Comparative evaluation of atracurium dosed on ideal body weight vs. total body weight in morbidly obese patients

Abstract

What is already known about this subject: Different conflicting reports have been published for the use of atracurium in morbidly obese patients. Dosing of atracurium based on lean body mass, total body weight, and total body weight with a dose reduction for every 10 kg more than 70 kg have been proposed.

What this study adds: The current prospective randomized double-blind study compares atracurium 0.5 mg kg(-1) ideal body weight vs. 0.5 mg kg(-1) total body weight when used as a muscle relaxant in morbidly obese patients undergoing bariatric surgery. Based on our results in patients with body weights varying from 112 to 260 kg, we have concluded that atracurium 0.5 mg kg(-1) ideal body weight results in a predictable profile of muscle relaxation allowing for adequate intubation conditions and recovery of muscle strength within 60 min with lack of need for antagonism. A dose-dependent prolongation of action is shown when dosing is based on total body weight.

Aims: This double-blind randomized study evaluated atracurium dosing based on ideal body weight vs. total body weight for muscle relaxation in morbidly obese patients undergoing bariatric surgery.

Methods: Twenty patients (body weight 112-260 kg, BMI 38-79 kg m(-2) ) were randomized to receive atracurium 0.5 mg kg(-1) ideal body weight vs. 0.5 mg kg(-1) total body weight. Primary endpoint was neuromuscular blockade using train-of-four ratios (TOF ratios) and secondary endpoints were intubation conditions and need for antagonism with neostigmine.

Results: In the ideal body weight group, times to recovery of TOF ratio from 0 to 5%, 50% and 75% were significantly shorter [TOF ratio from 0 to 5%: mean difference 30 min (95% CI 23, 39 min)] and with lower variability compared with the total body weight group. In the total body weight group there was a significant correlation between atracurium dose and time to a TOF ratio of 5% (r= 0.82, P < 0.001), which was absent in the ideal body weight group (r= 0.24). In both groups, intubation conditions were good while 70% of the patients in the total body weight group needed neostigmine at the end of surgery compared with 0% in the ideal body weight group.

Conclusion: In morbid obesity (112-260 kg), atracurium 0.5 mg kg(-1) ideal body weight results in a predictable profile of muscle relaxation allowing for adequate intubation conditions and recovery of muscle strength to a TOF ratio >90% within 60 min with lack of need for antagonism. A dose-dependent prolongation of action is shown when dosing is based on total body weight.