Onset time, endotracheal intubating conditions, and plasma histamine after cisatracurium and vecuronium administration

Cisatracurium is a nondepolarizing muscle relaxant with a slow onset. We performed a prospective, randomized, double-blind clinical trial in 60 patients (ASA physical status I or II) to assess whether cisatracurium (0.15 or 0.25 mg/kg) or vecuronium (0.15 mg/kg), administered as a bolus immediately after induction of anesthesia with fentanyl and thiopental, would provide a faster onset time and better tracheal intubating conditions than previously reported. We sought to determine whether patients given muscle relaxants in this commonly used induction sequence would exhibit cutaneous, systemic, or chemical evidence of histamine release. Onset time of the relaxants was determined by using mechanomyography. Intubating conditions were scored on a defined interval scale by an anesthesiologist blinded to the relaxant administered. Heart rate and arterial blood pressure were measured noninvasively every minute from 10 min before to 5 min after the application of the muscle relaxant. Mean (+/- SD) onset times for 0.25 mg/kg cisatracurium (68.3 +/- 19.5 s) and for 0.15 mg/kg vecuronium (69.5 +/- 29.2 s) were significantly different from those in the 0.15 mg/kg cisatracurium group (105 +/- 41.2 s). The intubating conditions were better with the larger dose of cisatracurium or vecuronium (P < 0.03). Although plasma histamine levels were not statistically different among groups, levels >1 ng/mL were observed in 5 of 40 patients who received cisatracurium but in none of the 20 patients who received vecuronium. There were no significant hemodynamic differences among the groups. In a dose of 0.25 mg/kg, cisatracurium has as rapid an onset time as vecuronium 0.15 mg/kg, but the former shows evidence of histamine release. Implications: Cisatracurium has been considered a drug with a relatively slow onset but that has the significant benefit of being devoid of chemically mediated histamine release. In this study, we describe an onset time faster than previously reported when cisatracurium was given immediately after thiopental. We also note that several patients had abnormal histamine levels after cisatracurium administration.