氧供需平衡

BalanceofOxygenSupplyandDemand四川大學華西醫(yī)院麻醉科魏蔚氧輸送oxygentransport(O2T)外呼吸血液循環(huán)組織肺通氣肺換氣氧在血液中的運輸氧在組織中釋放氧瀑布O2Cascade氧從空氣進入細胞的線粒體內(nèi)要經(jīng)歷一系列過程，包括：肺通氣、肺換氣、氧在血液中的運輸及氧在組織的釋放四個步驟。也有學者把氧運輸過程中，從空氣中氧分壓159mmHg至細胞內(nèi)的3~4mmHg的巨大落差形象地稱為氧瀑布?？諝?/p>

上呼吸道飽和蒸汽壓=47mmHgPiO2=(760-47)0.2094=149mmHg

肺泡

二氧化碳-PACO2,約等于PaCO2.PAO2=PIO2–PaCO2/R.-R為呼吸商.-R＝0.8.-PAO2=149–(40/0.8)=100mmHgSummaryThefactorsinfluencetransportofoxygenCardiacoutputBloodoxygencontent(CaO2)Theaffinityofhemoglobinforoxygen外呼吸血液循環(huán)組織血紅蛋白與氧的結(jié)合量1g血紅蛋白最多可結(jié)合1.34ml的氧氣。(1.39mlwhenthehemoglobinischemicallypure)如果Hb=15g/100ml,最大結(jié)合的氧量=15*1.34=20.1ml/100ml在組織內(nèi)釋放的氧量動脈血:SaO2=97%,CaO2=19.4ml/100ml混合靜脈血:PvO2=40mmHg,SvO2=75%CvO2=14.4ml/100mlC(a-v)O2=19.4-14.4=5ml/100ml攝氧率（utilizationcoefficient/oxygenextraction）Thepercentageofthebloodthatgivesupitsoxygenasitpassesthroughthetissuecapillariesiscalledtheutilizationcoefficient.-normalvalueisabout25%.-duringexercise,canincreaseto75~85%.PhysiologicalsupplydependencyThenormalrelationshipisfora4:1ratiobetweenDO2andVO2.↑or↓inCOandDO2donotaffectoxygenconsumption.PathologicalsupplydependencyRelationshipbetweenDO2andVO2seenincriticallyillpatients,whenincreasesinCOorincreasesinoxygendelivery,resultinparallelincreasesinVO2.氧-血紅蛋白解離曲線

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是每分鐘供給機體的氧量。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)正常情況下，200~250ml/min..氧需

OxygendemandOxygendemandistheactualamountofoxygenneededperminute.-iscloselyrelatedtotheoxygenconsumption;-Undersomeconditions,demandmayexceedconsumption.氧供需失衡時機體的代償機制CO↑.血流再分布.細胞攝氧率↑.Monitoring?理想部位：線粒體難點：細胞內(nèi)的氧合狀況無法直接監(jiān)測思路：對氧輸送過程進行監(jiān)測測定Hct及Hb的方法全血細胞分析儀--Hct、Hb血氣分析儀–Hct、Hb血紅蛋白分光光度儀--Hb離心機—HctSpO2monitoredbyPulseoximetrysince1980

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

IfR940/R660=1,SO2=85%TranscutaneousSpO2monitoringTwotypesoximetry:反射式脈搏氧飽和度探頭Theesophagealprobe(ESOX,ARISTOMedical,Chicago,IL)BloodgastensionmeasurementMixedvenousbloodoxygensaturation(SvO2)SvO2monitoring連續(xù)頸內(nèi)靜脈血氧飽和度監(jiān)測經(jīng)氣管混合靜脈血氧飽和度監(jiān)測術(shù)中常用的CO監(jiān)測方法右心飄浮導管Picco(外周動脈)FloTrac傳感器TEE由動脈壓力波形計算COCO

=HR*Sd(AP)*χ

PiCCOUsingPiCCOtypicallyrequiresinsertionofathermodilutioncatheterinthefemoraloraxillaryarteryinsteadofastandardarterialline.Anyavailablecentralvenouscathetercanbeusedtoinjectthesolutionforthethermodilutionanalysis.術(shù)中TEE測量COM型法短軸縮短率：FAC=(EDA-ESA)/EDA;自動邊緣識別系統(tǒng)（ABD）二維Simpson法SV=LVEDV-LVSDV多譜勒法SV=時間速度積分X橫截面積三維法Calculationofthe"shuntfraction"Qt=totalcardiacoutputQs=shuntedportionofcardiacoutputQns=normalpulmonaryend-capillarybloodflowthatisnotshuntedpastabnormalalveoliQt=Qs+QnsorQns=Qt-QsCalculationofthe"shuntfraction"Calculationofthe"shuntfraction"氧供需平衡的監(jiān)測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決定DO2與VO2的因素DO2VO2HbSaO2COSvO2HbCOSaO2.術(shù)中影響氧供的因素DO2CO/Hb100%50%25%缺氧低氧血癥：PaO2<60mmHg缺氧類型HypotonicanoxiaAnemicanoxiaCirculatoryanoxiaHistogenousanoxia外呼吸血液循環(huán)組織氧治療Controlledoxygentreatmentisusedinthosewhoneedsupplementaloxygenbutnotrelyontheirhypoxicdrivetocontinuebreathing.-anincreaseinPaCO2showtheyrelyonhypoxicdrive.

Therulesofoxygentreatment

(1)Giveoxygenasmuchasyoucanatfirst,andthenreduceit,guidedbybloodgasmeasurements.(2)Oxygentreatmentwillworkonlyifthepatienthasapatentairwayandisbreathing.(3)Definitivetreatmentofhypoxiadependsontheunderlyingcause.Givingoxygenisaho