Earlyapplicationofairwaypressurereleaseventilationmayreducethedurationofmechanicalventilationin

acuterespiratorydistresssyndromeIntensiveCareMedicine201743:1648-1659

Introduction

• MVisessentialinpatientswithARDSbutcancauselunginjuryduetoregionalalveolarstretchandorrepetitivealveolarcollapsewithshearing• Ideallyshouldmaintainlungunitsopenthroughoutventilatory cycle• Difficultwhenlungisheterogenous

• InconventionalMV,selectionof“optimum”PEEPtobalancerecruitmentagainstoverdistensionisstillanunresolvedproblem• Mortalityremainshighamongthosereceivingmechanicalventilation

Introduction

• AirwayPressureReleaseVentilation(APRV)deliverscontinuouspositiveairwaypressurewithbriefintermittentreleasephase• Allowsonlypartialreleaseoflungvolumeandspontaneousbreathingthroughouthighlevel• InanimalswithARDS,APRV:• Improvedalveolarrecruitmentandgasexchange• Increasedhomogeneity• Reducedlunginjury

• DataonAPRVinARDSlimitedandusuallysourcedfromsmalltrialswithoutdatedsettings

Hypothesis

• InpatientswithARDS,earlyapplicationofupdatedAPRVmethodologywouldbetterimproveoxygenationandrespiratorysystemcomplianceandreducethedurationofmechanicalventilationcomparedtoconventionalLTV

MaterialsandMethods

• CriticalCareDepartmentofWestChinaHospitalofSichuanUniversity,SichuanProvince• Enrollment May2015-Oct2016• Appropriateethicssought• Allocationappropriatelyrandomised

InclusionCriteria

• DiagnosticcriteriaforARDS(Berlin)• PF<250• Intubatedandventilated<48hrspriortoinclusion

ExclusionCriteria

• Pregnancy• Anticipatedventilation<48hrs• Intracranialhypertension(incl suspected)• Neuromusculardisorders• SevereCOPD• Pre-existingconditionswith6/12mortality>50%• Documentedbarotrauma• TreatmentwithECMO• Refractoryshock• Lackofcommitmenttolifesupport• Age<18or>85

VentilatorSettings- Initial

• VCV(PuritanBennet840)• Pplat<30cmH20• PaO2 7.3-13.3kPa• pH>7.30

VentilatorSettings- LTV

• Vt 6ml/kgPBW(?)• PEEPlevelsadjustedbyPEEP-FiO2 table• Vt andRRregulatedtoachievepHandPplat accordingtoARDSnetprotocol• Inhypotension/ptx,PEEPcouldbefurthertitrated• IfPF<150withFiO2 >0.6,PEEPcouldbefurtheroptimised• IfsevereacidosispH<7.15,RRincreasedto35/min• Ifsevererespiratoryacidosispersisted,NAHCO3 couldbegiven

VentilatorSettings- APRV

• Phigh=Pplat• Plow=5cmH2O• Tlow 1-1.5*expiratorytimeconstantthenadjustedtoachievePEFRof>50%PEFR• Releasefrequency10-14/min• Thigh indirect• AimedforMVspont tobe30%MVtotal

ProcedureBothGroups

• Supportivetherapies(recruitment,proning,NMB,iNO)inbothgroupsasrequired• Rescuemeasures(incl ECMOandHFOV)atcliniciandiscretion• Usualcare• InLTV,dailysedationholdsandSBT• InAPRV,initiallyreducedPhigh by2cmH2Oandreducedreleaserateby2/mintwicedaily• ThenonceonPhigh 20cmH20andFiO2 0.4,sameweaning

• ExtubatedwhenSBTsuccessful

Endpoints

• Primary– Ventilatorfreedaysatday28• Secondaryendpoints• Oxygenation• Pplat,MAP,compliance• Clinicaloutcomes

StatisticalAnalysis

• Meanventilatorfreedays14.5+-10.4• ReportedthatAPRVcouldshortendurationby6days• Conservativeestimateofsamplesize=110

Results

Discussion

• ComparedwithLTVgroup,theAPRVgrouphad:• Shorterdurationofventilation• Improvedoxygenation• Improvedcompliance• Decreasedplateaupressure• Reducedsedation• ShorterlengthofICUstay*• Higherrateofsuccessfulextubation*• Lowertracheostomyrate*

• *Non-significant

Discussion

• Nodifferencein:• Hospitallengthofstay• ICUmortality• Incidenceofpneumothorax

Discussion

• Accordingtorecentexperimentalfindings,setPhigh nottoexceed30cmH20andTlow tobe>50%PEFR,thesesettingswerecombinedwithAPRVsettingsandsedationtitrationtoachievespontaneousbreathtargetlevel• CollateralchannelsofventilationsuchastheporesofKohnwhichmightbeadditionalpathwaystofacilitaterecruitmentandredistributealveolarvolumethroughoutthelungovertime• Otherstudiesindicatethattheprocessofrecruitmentandderecruitmentoflungunitsshouldbedeterminednotonlybypressurebutalsobytime.• APRVfavouredhaemodynamicimprovementandreducedsedativeandparalysisused

Discussion

• APRVgroupassociatedwithmoredayswithoutmechanicalventilationatD28andashorterICUstaythantheLTVgroup• Possibleexplanations:• EarlyuseofAPRVimprovespulmonaryfunctionsuchasgasexchangeandrespiratorycompliance• RecentexperimentshavealsodocumentedthatearlypreventativeuseofAPRVcanmoreeffectivelyblockARDSdevelopmentthanLTV• APRVallowsmoderatespontaneousventilation,reducessedationandparalysisrequirement,anddecreasesdurationofmechanicalventilation• Inthestudy,respiratorytherapiststitratedAPRVsettingsanddosagesofsedativesetc.• Theyalsoguidedweaning

Limitations(Author)

• Studynotblinded• Samplesizesmall• Possibilityofknowledgebias(althoughtheydidasmallertrialfirstandfoundalltherapistswelltrainedandskillfully usedstudyprotocol• MorepatientswithcoexistingchronicdiseasesintheLTVgroup• Studydidnotmeasurepatient-ventilatorsynchrony

Conclusion

• ComparedwithconventionalLTV,theearlyapplicationofAPRVinpatientswithARDSwasassociatedwithbetteroxygenationandrespiratorysystemcompliance,lowerplateauairwaypressure,lesssedationrequirement,moreventilator-freedaysatday28,andashorterdura- tion ofICUstay.

MyThoughts

• Thisissinglecentrewithapopulationunlikeours(young,thin)• TheyareclearlyAPRVenthusiasts,ifanythingtheyareuncertainwhattheyaredoingwithLTV!!(sedation,tracheostomyrate)• TheyuseVCVnotPCV• I’munclearthatyoucanmeasurerespiratoryphysiologyinthesamewaywithAPRV• AmovetoAPRVwouldbeaparadigmshiftoftheorderofnegativepressure->positivepressureventilation• Wouldneedcompletebuy-in• Berlinguidance?