title: An external monitoring site at the neck cannot be used to measure neuromuscular blockade of the larynx.
abstract: 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 microg . 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.
authors.affiliation: Neuromuscular Research Group (NRG), Department of Anesthesiology, Centre Hospitalier de l'Université de Montréal (CHUM) Hôtel-Dieu, Université de Montréal, Canada.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Hemmerling
authors.forename: Guillaume
authors.initials: G
authors.lastname: Michaud
authors.forename: Stéphane
authors.initials: S
authors.lastname: Deschamps
authors.forename: Guillaume
authors.initials: G
authors.lastname: Trager
mesh_terms: D000328:Adult; D000769:Anesthesia, Inhalation; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007821:Laryngeal Muscles / Q000502:physiology; D007830:Larynx / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009119:Muscle Contraction / Q000502:physiology; D009213:Myography; D009333:Neck / Q000502:physiology*; D019148:Neuromuscular Blockade; D012009:Recurrent Laryngeal Nerve / Q000502:physiology