Influence of the amount of skeletal muscle mass on rocuronium-induced neuromuscular block.

Objective: To evaluate the effects of skeletal muscle mass on the rocuronium-induced neuromuscular block.

Design: A prospective, double-blinded, observational study.

Setting: A tertiary care university hospital.

Population: One hundred one patients aged 18-65 years who were scheduled to undergo major surgery lasting more than 1 h under general anaesthesia.

Methods: All participants underwent body composition analysis before anaesthesia and were allocated into two groups; the muscular and non-muscular group, according to skeletal muscle mass. During anaesthesia induction, rocuronium 1.0 mg kg of total body weight was injected followed by neuromuscular monitoring using train-of-four stimulation every 15 s.

Main Outcome Measures: The onset time of rocuronium included the elapsed time from the rocuronium injection until 95% depression of first twitch (T1) and the time to no response to TOF stimulation. The duration was evaluated as the elapsed time from the rocuronium injection to 25% recovery of the final T1 (T), and the time to the reappearance of T1 (T) and T4 (T). These pharmacologic data were compared between two groups.

Results: There was no significant difference in the onset time of rocuronium between the two groups. However, T (min) was significantly shorter in the muscular group than in the non-muscular group (p =  0.035 and p =  0.014 in males and females, respectively). T and T were also shorter in the muscular group than in the non-muscular group.

Conclusions: Total body weight-based dosing of rocuronium might prolong the neuromuscular relaxation effect in patients with a small amount of skeletal muscle.