Mechanicalventilationinsevereasthma

（criticalcare2005）2010-4-8宋文良哮喘機械通氣Mostofthesepatientsrespondwelltooxygen,steroids,beta-agonists,anticholinergics,andothermedications.Fewerthan5%ofasthmaticsadmittedtoapediatricintensivecareunitrequiremechanicalventilation.哮喘機械通氣pathophysiologyChronicairwayinflammationAirwayobstructionGas–trap(FRCincrease)→V/Qimbalance→hypoxemia,metaboliticacidosis,respiratoryacidosis哮喘機械通氣TimetointubateandmechanicalventilationMainlydependclinicaljudjementMarkersofdeteriorationincluderisingcarbondioxidelevels(includingnormalizationinapreviouslyhypocapnicpatient),exhaustion,mentalstatusdepression,haemodynamicinstabilityandrefractoryhypoxaemia哮喘機械通氣Pressure-controlmodeAdvantage：slowairflow，aimedpipDisadvantages：VtchangewithairwayresistanceVolume-controlmodeAdvantage：fixedVt，Disadvantage：lungoverinflation哮喘機械通氣DEVELPOMENTOFGASITRAPPING哮喘機械通氣Measuregastrappingmeasureend-expiratorypressureinthelungs.Iftheexpiratoryportoftheventilatorisoccludedatend-expiration,thentheproximalairwaypressurewillequilibratewithalveolarpressureandpermitmeasurementofauto-PEEP(endexpiratorypressureaboveappliedPEEP)attheairwayopening哮喘機械通氣Howtoavoidgas-trappingControlledhypoventilation(reducedtidalvolumes[lessgastoexhale]reducedrespiratoryrates[longerexpiratorytime]),relievingexpiratoryflowresistance(frequentairwaysuctioningifnecessary,bronchodilators,steroids,large-boreendotrachealtube),reducinginspiratorytimebyincreasingtheinspiratoryflowrateorincorporatingnondistensibletubing,reducingtheneedforhighminuteventilationbydecreasingcarbondioxideproduction(e.g.sedation/paralysis,controllingfever/pain).哮喘機械通氣PermissivehypercapniaMaintainph》7.2Orarterialcarbondioxidetension《90mmHg哮喘機械通氣ExternalpeepapplicationMayreduceworkofbreathing，preventgas-trappingbysplintingairwayopen哮喘機械通氣哮喘機械通氣Initialventilatorsettingventilatorinitiallybeusedinpressurecontrolmode,settingthepressuretoachieveatidalvolumeof6–8ml/kg,respiratoryrateof11–14breaths/minandPEEPat0–5cmH2O.Weuse