Priming with rocuronium accelerates the onset of neuromuscular blockade

To investigate the effects of priming rocuronium on the time course of neuromuscular blockade.

Prospective, controlled, randomized clinical study.

University teaching hospital.

42 ASA physical status I and II patients undergoing peripheral surgery with general anesthesia.

Following a standardized propofol-fentanyl induction, patients in Group 1 (n = 21) received a priming dose of rocuronium 0.06 mg/kg followed two minutes later by an intubating dose of rocuronium 0.54 mg/kg. Patients in Group 2 (n = 21) received a saline placebo injection followed two minutes later by rocuronium 0.6 mg/kg. Anesthesia was maintained with isoflurane and nitrous oxide 60% in oxygen.

Neuromuscular function was assessed at the wrist using mechanomyography with a single-twitch mode of stimulation at a frequency of 1 Hz until tracheal intubation and at 0.1 Hz thereafter. The times from injection of the intubating dose of rocuronium until 95% suppression of the twitch tension (onset time), recovery of twitch tension to 25% of control (clinical duration of action), and the time from 25% to 75% spontaneous recovery of twitch tension (recovery index) were recorded. The trachea was intubated at 95% depression of the twitch tension and the intubating conditions were graded using a 3-point scale. The onset times with priming rocuronium (34 +/- 6 s) were significantly shorter (p < 0.01) than those without priming (59 +/- 14 s). The intubation conditions were similar in the two groups; however, the intubating times with priming were significantly shorter. The clinical duration of action and the recovery index did not differ significantly between the two groups.

Priming rocuronium decreased the onset times and thus, the intubating times without increasing the clinical duration of action or recovery index.