Fetal vascular responses to maternal nicardipine administration in the hypertensive ewe.

Calcium channel blockers such as nicardipine act as arterial vasodilators and are effective in the treatment of hypertension. Although they are also effective tocolytic agents, fetal effects have not been fully studied. Fifteen chronically catheterized near-term ewes were studied. Maternal and fetal cardiorespiratory parameters were measured in the control period and again 15 minutes after maternal venous infusion of angiotensin II. Nicardipine 20 micrograms/kg/min was given over 2 minutes and maternal and fetal cardiorespiratory parameters and fetal blood flow were measured 5.30 and 60 minutes later. Nicardipine reversed maternal hypertension and produced transient tachycardia. Fetuses responded initially with transient bradycardia and then developed hypercapnia and acidemia (p less than 0.03) by 60 minutes after nicardipine. Fetal placental blood flow decreased and vascular resistance increased by 5 minutes after nicardipine but returned toward control values after 30 minutes. Unexpectedly we observed the death of five fetuses by 65 minutes after nicardipine. We conclude that the administration of nicardipine in the hypertensive ewe results in significant alterations of fetal cardiorespiratory status and placental function that may lead to acidemia.