Rational Design of End-Points to Evaluate Performance of the C-MAC D-Blade Videolaryngoscope During Routine and Difficult Intubation

Abstract

To the Editor Regarding the evaluation by Cavus et al.1 of the C-MAC D-blade videolaryngoscope (C-MAC D) during routine and difficult intubation, in addition to the limitations described in the discussion, we note other issues that make interpretation of the performance of C-MAC D questionable. First, the difference of laryngoscopic views (using the modified Cormack–Lehane [C-L] classification) between the C-MAC D and Macintosh laryngoscope (MLS) was stated as the final end point of performance. However, Cormack and Lehane2 proposed their classification of laryngoscopic views during laryngoscopy using a Macintosh blade, which requires alignment of the oral, pharyngeal, and laryngeal axes. In contrast, the C-MAC D does not require alignment of the oral, pharyngeal, and tracheal axes, because the laryngoscopic view is obtained from a camera positioned at approximately 3.5 cm from the blade tip. Also, it was not clear whether an optimal/best attempt at direct laryngoscopy had been required when assessing the laryngoscopic view with the MLS. We are concerned that only comparing the change of the laryngoscopic views may bias the results towards the C-MAC D, and lack of a requirement for an optimal/best attempt at direct laryngoscopy may have underestimated performance using the Macintosh blade. Second, the study also evaluated performance of the C-MAC D used as a rescue device when direct laryngoscopy failed. However, the authors did not provide a clear definition of failed laryngoscopy. In other words, was failed laryngoscopy defined as a C-L grade 3 or 4 laryngoscopic view with the first attempt using a MLS? If so, for an experienced anesthesiologist, although it may be difficult to obtain a good laryngoscopic view during direct laryngoscopy, it is usually possible to insert the endotracheal tube when this laryngoscopic view is present.3 Furthermore, an important feature of direct laryngoscopy is that it provides a complete view enabling use of a gum elastic bougie. Previous studies have shown that the tracheas of >90% of patients with a C-L grade 3 and 4 laryngoscopic views can be successfully intubated using a direct laryngoscope with or without a gum elastic bougie at first or second attempt.4,5 In contrast, in this study, 30% of patients with a C-L grade 3 and 4 laryngoscopic views (6 of 20) required more than 1 attempt to achieve successful intubation with the C-MAC D under a good laryngoscopic view. Therefore, without comparing data regarding number of intubation attempts, intubation time, success rate, and complications of intubation using the C-MAC D with the standard airway device such as the MLS, we believe that any exact conclusion regarding performance of C-MAC D in routine and difficult intubation may be not justified.6 Finally, and as acknowledged, one of the authors serves on the advisory board of the sponsor manufacturer of the C-MAC D, raising a possibility, albeit unintended, of bias in performance of the study. Fu S. Xue, MD Xu Liao, MD Yu J. Yuan, MD Qiang Wang, MD Department of Anesthesiology Plastic Surgery Hospital Chinese Academy of Medical Sciences and Peking Union Medical College Beijing, People's Republic of China [email protected]