Effect of body mass index on the ED50 volume of bupivacaine 0.5% for supraclavicular brachial plexus block.
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.
Gupta
P K
PK
Leeds Institute of Molecular Medicine, University of Leeds, UK.
Pace
N L
NL
Hopkins
P M
PM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000494:pharmacology; D015992:Body Mass Index; D001917:Brachial Plexus / Q000187:drug effects* / Q000648:ultrastructure; D002045:Bupivacaine / Q000008:administration & dosage* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D018084:Ultrasonography, Interventional; D034941:Upper Extremity / Q000601:surgery
D000779:Anesthetics, Local; D002045:Bupivacaine