Background: Preliminary studies suggest that desflurane and isoflurane potentiate the action of muscle relaxants equally. However, variability between subjects may confound these comparisons. A crossover study was performed in volunteers on the ability of desflurane and isoflurane to potentiate the neuromuscular effect of vecuronium, to influence its duration of action, and on the magnitude and time course of reversal of potentiation when anesthesia was withdrawn.
Methods: Adductor pollicis twitch tension was monitored in 16 volunteers given 1.25 MAC desflurane on one occasion, and 1.25 MAC isoflurane on another. In eight subjects, vecuronium bolus dose potency was determined using a two-dose dose-response technique; the vecuronium infusion dose requirement to achieve 85% twitch depression also was determined. Also in these subjects, the magnitude and time course of spontaneous neuromuscular recovery were determined when the anesthetic was withdrawn while maintaining a constant vecuronium infusion. In the other eight subjects, the time course of action of 100 micrograms/kg vecuronium was determined.
Results: Vecuronium's ED50 and infusion requirement to maintain 85% twitch depression were 20% less during desflurane, compared to isoflurane, anesthesia; vecuronium plasma clearance was similar during the two anesthetics. After 100 micrograms/kg vecuronium, onset was faster and recovery was longer during desflurane anesthesia. When the end-tidal anesthetic concentration was abruptly reduced from 1.25 to 0.75 MAC, twitch tension increased similarly (approximately 15% of control), and time for the twitch tension to reach 90% of the final change was similar (approximately 30 min) with both anesthetics. Decreasing anesthetic concentration from 0.75 to 0.25 MAC increased twitch tension by 46 +/- 10% and 25 +/- 7% of control (mean +/- SD, P < 0.001) with desflurane and isoflurane, respectively; 90% response times for these changes were 31 +/- 10 min and 18 +/- 7 min (P < 0.05), respectively.
Conclusions: Desflurane potentiates the effect of vecuronium approximately 20% more than does an equipotent dose of isoflurane.