The effects of maternal isoflurane-oxygen
anesthesia (
isoflurane, 1% inspired) were measured in eight
pregnant ewes and their
asphyxiated singleton
fetuses. Stable
fetal asphyxia, indicated by a stable
fetal arterial pH of 7.1-7.2 units, was produced by maternal
uterine artery occlusion. Maternal and
fetal heart rates and
blood pressures; maternal
uterine artery flow; maternal
arterial,
fetal arterial, and
sagittal sinus pH; and
blood gas tensions were determined during an awake control period, during
fetal asphyxia alone, and during
fetal asphyxia plus isoflurane-oxygen. Measurements of representative
fetal whole
organ blood flows,
cardiac output, and cerebral oxygen consumption were also made during each of the three experimental periods. During
asphyxia alone regional and total
brain,
heart, and
adrenal flows increased above control while
flow to the
spleen and carcass decreased. Similar responses were seen during
asphyxia plus isoflurane-oxygen.
Fetal arterial and
sagittal sinus pH,
base excess, po2, and
oxygen saturation decreased, and
hydrogen ion concentrations and pco2 increased during
asphyxia alone and
asphyxia plus isoflurane-oxygen. Cerebral oxygen consumption decreased significantly from control during
asphyxia plus isoflurane-oxygen, whereas no significant changes occurred in cerebral oxygen delivery. These results support the conclusions that in the
asphyxiated fetus: 1)
acidosis is increased; 2)
cardiac output is redistributed to
vital organs; and 3) the balance of cerebral oxygen supply-to-demand is maintained during maternal isoflurane-oxygen
anesthesia.
