This Article Full Text (PDF) Submit a scholarly reply Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hemmerling, T. M. Search for Related Content PubMed Articles by Hemmerling, T. M.

REPLY

Centre Hospitalier de l’Université de Montréal (CHUM), Montreal, Canada, E-mail: thomashemmerling{at}hotmail.com

We thank Drs. Fabregat and De Arce for their interest in our article.¹ It is interesting to see the tracing of neuromuscular monitoring at the adductor pollicis muscle in the case they present; it demonstrates the rather inadequate relevance of this muscle for estimating laryngeal relaxation. Whereas train-of-four (TOF)-monitoring at this muscle showed surgical relaxation with a TOF-ratio less than 0.25, the patient emitted high-pitched snoring sounds from the larynx demonstrated inadequate relaxation of the larynx.

We would agree with their explanation that intermittent exposure to air flow during positive pressure ventilation – which has become more and more popular with the use of laryngeal mask airways – can cause microtrauma at the vocal cords which is aggravated when these cords are not fully relaxed. Whether air temperature has an influence on incidence or severity of these microtraumas can only be speculated upon. We would assume that the amount of air flow, especially the pressure with which a given volume is applied, plays the dominant role in not only the occurrence of vocal cord microtrauma, but also the incidence of ‘snoring sounds’.

It is true that the flow volume was not stated in our case report. In order to diminish the pressures and the air volume, a principle of ‘low volume – high frequency – ventilation’ has been adopted. We usually opt for a ventilation frequency of 14 to 16·min^–1 min to achieve inspiratory pressures of less than 20 mmHg. In our view, this not only reduces the incidence of vocal cord micro-trauma but also the risk of accidental insufflation of air into the esophagus and stomach, as well as displacement of the laryngeal mask airway. It is our view that proper insertion of a laryngeal mask airway should provide a sufficiently "tight" seal so that the expired volume approximates the ventilator setting with no audible air leakage. Low-flow anesthesia and the use of humidified gases should - as Drs. Fabregat and De Arce recommend - be a standard in modern anesthesia.

Reference

1 Hemmerling TM, Michaud G, Deschamps S, Trager G. ‘Patients who sing need to be relaxed’--neuromuscular blockade as a solution for air-leaking during intermittent positive pressure ventilation using LMA (Letter). Can J Anesth 2005; 52: 549.[Free Full Text]

This Article Full Text (PDF) Submit a scholarly reply Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hemmerling, T. M. Search for Related Content PubMed Articles by Hemmerling, T. M.