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Version of Record online: 14 MAR 2011
Anaesthesia © 2011 The Association of Anaesthetists of Great Britain and Ireland
Volume 66, Issue 4, pages 316–317, April 2011
How to Cite
Teoh, W. H. L., Shah, M. K. and Sia, A. T. H. (2011), A reply. Anaesthesia, 66: 316–317. doi: 10.1111/j.1365-2044.2011.06686.x
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- Issue online: 14 MAR 2011
- Version of Record online: 14 MAR 2011
We thank Dr Mines and Ahmad for their interest in our study, and comments on our secondary outcome measures, namely the validity of comparative laryngeal views and use of external laryngeal pressure. They argue that the Cormack and Lehane views obtained through direct laryngoscopy with the Macintosh laryngoscope are not statistically comparable with laryngeal views obtained from videolaryngoscopes because the Pentax Airway Scope, C-MAC and Glidescope’s images are obtained from varying distances between the camera and the tip of the blade.
We would stress that ours was a clinical study comparing videolaryngoscopy performance in 400 patients, as manikins do not simulate intubation reliably . The primary outcome of our study was intubation time and the data were normally distributed when subjected to Kolmogorov–Smirnov testing, hence our results are both valid and significant. We found faster intubation times with the Airway Scope compared with the C-MAC and Glidescope. We included the Macintosh blade group as a control, and graded the laryngoscopic view on the first intubation attempt (without external laryngeal pressure), and found the intubation time with the Macintosh to be comparable with the Airway Scope in the hands of experienced anaesthetists, even with 58% grade-1 and five grade-3 laryngeal views encountered with the Macintosh, vs 97% grade-1 and zero grade-3 views with the Airway Scope.
A laryngeal grading system based on pure videolaryngoscopic views has yet to be defined. In general clinical practice, most clinicians would still use the Cormack and Lehane system  to grade laryngeal views and communicate intubation difficulty, despite alternative classifications (albeit still based on direct laryngoscopy techniques) that may be more discriminatory from a research viewpoint. In our discussion, we alluded to two of these. The percentage of glottic opening score  represents the portion of glottis seen, and is defined anteriorly by the anterior commissure and posteriorly by the interarytenoid notch. The intubation difficulty score  incorporates seven variables, including the Cormack and Lehane grade minus one.
In our study, the videolaryngoscope screen was placed in full view of the airway operator and assisting personnel at the head of the bed. Whether accidental or intentional, the effect of a higher intubation success from an assistant who can provide better directed external laryngeal pressure and coordinated assistance, from the ability to view the procedure, cannot be quantified from this study, and requires a different study design. Both the C-MAC and Glidescope have this shared viewing feature and yet had comparable intubation times with each other that were longer than those in the Macintosh group, despite 38 blind external laryngeal manipulations. This could be due to the study investigators’ having more than 10 years’ experience with direct laryngoscopy. We would emphasise that clinically, the improved view offered by videolaryngoscopy compared with conventional intubation techniques is more important for the intubator than the difference in the view for the assistant.
No external funding and no competing interests declared. Previously posted at the Anaesthesia Correspondence website: http://www.anaesthesiacorrespondence.com.