高频通气.ppt

HighFrequencyVentilation通气频率通气频率正常频率正常频率4倍以上倍以上(在成人在成人60次次min)，而潮气量接近或低于解剖无效腔容积的机，而潮气量接近或低于解剖无效腔容积的机械通气模式。械通气模式。高频通气是一种低周期压力变化和超生理呼吸频率的肺高频通气是一种低周期压力变化和超生理呼吸频率的肺泡通气方法，具有低潮气量、低气道压、低胸内压，不泡通气方法，具有低潮气量、低气道压、低胸内压，不使肺泡反复启闭，不产生剪切力。使肺泡持续扩张下保使肺泡反复启闭，不产生剪切力。使肺泡持续扩张下保持有效通气和换气低气道压可减少肺组织及气道压损持有效通气和换气低气道压可减少肺组织及气道压损伤，循环于扰小，气体弥散好，改善氧合快、可迅速提伤，循环于扰小，气体弥散好，改善氧合快、可迅速提高血氧饱和度，纠正低氧血症。高血氧饱和度，纠正低氧血症。HighfrequencyjetventilationHighfrequencyoscillatoryventilation(HFOV)HFOV is a ventilatory mode in which highfrequency,lowamplitude,pressure oscillationsofgas,at 5-15 Hz(up to 900 breaths/min),aregeneratedintheairways,togetherwithhighmeanairwaypressuresandlowtidalvolumes(1-2ml/Kg).Both the inspiratory and expiratory phases ofventilationareactive.高频振荡通气（高频振荡通气（HFOV）急急性肺损伤性肺损伤(ALl)、急性呼吸窘迫综合征、急性呼吸窘迫综合征(ARDS）小儿或新生儿呼吸窘迫综合征小儿或新生儿呼吸窘迫综合征(NRDS)慢性阻塞性肺病慢性阻塞性肺病(COPD)支气管镜检查或手术支气管镜检查或手术气漏综合征气漏综合征胸腔和上腹部手术胸腔和上腹部手术Fivedifferentmechanismshavebeenproposed:1.TransitTimeProfile2.InterregionalGasMixing3.AugmentedDispersion(TaylorDispersion)4.AsymmetricVelocityProfiles5.MolecularDiffusionThelungcompartmentisnotauniformstructureand transit times to alveolar units will vary inproportiontothelengthofthebronchialairways.Proximal alveolar units with short transit timeswill therefore ventilate before distal units andadequate gas exchange may occur in proximalunits,bydirectbulkconvection,whentidalvolumesarelow.1.TransitTimeProfileThe time that alveolar units take tofill duringventilation depends on their compliance(C)andresistance(R)toairflow:T=RxC2.InterregionalGasMixingConsequently,units with short time constants(lowcompliance,lowresistance)fillandemptymorerapidly.Attheendofexpiration,alveolarunitswithshorttimeconstants(fast units)are empty and ready to fill,whereasunitswithlongtimeconstants(slowunits)arestillemptying.Consequently,gasmovesfromslowunitstofastunits.Duringinspirationtheoppositeoccursandgasmovesfrom fast to slow units.This movement has beennamedPendelluftmovement.2.InterregionalGasMixingGasdispersionresultsfromtheinteractionbetweentheaxialvelocityprofileandradialdiffusionofgasesinmotion.3.AugmentedDispersion(TaylorDispersion)Gasdispersionresultsfromtheinteractionbetweentheaxialvelocityprofileandradialdiffusionofgasesinmotion.3.AugmentedDispersion(TaylorDispersion)Turbulence,accentuatedvelocitiesandswirlsofgasall occur at the bifurcations in the airways whichresultsingreatergasdispersion.Athigherfrequencies,inertialeffectsbecomemoremarkedandthevelocityprofilesaremoreexaggerated.Theneteffectis,thateventhoughbulkaxialflowislowwithventilatorymodessuchasHFOV,thealteredvelocity profiles and interactions which occur in abranchingsystem,resultingreatergasdispersion.4.AsymmetricVelocityProfiles5.MolecularDiffusion1.TransitTimeProfile2.InterregionalGasMixing3.AugmentedDispersion(TaylorDispersion)4.AsymmetricVelocityProfiles5.MolecularDiffusion