Comparing Emergency Intubation with Direct and Video Laryngoscopy

To the Editor: In a randomized controlled trial comparing direct versus video laryngoscopy using the C-MAC videolaryngoscope for tracheal intubation in the emergency department, Driver et al.1 showed that when direct laryngoscopy was planned for the first attempt, video laryngoscopy did not provide superior efficacy to direct laryngoscopy with respect to the success rate of first attempt and duration of intubation attempt. This is first clinical study comparing intubation performance of direct versus video laryngoscopy using the randomized controlled trial, which is the criterion standard for evaluation of any intervention. The authors had attempt to control most of the known factors affecting the emergency intubation, such as reasons for intubation, potential difficult airway, uses of anesthetics and neuromuscular blocking drugs, etc. Other than the limitations described in the discussion, however, there are several issues of this study that need to be clarified. First, the readers were not provided with the type of C-MAC blade used in this study. There are the commercially disposable plastic and reusable metal blades available. The reusable version is a Macintosh-type metal blade, whereas the disposable version is a plastic blade with marked thickening of both the web and flange sections. The marked thickness of disposable plastic blade can significantly reduce the workable pharyngeal space and pharyngeal view, making manipulation and passage of the tracheal tube difficult.2 Second, the authors did not specify the intubation procedures. We noted that more than 70% of intubation needed the aid of a tracheal tube introducer in this study. Furthermore, mean duration of first attempt was about 60 seconds. It was unclear whether or not the tracheal tube was used with a stylet at first attempt. Regardless of direct or video laryngoscopy for emergency intubation, the use of a stylet is actually valuable in controlling the direction of passage of a tracheal tube. By providing increased rigidity and malleability, it allows more control of the tracheal tube, especially when tracheal intubation is performed with video laryngoscopy. It has been shown that use of the stylet can significantly reduce the intubation difficulty with the C-MAC videolaryngoscope, especially for patients with difficult airways.3 Furthermore, distal angle of the stylet can significantly affect the intubation performance of C-MAC videolaryngoscope.4 It is generally believed that, when speed of intubation is important (as in emergent patients), a tracheal tube should always be equipped with a stylet. Third, when reporting the proficiency level of investigators with the tested devices, only providing postgraduate years is not enough because a different learning curve is required for intubation with direct and video laryngoscopy. It has been shown that the learning curve of direct laryngoscopy is quite fat; anesthesia residents in controlled environments cannot increase their intubation success rate to 90% until they have performed the procedure on 57 patients.5 However, the C-MAC videolaryngoscope has a rapid learning curve; anesthesiologists without previous experience with the C-MAC videolaryngoscope can achieve a 99.6% intubation success rate in patients with normal and difficult airways.6 Moreover, the available literature provides compelling evidence that video laryngoscopy is associated with higher intubation success rate and faster intubation time only for inexperienced operators, but provides no benefit in either of these outcomes with experienced operators.7 Here, we would like to echo Behringer and Kristensen8 that for the results of a comparative study to be valid, the investigators performing intubation must be equally proficient with tested devices to avoid bias. We are concerned that the different proficiency levels of investigators with the intubation using direct and video laryngoscopy would have confounded interpretation of their results. We argue that addressing the above issues would further clarify the transparency of this study and improve interpretation of study results.