Long-term acid-base measurements in the fetaland maternal baboon

OBJECTIVE: The purpose of the study was to examine the relationship between maternal and fetal acid-base indexes in the baboon. STUDY DESIGN: Eight animals maintained in a tether system were studied during the third trimester. Results were analyzed using analysis of variance. RESULTS: After recovery from surgery, pH in carotid artery blood of the fetus was 7.40 +/- 0.027 (mean +/- SD), PO2, 27.5 +/- 3.45 mm Hg; PCO2, 34.0 +/- 2.37 mm Hg; base deficit, 3.0 +/- 2.15 mEq/L; Hot, 33.4% +/- 2.69% and HbO2, 61.3% +/- 8.65%. The corresponding values in the mother were 7.48 +/- 0.035, 100.7 +/- 9.44 mm Hg, 26.4 +/- 2.95 mm Hg, 3.6 +/- 1.71 mEq/L, 32.6% +/- 4.0% and 97.9% +/- 1.28%, respectively. All indexes remained essentially the same until the onset of active labor, at which time the fetus became slightly acidotic and hypoxemic (pH less than 7.35, HbO2 less than 50%). CONCLUSION: The baboon fetus has slightly higher pH2 and lower PaCO2 than the human fetus and PaO2, base deficit, and maternal-fetal gradients across the placenta in these two primate species are comparable.