ARDS –A Brief Overview - KRCS - Kansas Respiratory Meeting/2012_ARDS...Outline • Definition of ARDS • Epidemiology of ARDS • Pathophysiology of ARDS • Ventilator management

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  • ARDS ABriefOverview

    LucasPitts,M.D.AssistantProfessorofMedicine

    PulmonaryandCriticalCareMedicineUniversityofKansasSchoolofMedicine

  • Outline DefinitionofARDS EpidemiologyofARDS PathophysiologyofARDS Ventilatormanagementstrategies

    Lowtidalvolumeventilation Permissivehypercapnia Openlungventilation Recruitmentmaneuvers Proneventilation Highfrequencyventilation

    Nonventilatory andnoveltherapies

  • Introduction

    Conditionfirstdescribedin1960s DescribedbymilitarycliniciansinVietnamasshocklung

    Simultaneouslydescribedasadultrespiratorydistresssyndrome

    Terminologychangedwhenitwasdiscoveredthatpersonsofanyagecouldbeaffected acuterespiratorydistresssyndrome

  • Definitions

    Acuteonsetofbilateralpulmonaryinfiltratesconsistentwithpulmonaryedema Withoutevidenceofelevatedleftatrialpressure

    PCWP18mmHg

    ALI(acutelunginjury)andARDSaredifferentiatedbydegreeofhypoxemia ALI P/Fratioof201to300mmHg ARDS P/Fratioof200mmHg

  • P/FRatio

    PaO2requiresABGanalysistodetermine Canbedifficulttoobtain insomepatients

    SpO2isareasonablesubstitute(Rice,2007) SpO2/FiO2235predictedP/F200 SpO2/FiO2315predictedP/F300

    ALI/ARDSisanarbitrarydefinition

  • Oxyhemoglobin DissociationCurve

  • Epidemiology

    Incidence(Rubenfeld, 2012) ALI

    86per100kpersonyears ARDS

    64per100kpersonyears Increasesdramaticallywithpatientage

    16/100kpersonyears(1519y/o) 306/100kpersonyears(7584y/o)

    Approximately190,000casesofALIintheU.Seachyear

  • Epidemiology

    1015%ofICUpatientsmeetcriteriaforALIorARDS 20%ofthosemechanicallyventilated

    Incidenceappearstobedecreasing(Li,2010) DeclineinhospitalacquiredARDS ThosewithARDStendtobemuchsickerthantheyusedtobe

  • Epidemiology

    Previouslyhadamortalityrategreaterthan50%(Ashbaugh,1967)

    Mortalitydecreasedto2938%duringthe1990s Mortalityappearstobecontinuingtodecline,nowapproaching25%

    AminorityofpatientswithARDSdieexclusivelyfromrespiratoryfailure

    Mostpatientssuccumbtosecondarycomplicationsortheirprimaryillness

  • Pathophysiology

    ARDSischaracterizedbyaccumulationoffluidandprotienaceousdebrisinthealveoliandinterstitium ofthelung

    Normallungfunctionrequiresdry,patentalveolitobecloselyapproximatedtoperfusedcapillaries

  • Pathophysiology

    Fluidcrossespulmonarycapillarymembranesundercontrolofhydrostaticandoncoticforces

    Serumproteinremainsintravascular Smallquantitiesoffluidarenormallyallowedintotheinterstitium

    Threemechanismsnormallypreventalveolaredema Retainedintravascularprotein Interstitiallymphaticreturn Capillaryepithelialtightjunctions

  • Pathophysiology

    ALI/ARDSareconsequencesofalveolarinjuryleadingtodiffusealveolardamage

    Lunginjuryleadstoreleaseofproinflammatorycytokines Neutrophilsarerecruitedtothelungs

    Toxicmediatorsarereleaseddamagingcapillaryandalveolarendothelium

    Proteinescapesfromthevascularspace Fluidoverwhelmslymphatics andfillsairspaces

    Alveolarcollapseensues

  • ConsequencesofInjury

    Impairmentofgasexchange V/Qmismatching

    Shuntingleadstohypoxemia IncreaseddeadspaceimpairsCO2 elimination

    Decreasedlungcompliance Stiffnessofnonaerated lung Smallertidalvolumescanleadtomarkedlyelevatedairwaypressures

    Pulmonaryhypertension

  • ThreeStagesofARDS Exudativestage

    Diffusealveolardamage Proliferativestage

    Resolutionofpulmonaryedema ProliferationoftypeIIpneumocytes Squamousmetaplasia Interstitialinfiltration Collagendeposition

    Fibroticstage Obliterationoflungarchitecture Cystformation Fibrosis

  • Etiologies

    Manydifferentpotentialetiologies Morethan60possiblecauseshavebeenidentified

    Sepsis MostcommoncauseofALI/ARDS Concurrentalcoholismmarkedlyincreasesrisk

    70%vs.30%

    Aspiration ALI/ARDSdevelopsinapproximately33%ofhospitalizedpatientswithwitnessedaspiration

  • Etiologies Pneumonia

    CAPismostcommoncauseofoutofhospitaldevelopmentofALI/ARDS1

    NosocomialpneumoniawellrecognizedtoprogresstoALI/ARDS

    Severetrauma Bilaterallungcontusion Fatembolismfollowinglongbonefractures

    Delayedonset 12to48hoursfollowingtrauma Manypatientspredisposedtosepsis TraumarelatedALI/ARDScarriesmorefavorableprognosisthanALI/ARDSfromothercauses2

    1. BaumannWR.Incidenceandmortalityofadultrespiratorydistresssyndrome:aprospectiveanalysisfromalargemetropolitanhospital.Crit CareMed1986;14(1):14.2. Calfee CS,EisnerMD,WareLB,etal.Traumaassociatedlunginjurydiffersclinicallyandbiologicallyfromacutelunginjuryduetootherclinicaldisorders.Crit CareMed2007;35(10):22432250.

  • Etiologies

    Massivetransfusion >15unitsofPRBCisariskfactorforthedevelopmentofALI/ARDS1

    Selectionbias? TRALI

    Developmentwithin6hoursoftransfusion LungandHSCT

    Primarygraftfailureinlungtransplantrecipients Poorpreservationofdonororgan

    DAH,engraftmentsyndrome,infectionsinHSCTrecipients

    1. HudsonLD.Clinicalrisksfordevelopmentoftheacuterespiratorydistresssyndrome.AmericanJournalofRespiratoryandCriticalCare Medicine1995;151(2):293301.

  • Etiologies

    Overdoseandtoxicity(Reed,etal.) Aspirin,cocaine,opioids,phenothiazines,tricyclicantidepressants

    Protamine,nitrofurantoin,systemicchemotherapy(attherapeuticdosages)

  • InitialCourse

    Pulmonaryabnormalitiesdevelopwithin48to72hoursfollowingtheincitingevent Rapidworseningofclinicalstatuscommon

    ABGgenerallyindicatesrespiratoryalkalosis,hypoxemia Hypoxemiaduetophysiologicshunting

  • ARDSInitialCXR

  • SubsequentCourse

    Followingtheinitialacutephaseofdisease,patientsmaytakeoneoftwocourses: Improvementinventilatory requirementsaccompaniedbyradiographicimprovement

    Entranceintotheorganizing/fibroticphaseofARDSwithpersistentventilatordependenceandradiographicabnormality

  • Complications

    ALI/ARDSisassociatedwithmanycomplicationsgenerallyseeninstatesofcriticalillness

    ComplicationsspecifictoALI/ARDS Barotrauma Sedation/paralysis

  • Barotrauma

    Aresultofpulmonaryparenchymaltissuebreakdownandagenerallyuniformneedforpositivepressureventilation

    Incidenceappearstobe13%amongpatientsusinglowtidalvolumeventilationstrategies

    HighestlevelsofbarotraumafoundamongpatientsreceivinghighPEEP Meanairwaypressure,plateaupressure,anddrivingpressuredidnotpredictbarotrauma

    1. EisnerM,ThompsonB,Schoenfeld D,Anzueto A,Matthay M,NetworkTARDS.AirwayPressuresandEarlyBarotraumainPatientswithAcuteLungInjuryandAcuteRespiratoryDistressSyndrome.AJRCCM2002;165(7):978982.

  • ConsequencesofSedationandParalysis

    Prolongeddepressionofmentalstatus Persistentneuromuscularweakness

    Criticalillnessmyopathy Mostprominentwhenneuromuscularblockingagentsareusedinconjunctionwithcorticosteroids

  • Ventilatory Strategies

    LowTidalVolumeVentilation Permissivehypercapnia Openlungventilation Recruitmentmaneuvers Proneventilation Highfrequencyventilation

  • LowTidalVolumeVentilation

  • LowTidalVolumeVentilation

    Randomized861patientswithALI/ARDStotraditionalventilationversuslowertidalvolumeventilation Traditionalventilation:initialVt 12mL/kg;plateaupressure50cmH2O

    Lowertidalvolumeventilation:initialVt 6mL/kg;plateaupressure30cmH2O

    Studyabortedbecausemortalitywassignificantlylowerinthelowertidalvolumegroup(31.0%vs.39.8%)

    Numberofdayswithoutventilatorincreasedinlowertidalvolumegroup(12vs.10)

  • LowTidalVolumeVentilation

    PreponderanceofqualityevidencehasshownLTVVimprovesmortalityandotheroutcomesinARDS

    Reductioninmortalityandincreasesinventilatorfreedays

  • PotentialHarmofLTVV WasnotassociatedwithanyclinicallyimportantadverseoutcomesintheARMAtrial

    AutoPEEP HigherrespiratoryratesarerequiredforLTVVtomaintainthesameminuteventilation

    Mayleadtohemodynamicinstability Sedation

    WOBandventilatorasynchronymayincreasewithLTVV Initialneedforincreasedsedationwhenventilationinitiated,butdoesnotappeartopersist

    PosthocanalysisofARMAtrialdidnotfindanydifferencesinsedationdurationamongpatientgroups

  • BreathStacking

    Canoccurdespitesedation CausesepisodicdeliveryofhigherVt whichmayunderminebenefitsofLTVV

    CanbeamelioratedbydeliveringslightlyhigherVt Pplat shouldremain30cmH2O

  • BreathStacking

    1. J.Pediatr.(RioJ.) vol.83 no.2 suppl.0 PortoAlegre May 2007

  • ApplicationofLTVV

    AthresholdPplat belowwhichsafetyiscertainisnotknown Goalof30isderivedfromARMAtrial Plateaupressureshouldbekeptaslowaspossible

    Oxygenationgoal PaO2 between5580mmHg SpO2 between8895%

  • PermissiveHypercapnia

    Theunderstandingthatprotectivelungventilationstrategieswilloccasionallylimitalveolarventilation

    Lowtidalvolumeventilationwillsometimesleadtohypercapnia,whichhasbeenshowntobegenerallywelltoleratedintrials

    Safeformostpatients Somepatientsexistinwhompermissivehypercapnia maybeharmful

  • ContraindicationstoPermissiveHypercapnia

    Cerebraldisease Masslesions,trauma,cerebraledema Seizuredisorder

    Hypercapnia isassociatedwithcerebralvasodilitation Increasescerebralbloodflow

    MaycauseincreasedICPandpotentiallyreduceCPP

    Maylowerseizurethreshold Associatedwithintraventricular hemorrhageinneonates

    1. Feihl F.Permissivehypercapnia.Howpermissiveshouldwebe?AmericanJournalofRespiratoryandCriticalCareMedicine1994;150(6):172237.

  • Hypercapnia maybeHarmful

    Patientswithsignificantheartdisease Increasedsympathetictone

    Patientstakingbetablockers Negativeinotropiceffects

    Hypovolemia Systemicvasodilation Leadstohypotension

  • OpenLungVentilation

    Combineslowtid