肺下垂区域为主，机械通气时气体主要进入非下垂区域COPD和哮喘患者除存在肺内气体分布不匀外，还存在较严重的小气道塌陷气流的波形（方波和正弦、加速波和减速波）对气体的分布无明显影响,机械通气时肺内气体分布,MV,exp,insp,SB,exp,insp,Froese,Bryan1974,Pleuralpressure,-13cmH2O,+4cmH2O,-2cmH2O,-10cmH2O,MV,SB,Roussosetal1976,Relaxeddiapragm,Tenseddiapragm,提倡应用自主通气模式,压力-容积曲线,P-V曲线的测定方法,大注射器法吸气阻断法持续气流法准静态顺应性测定注意事项镇静、肌松近口端压力和流速监测注意干扰因素（如明显腹胀）,大注射器法,费时、费力需脱开呼吸机安全性差不易标准化很少应用,Volume,Pressure,持续气流法,Slow(5-10lpm)inspiratoryflowwithlargeVtandZEEPTheinspiratorycurveofthedynamicP-VloopcloselyapproximatesthestaticcurveTheflow-resistivepressurecomponentcouldbesubtractedEasytoperform,fastandrelativelycomfortable,Pressure,Volume,LPIflex,UPIflex,inspiration,Staticcurve,UpperAndLowerInflectionPoints,UpperAndLowerInflectionPoints,Alveolaroverdisention,Alveolarcollapse,P,T,UpperAndLowerInflectionPoints,Alveolarcollapse,P,T,Lowerinflectionpointsarethoughttobeapointofcriticalopeningpressure,PEEP对血流动力学的影响,Ppl=PEEPCL/（CL+CW）正常人CLCW，故Ppl1/2（PEEP）相当于大约一半的胸腔内压（PEEP或PEEPi）传递到胸膜腔，引起胸内压增高。当肺实变、肺顺应性减小时，传递比例减少。而胸壁顺应性减小时，气道内压力向胸膜腔内传递增加。ARDSPEEP水平在15cmH2O以下，可不必考虑对PCWP读数的影响。肺顺应性增大（肺气肿）或胸壁顺应性减小时较低水平的PEEP就可能干扰肺毛细血管楔压的判断，测定值高于实际水平。,PEEP对血流动力学的影响,CompensationofthePCWPforPEEP:CompliantlungscorrectedPCWP=PCWP-PEEP(mmHg)NoncompliantlungscorrectedPCWP=PCWP-1/4PEEP(mmHg)PEEP(cmH2O)/1.36=PEEP(mmHg),Auto-PEEP检查方法,呼气末阻断气流法当存在严重气道狭窄及气体陷闭时不能反映真实的肺泡压力，用平台压更准确吸气末肺容积（VEI）食道内压测定,Auto-PEEPManeuver,PressExpPausekeytoscheduleautomaticexpiratorypausemaneuverDuringthenextexhalation,theinspiratoryandexpiratoryvalveswillcloseandpressurewillequilibratebetweenthecircuitandthepatient,autoPEEP临床迹象,不能解释的心动过速、低血压，特别是机械通气治疗刚开始时（由人工通气过度为机械通气时）患者触发每次呼吸非常费力患者的吸气努力并非每次都能触发呼吸下一次吸气开始时呼气（喘鸣音）仍在进行压力流速图形显示异常,AirTrapping,Inspiration,Expiration,Time(sec),Flow(L/min),autoPEEP监测,autoPEEP的处理,改变呼吸机参数增加呼气时间，减少通气频率，减少潮气量降低病人的通气需要减少碳水化合物的摄取，减少死腔通气，治疗焦虑、寒战、疼痛、发热减低呼吸道阻力（用大口径的气管插管，经常吸痰避免分泌物潴留，应用支气管扩张剂）加用适当的外源性PEEP，一般为PEEPi的75%左右,死腔通气问题,解剖死腔正常人100-150ml机械通气时可明显增大（延长管、湿化器）肺泡死腔肺栓塞时VD/VT可显著增大（0.6）COPD、Asthma时V/Q比例失衡，VD/VT增大VD/VT增大将导致分钟通气量显著增大,呼吸力学测定的质量控制,NosignificantleaksComplianceshouldsubtractoutcircuitcompliance,especiallyinpediatricsManualcalculationsoftencontributetoerrors,RespiratoryMechanicsRequirementsForAccuracy,ThepatientmustbeatrestduringpeakandplateaupressuremeasurementsAddingplateaushouldnotrestrictexhalationandcreateauto-PEEPPlateautimemustnotbetooshortortoolong,PatientEffortDuringInspiratoryPlateau,PlateauPressure=?,PlateauTimeTooShort,Resultsinfalselylowcompliancevalues!,InsufficientExhalationTime(Auto-PEEP),500,20-10,=50ml/cmH20,Resultsinfalselylowcompliancevalues!,StaticComplianceLeaksand/orTooLongaPlateau,Resultsinfalselyhighcompliancevalues!,AirLeak,Volume(ml),Time(sec),AirLeak,Volume(ml),Pressure(cmH2O),AirLeak,AirLeak,Inspiration,Expiration,Volume(ml),Flow(L/min),AirLeakinmL,NormalAbnormal,ResponsetoBronchodilator,Before,Time(sec),Flow(L/min),PEFR,After,LongTE,HigherPEFR,ShorterTE,InadequateInspiratoryFlow,AdequateFlow,Time(sec),InadequateFlow,Paw(cmH2O),InadequateInspiratoryFlow,Flow(L/min),Time(sec),NormalAbnormal,ActiveInspirationorAsynchrony,FlowversusTime,ACCELERATING,DECELERATING,SINE,SQUARE,LungComplianceChangesandtheP-VLoop,Volume(mL),PresetPIP,VTlevels,Paw(cmH2O),COMPLIANCEIncreasedNormalDecreased,PressureTargetedVentilation,OptimisingPEEP,V,P,V,P,VolumevsTime,Inspiration,Expiration,Time(sec),Volume(ml),TI,呼气阻力增加,Prolongedexpiratoryflowindicatesanobstructiontoexhalationandmaybecausedbyobstructionofalargeairway,bronchospasm,orexpiratoryvalvefailureoftheventilator,Time,Flow,吸气时间过短,SpontaneousinspirationiseasybutexpisimpededLongerI-timesmaycauseasynchrony,InsufficientExpiratoryTime,ExpiratoryflowisunabletoreturntobaselinepriortotheinitiationofthenextmechanicalbreathIncompleteexhalationcausesgastrapping,dynamichyper-expansionandthedevelopmentofintrinsicPEEP,Time,Flow,End-ExpiratoryFlow,