Effect of concentration of local anaesthetic solution on the ED₅₀ of bupivacaine for supraclavicular brachial plexus block

Abstract

Background: The aim of this trial was to compare the effect of concentration of bupivacaine solution on the ED₅₀ dose required for supraclavicular brachial plexus block.

Methods: Nineteen 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.

Results: The 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 ED₅₀ 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.

Conclusions: Our study demonstrates that the ED₅₀ 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.

Keywords: anaesthetic techniques, regional, brachial plexus; anaesthetics local, bupivacaine; equipment, ultrasound machines; potency, anaesthetic, ED50.