The effect of cisatracurium and rocuronium on cisatracurium precurarization and the priming principle.

STUDY OBJECTIVE

To demonstrate the effect of administering a precurarizing dose of cisatracurium or rocuronium on the speed of onset of cisatracurium, and to review the possible mechanisms and value of the priming principle.

DESIGN

Double-blind, randomized, controlled trial.

SETTING

Inpatient anesthesia in a university teaching hospital.

PATIENTS

90 ASA physical status I and II patients undergoing elective surgery requiring endotracheal intubation.

INTERVENTIONS

Three groups of 30 patients each were investigated. Following induction of anesthesia with fentanyl and propofol, Group 1 received cisatracurium 0.015 mg.k(-1), Group 2 received rocuronium 0.09 mg. kg(-1), and Group 3 (control) received normal saline. Six minutes after priming, Groups 1 and 2 received cisatracurium 0.135 mg. kg(-1) whereas Group 3 received cisatracurium 0.15 mg. kg(-1).

MEASUREMENTS AND MAIN RESULTS

In each group, first twitch height and the train-of-four ratios were recorded every 10 seconds after the initial priming dose. Intubation was attempted after the first twitch height became less than 15% of baseline. The decrease in the train-of-four ratios at 6 minutes was 0.97 for cisatracurium and 0.85 for rocuronium. The onset of muscle relaxation was significantly faster after priming with cisatracurium and rocuronium (71.7 +/- 21.3 and 65 +/- 19.8 sec, respectively) compared with control (148.7 +/- 43.1 sec). Females receiving both muscle relaxants had a faster onset of paralysis than did males (65.9 +/- 20.6 vs. 79.2 +/- 20.6 and 55 +/- 14.5 vs. 71.7 +/- 20.4 sec). Intubation conditions were either excellent or satisfactory in all patients.

CONCLUSIONS

Six minutes after precurarization, there is no significant difference between rocuronium and cisatracurium when used as priming drugs. An even faster onset time with both drugs was demonstrated in females. The use of priming doses of 25% to 30% of ED(95) may cause symptomatic muscle weakness. The mechanisms of the priming principle are discussed.