Effect of magnesium sulfate on maternal and fetal hemodynamics and fetal brain function and metabolism

The hemodynamic effects, brain function, and metabolism of magnesium sulfate (MgSO4) were studied in seven fetal sheep experiments at 139 +/- 1.3 SE days of gestation. MgSO4 was intravenously infused to six gross-bred pregnant ewes at a rate of 4 gm/4 minutes as a loading dose, and 1.5 gm/60 minutes as a maintenance dose. There were no significant changes in maternal pH, PO2, O2 saturation, O2 content, HCO-3, glucose or lactate concentrations, or blood pressure at the end of the infusion. However, maternal heart rate decreased significantly from the mean baseline of 117 +/- 12.4 beats/minute at the end of the 60-minute infusion but recovered 30 minutes later. Uterine blood flow remained unchanged. Maternal Mg2+ levels rose significantly (P less than 0.005) at 60 minutes and remained elevated. No significant changes in fetal pH, PO2, PCO2, lactate, and Mg2+ concentration were noted during infusion. However, fetal heart rate increased significantly (P less than 0.025) at the end of infusion. Fetal hypotension was also noted at the end of the infusion (P less than 0.02). Cerebral blood flow did not change significantly throughout the experiment. However O2 consumption decreased temporarily at 15 and 30 minutes into infusion, which returned to baseline thereafter. Fetal glucose consumption and electroencephalogram remained unchanged throughout the experiment. Maternal infusion of MgSO4 does not exert any deleterious effects on the acid-base status of the mother or fetus. It increases the fetal heart rate and causes fetal hypotension, without any significant effects on the fetal brain function and metabolism.