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ANESTHETIC PHARMACOLOGY

Ephedrine Fails to Accelerate the Onset of Neuromuscular Block by Vecuronium

Ryu Komatsu, MD^*, Osamu Nagata, MD^*, Makoto Ozaki, MD^*, and Daniel I. Sessler, MD

*Department of Anesthesiology, Tokyo Women’s Medical University, Tokyo, Japan; and Outcomes Research^TM Institute and Departments of Anesthesiology and Pharmacology & Toxicology, University of Louisville, Louisville, Kentucky

Address correspondence and reprint requests to Ryu Komatsu, MD, Department of Anesthesiology, Tokyo Women’s Medical University, 8-1 Kawadacho, Shinjuku, Tokyo 162-8666, Japan. Address e-mail to ryu0724{at}m09.\|[agr ]\|;-net.ne.jp.

The onset time of neuromuscular blocking drugs is partially determined by circulatory factors, including muscle blood flow and cardiac output. We thus tested the hypothesis that a bolus of ephedrine accelerates the onset of vecuronium neuromuscular block by increasing cardiac output. A prospective, randomized study was conducted in 53 patients scheduled for elective surgery. After the induction of anesthesia, the ulnar nerve was stimulated supramaximally every 10 s, and the evoked twitch response of the adductor pollicis was recorded with accelerometry. Patients were maintained under anesthesia with continuous infusion of propofol for 10 min and then randomly assigned to ephedrine 210 µg/kg (n = 27) or an equivalent volume of saline (n = 26). The test solution was given 1 min before the administration of 0.1 mg/kg of vecuronium. Cardiac output was monitored with impedance cardiography. Ephedrine, but not saline, increased cardiac index (17%; P = 0.003). Nonetheless, the onset of 90% neuromuscular block was virtually identical in the patients given ephedrine (183 ± 41 s) and saline (181 ± 47 s). There was no correlation between cardiac index and onset of the blockade. We conclude that the onset of the vecuronium-induced neuromuscular block is primarily determined by factors other than cardiac output. The combination of ephedrine and vecuronium thus cannot be substituted for rapid-acting nondepolarizing muscle relaxants.

IMPLICATIONS: Ephedrine increased cardiac index but failed to speed onset of neuromuscular block with vecuronium. We conclude that ephedrine administration does not shorten the onset time of vecuronium.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999