Onset of vecuronium-induced neuromuscular block after a long priming interval

We examined whether a new application of the priming principle, i.e., having the priming dose of vecuronium administered before the insertion of the epidural catheter, would hasten the onset of the neuromuscular block induced by the intubating dose of vecuronium.

Forty-five adult female patients scheduled for general anesthesia combined with epidural anesthesia were studied. In group A ( n = 15), the priming dose of vecuronium, 0.01 mg.kg(-1), was administered before insertion of the epidural catheter. The intubating dose of vecuronium, 0.09 mg.kg(-1), was given after the insertion of the epidural catheter. In group B ( n = 15), the priming dose of vecuronium, 0.01 mg.kg(-1), was given 4 min before the intubating dose of vecuronium, 0.09 mg.kg(-1). In the control group ( n = 15), no priming dose was given, and only the intubating dose of vecuronium, 0.10 mg.kg(-1), was administered. In all three groups, general anesthesia was induced with propofol 2.5 mg.kg(-1), and the trachea was intubated when T1/control value (control twitch height in response to train-of-four stimuli) was less than 0.1.

In group A, the priming dose was given 16 +/- 3 min (mean +/- SD) before the administration of the intubating dose. The times to onset of neuromuscular block in groups A and B, and the control group were: 145 +/- 30, 184 +/- 45, and 219 +/- 23 s, respectively ( P < 0.05 among the three groups). In all three groups, intubating conditions (graded on a four-point scale) were excellent ( P = 0.59). Before the induction of anesthesia, symptoms of paralysis were observed in 5, 4, and 0 patients in groups A and B and the control group, respectively ( P < 0.05 between group A or B vs control group).

If the priming dose of vecuronium is given after a long priming interval (16 +/- 3 min), the time to onset of the neuromuscular block caused by the intubating dose of vecuronium is markedly shorter than when the conventional priming interval of 4 min is employed.