氧供需平衡-麻醉课件

氧供需平衡

BalanceofOxygenSupplyandDemand四川大学华西医院麻醉科魏蔚氧输送oxygentransport(O2T)外呼吸血液循环组织肺通气肺换气氧在血液中的运输氧在组织中释放氧瀑布O2Cascade氧从空气进入细胞的线粒体内要经历一系列过程，包括：肺通气、肺换气、氧在血液中的运输及氧在组织的释放四个步骤。也有学者把氧运输过程中，从空气中氧分压159mmHg至细胞内的3~4mmHg的巨大落差形象地称为氧瀑布。空气

上呼吸道饱和蒸汽压=47mmHgPiO2=(760-47)0.2094=149mmHg

肺泡

二氧化碳-PACO2,约等于PaCO2.PAO2=PIO2–PaCO2/R.-R为呼吸商.-R＝0.8.-PAO2=149–(40/0.8)=100mmHg

动脉血氧从肺泡进入肺静脉氧分压通常下降5–10mmHg.PAO2=95mmHg

毛细血管

静脉血毛细血管和组织间液间的较大的氧分压差（30mmHg）使得氧气迅速由血液向组织弥散。SummaryThefactorsinfluencetransportofoxygenCardiacoutputBloodoxygencontent(CaO2)Theaffinityofhemoglobinforoxygen外呼吸血液循环组织血红蛋白与氧的结合量1g血红蛋白最多可结合1.34ml的氧气。(1.39mlwhenthehemoglobinischemicallypure)如果Hb=15g/100ml,最大结合的氧量=15*1.34=20.1ml/100ml在组织内释放的氧量动脉血:SaO2=97%,CaO2=19.4ml/100ml混合静脉血:PvO2=40mmHg,SvO2=75%CvO2=14.4ml/100mlC(a-v)O2=19.4-14.4=5ml/100ml摄氧率（utilizationcoefficient/oxygenextraction）Thepercentageofthebloodthatgivesupitsoxygenasitpassesthroughthetissuecapillariesiscalledtheutilizationcoefficient.-normalvalueisabout25%.-duringexercise,canincreaseto75~85%.PhysiologicalsupplydependencyThenormalrelationshipisfora4:1ratiobetweenDO2andVO2.↑or↓inCOandDO2donotaffectoxygenconsumption.PathologicalsupplydependencyRelationshipbetweenDO2andVO2seenincriticallyillpatients,whenincreasesinCOorincreasesinoxygendelivery,resultinparallelincreasesinVO2.氧-血红蛋白解离曲线

EffectsonOxygen-HemoglobinDissociationCurve

PaO270090-100604026.7SaO210095-98907550Thecausesofaleft-shiftedoxy-Hbcurve

(P50<27mmHg)Alkalosis–theBohreffectHypothermiaAbnormalandfetalHbCarboxyhemoglobin,MethemoglobinDecreased2,3-diphosphoglycerateThecausesofaright-shiftedoxy-Hbcurve

(P50>27mmHg)IncreasedhydrogenionsIncreasedCO2IncreasedtemperatureIncreased2,3-diphosphoglycerate(DPG)氧供

OxygendeliveryDO2DO2是每分钟供给机体的氧量。DO2=(0.0031×PaO2+1.34×Hb×SaO2)×CODO2=1.34×Hb×SaO2×CO如果CO=5L,Hb=15g，DO2=1.34×150×1×5=1005ml/L氧耗

Oxygenconsumption

(VO2)Oxygenconsumptionistheactualamountofoxygenconsumedperminute.VO2=CO×(CaO2-CvO2)(ml/min)正常情况下，200~250ml/min..氧需

OxygendemandOxygendemandistheactualamountofoxygenneededperminute.-iscloselyrelatedtotheoxygenconsumption;-Undersomeconditions,demandmayexceedconsumption.氧供需失衡时机体的代偿机制CO↑.血流再分布.细胞摄氧率↑.Monitoring?理想部位：线粒体难点：细胞内的氧合状况无法直接监测思路：对氧输送过程进行监测测定Hct及Hb的方法全血细胞分析仪--Hct、Hb血气分析仪–Hct、Hb血红蛋白分光光度仪--Hb离心机—HctSpO2monitoredbyPulseoximetrysince1980

SO2=O2Hb/(O2Hb+HHb)(%)

IfR940/R660=1,SO2=85%TranscutaneousSpO2monitoringTwotypesoximetry:反射式脉搏氧饱和度探头Theesophagealprobe(ESOX,ARISTOMedical,Chicago,IL)BloodgastensionmeasurementOxygenpressure(PO2)PO2istomeasuredirectlyfromabloodsample,usuallybyusingaClarkelectrode.Carbondioxidepressure(PCO2)

PCO2electrodesworkbymeasuringthechangeinpHinducedwhenbloodequilibrateswithapotassiumchloride/sodiumbicarbonatesolution.Mixedvenousbloodoxygensaturation(SvO2)SvO2monitoring连续颈内静脉血氧饱和度监测经气管混合静脉血氧饱和度监测右心飘浮导管Picco(外周动脉)FloTrac传感器TEE由动脉压力波形计算COCO

=HR*Sd(AP)*χ

PiCCOUsingPiCCOtypicallyrequiresinsertionofathermodilutioncatheterinthefemoraloraxillaryarteryinsteadofastandardarterialline.Anyavailablecentralvenouscathetercanbeusedtoinjectthesolutionforthethermodilutionanalysis.M型法短轴缩短率：FAC=(EDA-ESA)/EDA;自动边缘识别系统（ABD）二维Simpson法SV=LVEDV-LVSDV多谱勒法SV=时间速度积分X横截面积三维法Calculationofthe"shuntfraction"Qt=totalcardiacoutputQs=shuntedportionofcardiacoutputQns=normalpulmonaryend-capillarybloodflowthatisnotshuntedpastabnormalalveoliQt=Qs+QnsorQns=Qt-QsCalculationofthe"shuntfraction"Qt(CaO2)=totaloxygendeliveredtothebody(DO2)Qs(CvO2)=oxygencontentofshuntedbloodQns(CcO2)=oxygencontentofend-capillarybloodTotaloxygendeliveredequalsthesumofoxygeninbothshuntedandnon-shuntedblood

Qt(CaO2)=Qs(CvO2)+Qns(CcO2)Calculationofthe"shuntfraction" Substituting(Qt-Qs)forQnsQt(CaO2)=Qs(CvO2)+(Qt-Qs)(CcO2)Qt(CaO2)=Qs(CvO2)+Qt(CcO2)-Qs(CcO2)Qs(CcO2-CvO2)=Qt(CcO2-CaO2) TheintrapulmonaryshuntequationQs/Qt=CcO2-CaO2/CcO2-CvO2

氧供需平衡的监测SvO2

60%~80%Oxygenextractionratio(O2ER)

O2ER=(CaO2-CvO2)/CaO2Lacticacid

<2.0mmol/LIntramucosalpH

>7.32GastrictonometrydeterminesintraluminalPCO2whichisassumedtobeinequilibriumwithPCO2inthegastricmucosa.IntramucosalpH(pHim)canbecalculatedbytheHenderson-HasselbachequationusingthePCO2valuedeterminedbygastrictonometryandthebicarbonateconcentrationinarterialblood.Baigorri

etal.CriticalCare19971:61

doi:10.1186/cc104决定DO2与VO2的因素DO2VO2HbSaO2COSvO2HbCOSaO2.DO2CO/Hb100%50%25%缺氧低氧血症：PaO2<60mmHg缺氧类型HypotonicanoxiaAnemicanoxiaCirculatoryanoxiaHistogenousanoxia外呼吸血液循环组织氧治疗Controlledoxygentreatmentisusedinthosewhoneedsupplementaloxygenbutnotrelyontheirhypoxicdrivetocontinuebreathing.-an