高流量氧疗的生理效应,俞康龙

高流量氧疗的生理效应PhysiologicalEffectofHighFlowNasalCannula(HFNC)Therapy上海交通大学第一人民医院急诊与危重病科俞康龙COIstatementTheauthorhasnoconflictofinteresttodeclare.HighFlowaninterestingoxygenationmethod-novel-magic-gentleandmoderateHFNCshinesduringRSIPutthebigcannulaeintoyourpatient’snoseandlet’rrip.AddafacemaskorNIVorwhateveryourpreoxygenationpleasure,thenpushyourmedsandlaughtoyourselfasthesaturationrisesduringapnea.Whistlesweetlyastheinternilluminateseveryinchofthesoftpalatewithgreatdetermination.Hell,goseeanotherpatientandtellhimtocallyouwhenhe’sgivenup.Youremember,though,thedaysofthegiants.Whenbeingregardedasaskilledlaryngoscopistmeantsomething.Whenthewordairwaymadeinternistsscatterlikemice.Whenitwasn’tsoeasytosavealife.•PatrickBouvierKennedydiesofrespiratorydistresssyndrome(RDS),34weeksgestation,birthweight2100gms.1963•MariaDelivoria-Papadopoulos•Firstsuccessfulventilationofapreterminfantwithhyalinemembranedisease(Assistedventilationinterminalhyalinemembranedisease.Arch.Dis.Child.,39:481-484,19641971GregoryUseofcontinuouspositiveairwaypressure(CPAP)forrespiratorydistresssyndrome(RDS)Oxygentherapy&oxygendeliverydevicesOxygenTherapyLowflowsystemsHighflowsystemsNasalcannulaFacetentO2tentVenturimaskPRBMNRBMNIV(CPAP)ETtubeSimplemaskHFNCTheroleofHFNCinrespiratorytherapyWhatisHFNC?a“new”methodsofoxygentherapyair/oxygenappliedtopatientathighflowratesair/oxygenrunthroughanasalcannulaair/oxygeniswellconditionedbysufficientwarmthandhumidification--socalledheated,humidifiedhigh-flownasalcannula(HHHFNC)therapy2-70L/minMechanismsofactionforHFNCWashoutofnasopharyngealdeadspaceReductionofinspiratoryresistance(workofbreathing)byprovidingadequateflowImprovedmechanicsbysupplyingadequatelywarmedandhumidifiedgasReductioninthemetaboliccostofgasconditioningProvisionofdistendingpressureWashoutofnasopharyngealdeadspaceThehighvolumetricflowspouringfromasmallborecannulacausehighvelocityflowswhichcreateturbulentenergytoflushtheupperairwayofexpiratorygas.Deadspacewashoutimprovesventilationanatomicaldeadspaceinadults≥30%oftidalvolumeinneonates≈50%oftidalvolumechangethegascompositioninnasopharyngealspacereducerebreathingexpiredCO2increasethefractionofinspiredO2increasealveolarventilationefficiencyMV=(VT–VD)xRRPaCO2=PeCO2/(1–VD/VT)PaO2=(PBO2–PH2O)xFiO2–PaCO2/R–PA-aO2CO2washoutduringHFNCwithdifferentflowratesNHFrates0L/min30L/min60L/minMidwaythroughexpiration(t=1.2s)Endofexpiration(t=2.2s)VanHoveSC,etal.AnnBiomedEng(2016)44:3007-3019.Highflowandhighvelocityincreasealveolarventilationefficiencylikelyminimizetheinspiratoryresistanceassociatedwiththenasopharynxbyprovidingnasopharyngealgasflowsthatmatchorexceedapatient'speakinspiratoryflowCoandaeffectoccuringinthenasopharyngealregionduringexpirationpotentiallyassistexpiratoryeffortsbringaboutadecreaseinworkofbreathingandrespiratoryratecreatemoreturbulentenergyformoreeffectivewashoutflushtheexpiratorygasfromtheupperairwayquicklyduringtheexhalationphaseofbreathing,whichiscriticalinpatientswithrapidbreathingVentilatoryResponsestoHFNCMündelTetal.MechanismsofnasalhighflowonventilationduringwakefulnessandsleepJApplPhysiol,2013.114:1058–1065MucociliarytransportsystemHealthciliatedepitheliumDamagedciliatedepithelium缺乏湿度增加感染危险加重呼吸负担小气道闭合细胞损伤(2):215-28TemperatureandhumidityLowtemperaturedoesmeaninsufficienthumidity.Enoughwatersupplementdoesnotalwaysmeansufficienthumidity.Anadultmayrequireapproximately150calories/min(10kcal/h)forconditioninginspiratoryairfromambienttoBTS.KacmarekRM,etal.Egan'sFundamentalsofRespiratoryCare.St.Louis,MO:Elsevier/Mosby,2013.InspiredgasneedsconditioningRespirationwithambientgas,notwarmedorhumidified,inducedbronchoconstrictionresponse,andresultedinasignificantdecreaseinbothpulmonarycompliance.ThenasalairpassagesexpendquiteafewenergytowarmandhumidityinspiratoryairfromambienttoBTS.Studiesfromthe1990'sdemonstratedthenegativeeffectsofusingnon-warmed,non-humidifiedgastosupportrespiration.FlowandPressurefundamentalsHFNCisintendedtobeanopensystem,withflowdeliveredtoapatientvianasalcannula,wherethecannulaprongsdonotoccludethenaresandwherethepatient’smouthisnotheldclosed.Inthisopensystem,thepressureineachcompartmentisafunctionoftheresistor(s)thatlieinseriesdownstreamfromthatcompartment.Inthisregard,circuitpressureswillalwaysbesubstantiallygreaterthanpressureinthenasopharynx.Factorsdeterminnasopharyngealpressuretheflowsettingthepatient’suniqueanatomicaldimensionstheleakoutofthenosearoundtheprongsandoutofthemouth(ODofcannulaprongvs.IDofnares)MechanismsofAction:HFNCDiffersfromCPAPMündelTetal.MechanismsofnasalhighflowonventilationduringwakefulnessandsleepJApplPhysiol,2013.114:1058–1065Effectsofflowonairwaypressured