Comparison of automated intermittent low volume bolus with continuous infusion for labour epidural analgesia

Delivery of local anaesthetics via automated intermittent bolus has been shown to improve epidural analgesia compared to delivery via continuous epidural infusion. However, the optimal bolus volume has not been investigated. This randomised, double-blind study compared the analgesic efficacy of automated intermittent bolus (volume 2.5 ml every 15 minutes) with that of a continuous epidural infusion (10 ml/hour) for the maintenance of labour epidural analgesia, to determine whether the advantages previously demonstrated for automated intermittent bolus over continuous epidural infusion are retained at this low bolus volume. With the approval of the Hospital Ethics Committee, we recruited 50 parturients who received combined spinal epidural analgesia with intrathecal ropivacaine 2 mg and fentanyl 15 mg. For epidural maintenance, participants were randomised to either the automated intermittent bolus group (2.5 ml automated intermittent epidural boluses of ropivacaine 0.1% plus fentanyl 2 mu g/ml delivered over a two-minute period every 15 minutes) or the continuous epidural infusion group (continuous epidural infusion of ropivacaine 0.1% plus fentanyl 2 mu g/ml at 10 ml/hour). The primary study outcome was the incidence of pain during labour that required management with supplemental epidural analgesia. There were no significant differences between the two regimens in terms of breakthrough pain (automated intermittent bolus 36% [9/25] vs continuous epidural infusion 32% [8/25], P=0.77). At the doses used in this study, maintenance of labour analgesia using automated intermittent bolus at a bolus volume of 2.5 ml every 15 minutes does not decrease the incidence of breakthrough pain or improve analgesic efficacy compared to continuous epidural infusion.