The pharmacodynamic effects of rocuronium when dosed according to real body weight or ideal body weight in morbidly obese patients

We investigated the pharmacodynamic effects of rocuronium on morbidly obese patients. Twelve morbidly obese female patients (body mass index >40 kg/m(2)) admitted for laparoscopic gastric banding were randomized into two groups. Group 1 (n = 6) received 0.6 mg/kg of rocuronium based on real body weight, whereas Group 2 (n = 6) received 0.6 mg/kg of rocuronium based on ideal body weight. In a control group of six normal-weight female patients admitted for laparoscopic surgery, rocuronium was dosed on the basis of their real body weight. Neuromuscular transmission was monitored by using acceleromyography of the adductor pollicis; anesthesia was induced and maintained with remifentanil and propofol. The onset time tended to be shorter in Group 1 and the control group compared with Group 2, but this did not achieve statistical significance. Duration of action to 25% of twitch tension was more than double in Group 1 (55 min) compared with the other two groups (22 and 25 min; P < 0.001). Duration of action was similar between Group 2 and control. Recovery index tended to be longer in Group 1, but without a significant difference. In conclusion, in morbidly obese patients, the duration of action of rocuronium is significantly prolonged when it is dosed according to real body weight. Therefore, the dosage should be assessed on the basis of ideal rather than on real body weight in clinical practice.