Evolution of vecuronium requirements for stable mechanical effect: comparison with or without previous succinylcholine administration.

To evaluate possible interactions between residual succinylcholine and vecuronium, the amount of vecuronium required to maintain the twitch height (TH) at 10% of its initial value was measured over a 90-min period by the on-demand infusion method in two series of 15 adult patients (ASA class I-II). One group, the vecuronium treatment (V) group, received 70 micrograms X kg-1 of vecuronium and the on-demand infusion. The second group, the succinylcholine-vecuronium treatment group (SV), was given 30 micrograms X kg-1 of vecuronium and on-demand infusion 5 min after the complete recovery of TH after administration of 1 mg X kg-1 of succinylcholine. During the first 10 min, the amount of vecuronium required to maintain TH at 10% of its control was significantly greater in the group given V than in the group given SV, 15122 +/- 856 (mean +/- SEM) vs 9851 +/- 486 micrograms X m-2 X hr-1 (P less than 0.001). Thereafter, the amount of vecuronium required to maintain TH at 10% of control was similar: 2808 +/- 275 and 3068 +/- 206 micrograms X m-2 X hr-1. When the infusion of vecuronium was stopped after 90 min, the time required for spontaneous recovery from 25 to 75% of control TH levels was similar: 20.1 +/- 3.3 min in the group given V and 18.9 +/- 2.5 min in the group given SV (not significant). We conclude that after a vecuronium on-demand infusion of long duration (lasting more than 90 min), previous succinylcholine administration does not interfere with late vecuronium requirements and the spontaneous rate of recovery of TH.