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Guys Hospital; London, UK; donald.miller{at}kcl.ac.uk
To the Editor:
A recent paper by Lange et al. (1) reported the first independent study comparing the laryngeal mask airway (LMA) classic with the streamlined pharynx airway liner airway (SLIPA). Despite the inherent bias in the study given the comparison between users with differing levels of experience with the two devices, i.e., experienced users of the LMA compared with novices with the SLIPA, the two significant differences between the airways found in the study are most instructive. The first was the higher incidence of gastroesophageal insufflation (19%) than with the LMA (3%) and may relate to the choice of size used. The SLIPA sizes 47–57 are equivalent to LMA sizes 3–5.5. The authors in their study used LMA sizes 4–6 in comparison. This would explain the much lower seal pressures measured than the seal pressures that I obtained using the SLIPA (2). This is understandable as clinicians are generally always conservative when starting to use a new device.
The second significant finding is that fewer patients in the SLIPA group compared with those in the LMA group complained of sore throats, despite the harder appearance of its thermoplastic material (softens as it heats up to body temperature).
The authors incorrectly stated that the SLIPA that was tested in the clinical and laboratory study (3) "differed markedly" from the version that they tested. In reality, the only difference was one of esthetics relating to the inconsequential shape of the stem of the SLIPA and not the shape, size, or material of the all important chamber aspect of the SLIPA. In essence, the characteristics tested in the Lange study, including the sealing characteristics, were identical in all performance related matters.
Finally, Lange et al. incorrectly concluded that the greater incidence of gastroesophageal insufflation may suggest a greater risk of aspiration. They should have used the word regurgitation instead. To have concluded that the risk of aspiration is greater with the SLIPA is to ignore a specific design characteristic that effectively prevents aspiration of regurgitated material because it has 15 times the storage capacity of the LMA for trapping liquids within its chamber (3).
Footnotes
Miller is the inventor of the SLIPA airway.
REFERENCES
This article has been cited by other articles:
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  M. Lange, N. Roewer, and F. Kehl The Conventional LMA(R): Benchmark for Assessing Supralaryngeal Airway Efficacy? Anesth. Analg., November 1, 2007; 105(5): 1509 - 1509. [Full Text] [PDF]
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