Effects Upon the Fetus of Oxygen Administration to the MotherA Study in Monkey

Abstract

Catheters were placed into assorted arteries and veins of 8 anesthetized pregnant monkeys and their fetuses. O2-sensitive electrodes were also inserted s.c. into 3 of 8 fetuses. Periodic samples of maternal and fetal blood were analyzed for PO2 [partial pressure of oxygen], PCO2 [partial pressure of CO2] and pH. O2 administration to the mothers reliably increased the PO2 of blood from the fetal carotid artery and less constantly augmented the PO2 of blood withdrawn from the femoral artery and vein. During 5-6 h of study the O2 tension of fetal blood samples of all animals progressively declined. The most marked declines in PO2 values at all fetal sites were regularly observed at those times as (or after) the mothers emerged from anesthesia. At these times also, the magnitudes of the increases in fetal blood PO2 brought about by administering O2 to the mothers diminished markedly and in parallel at all sample sites. The closely similar magnitudes of these various reductions at all fetal sample sites indicated that the basic mechanisms leading to decreased O2 delivery lie outside the fetuses and were most likely due to decreased maternal blood flow to the uterus because of increased maternal sympathetic stimulation. These reductions in O2 delivery to the fetus were regularly reversed by re-anesthetizing the mothers. The studies carried out with O2-sensitive electrodes demonstrated that administering O2 to the mothers regularly increased FO2 of fetal tissues but after a 50 s delay.