呼吸衰竭RespiratoryFailure英文

RespiratoryFailureRESPIRATORYFAILURE“inabilityofthelungtomeetthemetabolicdemandsofthebody.Thiscanbefromfailureoftissueoxygenationand/orfailureofCO2homeostasis.”RESPIRATORYFAILUREDefinitionRespirationisgasexchangebetweentheorganismanditsenvironment.FunctionofrespiratorysystemistotransferO2fromatmospheretobloodandremoveCO2fromblood.ClinicallyRespiratoryfailureisdefinedasPaO2<60mmHgwhilebreathingair,oraPaCO2>50mmHg.Respiratorysystemincludes:

CNS(medulla)Peripheralnervoussystem(phrenicnerve)RespiratorymusclesChestwallLungUpperairwayBronchialtreeAlveoliPulmonaryvasculaturePotentialcausesofRespiratoryFailureHYPOXEMICRESPIRATORYFAILURE(TYPE1)PaO2<60mmHgwithnormalorlowPaCO2

normalorhighpHMostcommonformofrespiratoryfailureLungdiseaseisseveretointerferewithpulmonaryO2exchange,butoverallventilationismaintainedPhysiologiccauses:V/QmismatchandshuntHYPOXEMICRESPIRATORYFAILURECAUSESOFARTERIALHYPOXEMIA

1. FiO2 2. Hypoventilation(PaCO2)Hypercapnic3. V/Qmismatch Respiratoryfailure (eg.COPD) 4. Diffusionlimitation? 5. Intrapulmonaryshunt -pneumonia -Atelectasis -CHF(highpressurepulmonaryedema) -ARDS(lowpressurepulmonaryedema)

CausesofHypoxemicRespiratoryfailureCausedbyadisorderofheart,lungorblood.EtiologyeasiertoassessbyCXRabnormality: -NormalChestx-ray Cardiacshunt(righttoleft) Asthma,COPD Pulmonaryembolism

HyperinflatedLungs:COPDCausesofHypoxemicRespiratoryfailure(cont’d.)FocalinfiltratesonCXR Atelectasis PneumoniaAnexampleofintrapulmonaryshuntCausesofHypoxemicRespiratoryFailure(cont’d.)DiffuseinfiltratesonCXRCardiogenicPulmonaryEdemaNoncardiogenicpulmonaryedema(ARDS)InterstitialpneumonitisorfibrosisInfectionsDiffusepulmonaryinfiltratesHypercapnicRespiratoryFailure

(TypeII)PaCO2>50mmHgHypoxemiaisalwayspresentpHdependsonlevelofHCO3HCO3dependsondurationofhypercapniaRenalresponseoccursoverdaystoweeksAcuteHypercapnicRespiratoryFailure(TypeII)AcuteArterialpHislowCauses -sedativedrugoverdose -acutemuscleweaknesssuchasmyastheniagravis -severelungdisease: alveolarventilationcannotbemaintained(i.e.Asthmaorpneumonia)Acuteonchronic:ThisoccursinpatientswithchronicCO2retentionwhoworsenandhaverisingCO2andlowpH.Mechanism:respiratorymusclefatigueCausesofHypercapnicRespiratoryfailureRespiratorycentre(medulla)dysfunctionDrugoverdose,CVA,tumor,hypothyroidism,centralhypoventilationNeuromusculardisease Guillain-Barre,MyastheniaGravis,polio,spinalinjuriesChestwall/Pleuraldiseases kyphoscoliosis,pneumothorax,massivepleuraleffusionUpperairwaysobstruction tumor,foreignbody,laryngealedemaPeripheralairwaydisorder asthma,COPDClinicalandLaboratoryManifestation

(non-specificandunreliable)Cyanosis-bluishcolorofmucousmembranes/skinindicatehypoxemia-unoxygenatedhemoglobin50mg/L-notasensitiveindicatorDyspnea-secondarytohypercapniaandhypoxemiaParadoxicalbreathingConfusion,somnolenceandcomaConvulsionsASSESSMENTOFPATIENTCarefulhistoryPhysicalExaminationABGanalysis-classifyRFandhelpwithcause 1)PaCO2=VCO2x0.863

VA 2)P(A-a)02=(PiO2-PaCO2)–PaO2

RLungfunction OVPvsRVPvsNVPChestRadiographEKGClinical&LaboratoryManifestationsCirculatorychanges -tachycardia,hypertension,hypotensionPolycythemia-chronichypoxemia-erythropoietinsynthesisPulmonaryhypertensionCor-pulmonaleorrightventricularfailureManagementofRespiratoryFailurePrinciplesHypoxemiamaycausedeathinRFPrimaryobjectiveistoreverseandpreventhypoxemiaSecondaryobjectiveistocontrolPaCO2andrespiratoryacidosisTreatmentofunderlyingdiseasePatient’sCNSandCVSmustbemonitoredandtreated

OxygenTherapySupplementalO2therapyessentialtitrationbasedonSaO2,PaO2levelsandPaCO2GoalistopreventtissuehypoxiaTissuehypoxiaoccurs(normalHb&C.O.) -venousPaO2<20mmHgorSaO2<40% -arterialPaO2<38mmHgorSaO2<70%IncreasearterialPaO2>60mmHg(SaO2>90%)orvenousSaO2>60%O2doseeitherflowrate(L/min)orFiO2(%)RisksofOxygenTherapyO2toxicity:-veryhighlevels(>1000mmHg)CNStoxicityand seizures-lowerlevels(FiO2>60%)andlongerexposure:- capillarydamage,leakandpulmonaryfibrosis-PaO2>150cancauseretrolentalfibroplasia-FiO235to40%canbesafelytoleratedindefinitelyCO2narcosis:-PaCO2mayincreaseseverelytocauserespiratory acidosis,somnolenceandcoma-PaCO2increasesecondarytocombinationof a)abolitionofhypoxicdrivetobreathe b)increaseindeadspaceMECHANICALVENTILATIONNoninvasivewithamaskInvasivewithanendobronchialtubeMVcanbevolumeorpressurecycledForhypercapnia:-MVincreasesalveolarventilationandlowers PaCO2,correctspH -restsfatiguesrespiratorymusclesForhypoxemia:-O2therapyalonedoesnotcorrecthypoxemia causedbyshunt -Mostcommoncauseofshuntisfluidfilledor collapsedalveoli(Pulmonaryedema)POSITIVEENDEXPIRATORYPRESSURE(PEEP)PEEPincreasestheendexpiratorylungvolume(FRC)PEEPrecruitscollapsedalveoliandpreventsrecollapseFRCincreases,thereforelungbecomesmorecompliantReversalofatelectasisdiminishesintrapulmonaryshuntExcessivePEEPhasadverseeffects-decreasedcardiacoutput-barotrauma(pneumothorax,pneumomediastinum)-increasedphysiologicdeadspace-increasedworkofbreathingPULMONARYEDEMAPulmonaryedemaisanincreaseinextravascularlungwaterInterstitialedemadoesnotimpairfunctionAlveolaredemacauseseveralgasexchangeabnormalitiesMovementoffluidisgovernedbyStarling’sequation QF=KF[(PIV-PIS)+(IS-IV)

QF=rateoffluidmovementKF=membranepermeabilityPIV&PISareintravascularandinterstitialhydrostaticpressuresISandIVareinterstitialandintravascularoncoticpressures reflectioncoefficientLungedemaisclearedbylymphaticsAdultRespiratorydistressSyndrome(ARDS)VarietyofunrelatedmassiveinsultsinjuregasexchangingsurfaceofLungsFirstdescribedasclinicalsyndromein1967byAshbaugh&PettyClinicaltermssynonymouswithARDS Acuterespiratoryfailure Capillaryleaksyndrome DaNangLung ShockLung TraumaticwetLung AdulthyalinemembranediseaseRiskFactorsinARDS

Sepsis3.8%Cardiopulmonarybypass1.7%Transfusion5.0%Severepneumonia12.0%Burn2.3%Aspiration35.6%Fracture5.3%Intravascularcoagulopathy12.5%Twoormoreoftheabove24.6%PATHOPHYSIOLOGYANDPATHOGENESISDiffusedamagetogas-exchangingsurfaceeitheralveolarorcapillarysideofmembraneIncreasedvascularpermeabilitycausespulmonaryedemaPathology:fluidandRBCininterstitialspace,hyalinemembranesLossofsurfactant:alveolarcollapseCRITERIAFORDIAGNOSISOFARDSClinicalhistoryofcatastrophicevent PulmonaryorNonpulmonary(shock,multisystem trauma) Exclude chronicpulmonarydiseases leftventricularfailureMusth