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Anesth Analg 2005;100:1718-1722
© 2005 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000152189.85483.0E

TECHNOLOGY, COMPUTING, AND SIMULATION

An External Monitoring Site at the Neck Cannot Be Used to Measure Neuromuscular Blockade of the Larynx

Thomas M. Hemmerling, MD, DEAA, Guillaume Michaud, Stéphane Deschamps, MSc, and Guillaume Trager, MSc

Neuromuscular Research Group (NRG), Department of Anesthesiology, Centre Hospitalier de l’Université de Montréal (CHUM) Hôtel-Dieu, Université de Montréal, Canada

Address correspondence and reprint requests to T.M. Hemmerling, MD, DEAA, Department of Anesthesiology, Université de Montréal, Hôtel-Dieu, 3580, rue St-Urbain, Montréal (Québec) H2W 1T8, Canada. Address e-mail to thomashemmerling_2000{at}yahoo.com.

Using phonomyography, a new monitoring technique of neuromuscular blockade (NMB), we compared NMB after mivacurium 0.1 mg/kg at the lateral cricoarytenoid muscle (LCA) with a possible external monitoring site of the larynx. In 12 patients, data were obtained at both sites using phonomyography. Anesthesia was induced with remifentanil 0.25–0.5 µg · kg–1 · min–1 followed by propofol 2–3 mg/kg. A small piezo-electric microphone was positioned beside the vocal cords into the muscular process at the base of the arytenoid cartilage to record acoustic signals from the contraction of the LCA. A second microphone was positioned at an external site, lateral to the trachea, just below the thyroid notch. The recurrent laryngeal nerve was stimulated supramaximally using train-of-four (TOF) stimulation every 12 s. Onset, maximum effect, and offset of NMB were measured and compared. Peak effect, time to reach (T) 25%, 75%, and 90% of control twitch response, and TOF recovery to TOF ratios 0.5–0.8 were significantly longer at the external site. The onset time was not significantly different between the two sites. We used phonomyography with a microphone placed at the neck to evaluate the possibility to externally monitor NMB at the larynx. When compared with LCA, we found a more pronounced peak effect and longer offset of NMB. The acoustic signals recorded at this external site are unlikely to stem from laryngeal muscle contraction but are rather a result of contraction of the strap muscles of the neck.






Lippincott, Williams & Wilkins 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 HighWire Press
Copyright © 2005 by the International Anesthesia Research Society.