Should the Twitch Height be Kept Lower in Anesthesia Using Propofol Than that Using Sevoflurane?

Volatile anesthetics, but not propofol, potentiate in general vecuronium-induced neuromuscular block. This study elucidated whether the amplitude of the first electromyographic response (T1) to a sequence of four stimulations should be kept at a lower level in anesthesia using propofol than that using sevoflurane. With the approval of the Kyoto City Hospital Ethics Committee, 119 patients undergoing elective operations were assigned randomly to the sevoflurane group or the propofol group. Anesthesia was induced with thiamylal and maintained with sevoflurane and nitrous oxide in two sevoflurane groups (S-30% and S-20%). Anesthesia was induced with propofol and maintained with propofol and nitrous oxide in two propofol groups (P-30% and P-20%). Vecuronium (0.1mg•kg-1) was given intravenously in all cases and an increment of 0.02mg•kg-1 was given when T1 had recovered to 30% of its control value in S-30% and P-30%, and 20% in S-20% and P-20%. Cases where additional vecuronium was required clinically were counted as "failures". The failure rate did not vary significantly among three of the four groups, but was significantly higher in P-30%. We conclude that T1 should be kept at 20% or lower in anesthesia with propofol, but can be at a higher percentage with sevoflurane.