In non-obese patients, duration of action of rocuronium is directly correlated with body mass index

Background Administration of neuromuscular blocking agents using a dose calculated on actual body weight carries a risk of prolonged duration of action in obese patients whose body mass index (BMI) is > 30 kg·m −2 . In the present study, we hypothesized that there could be a correlation between BMI and the duration of action of rocuronium administered according to actual body weight in non-obese patients, in particular, overweight (BMI 25-30 kg·m −2 ) and underweight patients (BMI < 18.5 kg·m −2 ). Methods Sixteen female patients (BMI 15-30 kg·m −2 , aged 45-60 yr) scheduled for elective surgery under total intravenous anesthesia were included in this study. Rocuronium 0.9 mg·kg −1 was administered, and adductor pollicis train-of-four responses following ulnar nerve stimulation were monitored every minute with acceleromyography. The times from the injection of rocuronium until spontaneous recovery of first twitch to 5% (5% Duration) and 25% (25% Duration) of baseline were measured, and the correlation with BMI was analyzed. Results A significant correlation between 5% Duration and BMI (r 2 = 0.56; P < 0.001) was found by linear regression analysis. A significant correlation was also found between 25% Duration and BMI (r 2 = 0.49; P = 0.003). Conclusion In adult female patients with a BMI in the range of 15-30 kg·m −2 , the duration of action of rocuronium increases with BMI when the drug is administered on the basis of mg per actual kg body weight.