Characteristics of Succinylcholine-Produced Phase II Neuromuscular Block during Enflurane, Halothane, and Fentanyl Anesthesia

Publisher Website
Google Scholar
Abstract
The characteristics of phase II neuromuscular block following repeated i.v. injections of succinylcholine (SCh) were determined in 15 adult patients during enflurane, halothane or fentanyl-nitrous oxide anesthesia. The onset of phase II block (train-of-4 ratio (T4) equal to 0.5) occurred following a cumulative SCh dose of 4.4 .+-. 0.3 (SEM) mg/kg of enflurane, 5.1 .+-. 0.5 mg/kg of halothane or 6.4 .+-. 0.5 mg/kg of fentanyl. The cumulative SCh dose producing phase II block during fentanyl-nitrous oxide anesthesia was significantly greater than during enflurane (P < 0.01) or halothane (P < 0.05) anesthesia. It is predicted that the likelihood that phase II blocking developing is less during fentanyl administration than during enflurane or halothane anesthesia. An abrupt transition from phase I to phase II neuromuscular block, as evidenced by an accelerated decrease in the Tr ratio, was observed during enflurane or halothane anesthesia as the cumulative SCh dose approached 3-5 mg/kg. The transition phase was delayed during fentanyl-nitrous oxide anesthesia, occurring after a cumulative SCh dose of 4-7 mg/kg. Following this transition, tachyphylaxis (decreased time between SCh injections) was observed in each study group. The T4 ratio in all 3 study groups stabilized at 0.15-0.25 after 7-8 mg/kg.