Effects of equipotent ephedrine, metaraminol, mephentermine, and methoxamine on uterine blood flow in the pregnant ewe

Abstract

To evaluate the safety of prophylactic vasopressor administration prior to obstetric conduction anesthesia, equipotent doses of ephedrine, metaraminol, mephentermine, and methoxamine were administered to 16 nonanesthetized pregnant ewes near term. When the maternal blood pressure was increased by 50%, uterine blood flow was unchanged with ephedrine and was reduced 20% with mephentermine (P > 0.05); 45% with metaraminol (P < 0.05) and 62% with methoxamine (P > 0.05). Metaraminol and methoxamine consistently decreased uterine blood flow at all levels of maternal blood pressure elevation. No significant change in fetal blood gas and acid base variables was demonstrated.