Pancuronium-induced neuromuscular blockade, and its antagonism by neostigmine, at 29, 37, and 41 c

To determine the effects of variations in temperature on the neuromuscular blockade produced by pancuronium, the drug was infused intravenously into 18 cats anesthetized with chloralose and urethane at a constant continuous rate to produce and maintain 90 per cent depression of twitch tension of the anterior tibial muscle following supramaximal stimulation of the peroneal nerve. The mean (+/-SE) infusion rates of pancuronium needed were 0.44 +/- 0.05, 0.99 +/- 0.11, and 1.05 +/- 0.09 microng/kg/min (r = 0.73) at 29, 37, and 41 C, respectively. In contrast, the doses of neostigmine necessary for 50 per cent antagonism of the pancuronium-induced depression of twitch tension were not significantly different at the three temperatures. The time required to achieve peak neostigmine effect was longer at the lowest temperature. The durations of neostigmine action were longer at 29 and 37 than at 41 C. It is concluded that hypothermia augments neuromuscular blockade produced by pancuronium and prolongs the time to peak effect, and possibly the duration of action, but not the dose of neostigmine needed to antagonize the blockade.