Can you compare the views of videolaryngoscopes to the Macintosh laryngoscope?

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Teoh et al. [1] are to be applauded for their efforts in comparing three video-laryngoscopes (the Pentax Airway Scope (Pentax AWS; Pentax, Tokyo, Japan); the C-MAC™ (Karl Storz, Tuttlingen, Germany); and the Glidescope® (Verathon, Bothell, WA, USA)) with the standard Macintosh laryngoscope for tracheal intubation.

Quite rightly, the primary outcome of the study was time to successful intubation, but we would like to comment on some of the secondary outcome measurements. The authors compared the Cormack and Lehane grade obtained using the four different laryngoscopes, but we would argue that the views obtained are not comparable. The Cormack and Lehane [2] view is defined as the view obtained during direct laryngoscopy. This is therefore the view obtained by aligning the oral, pharyngeal and laryngeal axes. With the videolaryngoscopes, the image is obtained from a camera positioned at a variable distance from the tip of the blade; in the Glidescope (size 4) this is 5.5 cm from the tip, whereas in the C-MAC it is 3.5 cm and it is approximately 3 cm in the Pentax Airway Scope. We would therefore argue that the different views are not statistically comparable, with the Macintosh laryngoscope or with each videolaryngoscope.

We were also interested in the use of manoeuvres to aid intubation, in particular the use of external laryngeal pressure. The authors did not state whether their assistants were also able to see the screen during external laryngeal pressure, which was required in 31% of cases with the C-MAC and 11% with the Glidescope. One of the authors of this letter has previously suggested that if the assistant performing the external manipulation was allowed to see the view obtained on the screen in the videolaryngoscope groups, then they may have improved the view obtained further, as the direct feedback obtained from the videolaryngoscope allows the assistant to provide a much better and coordinated view for the anaesthetist during external laryngeal manipulation [3]. If the assistant was allowed to see the view from the videolaryngoscopes, then could this group be compared to the Macintosh group (which required 38 ‘blind’ external laryngeal manipulations)? This would also affect the intubation time and ease of tracheal tube intubation in those patients who required external laryngeal pressure, possibly improving the times and scores, respectively.

No external funding and no competing interests declared. Previously posted at the Anaesthesia Correspondence website: http://www.anaesthesiacorrespondence.com.

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