Oxygen consumption in fetal lambs after maternal administration of sodium pentobarbital.

To determine whether anesthesia lowers fetal oxygen consumption, sodium pentobarbital (10 mg/kg) was given intravenously to seven chronically instrumented pregnant ewes (123 to 144 days' gestation). Oxygen consumption fell by 23% in association with a rise in fetal vascular PO2. Fetal breathing movements were abolished for 50.5 minutes, while the number of fetal heart rate accelerations fell by 80% in the first 30 minutes after pentobarbital injection. It is concluded that anesthesia reduces fetal oxygen consumption, probably by abolishing skeletal muscle activity, and perhaps also by reducing cerebral metabolic rate.