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Abstract

Editor, Thank you for the opportunity to respond to the comments of Sorbello et al.1 made with respect to our article investigating the use of ultrasound to guide life-saving cannula tracheotomy.2 First, we support their suggestion that anaesthetists must take all reasonable steps to prevent ‘cannot intubate, cannot ventilate’ (CI–CV) scenarios. In situations wherein a difficult airway is predicted, then in many cases, awake fibreoptic intubation or awake tracheostomy will be the safest management plan and should be used. This is just one message from the recent fourth UK National Audit Project (NAP4) that investigated major complications of airway management.3 The report also highlighted that preemptive cannula cricothyroidotomy prior to induction of general anaesthesia is another potentially valuable technique. However, although the anaesthetist must try and avoid CICV scenarios, he should nevertheless still be prepared should they occur. Predictive tests will not identify all difficult airways and in one in five of the anaesthetic cases of CI–CV in NAP4, no difficulty in airway management was predicted.3 Furthermore, CI–CV events may occur in spite of attempts to prevent them and there are multiple case reports of complete airway obstruction precipitated by the process of awake fibreoptic intubation.3–5 Second, Sorbello et al. make a valid observation that our model had largely muscle overlapping the airway as opposed to fat, as would be the case in an obese patient. However, although the sonographic characteristics of these tissues may not be the same, we would expect to be able to identify a trachea at a depth of at least 3–4 cm whether it was under fat or muscle. This will vary depending on the frequency of the ultrasound probe used and the experience of the operator. Ezri et al.6 used ultrasound to identify tracheas that were at least as deep as 35 mm in a morbidly obese population. Although the cartilages of the larynx and trachea are relatively hyperechoic,7 it is conceivable that if the airway is compressed or occluded, it could be difficult to visualise. Finally, based on our extensive experience of their use in an animal model, we would disagree with the suggestion that cannulation might be quicker with a Cook emergency transtracheal airway catheter (Cook, Bloomington, USA) than the 14-G Insyte cannula (Becton Dickinson UK Ltd, Oxford, UK) that we used in our study. Due to its larger diameter trocar, greater wall thickness and ribbed design, the Cook ETAC requires considerably more force to insert (our own unpublished laboratory data) and so the procedure is more difficult and unlikely to be faster.