Further developing the evidence base for videolaryngoscopy

Recently, Vowles and colleagues evaluated the use of different intubating adjuncts to videolaryngoscopy (VL) in a simulated difficult airway. ¹ The authors should be congratulated for investigating one of the key questions regarding the use of VL in clinical practice, namely which adjunct is most appropriate for facilitating intubation with a specific VL device, and in a specific clinical scenario. This question sits alongside the consideration as to which VL device best suits the variety of specific airway challenges encountered in clinical practice, as being an area of some uncertainty.

A Cochrane Database systematic review concluded that VL was associated with significantly fewer failed intubations than direct laryngoscopy (DL), and other meta-analyses have further demonstrated increased first-pass intubation success with VL, particularly in the context of a known difficult airway.^2–4 However, heterogeneity in study design and size, clinical location, and patient population (particularly relating to the presence of a known difficult airway), has limited conclusions regarding individual devices and specific scenarios.

VL devices tend to be considered as a homogeneous group, likely out of necessity rather than by intention, despite numerous important differences in design, most prominently relating to blade style (Macintosh-type versus hyperangulated blade). Given the individual design features it is important to consider devices separately, as well as part of a ‘VL cohort’, particularly when we consider the specific challenges likely to be posed by the patient.

Vowles and colleagues simulated a difficult airway, with an inflated tongue, a fixed neck, and an anteriorly displaced larynx, features which would understandably hinder attempts to bring the oral, pharyngeal, and laryngeal planes into alignment, and potentially favour the use of a hyperangulated blade. ¹ Anaesthetists and intensivists manage the airway in a range of situations where the challenges posed, and thus the indications for VL, will vary. Arguably, given the increasing access to VL devices and the selection available to the airway practitioner, the evidence should evolve to consider the interplay of specific device features with individual airway challenges. Recently, a randomised controlled trial and a network meta-analysis investigated the use of specific VL devices in the management of patients with cervical spine immobilisation, reporting specific VL devices associated with a greater first-pass success when compared with DL.^5,6

Akin to the use of specific devices for specific challenges is the question faced by Vowles and colleagues, relating to the use of introducers and adjuncts. Some devices are intended for use with preformed introducers, designed to optimise use of an accompanying VL device, whereas others do not have specific adjuncts, resulting in marked variation in practice and in the literature regarding adjunct–device pairing. Vowles et al. evaluated the use of an unchannelled hyperangulated device (APA VL, AAM Healthcare, Venner Group, Singapore) with different adjuncts. Their primary outcome was time to intubation, which was found to be shortest with the Frova introducer (Cook Medical, Bloomington, IN, USA), compared with the flexible tip bougie (Construct Medical, Melbourne, Victoria) and flexible bronchoscope (Ambu aScope, Ballerup, Denmark) (33.2 versus 34.9 versus 44.8 seconds, P<0.05). ¹

Choice of both specific VL device and adjunct is of considerable importance, and will have a profound impact on the success of airway management. Echoing the call for more evidence regarding the marriage of certain VL devices with specific airway challenges, the appropriate selection of intubating adjunct, for device and airway, should be considered. Emphasising the importance of correct adjunct selection, in the aforementioned network meta-analysis, first-pass intubation success was markedly improved with use of the preformed (GlideRite) stylet for the GlideScope (Verathon Medical Inc., Bothell, WA, USA), relative to Macintosh DL, but worsened with two adjuncts not specifically designed for this device. ⁶

For an increasing number of anaesthetists and intensivists, VL is a routine part of airway management, and growing availability and familiarity with the range of devices means many practitioners have adopted a two-tiered approach, considering first whether VL is indicated, before deciding which specific device and adjunct should be used. Therefore, the evidence base should be further developed to reflect this increasingly complex area, considering both the patient and operator factors which influence this decision. This evidence should be developed with consideration given to the outcomes under investigation, as even seemingly highly related metrics, such as rate of first-pass intubation success and time to intubation, are subtly different, with conceivable situations where one is preferable to the other, and performance in these measures will dictate clinical selection. Furthermore, the emerging evidence will need to be placed in the context of its conduct, in the simulated or real airway, and in terms of VL experience of the operator. This approach should allow a fuller assessment of the optimal combination of device, adjunct, and patient, and enable an approach to VL that reflects traditional practice regarding consideration of the use of different laryngoscopes for DL.