Effects of phenylephrine and sodium salicylate on maternal and fetal cardiovascular indices and blood oxygenation in sheep.

Phenylephrine and sodium salicylate, separately and in combination, in doses equivalent to the phenylephrine in one "cold" tablet and the sodium salicylate in three aspirins, were infused into conscious, chronically cannulated ewes in the third trimester of pregnancy. Maternal and fetal indices were recorded before (control), during, and after infusion. Phenylephrine depressed uterine blood flow and maternal heart rate (both, 40% below control) and increased maternal mean arterial blood pressure 50%; in the fetus, it depressed arterial blood Po2 (30%) and blood pH, but increased Paco2 and had little effect on mean arterial blood pressure and heart rate. Salicylate alone had no significant effect on maternal and fetal indices, and sodium salicylate plus phenylephrine produced changes similar to those with phenylephrine alone. We conclude that phenylephrine in the maternal circulation could have detrimental effects on the fetus, particularly when fetal Pao2 is depressed as by cord compression during delivery.