Studies of circulation and acid-base balance in pregnant sheep: II. The effect of magnesium sulfate infusion.

Ten infusions of magnesium sulfate, in clinical doses for toxemia therapy, were administered to seven chronically catheterized ewes at 109-126 days' gestation. Maternal and fetal Mg++ concentrations in arterial serum indicated hindered placental passage. A significant decrease in maternal arterial oxygen pressure and hemoglobin was seen at 15 minutes. A significant increase in maternal arterial carbon dioxide pressure and transient maternal hypotension and tachycardia were seen at five minutes. Fetal effects of maternal infusion were minimal and transient. All maternal and fetal parameters returned to control levels by 90 minutes.