Changes in onset time of rocuronium in patients pretreated with ephedrine and esmolol - the role of cardiac output

Background: We investigated the hypothesis that manipulation of cardiac output ( CO) with esmolol (Es) or ephedrine ( E) affects the onset time of rocuronium. Methods: Following anesthesia induction, 33 patients received E (70 mug kg(-1)), Es (500 mug kg(-1)) or placebo (P) 30 s before rocuronium (0.6 mg kg(-1)) administration. Cardiac output was measured non-invasively after intubation every 3 min. The interval from the end of rocuronium administration to the disappearance of all twitches was considered to be the onset time. Results: Onset time was shorter after E (52.2 +/- 16.5 s) and longer after Es (114.3 +/- 11.1 s) compared with P (87.4 +/- 7.3 s) (P< 0.0001). Cardiac output increased ( P< 0.05) in group E for 15 min after rocuronium. In group Es, CO decreased ( P< 0.05) at 3 and 6 min. Cardiac output was higher in group E vs. group Es, 3-6 min post administration of rocuronium ( P = 0.015). Conclusion: Pretreatment with E or Es appears to affect the onset time of rocuronium by altering CO as measured with the NICO(TM) (Non-Invasive Cardiac Output) monitor (Novametrix Medical Systems Inc., Willingford, CO).