Effects of bupivacaine and calcium antagonists on human uterine arteries in pregnant and non-pregnant women.

Abstract

Bupivacaine is a local anesthetic commonly used in obstetrical practice. Although not generally constrictive, it has a constricting effect on blood vessels in clinically used doses, and when administered close to the uterine vasculature, as in a paracervical blockade, it can induce severe fetal bradycardia and thus be hazardous to the fetus. The bupivacaine-induced vasoconstriction on uterine arteries from pregnant and non-pregnant women was effectively reduced by two different calcium antagonists, verapamil and nifedipine. In non-pregnant women, nifedipine (2.9 x 10(-7) mol.l-1) administered simultaneously with bupivacaine (5.8 x 10(-4) mol.l-1) caused a 96% and verapamil (10(-5) mol.l-1) an 84% reduction as compared with the control vessel where only bupivacaine (5.8 x 10(-4) mol.l-1) was administered. In pregnant women, nifedipine 2.9 x 10(-7) mol.l-1 and 2.9 x 10(-6) mol.l-1 produced 66% and 79% reductions, respectively. It is possible that calcium antagonists administered together with bupivacaine in paracervical blockade could reduce the risk of fetal bradycardia.