Third generation supraglottic airways: is a new classification needed?

Editor—I have to admit that I am responsible for the academic use of theword ‘generation’ in a reclassification that was recently published in two places. 2 I also have to admit that it is likely to cause confusion if the same terms are used in two different classifications. However, Professor Cook’s use of the term for first generation does not apply to extraglottic airways but only to the laryngeal mask airway by reason of chronology (see precursor to Combitube below). ProfessorCook’s second generation is therefore second generation from the laryngeal mask airway point of view alone. Granted, it is a step change for the laryngealmask airway to include a gastric tube, but it is not a step change in the basic functions of extraglottic airway devices (EADs). Might it be that Professor Cook defines in his letter first generation supraglottic airway devices (SADs) as ‘simple airway tube’ because he is trying to avoid having to include sealing in the definition?Would one call a Guedel airway that is a simple airway tube that occupies a supraglottic or extraglottic position an SAD? If Professor Cook’s definition was correct and sealing was not a vital and essential characteristic of all EADs, then I would have no basis to use the word ‘generation’ in a classification. But the fundamental essential characteristic in any EAD is that it is an airway conduit that seals in the pharynx. We understand the implication of the necessary seal without having theneed toqualify it bysaying extraglottic sealing airwaydevice when we refer to EADs. If it does not seal, it does not qualify as an EAD or SAD. Aspiration protection and intubation through the device are non-essential features that may or may not be present. ProfessorCook’s objection tomyusing the term ‘generation’ in a classification of EADs appears to be driven by the noble objective of giving full credit to the magnificence of the laryngeal mask airway invention, thefirst EAD really to change thepractice of anaesthesia. However,whyProfessorCook’s choice of the term ‘generation’ is inappropriate and an unfortunate choice is explained in the article thatMichalek and Iwrote. As I see it, I think that the inappropriate use of ‘third generation’ by the commercial references, but not academic references, which Professor Cook refers to in his letter, may suffer from the same issue of referring to improved features (aspiration protection, conduit for intubation, bite block etc.) that do not constitute fundamental step changes in the essential function of extraglottic airways as new generations. But for the purpose of clarity, let me explain how I see it again in a differentway. Please understand that I amnot trying to dilute the importance of the laryngeal mask airway by including Combitube in first generation devices. The meaning of the word generation has two components: first, chronology; and second, birth of a new thing that involves a step change. Professor Cook’s use of theword in his classificationhasneither component, because the second generation was invented before the first generation (Combitube was invented before the laryngeal mask airway), 4 and his second generation has nothing to do with a step change in EADs but in laryngeal mask airway alone. So that is why it would seem to be an unfortunate choice. Improving the laryngeal mask airway to minimize the risk of aspiration is an important provision of an additional feature butnot a step change in the concept of EADs. Themagnitude of importance is an insufficient basis for it to constitute a step change in concept of EADs even though, from the point of view of the laryngeal mask airway, it may be. Finally, the classification we proposed 2 is consistent with both requirements to fulfil the role of new generations. The sequential development of devices with three different sealingmechanisms, with the first developed in the 1980s, the second in the 2000s, and the third in the present decade, represents a logical progression, each with different advantages. I would think that the third generation self-energizing sealing devices, such as Baska, do provide us with the potential to use higher inflation pressures, especially if we are to extend the use of EADs to encroach further on the use of tracheal tubes, such as for the morbidly obese, with less risk of neuropraxias. We probably need to wait for more than amillion uses to find out whether this is true. For all these reasons, therefore, I would disagree with Professor Cook regarding his opinion on third generation. Regarding the call for a new updated classification, I would agree with him that this is necessary. A classification of extraglottic airways along the lines we have proposed already would make a good starting point. Regarding what he refers to as second generation devices, I would say thatmost extraglottic airways have aspiration protection features that should be looked at and classified. I have already done that and built a vomit/regurgitation model to measure the effectiveness of these features for all the different types of EADs, presented at the Difficult Airway Society meeting in November 2013, where Professor Cook was one of the judges.