Effect of body mass index on the ED50 volume of bupivacaine 0.5% for
supraclavicular brachial plexus block.
Author(s): Gupta PK, Pace NL, Hopkins PM.
Affiliation(s): Leeds Institute of Molecular Medicine, University of Leeds, UK.
Publication date & source: 2010, Br J Anaesth. , 104(4):490-5
BACKGROUND: The aim of this study was to determine whether the ED(50) dose of
bupivacaine 0.5% for supraclavicular brachial plexus block increases with
increasing body mass index (BMI).
METHODS: This double-blind, non-randomized trial followed an up-and-down
sequential allocation design. Adult patients undergoing elective upper limb
surgery under ultrasound-guided supraclavicular brachial block were recruited. A
preliminary study was used to guide the dosing schedule for the main study in
which patients were divided into three groups according to their BMI (Group A,
BMI >27 kg m(-2); Group B, BMI 24-27 kg m(-2); Group C, BMI <24 kg m(-2)). The
study design and analysis followed Dixon's small sample model using a 'nominal'
sample size of six per group.
RESULTS: Twenty-one patients were recruited to the preliminary study. Using
isotonic regression, the ED(50) for bupivacaine 0.5% was estimated to be 8.9 ml
[95% confidence interval (CI) 7.8-15.9]. In comparison, the ED(50) volume was
found to be 10.8 ml (95% CI 5.9-19.7) using the Dixon-Massey formula. In the main
study, six patients were recruited in each group with mean (range) BMI of 31.5
(27.2-38.8) kg m(-2) in Group A, 25.6 (24.4-26.3) kg m(-2) in Group B, and 21.6
(19.7-23.8) kg m(-2) in Group C. The ED(50) (95% CI) for Groups A, B, and C were
8.9 (6.2-12.7), 10.7 (7.5-15.4), and 13.4 (9.3-19.1) ml, respectively (P=0.05 for
Group A vs Group C).
CONCLUSIONS: Our study demonstrates that the ED(50) of bupivacaine 0.5% does not
increase with an increase in BMI. We found evidence of a possible inverse
relationship between ED(50) and BMI.
|