We read with interest Bazin and Constantin's letter addressing the issue of whether all single-use laryngeal masks are the same [1]. The authors present a case of failure of a Soft Seal™ laryngeal mask (Smiths Medical, Hythe, UK) but success of the LMA-Unique™ (Intavent Orthofix, Maidenhead, UK) in a 26.5 kg child, which they attribute to the presence of mask aperture bars on the LMA-Unique preventing epiglottic downfolding and airway obstruction. We would like to challenge this conclusion and present some preliminary information about the utility of the mask aperture bars. After placement, the authors encountered a massive air leak and airway obstruction, inserted a fibreoptic scope, identified the epiglottis obscuring the vocal cords (their Fig. 7), withdrew the Soft Seal laryngeal mask, and replaced it with a similar-sized LMA-Unique, which resulted in a clear airway and an unobstructed view of the vocal cords (their Fig. 8). In our experience, one of the most common causes of the epiglottis obscuring the vocal cords is inadequate depth of insertion resulting in the distal cuff sitting into the laryngopharynx rather than the hypopharynx [2], as appears to have occurred in Fig. 7. This can be caused, for example, by insertion with the cuff inflated or the mask being too big, but has little to do with the lack of mask aperture bars. It would helpful if the authors could tell us which insertion technique was used, whether the cuff was pre-inflated and if so, by how much, and whether there were any clinical signs of correct positioning [3]. Did the authors document the intracuff pressure? This would provide information about whether the size was suitable for the patient. Certainly, most clinicians in this situation would have reinserted the same Soft Seal laryngeal mask, perhaps using a different technique, such as with the cuff partially inflated, before reaching for an alternative device. One of us (AZ) has evaluated the utility of the mask aperture bars in over 400 patients managed with either the LMA-Unique (which has two bars) or the Cobra PLA™ (perilaryngeal airway) (Engineered Medical Systems, Indianapolis, IN) (which has 6–8 bars) (unpublished work) and has come to the conclusion that they serve no useful purpose, and might occasionally be detrimental. In 75% of patients there was no contact with the epiglottis indicating no function; in 20% there was light contact, indicating little function; and in 5% there was strong contact, indicating possible function, but in the majority of the latter cases the epiglottis herniated through the bars, a possible cause of trauma (1, 2). An alternative design strategy to mask aperture bars is to increase the distance between the epiglottis and airway tube by making the bowl deeper. In principle, this will decrease the frequency of the epiglottis herniating into the airway tube by increasing the distance between them. This design, although clinically unproven, has been incorporated in the Soft Seal laryngeal mask and the ProSeal™ LMA (Intavent Orthofix). LMA-Unique with epiglottis herniated through the mask aperture bars. Cobra PLA with epiglottis herniated through the mask aperture bars. We conclude that Bazin and Constantin's case was probably related to inadequate depth of insertion rather than the lack of mask aperture bars. Re-insertion would have been a better (and more economical) solution rather than using an alternative device. Our preliminary data add support to Al-Shaikh and Pilcher's findings that the mask aperture bars offer no benefit [4]. Finally, we consider that the design feature that will determine the best single-use laryngeal masks will be the presence or absence of a drain tube, as these offer substantial advantages in terms of protection against regurgitation and gastric insufflation, passage of a gastric tube, diagnosis of malposition, and insertion success, which approaches 100% using a gum elastic bougie deliberately placed in the proximal oesophagus as a guide to insertion [5].
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Jan 1, 2008
Dilip G Nayak + 2
Open Access
