The neuromuscular effects of sevoflurane and isoflurane alone and in combination with vecuronium or atracurium in the rat.

Sevoflurane was compared to isoflurane anesthesia alone and in combination with atracurium or vecuronium in 84 rats using the sciatic nerve-anterior tibialis muscle preparation. Both bolus injection and infusion rate techniques were used to evaluate these drug interactions. The ED(50) (dose which produced a 50% depression of twitch tension) of atracurium was 311 +/- 31 and 360 +/- 32 microg.kg(-1) during 1.25 MAC sevoflurane and isoflurane anesthesia respectively. The ED(50) of vecuronium was 190 +/- 27 and 149 +/- 14 microg.kg(-1) during 1.25 MAC sevoflurane and isoflurane anesthesia respectively. The mean infusion rates of atracurium and vecuronium required to maintain a 50% depression of twitch tension were 5.04 +/- 0.7 and 2.02 +/- 0.3 mg.kg(-1).hr(-1). These infusion rates were 5.04 +/- 0.7 and 2.02 +/- 0.3 mg.kg(-1).hr(-1) during 1.25 MAC sevoflurane and 3.73 +/- 0.3 and 1.81 +/- 0.4 mg.kg(-1).hr(-1) during 1.25 MAC isoflurane anesthesia respectively. With both atracurium and vecuronium, the infusion rate required to maintain a 50% depression twitch of tension was inversely related to the concentrations of isoflurane and sevoflurane. The authors conclude that sevoflurane is similar in potency to that of isoflurane in augmenting a vecuronium or atracurium induced neuromuscular blockade in a dose-dependent manner.