Optimum priming dose of vecuronium for tracheal intubation

To determine the optimum priming dose of vecuronium, we divided 173 surgical patients into five groups according to priming dose (0, 2.5, 5.0, 7.5, and 10 μg·kg^-1). For endotracheal intubation, we administered a priming dose of vecuronium, and then after 4 min, the remainder was injected for a total dosage of 0.15 mg·kg^-1. Onset time was determined by a 95% depression of twitch height as shown by electromyography (EMG) of the hypothenar muscles. This was measured by repeating the train-of-four (TOF) stimulation. An increased priming dose shortened the onset time; however, this shortening rate diminished when the dosage was above 7.5 μg·kg^-1. In the zero priming dose group there was a significant correlation between onset time and age, and between onset time and body mass index (BMI) in women (r=0.62 and -0.45, respectively); however, this correlation was not observed in men. A priming dose of 10 μg·kg^-1 showed a decrease of TOF ratio to 95% or less in 1 out of 25 cases. Although one-third of the patients in the 5 and 7.5 μg·kg^-1 groups complained of clinical symptoms such as ptosis, this was clinically allowable. We conclude that the optimum priming dose of vecuronium is 7.5 μg·kg^-1; however, in obese patients, a smaller dosage would be recommended.