Improving tracheal intubation outcomes requires deeper analysis of the three axes of tracheal tube orientation

I read with interest the network meta-analysis examining the relative performance of modern videolaryngoscopes by de Carvalho et al. [1]. The authors' call to action includes identifying strategies to translate better glottic visualisation into improved tracheal intubation efficacy. This call is most compelling in emergency tracheal intubations by relatively inexperienced non-anaesthetists in out-of-hospital or emergency department contexts [2]. Maximising the value of limited opportunities for first responders to practise tracheal intubation in controlled environments is crucial for improving field outcomes.

Peyton's teaching approach has been shown to speed learning and aid retention, particularly in small group or individual teaching environments [3]. This requires deconstructing and describing each step in a procedure precisely, followed by allowing the trainee to test their understanding by describing back the steps before completing the task themselves. We need to deconstruct the step of positioning and orienting the tracheal tube in order to pass it through the glottis, as a startling number of tracheal intubation attempts fail despite a full view of the cords. The complexity of this step appears to have gone unrecognised. Positioning and orienting an object in a three-dimensional space requires a total of six different numbers, each with a specific zero reference. While clinical language covers the three dimensions of position (left/right; anterior/posterior; and superior/inferior) the three axes of rotation of a free-floating object like a tracheal tube are not. The terms pitch, roll and yaw, originally from sailing but popularised by aviation, describe the three distinct rotations.

Some studies have investigated the rotation of hands during tracheal intubation [4], but there is limited research on the orientation of the tracheal tube itself. There is no published analysis of the interactions between each of the three rotations of a curved tracheal tube with a curved laryngoscope blade and maxillary dental arch during tracheal intubation. The orientation of the tracheal tube and the pressure at the tube-blade contact point significantly influence the anteroposterior position of the tracheal tube tip at the level of the glottis [5].

Overall, there seems to be an underlying assumption that correct tracheal tube three-dimensional orientation either develops with experience, as an unteachable competence, or can be circumvented by equipment modifications. Numerous studies show that relying on trainees to gain proficiency after 50–100 tracheal intubations leaves non-anaesthetists under-prepared for emergency tracheal intubations.

In my experience, the most common observable orientation error with a standard Macintosh blade is bending the proximal tracheal tube cephalad over the upper teeth. Despite this leading to a predictable posterior deflection of the distal tracheal tube tip, novices struggle to avoid this intuitive, but counterproductive, reflex. If we can provide specific alternative advice to novices, then perhaps they can more quickly learn to avoid this error. Preliminary three-dimensional computer simulation (Fig. 1) suggests the optimal orientation is to yaw the proximal tracheal tube laterally around the right upper teeth so the proximal tracheal tube can be pushed posteriorly. This pitches the tip anteriorly toward the glottis, and away from the oesophagus. Rolling, i.e. flopping the tracheal tube over so both ends point right, consistently lowers the tracheal tube tip away from the glottis [5]. More work is required to validate these early findings, but the geometry is readily appreciable by simply manipulating a laryngoscope and tracheal tube in one's own hands.

Figure 1

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Renders of the simulated upper airway during tracheal intubation showing the impact of 15° of yaw (a and b) compared with 45° of roll (c and d). The maxillary dental arch, front mandibular teeth, laryngoscope blade and tracheal tube are shown from the perspective of tracheal intubation (a and c) and from the right side (b and d). Panels (b) and (d) show the similar appearance of yaw and roll when viewed from the side despite the dramatic impact on tracheal tube tip location at the level of the glottis [5].

This three-dimensional complexity is avoided by channelled devices or the combination of hyperangulated videolaryngoscopy blades with rigid hyperangulated stylets, but as the work by de Carvalho et al. highlights, this approach is not a panacea and introduces additional complexities. Soiled airways and strongly sunlight environments further complicate the use of all video devices, with both difficulties more common in emergency settings. At least an operator with a Macintosh blade has a chance of passing a tracheal tube under direct vision.

Attempting to train first responders in the use of both conventional Macintosh blades and alternatives risks diluting the training of both, potentially making outcomes in the field worse. While the Macintosh blade remains in common use, we should aim to better understand how experts navigate around a Macintosh blade. Doing so will require observational studies. This will then enable us to test if we can speed the learning of those that come briefly through our operating theatres on their way to roles where lives will depend on this skill.