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 micro g kg-1), Es (500 micro g 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 (Non-Invasive Cardiac Output) monitor (Novametrix Medical Systems Inc., Willingford, CO).