Oral clonidine does not alter vecuronium neuromuscular blockade in anaesthetized patients

Abstract

Since clonidine, an α2-agonist, inhibits the release of norepinephrine or acetylcholine which can decrease nondepolarizing muscle relaxant-induced neuromuscular blockade, the authors examined whether clonidine given as an oral preanaesthetic medication would alter the onset, duration or recovery of a vecuronium neuromuscular blockade in lightly anaesthetized patients. Thirty-eight patients (aged 20-73 yr) randomly received oral clonidine either approximately 5 μg · kg-1 (n = 21) or none (n = 17), 90 min before arrival in the operating room. We measured acceleration of thumb contraction with ulnar nerve stimulation at the wrist to assess neuromuscular blockade. The onset time (the time from injection to decrease to 5% of baseline twitch height), duration (the time interval between injection and return of the first twitch to 25% of the baseline value), and recovery index (the time interval of the first twitch from 25% to 75% of the baseline value) of neuromuscular blockade from a single bolus of vecuronium 0.1 mg · kg-1 iv were determined and compared between the clonidine-treated and control patients during lower abdominal or extremity surgery under epidural plus general anaesthesia with fentanyl and nitrous oxide in oxygen. No differences were noted between the control and clonidine groups in onset time (100 ± 6 sec (mean ± SE) vs 101 ± 6 sec), duration (44.5 ±2.7 min vs 42.9 ±2.7 min), or recovery index (21.6 ± 2.8 min vs 19.1 ± 1.9 min) of neuromuscular blockade from vecuronium, respectively. These results show that oral preanaesthetic medication of clonidine 5 μg · kg-1 does not alter neuromuscular blockade induced with vecuronium 0.1 mg · kg-1 in patients during combined epidural and fentanyl/nitrous oxide general anaesthesia. © 1995 Canadian Anesthesiologists.