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Department of Anaesthesiology, Emergency, and Intensive Care Medicine; Georg August University Medical School; Goettingen, Germany; atimmer{at}zari.de
To the Editor:
In their recent paper comparing the PLA CobraTM and the Laryngeal Mask Airway (LMA) UniqueTM, Gaitini et al. (1) stated that the PLA Cobra’s significant advantages were ease of insertion, lower occlusion pressure, and reduced complications. Although these results are interesting, they may be incorrect because the authors introduced a systematic error into their study design: incorrect selection of LMA Unique size.
The authors state that they chose the size according to the manufacturer’s recommendation (2). However, the manufacturer offers two different guidelines. One guideline is based on gender: size 4 for women and size 5 for men. A second guideline is based on weight: size 3 for individuals weighing 30–50 kg, size 4 for individuals weighing 50–70 kg, and size 5 for individuals weighing >70 kg. The LMA Unique group contained 35 males and five females, which should have resulted in the use of 35 size 5 LMAs and five size 4 LMAs, according to strict adherence to the manufacturer’s gender-based size recommendations. If instead the study authors used the weight-based guidelines, then more than half of the patients should have had a size 5 LMA, since the weight distribution of the patients was 78.4 ± 15.3 kg, which suggests that more than half of the patients weighed >70 kg. In actuality, one size 5, three size 3, and 36 size 4 LMAs were used. This is not consistent with either the gender-based recommendation or the weight-based recommendation.
According to Brimacombe (3), appropriate size selection directly influences ease of insertion, efficacy of seal, ease of access to the respiratory and gastrointestinal tracts, noninterference with surrounding structures, and risk of trauma to the airway. Hence, the authors’ results, the amount of time and the number of attempts required to achieve effective airway control, difficulties with insertion, leak pressure, fiberoptic score, and side effects, may be incorrect, compromising the authors’ conclusions about the relative merits of the LMA Unique and the PLA Cobra.
REFERENCES
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