Anthropometric variables as predictors for duration of action of vecuronium-induced neuromuscular block

To identify the best anthropometric predictor for duration of action of neuromuscular block and to propose a better dosing regimen for vecuronium in obese patients, we studied 67 female patients (body weight 45-126 kg) anesthetized with thiopental, fentanyl, droperidol, and nitrous oxide. Twelve different anthropometric variables were evaluated as predictors for duration of action. Simple and multiple linear, least-squares, regression analyses were used. The predictors with the greatest correlation coefficients for duration of action of the vecuronium induction dose (100 micrograms/kg) were percentage of ideal body weight (%IBW) r2 = 0.389, P = 0.0001) and body mass index (r2 = 0.379, P = 0.0001). Body weight alone was also correlated to duration of action, but the r2 value was less (r2 = 0.312, P = 0.0001). The most significant predictors of the first supplementary dose of vecuronium (33 micrograms/kg) were the sum of subscapularis and suprailiac skin folds divided by surface area (r2 = 0.264, P = 0.0001) and %IBW (r2 = 0.261, P = 0.0001). We conclude that %IBW, the body mass index, and the sum of subscapularis and suprailiac skin folds divided by the surface area are the best predictors of duration of action of a vecuronium neuromuscular block.