Effect of severe cardiac valve regurgitation on the onset of the neuromuscular blocking action of pancuronium

Abstract

Monitoring the onset of neuromuscular block produced by nondepolarizing relaxants provides useful and important information on muscle relaxation and the timing of endotracheal intubation. Goat and her colleagues [1] initially reported that the onset and intensity of paralysis produced by gallamine were directly related to muscle blood flow. We also reported that the onset of neuromuscular blockade in the adductor pollicis muscles occurred more rapidly in patients given vecuronium via the pulmonary artery than in patients given the drug via a peripheral vein on the hand [2]. Furthermore, the onset time of a neuromuscular relaxant is governed by noncirculatory factors, such as the concentration gradient between plasma and receptor sites, the potency, and the administered dose [3,4]. It has also been reported that the onset of action of pancuronium is slower in children with congenital heart disease (CHD) than in children without CHD [5]. We examined the influence of severe cardiac valve disease on the time of onset of action of pancuronioum in adult patients.With approval from our institution's human research committee and the informed consent of the patients, 47 patients scheduled for elective cardiac surgery (coronary artery bypass graft, n = 22; valve replacement, n = 25) aged 17-78 years (mean, 55) and weighing 40-75 kg (mean, 58) were included. The severity of mitral or aortic regurgitation in 25 patients with cardiac Address correspondence to: H. Iwasaki Received for publication on May 30, 1997; accepted on September 27, 1997 valve disease was qualitatively assessed by cardiac catheterization before surgery and was graded on a scale of 1 to IV in severity. Patients with moderately severe (grade III) and severe (grade IV) regurgitation were included in this study. All patients received midazolam 2.5 mg and either atropine 0.5 mg or scopolamine 0.4mg i.m. lh before induction of anesthesia. Anesthesia was induced with midazolam 2.0-3.0 mg i.v. and maintained with fentanyl 10-25~g.kg -~ and 50%-60% nitrous oxide in oxygen administered by face mask. Before insertion of an endotracheal tube, ventilation was controlled manually to keep PETCO2 within the range of 35 to 40mmHg.At least 5rain after the induction of anesthesia, pancuronium 0.1mg.kg -~ was randomly administered through an indwelling cannula on the dorsum of the hand and was flushed by a fast-running infusion. Neuromuscular block was evaluated every 12s by the force-of-thumb adduction produced in response to supramaximal stimulation of the ulnar nerve with repetitive train-of-four using surface electrodes at the wrist (Myograph 2000, Biometer, Denmark).Immediately after the administration of pancuronium, the cardiac output was measured with a pulmonary artery catheter inserted preoperatively, using 10ml of iced 5% dextrose in all patients. The average of three measurements was taken as the cardiac index. Tracheal intubation was not performed until the relaxation, judged by twitch responses, was 95% or greater.The degree of neuromuscular block was measured...