Evaluation of intubating adjuncts to videolaryngoscopy in a simulated difficult airway: A manikin cross-over study

The use of videolaryngoscopy has increased significantly in recent years, supported by evidence of reduced failure and less airway trauma. ¹ This has also followed advice from the Difficult Airway Society (DAS) that videolaryngoscopes should be immediately available and that all anaesthetists should be trained in their use. ² However, the improvement in the view of the glottis, usually achieved with videolaryngoscopy, does not always correlate with easier intubation, as significant curves in the airway still need to be negotiated in order to place an endotracheal tube. In this situation an intubating introducer is often used, although many factors will influence which introducer is most useful for facilitating intubation. Most introducers tend to be straight or can be moulded to some extent to the curves of the airway or the laryngoscope blade, but usually this curvature cannot be altered during the intubation attempt. However, Brunckhorst and colleagues evaluated a novel bougie designed with a flexible tip to help steer the introducer around the curves of the airway. ³ This flexible tip bougie has further been found to be useful in negotiating the curves of the airway via the nasal route in patients undergoing maxillofacial surgery. ⁴ We aimed to evaluate intubator performance with three different adjuncts to intubation with a videolaryngoscope: a Frova intubating introducer (Cook Medical, Bloomington, IN, USA); the flexible tip bougie (Construct Medical, Melbourne, Victoria, Australia); and a flexible bronchoscope (Ambu aScope, Ballerup, Denmark), used without the video screen. The latter two of these devices are able to be steered by the intubator during the intubation attempt. Our null hypothesis was that all techniques were equivalent in their efficacy to achieve intubation.

We recruited 56 anaesthetists from our departments with a wide range of experience. The project was registered with our hospital research departments and was exempt from ethics committee approval as participation in the study was voluntary, no patients were involved, and performance of volunteers was not assessed. All participants had five minutes to familiarise themselves with the manikin setup and intubating equipment and had received written information prior to attending. The manikin was a Trucorp AirSim (Trucorp, Lurgan, N. Ireland) with tongue inflated, the neck fixed in the neutral position and the larynx displaced anteriorly and was standardised for each intubation attempt, with a percentage of glottis opening (POGO) score of 0% on direct laryngoscopy confirmed for each participant. Participants were tasked to intubate with an APA videolaryngoscope (AAM Healthcare, Venner Group, Singapore), using the unchanneled hyperangulated airway blade with each of the intubating adjuncts in turn. One attempt was allowed with each adjunct and there was no upper limit to the time allowed. Participants were randomly assigned using a random number generator to the order in which they used the adjuncts. The same assistant was present for all attempts, and for intubations with the flexible bronchoscope held the videolaryngoscope as this is a two-person technique. The primary outcome was time to intubation, defined as time from the tip of the laryngoscope passing the lips to the first inflation breath. Secondary outcomes were time to insert introducer once a view of the glottis was achieved and user ease of use. Results are described as median (interquartile range) and groups were compared using a Wilcoxon signed rank test.

The experience of participants ranged from novice to 38 years, median 10 (4.75–18). The time to intubation was 33.2 (27.9–41.9) versus 34.9 (30.5–45.2) versus 44.8 (35.4–57.5) seconds with the Frova introducer, flexible tip bougie and flexible bronchoscope, respectively, with participants’ performance with the latter being significantly slower when compared to the Frova or flexible tip bougie (P < 0.05). The times to insert the introducer once the glottis had been visualised were, respectively, 15.4 (12.2–19.9) versus 18.2 (14.7–25.5) versus 27.4 (22.2–36.5) seconds with no statistically significant difference between the groups. Participants’ rating of ease of use for each of the introducers was on a scale of 0–100, 80 (68.5–91.8) versus 82 (66.5–90) versus 75.5 (61.0–90.0) for the Frova introducer, flexible tip bougie and flexible bronchoscope, respectively.

Our results show that, overall, our participants’ times to perform intubation with the three techniques were similar, although times with both the Frova introducer and the flexible tip bougie were significantly faster than with the flexible bronchoscope. One explanation for this might be that using the flexible bronchoscope with a videolaryngoscope in this manner requires two airway operators and this coordination is technically more difficult, in order to achieve a good view of the glottis and manipulate the scope under videolaryngoscope guidance simultaneously, to facilitate intubation. The times to intubation with the Frova introducer and flexible tip bougie were similar, despite our participants having significantly less experience with the flexible tip bougie, which is relatively new to the market and not widely available. The flexible tip bougie was also deemed to be the easiest technique to use by our participants, despite being an unfamiliar technique, although overall the quantitative scores for the three techniques were similar. Qualitative comments provided by our participants at the time of data collection also highlighted the benefit of being able to control the tip of the introducer during the intubation attempt. The main limitation of this study is that it is a manikin study and it would be useful to perform further evaluation in a clinical context with patients in whom difficult airway management is known or predicted to be difficult. Our results can also only be applied to the APA videolaryngoscope with a hyperangulated blade, and it would be useful to evaluate these introducers in conjunction with other types of videolaryngoscope. In addition, we acknowledge that the technique of using a flexible bronchoscope as a bougie that can be steered towards the glottis under guidance from a videolaryngoscope was not only significantly different to the other two techniques, but also one our participants were likely to be unfamiliar with. However, this technique is described in the literature as both a planned airway strategy ⁵ and also as a rescue technique when the option of an asleep fibreoptic intubation is not available. ⁶

We have shown that, overall, our participants’ performance with the three introducers was similar, despite them having very little experience with the techniques requiring control of the introducer tip during the intubation attempt. Their feedback also suggests some benefit of an introducer that can be steered by the operator when using a videolaryngoscope to facilitate endotracheal intubation. Further clinical evaluation would now be beneficial in patients with either predicted or known difficult airway management requiring intubation.