Effect of concentration of local anaesthetic solution on the ED 50 of bupivacaine for supraclavicular brachial plexus block

Abstract

BackgroundThe aim of this trial was to compare the effect of concentration of bupivacaine solution on the ED50 dose required for supraclavicular brachial plexus block.MethodsNineteen ASA I, II, or III patients of either sex undergoing elective upper limb surgery under ultrasound-guided supraclavicular brachial block were recruited in this double-blind, randomized trial which followed an up-and-down sequential allocation design. The patients were randomly allocated to three groups who then received 0.25%, 0.375%, or 0.5% bupivacaine. The study design and analysis followed Dixon's small sample model using a 'nominal' sample size of six in each group. The data from previous research were used to guide the dose levels and dose intervals for the three groups.ResultsThe median effective volume [95% confidence interval (CI)] for 0.25%, 0.375%, and 0.5% bupivacaine for supraclavicular block was 26.8 (18.6-38.4), 18.1 (12.1-26.0), and 12.0 (8.4-17.3) ml, respectively. The ED 50 dose (95% CI) for 0.25%, 0.375%, and 0.5% bupivacaine was 66.9 (46.6-96.0), 68.0 (47.4-97.6), and 60.1 (41.8-86.3) mg, respectively. The difference in the ED50 dose between the three concentrations was not statistically significant.ConclusionsOur study demonstrates that the ED 50 dose of bupivacaine for supraclavicular block is not dependent on the concentration. Lowering the concentration or the strength of the local anaesthetic leads to an increase in the volume required for successful block. © The Author [2013]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved.