Nitroglycerin to facilitate fetal extraction during cesarean delivery

To determine the efficacy of nitroglycerin in easing fetal extraction in elective cesarean deliveries in comparison with placebo and to collect maternal and fetal pharmacologic data after administration of nitroglycerin.

This randomized, double-blind clinical and descriptive pharmacokinetic study was carried out at the gynecology departments at Virchow Hospital and Charité Hospital (both university hospitals of Humboldt University, Berlin, Germany) between June 1994 and July 1996 in patients scheduled for elective cesarean delivery under general anesthesia. At the time of the uterine puncture incision, either 0.25 mg or 0.5 mg of nitroglycerin or a physiologic saline solution was administered as an intravenous bolus. Intraoperatively, maternal and neonatal pulse rates and blood pressure were monitored closely. The surgeons estimated reduction in uterine tone and the ease of fetal extraction by means of defined scales. Plasma concentrations of nitroglycerin and its metabolites were measured in maternal venous blood and from umbilical blood.

Ninety-seven patients were included in the statistical evaluation of the study; 32 received 0.25 mg of nitroglycerin, 34 received 0.5 mg of nitroglycerin, and 31 received placebo. The evaluation of the surgeons' estimation revealed no significant difference in ease of fetal extraction (statistical power 0.7) and no significant reduction in uterine tone under treatment with both nitroglycerin dosages in comparison with placebo. Only substance-specific maternal side effects were noted. The neonates' conditions were not affected by administration of nitroglycerin. The median fetal-maternal ratio of venous nitroglycerin plasma levels was approximately 1:400 in the 0.25-mg nitroglycerin group and 1:160 in the 0.5-mg nitroglycerin group. Approximately 11-12 times more nitroglycerin was detected in the venous umbilical branch than in the arterial branch.

Administration of nitroglycerin leads to no clinically relevant easing of fetal extraction, at least not in elective cesarean deliveries after the 34th week of gestation. With regard to pharmacokinetics, the measured median fetal-maternal venous nitroglycerin concentration was 1:400 in the 0.25-mg group and 1:160 in the 0.5-mg group.