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LETTERS TO THE EDITOR

Neuromuscular Blockade at Laryngeal Muscles

Department of Anesthesiology and General Intensive Care (B), Medical University of Vienna, Vienna, Austria, andrea.michalek-sauberer@univie.ac.at

To the Editor:

We have read with great interest the article by Hemmerling et al. (1). The authors are to be congratulated on their innovative technique to noninvasively monitor neuromuscular function at muscle sites not easily accessible to neuromuscular monitoring by conventional techniques. In their paper, Hemmerling et al. cited our study performed in cats (2). We measured the neuromuscular effects of vecuronium and rocuronium in antagonistic laryngeal muscles using needle electromyography.

We want to correct a printing error that occurred in Hemmerling et al. (1) in citing our results. Contrary to what is written in their paper ("...they found a longer recovery time at the PCA [i.e., posterior cricoarytenoid muscle] in comparison to the LCA [i.e., lateral cricoarytenoid muscle]"), in our experiments the lateral cricoarytenoid muscle was always the last muscle to recover after both vecuronium and rocuronium. Neuromuscular recovery in the lateral cricoarytenoid muscle was longer than in the posterior cricoarytenoid muscle and the anterior tibial muscle in cats. Therefore, the conclusion from our work was that "glottis closure recovers later than vocal cord abduction in cats".

By the way, in their recent review, Hemmerling and Donati (3) correctly cited our observations in the laryngeal muscles of cats.

References

1. Hemmerling TM, Michaud G, Trager G, Donati F. Simultaneous determination of neuromuscular blockade at the adducting and abducting laryngeal muscles using phonomyography. Anesth Analg 2004; 98: 1729–33.[Abstract/Free Full Text]
2. Michalek-Sauberer A, Gilly H, Steinbereithner K, Vizi S. Effects of vecuronium and rocuronium in antagonistic laryngeal muscles and the anterior tibial muscle in the cat. Acta Anaesthesiol Scand 2000; 44: 503–10.[Web of Science][Medline]
3. Hemmerling TM, Donati F. Neuromuscular blockade at the larynx, the diaphragm and the corrugator supercilii muscle: a review. Can J Anaesth 2003; 50: 779–94[Web of Science][Medline]

Response

Neuromuscular Research Group (NRG), Department of Anaesthesiology, Université de Montréal, Montréal, Canada, thomashemmerling_2000@yahoo.com

In Response:

We thank Drs. Michalek-Sauberer and Gilly for their interest in our article (1) and their correction of a printing error which occurred when we cited the results of their investigation of neuromuscular blockade (NMB) at several laryngeal muscles in cats (2). In the discussion section, a printing error occurred. They actually found a shorter recovery time of NMB at the posterior cricoarytenoid muscle (PCA), which abducts vocal cords, than at the lateral cricoarytenoid muscle (LCA)—an adducting laryngeal muscle—after rocuronium and vecuronium in cats, not a longer recovery time. We apologize for this error.

Since there are very few studies on this topic with very different results—and very different study setup—depending on the subjects studied, we have added a summarizing table (Table 1) of all studies and their findings that investigated NMB at different laryngeal muscles (1–5). We hope that readers might find this table of use concerning this interesting field of research.

1. Hemmerling TM, Michaud G, Trager G, Donati F. Simultaneous determination of neuromuscular blockade at the adducting and abducting laryngeal muscles using phonomyography. Anesth Analg 2004; 98: 1729–33.
2. Michalek-Sauberer A, Gilly H, Steinbereithner K, Vizi ES. Effects of vecuronium and rocuronium in antagonistic laryngeal muscles and the anterior tibial muscle in the cat. Acta Anaesthesiol Scand 2000; 44: 503–10.
3. Iwasaki H, Igarashi M, Namiki A, Omote K. Differential neuromuscular effects of vecuronium on the adductor and abductor laryngeal muscles and tibialis anterior muscle in dogs. Br J Anaesth 1994; 72: 321–3.[Abstract/Free Full Text]
4. Igarashi M, Iwasaki H. Mechanism of the differential sensitivity in the rat adductor and abductor laryngeal muscles to a non-depolarizing neuromuscular blocker. Br J Anaesth 1995; 75: 339–43.[Abstract/Free Full Text]
5. Iwasaki H, Igarashi M, Omote K, Namiki A. Vecuronium neuromuscular blockade at the cricothyroid and posterior cricoarytenoid muscles of the larynx and at the adductor pollicis muscle in humans. J Clin Anesth 1994; 6: 14–7.[Web of Science][Medline]

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