Rational comparison of tracheal intubation with direct and indirect laryngoscopes in a simulated trapped manikin

Abstract

Editor, In a randomised controlled crossover trial on an airway manikin simulating a trapped patient, Wetsch et al.1 found that none of five indirect laryngoscopes, including the Glidescope Ranger video laryngoscope, Storz C-MAC video laryngoscope, Pentax AWS, Airtraq optical laryngoscope and McGrath Series 5 video laryngoscope outperformed the Macintosh laryngoscope for emergency intubation. In our view, however, there are several aspects of this study that need to be clarified. The design of this study merits comment. We noted that all participants were anaesthetists with extensive experience of intubation with a Macintosh laryngoscope in the operating room and in emergency conditions; 80% of them were also board certified as emergency physicians, and 44% were currently active as emergency physicians responding to calls at the scene of emergencies. According to the participants’ demographics, we concluded that all participants had managed difficult airways caused by various factors and achieved proficiency with intubation using a Macintosh laryngoscope in the different conditions. However, the authors should have further specified whether some of the participants had performed emergency intubations with a Macintosh laryngoscope in a truly trapped patient during first aid. In this study, it was also unclear why practising intubation with the tested devices on the simulated difficult airway scenario was not allowed prior to the study, although all the participants had almost no clinical experience with any of the five indirect laryngoscopes. Previous studies on patients or airway manikins with normal and difficult airways have shown that a learning curve is indeed required for any of the indirect laryngoscopes, although it is rapid and steep.2–4 Actually, experience and competence with any of the new airway devices are critical for their successful use, especially when there is a difficult airway.5 Before the initiation of this study, therefore, the authors should have attempted to define proficiency with the uses of the different laryngoscopes for intubation on the simulated difficult airway scenarios. In this respect, we completely agree with Behringer and Kristensen5 that for the results of a comparative airway management study to be valid, participants must be equally proficient with each airway device to avoid bias. Because all participants were experienced with direct laryngoscope but inexperienced with indirect laryngoscopes, the results of this study may be biased against indirect laryngoscopy. This may account for the main finding that indirect laryngoscopes did not outperform the direct laryngoscope for emergency intubation. That is, the conclusion of this study may only suggest that the peak of the learning curve of each indirect laryngoscope has not been achieved by all study participants.6 One reason is that, as with any airway device, experience and skill must be obtained before using an indirect laryngoscope. Special training for the device is not only needed, but also practising intubation with the device should be undertaken on patients with a normal airway before using it for more difficult airways. It is worth mentioning that most airway devices require a learning curve of around 20 to 30 attempts for acquisition of reasonable competency, but performance continues to improve even after 100 cases.7 An additional issue raised by this article1 is that the Airtraq was defined as a video laryngoscope. In fact, it is an optical laryngoscope that utilises mirrors and lenses to visualise the glottis through a curved optical channel that mimics the anatomical airway.8 The image is transmitted to a proximal viewfinder which allows the operator to visualise the larynx and the intubation.9 If a proprietary Airtraq video camera adaptor is attached to the proximal viewfinder for viewing the larynx and the intubation on a video monitor, it functions as a video laryngoscope with a remote screen. A manikin study shows that attachment of a video camera system can improve the ease of intubation with the Airtraq during chest compression.10 In the literature, both the optical and video laryngoscopes are often designated as indirect laryngoscopes because they achieve laryngeal exposure through indirect imaging, using video cameras or a series of mirrors and prisms.11 Acknowledgements Assistance with the study: none declared. Sources of funding: None of the authors had any financial support. Conflicts of interest: None of the authors has a potential conflict of interest concerning this letter.