SummaryThe aim of this randomised, prospective, blinded study was to evaluate if stimulating catheters can decrease the minimum effective anaesthetic volume in 50% of patients during lumbar plexus block using mepivacaine 1.5% compared with standard catheters. Fifty-eight patients of ASA physical status 1-3 were randomly allocated to receive a lumbar plexus block via a stimulating or standard catheter, with 29 in each group. The first dose was 30 ml and subsequent doses were determined using the up-and-down staircase method. The minimum effective anaesthetic volume 50 was 12.2 ml (95% CI 7.3-17.1 ml) using the stimulating catheter and 24.8 ml (95% CI 23.2-27.5 ml) with the standard catheter (p < 0.0001). Complete lumbar plexus block was achieved with the initial dose of mepivacaine in 29 (100%) patients in the stimulating catheter group and 20 (69%) patients in the standard catheter group (p = 0.002). This study showed that use of a stimulating catheter halves the minimum effective anaesthetic volume 50 of mepivacaine 1.5% while increasing the success rate in patients receiving continuous lumbar plexus block.