I read the article by A. Bernardini and G. Natalini [1] with interest. The total number of patients in this study is very impressive (total 65 712), although not quite sufficient, due to the low incidence of pulmonary aspiration, as suggested in the study.

The total number of clinical aspirations in the study is low (10 in total), and the statistical tests such as propensity score and the multivariate logistic regression model used to calculate adjusted OR, can deviate the data in such a way that they may prove thestatistical insignificance but more importantly, may underestimate the clinicalsignificance [2].

Inadequate depth of anaesthesia, leading to displacement of a properly placed laryngeal mask airway (LMA), is probably one of the common reasons leading to pulmonary aspiration. A substantial proportion of these cases may thankfully be subclinical or mildly symptomatic, and so hopefully do not require hospital admission. This is likely to be the case in healthy patients, as were investigated in this study. The study also does not mention the timings and regularity of endotracheal suction to look for evidence of aspiration. Also, endotracheal suction through LMA can be challenging in certain cases.

The aspiration of gastric contents, with a LMA in situ, in the population studied may be multi-factorial and may  be explained by normal anatomical and physiological factors. This is particularly true when positive pressure ventilation is combined with tidal volumes of 8-10 ml/kg, as was the case in this study. Despite the apparently low risk of aspiration with the LMA shown in this study by rigorous statistical analysis, the importance of patient selection, and the appropriate LMA‘technique’ cannot be emphasised enough.

The study concludes that male sex and emergency operations are the only factors associated with clinical pulmonary aspiration.With increasingly ‘courageous’ and widespread use of LMAs in anaesthetic practice in the UK, these conclusions would need to be considered with caution. It may be possible that potential drawbacks of the applied statistics in this study may underestimate the actual clinical risk of aspiration and may especially encourage junior trainees to use LMAs in a slightly ‘less suitable’population.

Dr Priti Gandre

ST4, Barts and the London School of Anaesthesia 

References

1. Bernardini A, Natalini G. Risk of pulmonary aspiration with laryngealmask  airway and tracheal tube:analysis on        65712 procedures with positive ventilation. Anaesthesia 2009; 64: 1289-94.  

2.J Peat, B Barton. Medical Statistics: A Guide to Data Analysisand Critical Appraisal 2005. Blackwell Publishing Limited.