Beyond the scope: it is not only blade geometry of videolaryngoscopes but also the interplay with the adjuncts

Abstract

We thank Hughes and O'Sullivan for emphasising the importance of adjuncts when comparing videolaryngoscopes with different geometries [1]. We found a considerably larger difference (30%) between first-attempt tracheal intubation success rates of hyperangulated and Macintosh videolaryngoscopes than we expected based on previous study findings. However, it is essential to remember that our study investigated patients at highest risk of difficult tracheal intubation (e.g. 44% had a history of difficult tracheal intubation) and, as such, the high first-attempt success rate with hyperangulated blades (97%) seems remarkable, while the low rate with Macintosh videolaryngoscopy (67%) might be expected [2]. Furthermore, an independent observer assessed the first-attempt success (only one attempt at laryngoscopy and tracheal intubation) to eliminate any risk of self-reporting bias. Only consultant anaesthetists who were experienced with both types of videolaryngoscope and had received further training using manikins prepared to mimic difficult/very difficult videolaryngoscopy participated. This training included the use of bougies (FlexTip, P3 Medical, Bristol, UK; and Frova Intubating Introducer, Cook Medical, Limerick, Ireland), to rescue failed stylet-facilitated tracheal intubation [3].

We agree that the optimal airway adjunct for different videolaryngoscope blades remains unclear. Macintosh videolaryngoscopes can be used with or without stylets or bougies, while hyperangulated blades are intended to be used with stylets matching the curvature of the corresponding blade [4, 5]. There is growing evidence that bougies might also be beneficial with hyperangulated blades [3].

From our study, we have learnt that a better view does translate into higher success rates if appropriate adjuncts are used by skilled operators on difficult airways. The unique interplay between blade geometry and adjuncts is a key factor in making videolaryngoscopy-facilitated tracheal intubation successful. Macintosh and hyperangulated videolaryngoscopy may be regarded as two entirely different approaches. It remains unknown which pre-shaping of the styletted tracheal tube might be most effective in facilitating tracheal intubation with Macintosh videolaryngoscopes. To our knowledge, a rigid stainless-steel stylet exactly matching the curvature of C-MAC Macintosh blades is not yet commercially available. We consider it an important strength that we used stylets that were exactly aligned with the curvature of the corresponding blade as recently recommended [4] but still allowed the airway operators to reshape the stylet (which was rarely done and not systematically assessed) as we assumed this most accurately reflected current clinical practice. Bougies were used more frequently in patients allocated to the Macintosh group compared with those in the hyperangulated videolaryngoscopy group (16% vs. 2%); however, per protocol, the use of bougies was limited to cases where the initial stylet-facilitated tracheal intubation failed (18% vs. 3% respectively). This was almost exclusively in conjunction with severely restricted glottic views. The vocal cords were not visible in 35% of patients allocated to the Macintosh group compared with 5% of patients in the hyperangulated blade group. There were only two instances in which bougies were used despite an acceptable glottic view in patients allocated to the Macintosh group. This might have been due to suboptimal alignment between the tracheal tube and laryngeal inlet or other factors such as a narrowed upper airway or obstructive tumours. Considering this evidence, we disagree that suboptimal pre-shaping of the styletted tracheal tube is likely to have had a relevant contribution to lower success rates observed with Macintosh videolaryngoscopy.