The relationship between rate of administration of an intubating dose of rocuronium and time to 50% and 90% block at the adductor pollicis muscle

Objective. To determine the relationship between the rate of rocuronium inj ection and the onset time of neuromuscular block. Methods.After intravenous induction, 60 female patients (ASA I-II) were assigned randomly into 3 gro ups for rocuronium administration within 1-15, 15-30 or 30-60 seconds. Acce leromyography of the thumb was performed using train-of-four (TOF) stimulat ion. Times to 50% and 90% twitch depression of the first twitch of the TOF stimulation (T1) were recorded. Results. Injection time significantly influ ences time to 50% relaxation, but not time to 90% relaxation. Body mass ind ex is negatively correlated with time to 50% and 90% relaxation. Conclusion s. We conclude that rate of injection influences only the initial phase of development of the block and that slower injection times do not significant ly affect time to 90% relaxation at the adductor pollicis muscle.