ALI应力与应变

呼吸机相关肺损伤的力学机制---应力与应变杨毅东南大学附属中大医院重症医学科内容提要•机械通气现状与肺保护策略•潮气量与应变•平台压与应力•小结MechanicalVentilation:HistoricalOverview1000B.C.1000A.D1850A.DPhysiologicallyNaïvePeriod185019252000TechnologyAdvances1970198019902000+Physiology/Iatrogenesis/PhilosophyAJRCCM,2013,188,220-302004IncreaseduseofPSVmodeduringMVVtdecreasedovertime39%69%77%AJRCCM,2013,188,220-30PEEPincreasedovertime01234567199820042010PEEP(cmH2O)PEEPAJRCCM,2013,188,220-30机械通气的临床目标保证气体交换：可接受的氧及二氧化碳避免呼吸机相关肺损伤PIP=14PIP=45PIP=45TierneyAmRevRespirDis.1974,110:556-565.肺损伤的发生机制•容积伤•气压伤•萎陷伤•生物伤0.01.02.03.04.002468PressureShearforcePressurewedge机械通气的肺保护策略•容积伤：Vt6ml/IBW？•气压伤：Plat30cmH2O？•萎陷伤：合适的PEEP？•生物伤0.01.02.03.04.002468PressureShearforcePressurewedge内容提要•机械通气现状与肺保护策略•潮气量与应变•平台压与应力•小结小潮气量通气是ARDS肺保护性通气策略的重要内容6ml/kg潮气量：肺泡过度膨胀肺保护性通气策略面临困境正常通气区过度膨胀区20例69.9%8.1%10例23.1%63.0%30例患者VT6ml/kg吸气末和呼气末CTAmJRespirCritCareMed,2007,175:160-1666ml／Kg－－小潮气量非重力依赖区肺泡依然过度膨胀汤睿黄英姿中大医院重症医学科CritCareMed,2007,35:1509–1516.ARMA研究中，对于基础呼吸系统顺应性不同的患者，6ml/kg的潮气量对于病死率的影响不同AmJRespirCritCareMedVol172.pp1241–1245,2005平台压较高、顺应性明显减低时小潮气量通气获益更明显肺顺应性低(＜0.6mL/cmH2O/kg)，小潮气量降低病死率肺顺应性高(＞0.6mL/cmH2O/kg)，小潮气量增加病死率肺顺应性与小潮气量6ml/kg潮气量不适合所有患者CritCareMed,2005,33:1141-1142潮气量设置与肺的严重程度有关•ARDS肺顺应性、肺不均一性个体差异显著•更小潮气量•肺泡通气降低•肺泡塌陷•分流增加•高碳酸血症•重症ARDS•大量肺泡塌陷•“小”潮气量仍过度膨胀•潮气量应更小6ml／Kg的“小”潮气量不适合所有ARDS应变•Strain(应变)•由于应力导致的肺部结构的形变称为应变•应变定义为在初始状态基础上尺寸或形状的变化•Strain=VT/FRCMinimalStrainStrainAmJRespirCritCareMed2008,178：346–355VT不是应变呼吸力学vsStrain呼吸力学vsStrainStrain：Vt/FRC(EELV)Vt不变FRC(EELV)明显降低（降低50%）Strain增加1倍Ventilationaccordingtolungsize6名健康志愿者，12名ALI患者测定肺组织应变Strain=Vt/EELV测定肺泡灌洗液中炎症介质肺泡灌洗液中IL-6、IL-8浓度随着肺组织应变的增加而增加IntensiveCareMed,2012,38:240-7.IntensiveCareMed,2012,38:240-7.Strain0.27avoidVILI?Theeffectsoflowtidalventilationonlungstraincorrelatewithpulmonarycompliance•19ARDSpats•ChighVS.Clow•0.6ml/cmH2O·kg•ARDSNetPEEP/FiO2table•VTatbaselineandat6,8,10and12ml/IBW•Strain=Vt/EELVXieJianfeng.UnpublishedData应变0.27—VILISettingindividualVtbasedoncomplianceandstrainXieJianfeng.UnpublishedData潮气量的设置如何减缓VILI•应根据ARDS病变的严重程度个体化设置Vt–P/F-受多种因素影响-不能反映肺泡过度膨胀–呼气末肺容积–肺顺应性•Strain=Vt/FRC(EELV)控制潮气量=控制StrainARDS潮气量设定与ARDS严重程度相关内容提要•机械通气现状与肺保护策略•潮气量与应变•平台压与应力•小结controlgroups(highVT)lowVTgroupsrecommendedPplatlimit35保护性通气改善预后与平台压相关Plateaupressuresshouldbe≤30cmH2OForARDSpatsHighVtcouldinducedhighmortalityPlateaupressurehigherthan30cmH2OincreasemortalityAmJRespirCritCareMedVol177.pp1215–1222,2008AmJRespirCritCareMedVol175.pp160–166,2007促进肺泡扩张的压力=气道内压力-胸膜腔压力气道内压力胸膜腔内压力使肺泡扩张的压力是跨肺压应力•Stress(应力)•是每单位面积上用以平衡和对抗外部作用力而产生的内部反作用力分布•跨肺压Externalload(action)Reaction(stress)=ActionReactionStressP=0P=5P=10P=20P=30Ptp的升高会导致肺泡的过度膨胀平台压≠跨肺压AmJRespirCritCareMed,2008,178:346–355.由于EL/(EL+EW)个体差异明显，平台压≠跨肺压控制跨肺压=控制StressAmJRespirCritCareMed.2008;178(4):346-55.ForagivenPplattranspulmonarypressure(i.e.stress)differsconsiderablyamongpatientsStress=KxStrainStrainStressK=13.5cmH2OPLungwhenVT=FRCStress:PLung=Paw-Ppl=Paw-PesStrain(end-inspiratory):VT/FRC(EELV)K=angle应力和应变的关系MariniandGattinoniCritCareMed2004•VT6ml/kg,Pplat30cmH2O=lessstressandstrainStress(Plung):esophagealpressureStrain(Vt/FRC):FRCatzeroPEEPStrain=VT/FRCPplat=Plung+PcwStress6ml/IBW的小潮气量Pplat30cmH2O---安全吗？平台压均28cmH2O-NoVILI？XieJianfeng.UnpublishedDataAJRCCM2005,172:1241-5.Noobvious―safe‖PplatTidalVolumereductionlowersmortalityateveryPplatQuartileofPplat肺保护性通气策略•小潮气量和限制平台压是不够的•控制应力和应变EELV(FRC)与肺顺应性正相关XieJianfeng.UnpublishedData•BecauseCrsisstronglyrelatedtothevolumeofaeratedremainingfunctionallung•Drivingpressure(ΔP=VT/CRS)wouldbeanindexmorestronglyassociatedwithsurvivalthanVTorPEEP•Multilevelmediationanalysistoanalyzeindividualdatafrom3562patientswithARDSenrolledinninepreviouslyreportedrandomizedtrialsNEnglJMed.2015;372:747-55.NEnglJMed.2015;372:747-55.NEnglJMed.2015;372:747-55.Relativeriskofdeathassociatedtoincrementsin∆PwithineachofthetrialsNEnglJMed.2015;372:747-55.Survivalinpatientsunder―protective‖ventilatorsettingsNEnglJMed.2015;372:747-55.DecreasesinΔPowingtochangesinventilatorsettingswerestronglyassociatedwithincreasedsurvival.ΔP=VT/CRS16避免肺损伤！小结•ARDS患者需要实施保护性通气•目前的小潮气量和控制平台压对于肺保护是不够的•需要控制应变和应变Thankyou