In a randomised clinical study, Buléon et al.1 showed that the Heine XP plastic single-use blade resulted in an increase in the intubation failure rate and a worse laryngeal view compared with the Heine metallic reusable blade and the Callisto metallic single-use blade. The power of this study is its use of a large sample, and the authors have controlled some factors that can significantly affect the laryngeal visualisation and tracheal intubation, such as patient's characteristics and upper airway anatomy, blade sizes and use of anaesthetic and neuromuscular blocking drugs.2,3 Additionally, the authors openly discuss the limitations of their work. However, we note other issues of this study making interpretation of their results questionable.
First, in the method section, the authors stated that the position of the patients’ head and neck during direct laryngoscopy was recorded after intubation. In the results section, these data are not provided and compared. Proper positioning of the head and neck (for example, sniffing position) is essential for optimal laryngeal visualisation during direct laryngoscopy and inadequate positioning may result in prolonged or failed tracheal intubation attempts because of the inability to visualise the larynx.4 Moreover, we do not feel that the authors clearly described whether they had achieved an optimal attempt at laryngoscopy when evaluating the laryngoscopic views obtained with the three blades.
Second, there was no mention of how many experienced anaesthesiology nurses or physicians participated in this study. Metallic reusable blades are devices that are frequently used for tracheal intubation. There are many single-use blades on the market and these differ greatly in their main characteristics, such as configuration, quality and robustness.5–8 Unfortunately, the authors did not explain whether there were significant differences in shape, length, angulation, rigidity, light intensity and brightness field among the three blades that were tested in their study. More importantly, it remained unclear whether all participants had used the plastic and metallic single-use blades in routine tracheal intubation before this study. Differently shaped blades may require different laryngoscopic techniques and may even result in difficulty in laryngoscopy and tracheal intubation performed by a novice user.5,8 Thus, we cannot exclude the possibility that different experiences and proficiency levels of participants with the three blades tested in this study attribute to the findings. Here, we would like to share the viewpoint of Behringer et al.9 that in a comparative intubation study, for the results to be valid, participants must be equally proficient with each tested device in order to avoid bias.
Third, sample size was selected to detect a difference of 3% in the rate of intubation failure between the metallic reusable and the single-use blade groups and the plastic single-use blade group. However, of 1863 eligible patients, 190 (10.2%) were excluded from the final analysis because of missing data. The authors did not explain whether these excluded patients were equally distributed among the three study groups. A significantly higher rate of missing data in any group may have biased the final analysis of the results.
Fourth, the intubation difficulty scale (IDS) is the sum of the seven parameters associated with the intubation effort. An IDS score 1 to 5 indicates slight intubation difficulty and an IDS score more than 5 indicates moderate to major intubation difficulty.10 In this study, a notably higher IDS score in the plastic single-use blade group was mainly due to a higher number of patients with IDS scores 1 to 5 in the plastic single-use blade group compared with the metallic reusable and single-use blade groups. In clinical practice, intubation difficulty with IDS scores 1 to 5 should not be a problem for experienced anaesthesiologists. Adnet et al.10 demonstrated that when IDS was 5 or less, intubation time did not vary significantly. When IDS was more than 5, however, intubation time increased rapidly in relation to the score.10 As a result, an IDS score of more than 5 is often defined as difficult intubation and used as the primary outcome of a comparative study.8,11 In the study by Buléon et al.,1 the incidence of an IDS score of more than 5 did not significantly differ between the study groups.
Finally, apart from the blade types, interaction of many other factors can also affect the ease of laryngoscopy and success rate of tracheal intubation.3,4 Thus, we feel that the study by Buléon et al.1 does not provide high-level evidence to support the conclusion that the plastic single-use blade is less efficient than the metallic reusable and single-use blades.
Acknowledgements relating to this article
Assistance with the letter: none.
Financial support and sponsorship: none.
Conflicts of interest: none.
Comment from the editor: Dr Buléon and colleagues did not wish to respond to this letter.
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