Plasma concentrations of bupivacaine during continuous epidural analgesia in labour: The effect of adrenaline

Abstract

Continuous epidural analgesia has been provided for eighteen patients during the first and second stages of labour. Nine patients received bupivacaine 0.5 per cent with adrenaline 5 μg/ml, and nine bupivacaine alone, using a double-blind technique. The initial dose of bupivacaine was 30 mg, repeated and increased as necessary. A total of fifty-nine doses was given. Plasma concentrations of bupivacaine were measured in the mother throughout the blockade, and in the baby at delivery. The duration of action of bupivacaine was not significantly prolonged by adrenaline, though plasma concentrations were significantly reduced 20 minutes after the first dose and 40 minutes after the second. In neither treatment group did bupivacaine accumulate markedly in maternal plasma unless the second stage necessitated increased doses. Neonatal bupivacaine concentrations were always low and neonatal: maternal ratios increased by the use of adrenaline. It is thus uncertain whether adrenaline offered a significant advantage except with large doses of bupivacaine, when it reduced the likelihood of maternal intoxication. © 1971 John Sherratt & Son Ltd.