The comparative study of video laryngoscopes to the Macintosh laryngoscope

defining proficiency is critical

Editor,

We read with interest the report by Frohlich et al.¹ comparing the McGrath Series 5 Video Laryngoscope with the Macintosh direct laryngoscope. The role of various video laryngoscopes remains controversial. Unfortunately, much of the current literature pertaining to video laryngoscopy consists of case reports, mannequin studies or poorly designed clinical evaluations. Despite widespread enthusiasm for video laryngoscopy in routine and difficult airway management over the last decade, to date the scientific literature has imprecisely defined the role of these devices compared with traditional line of sight laryngoscopes. It is naive to assume that the negative findings of a published study lie entirely in the quality or utility of the new device, especially when compared with a device that has been the standard of practice for several decades. However, such comparative studies are critical in establishing the role of any new device or airway management technique. We must be cautious about drawing erroneous conclusions from inadequately rigorous studies.

The design of the study by Frohlich et al. merits comment. Did the authors do a power analysis in order to calculate their sample size of 60 patients? Ten anaesthetists were involved in a 60-patient study. Although the authors state that all of the anaesthetists participating in the study had prior experience with use of the McGrath Video Laryngoscope, they did not provide details concerning the nature of instruction provided to the study anaesthetists. Did the prior experience involve mannequins or patients with normal or difficult airways? More importantly, did the authors seek to define proficiency with the use of the McGrath Series 5 Video Laryngoscope prior to initiation of the study? If acceptable proficiency with a new device is not defined and confirmed prior to the initiation of a comparative study, then the conclusions of the study merely suggest that the peak of the learning curve of the McGrath has not been attained by many of the study anaesthetists.

The question of proficiency has been defined for other devices. Mulcaster et al.² performed a longitudinal study of traditional laryngoscopic intubation by novices in the operating room with 438 direct laryngoscopic intubations by 20 non-anaesthetist trainees, monitored by observation and video analysis. Using a general linear mixed-modelling approach, the number of direct laryngoscopic intubations required for the novices to acquire expertise was estimated. Statistical modelling suggested that a 90% probability of a ‘good intubation’ required 47 attempts. Proper insertion of the direct laryngoscope blade and proper lifting were critical to competency. The study by Mulcaster et al. concluded that teaching direct laryngoscopy using a mannequin model alone was inadequate for the training of non-anaesthesia personnel. The study urged a re-evaluation of training and competency in advanced airway management.

Competency with the various video laryngoscopic devices is not well defined. Confounding factors include laryngoscopists inexperience with either or both the reference or the new technique, or peculiarities of the specific device or device type [channelled, non-channelled, angulated (e.g. McGrath Series 5, GlideScope) or non-angulated (e.g. Story C-MAC, GlideScope Direct, McGrath Mac)]. Although we may not have a precise definition of competency, the failure rate of 12 out of 30 intubations (40%) in the study by Frohlich et al.¹ points strongly to a problem with the way in which the device was used. Other investigators, using the same device, had a much higher success rate for the first attempt at intubation.^3,4

The study by Frohlich et al. did not elucidate the manner of patient selection or the use of inclusion or exclusion criteria for their study. The authors did not define the airway characteristics of patients in each group. If the airways characteristics between the McGrath and Macintosh groups were not matched, this might influence the results.

Mihai et al.⁵ published a quantitative review and meta-analysis of a variety of studies on the efficacy of nonstandard laryngoscopes and rigid fibreoptic intubation aids. The systematic review revealed that much of the literature on that point was inconclusive. They hoped to summarise the available data in order allow a comparison of device performance in similar clinical settings, but found that most of the data are derived from normal patients with little reference to those with a known difficult airway. Their review confirmed that studies comparing the newer video laryngoscopes with the Macintosh direct laryngoscope are few and inadequate in design. Mihai et al. concluded that the new field of video laryngoscopy mandates re-evaluation of the research process involving airway management

Frerk and Lee⁶ argued that the introduction of a new laryngoscopic technique should be supported by evidence indicating superiority over the existing standard. They proposed a systematic process similar to that of new drug development, beginning with preclinical trials on animals (or mannequins) and progressing through specific patient populations, randomised controlled trials and phase 4 surveillance studies.

The study design by Frohlich et al. does not adequately address the question of the utility of the McGrath Series 5 Video Laryngoscope when compared with the Macintosh direct laryngoscope. It does serve to underscore the need for adequate training with the test device, clearer patient selection and characterisation, relevant clinical outcomes, definitions of learning and competency with video laryngoscopic devices. It also serves as a reminder of the need for more precise and organised study design in the field of airway management.

Acknowledgements

The authors have not received any financial support or sponsorship in the preparation of this article.

The authors would like to acknowledge the following potential conflicts of interest: E.C.B., S.L. and I.P.O. have served on the Speakers Bureau for Aircraft Medical (Edinburgh, Scotland, UK); R.M.C. is on the Speakers Bureau for Venation Medical (Bothell, Washington, USA).

Note from the Editors: Frolich et al. did not reply to our invitation to comment on this letter.