Uterine ArteryUmbilicalArteryP0,=100mmHgPo,=18mmHgBlood flow from the maternalCOz=15.2ml/dlCo,=8.0mldcirculation is momentarilySao2=95%Sao,=40%Pco, =32mm.HgPco,=55mmHginterrupted during aPH=7.42PH=7.21BE=-3.0mEqLBE=-9.0mEqLcontraction,Clinical and experimentaldataindicatethat fetaldeathoccurswhen50%ormoreofUterine blood fiowUmbilical blood fiow.transplacentaloxygen700ml/min500ml/minHb concentration:Hbconcentration:exchange is interrupted.12gm/d15gm/dlOxygen capacity.Oxygen capacity.16ml/dl2Hypoxia can easily occur.22mlldl(Total Qo,through(TotalQog,3.5kguterus:fetus:Anormalfetuscan withstand3.5ml/min)2.0ml/min)the stress of labor withoutsuffering from hypoxia becausesufficient oxygen exchangeUterine VeinUmbilical Veinoccurs during the intervalPo2=33mmHgPoz=28mmHgbetween contractions.CO,=10.5mldlCo,=15.0mldlSao,=60%Sao,=70%AfetuswhoseoxygensupplyisPoo,=40mmHgPcoz=45mmHgpH=7.30pH=7.32marginal cannot toleratetheBE#-6.0mEqLBE=-6.4mEqLstress of contractions and willFigure71Placentaltransferfoxygenandcarbondioxide.AdaptedfromBonicalbecome hypoxic.ObsttricAnagiaandnthsianddmterdamWodedrationfSocietiesAnesthesiologists,1980,p29
◼ Blood flow from the maternal circulation is momentarily interrupted during a contraction. ◼ Clinical and experimental data indicate that fetal death occurs when 50% or more of transplacental oxygen exchange is interrupted. ◼ Hypoxia can easily occur. ◼ A normal fetus can withstand the stress of labor without suffering from hypoxia because sufficient oxygen exchange occurs during the interval between contractions. ◼ A fetus whose oxygen supply is marginal cannot tolerate the stress of contractions and will become hypoxic
Changes under hypoxicconditionsBaroreceptors 压力感受器 and chemoreceptors inthe central circulation of the fetusinfluence the FHR by giving rise tocontraction-related or periodic FHRchanges.The hypoxia will also result in anaerobic厌氧的 metabolism. Pyruvate 丙酮酸盐 and lactic acidaccumulate, causing fetal acidosis
Changes under hypoxic conditions ◼ Baroreceptors 压力感受器 and chemoreceptors in the central circulation of the fetus influence the FHR by giving rise to contraction-related or periodic FHR changes. ◼ The hypoxia will also result in anaerobic 厌氧 的 metabolism. Pyruvate 丙酮酸盐 and lactic acid accumulate, causing fetal acidosis