氧供需平衡-麻醉课件

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1、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)0.20

2、94=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

3、(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、.4-14.4=5ml/100ml摄氧率（utilizationcoefficient/oxygenextraction）Thepercentageofthebloodthatgivesupitsoxygenasitpassesthroughthetissuecapillariesiscalledtheutilizationcoefficient.-normalvalueisabout25%.-duringexercise,canincreaseto75~85%.Physiologicalsupplyde

5、pendencyThenormalrelationshipisfora4:1ratiobetweenDO2andVO2.↑or↓inCOandDO2donotaffectoxygenconsumption.PathologicalsupplydependencyRelationshipbetweenDO2andVO2seenincriticallyillpatients,whenincreasesinCOorincreasesinoxygendelivery,resultinparallelincreas

6、esinVO2.氧-血红蛋白解离曲线EffectsonOxygen-HemoglobinDissociationCurvePaO270090-100604026.7SaO210095-98907550Thecausesofaleft-shiftedoxy-Hbcurve(P50<27mmHg)Alkalosis–theBohreffectHypothermiaAbnormalandfetalHbCarboxyhemoglobin,MethemoglobinDecreased2,3-diphosphogl

7、ycerateThecausesofaright-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×

8、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.-