A double-curved tube for McGrath® MAC videolaryngoscope-guided tracheal intubation.

Editor-- Videolaryngoscopes are useful for tracheal intubation in patients with and without difficult airways. Recently, guidelines and expert recommendations recommend the use of a videolaryngoscope for the initial attempt at tracheal intubation in patients with COVID-19, to maximise the first pass success rate and to minimise exposure of healthcare workers during the procedure. , Nevertheless, the efficacy of the videolaryngoscopes may differ considerably, and thus a suitable device should be chosen.3, 4, 5 One possible problem with the use of a videolaryngoscopes is that, even when the glottis is clearly seen on the monitor screen, it may be difficult to advance the tube toward the glottis, prolonging the time to tracheal intubation. This difficulty may occur when the laryngoscopist is inexperienced, the camera of a videolaryngoscope is positioned too close to the glottis (which negates the space needed for tube passage), a tracheal tube without a stylet is used, or when a tracheal tube is not formed to an optimal shape.4, 5, 6

We have been using the McGrath® MAC (Covidien, Tokyo, Japan) videolaryngoscope routinely, and have found, as reported, , that tracheal intubation was frequently not easy (incidence of 10–30%), even when the distal side of a tracheal tube (with a style inserted) was curved at several different angles. It was frequently difficult to drive the tip of the tube toward the glottis, whereas the tube frequently obscured the glottic view seen on the video monitor. In addition, when the tube was strongly curved, it was frequently difficult to remove the stylet after successful intubation.

We found that this problem could be solved by making two curves to the tube (Fig. 1 ): a stylet is placed in a tracheal tube, and the distal segment of the tube is curved to the shape of the blade and, at the proximal edge of the single-use blade, the tube is curved to the right at an angle of approximately 45 degrees to the vertical. Similar to insertion of a double-lumen tube, the tube is inserted from the right corner of the mouth, and the tip of the tube is advanced toward the glottis by rotating the tube, without obscuring the glottic view seen on the video monitor (Supplementary Appendix 1).

Fig 1

A double-curved tube for intubation using a McGrath® videolaryngoscope: a stylet is placed in a tracheal tube, and the distal segment of the tube is curved to the shape of the laryngoscope blade and, at the proximal edge of the single use blade, the tube is curved to the right at an angle of approximately 45o to the vertical.

Supplementary video related to this article can be found at https://doi.org/10.1016/j.bja.2021.09.033

The following is the supplementary data related to this article:

Supplementary video 1

Tracheal intubation using a double-curved tube with a McGrath® videolaryngoscope.

The institutional research ethics committee indicated that no approval for this report would be required, as the report was from a personal logbook (of NT, a 4th-year trainee) and no personal information of patients were included. We used this method in 361 adult patients (183 males and 178 females), using a size 3 standard blade of the McGrath® MAC in all the patients, who were all Asian and were relatively short in stature (<180 cm). In 61 of 361 patients, at least one of the following predictive factors for difficult laryngoscopy (using a Macintosh blade) was present: difficulty in mouth opening, restricted neck movement, macroglossia, micrognathia, protruded teeth, short neck, obesity (body mass index > 30 kg m−2), obscured view of the oropharynx (Mallampati class 3 or 4).

In 360 of 361 patients, the glottis could be seen at laryngoscopy, whereas in the remaining one patient, only the epiglottis (and not the glottis) could be seen. In the 360 patients with a clear view of the glottis at laryngoscopy, tracheal intubation was successful at the first attempt (without the need to re-adjust the shape of the tube) in 358 patients (99.4%: 95% confidence intervals: 98.0%–99.8%). There was no difficulty in removing the stylet in any of these patients. We did not formally measure the time required for tracheal intubation, but intubation was usually smooth, as shown in the Supplementary video. In the remaining two patients, tracheal intubation could not be achieved at the first attempt because the tip of the tube impacted the arytenoids. Tracheal intubation was successful at the second attempt in these patients by adding a slightly stronger curve to the tube.

In the one patient in whom the glottis could not be seen at laryngoscopy, tracheal intubation was unsuccessful at the first attempt. This patient was an obese woman with a small jaw and had an obscured view of the oropharynx on mouth opening (Mallampati class 3). The tip of a size 3 blade could be inserted deep enough, but only a small part of the glottis could be observed (by applying a downward pressure on the neck), and the tip of the tube could not be advanced toward the glottic opening. Tracheal intubation was successful at the second attempt, by preparing a tracheal tube with a bend angle of approximately 70o.

We did not carry out a formal randomised study, and all the intubation attempts were made by one anaesthetist (NT), and thus it is not possible to draw a firm conclusion whether or not our insertion method is superior to the conventional insertion methods. Nevertheless, when the glottis can be seen at laryngoscopy, insertion of a double curved tube would be easy in more than 98% of cases. In addition, several anaesthetists (including TA) at our department have routinely been using this insertion method, and have found it useful. We recommend using a double curved tube for a McGrath® MAC videolaryngoscope-aided tracheal intubation.

Declarations of interest

NT has no conflict of interest; TA is an editor of the British Journal of Anaesthesia.