Haemodynamic effects of repeated epidural test-doses of adrenaline in the chronic maternal–fetal sheep preparation

Abstract

A randomized crossover study was designed using the chronically instrumented pregnant sheep preparation to study the possible effects of epidural injection of adrenaline as a single compound on the circulation of mother and fetus. Three consecutive identical doses of adrenaline were administered epidurally with a 30 min interval between treatments. In a randomized crossover fashion two dosages (10 and 15 μg) were tested on different days. The day after the last epidural experiment the same doses of adrenaline were given intravenously (i.v.). Between the two i.v. doses a 30 min interval was allowed for values to return to baseline. Twenty-seven experiments were performed in eight ewes. Epidural administration of adrenaline did not affect maternal mean arterial pressure, maternal heart rate, uterine blood flow, fetal mean arterial pressure, fetal heat rate, or maternal and fetal blood gases and acid-base status. After i.v. administration of adrenaline the uterine blood flow decreased in a dose-dependent fashion, but the other haemodynamic variables were not affected. In conclusion, this study indicates that consecutive epidural injections of adrenaline have no significant effect on maternal and fetal haemodynamic responses, uterine blood flow, blood gases and acid–base status in the gravid ewe. However, an i.v. injection of 10 or 15 μg adrenaline decreases the uterine blood flow and could compromise the fetus.