高流量氧疗的生理效应高流量氧疗的生理效应PhysiologicalEffectofHighFlowNasalCannula(HFNC)TherapyCOIstatementTheauthorhasnoconflictofinteresttodeclare.HighFlowaninterestingoxygenationmethodnovelmagicgentleandmoderateHFNCshinesduringRSIPutthebigcannulaeintoyourpatientsnoseandletrrip.AddafacemaskorNIVorwhateveryourpreoxygenationpleasure,thenpushyourmedsandlaughtoyourselfasthesaturationrisesduringapnea.Whistlesweetlyastheinternilluminateseveryinchofthesoftpalatewithgreatdetermination.Hell,goseeanotherpatientandtellhimtocallyouwhenhesgivenup.Youremember,though,thedaysofthegiants.Whenbeingregardedasaskilledlaryngoscopistmeantsomething.Whenthewordairwaymadeinternistsscatterlikemice.Whenitwasntsoeasytosavealife.http:/emupdates.com/2012/03/01/thehighflownasalcannulaintheemergencydepartment/Pediatricianhaspromotedoxygentherapy1891E.BonnairedescribedO2inhalationsinthenewborn1963PatrickBouvierKennedydiesofrespiratorydistresssyndrome(RDS),34weeksgestation,birthweight2100gms.1963MariaDelivoriaPapadopoulosFirstsuccessfulventilationofapreterminfantwithhyalinemembranedisease(Assistedventilationinterminalhyalinemembranedisease.Arch.Dis.Child.,39:481-484,19641971GregoryUseofcontinuouspositiveairwaypressure(CPAP)forrespiratorydistresssyndrome(RDS)Oxygentherapy&oxygendeliverydevicesOxygenTherapyLowflowsystemsHighflowsystemsNasalcannulaFacetentO2tentVenturimaskPRBMNRBMNIV(CPAP)ETtubeSimplemaskHFNCTheroleofHFNCinrespiratorytherapyWhatisHFNC?la“new”methodsofoxygen therapylair/oxygenappliedtopatientathigh flowrateslair/oxygenrunthroughanasal cannulalair/oxygeniswellconditionedbysufficientwarmthandhumidification socalledheated,humidifiedhigh-flownasalcannula(HHHFNC)therapy2-70L/minMechanismsofactionforHFNClWashoutofnasopharyngealdeadspacelReductionofinspiratoryresistance(workofbreathing)byprovidingadequateflowlImprovedmechanicsbysupplyingadequatelywarmedandhumidifiedgaslReductioninthemetaboliccostofgasconditioninglProvisionofdistendingpressureWashoutofnasopharyngealdeadspaceThehigh volumetric flowspouringfromasmallborecannulacausehigh velocityflowswhichcreateturbulentenergytoflush the upper airwayofexpiratorygas.Deadspacewashoutimprovesventilationlanatomicaldeadspaceinadults30%oftidalvolumeinneonates50%oftidalvolumelchangethegascompositioninnasopharyngealspacelreducerebreathingexpiredCO2lincreasethefractionofinspiredO2lincreasealveolarventilationefficiencyMV=(VTVD)xRRPaCO2=PeCO2/(1VD/VT)PaO2=(PBO2PH2O)xFiO2PaCO2/RPA-aO2CO2washoutduringHFNCwithdifferentflowratesNHFrates0L/min30L/min60L/minMidwaythroughexpiration(t=1.2s)Endofexpiration(t=2.2s)VanHoveSC,etal.AnnBiomedEng(2016)44:3007-3019.HighflowandhighvelocityincreasealveolarventilationefficiencyllikelyminimizetheinspiratoryresistanceassociatedwiththenasopharynxbyprovidingnasopharyngealgasflowsthatmatchorexceedapatientspeakinspiratoryflowlCoandaeffectoccuringinthenasopharyngealregionduringexpirationpotentiallyassistexpiratoryeffortslbringaboutadecreaseinworkofbreathingandrespiratoryratelcreatemoreturbulentenergyformoreeffectivewashoutlflushtheexpiratorygasfromtheupperairwayquicklyduringtheexhalationphaseofbreathing,whichiscriticalinpatientswithrapidbreathingVentilatoryResponsestoHFNCMndelTetal.MechanismsofnasalhighflowonventilationduringwakefulnessandsleepJApplPhysiol,2013.114:10581065MucociliarytransportsystemHealthciliatedepitheliumDamagedciliatedepitheliumhttps:/www.fphcare.com/files/images/hospital/respiratory-care-continuum/full-width/mucociliary-disfunction-table/MucosalfunctionsdependentoninspiredhumidityWilliams,RB.RespireCareClinNAm1998Jun;4(2):215-28TemperatureandhumiditylLowtemperaturedoesmeaninsufficienthumidity.lEnoughwatersupplementdoesnotalwaysmeansufficienthumidity.lAnadultmayrequireapproximately150calories/min(10kcal/h)forconditioninginspiratoryairfromambienttoBTS.KacmarekRM,etal.EgansFundamentalsofRespiratoryCare.St.Louis,MO:Elsevier/Mosby,2013.InspiredgasneedsconditioninglRespirationwithambientgas,notwarmedorhumidified,inducedbronchoconstrictionresponse,andresultedinasignificantdecreaseinbothpulmonarycompliance.lThenasalairpassagesexpendquiteafewenergytowarmandhumidityinspiratoryairfromambienttoBTS.lStudiesfromthe1990sdemonstratedthenegativeeffectsofusingnonwarmed,nonhumidifiedgastosupportrespiration.FlowandPressurefundamentalsHFNCisintendedtobeanopensystem,withflowdeliveredtoapatientvianasalcannula,wherethecannulaprongsdonotoccludethenaresandwherethepatientsmouthisnotheldclosed.Inthisopensystem,thepressureineachcompartmentisafunctionoftheresistor(s)thatlieinseriesdownstreamfromthatcompartment.Inthisregard,circuitpressureswillalwaysbesubstantiallygreaterthanpressureinthenasopharynx.Factorsdeterminnasopharyngealpressureltheflowsettinglthepatientsuniqueanatomicaldimensionsltheleakoutofthenosearoundtheprongsandoutofthemouth(ODofcannulaprongvs.IDofnares)MechanismsofAction:HFNCDiffersfromCPAPMndelTetal.MechanismsofnasalhighflowonventilationduringwakefulnessandsleepJApplPhysiol,2013.114:10581065EffectsofflowonairwaypressureduringHFNClHigherflowratecreateshigherairwaypressure.lPressureisdifferentwhenmouthclosedoropen.lOnlymoderatepositiveairwaypressure(10cmH2O)canbegeneratedbyHFNC.ParkeR,etal.RespirCare2011;56(8):11511155.PositiveairwaypressureisnottheprinciplemechanismofHFNClThebasicflowsettingismeantfundamentallytoexceednormalinspiratoryflowratessoastoeliminateentrainmentofroomair,andenhancenasopharyngealwashouteffects.lExcessiveflowsinanattempttogeneratesubstantialdistendingpressuresshouldnotbeutilized.lToaccomplishtheactionsofdeadspacewashout,selectingnasalprongsshouldhaveanoutsidediameternomorethan50%oftheinsidediameterofthepatientsnares.lThus,onlymoderatenasopharyngealpressurecanbeexpected.SummaryofHHHFNCHighflowinpiratoryflowratesEliminateentrainmentofroomairWashoutofthenasopharyngealdeadspaceNasalcannulaOpenairsupplysystemwithhighvelocityWashoutofdeadspaceCreatepositiveairwaypressureHeater&humidifierConditioninspiratoryairfromATStoBTSProtectthefunctionsofmucociliarytransportsystemReducerespiratoryresistanceSaveenergytoconditioninspiratorygasComfortpatientduringhighflowtherapy