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Ninewells Hospital, Dundee, UK South Cleveland Hospital, Middlesbrough, UK
To the Editor:
We read with great interest the article analyzing laryngeal exposure with the articulating laryngoscope and external laryngeal manipulation (1). There are several points that we would like to raise concerning the article.
All the laryngoscopies in the study were performed in the same sequence by one laryngoscopist. The laryngeal views, although recorded, were also scored by the same laryngoscopist. This makes the study entirely unblinded for the laryngoscopist who is also an author.
The author and laryngoscopist in the study has previously published research on the McCoy laryngoscope and the percentage of glottic opening (POGO) scoring system. This work has suggested that the line of sight for the laryngoscopist may be worsened while using the articulating laryngoscope (2). This clearly introduces a possibility of bias against the levering laryngoscope.
To determine the POGO score, the laryngeal view was objectively recorded with a head-mounted imaging system. However, there was no suggestion that the POGO score was determined by objective measurement. It would seem that scoring was actually a subjective estimation of the percentage of glottic opening. Although the authors had previously found good intra- and interobserver reliability (3), this may not be equivalent to good accuracy. If 100% of the glottis is not visualized initially, we wonder how accurate the POGO scores can be. The subjective measuring of changes as small as 1% may not be entirely accurate either, and a predetermined change of 5%–10% may have been more reliable. The articulating laryngoscope was found to worsen the POGO scores ranging from 1% to 76%. We feel that it would be more meaningful to have some information on the spread of results within this range, as this may change the interpretation of the findings. We also feel that the recorded images may have been objectively measured to provide more accurate data.
Although the Cormack-Lehane grading system was intended as a teaching tool in obstetric anesthesia (4), it has become an everyday grading system (5). It is accepted that the original grading system lacks sensitivity (5), and we feel that the POGO score may address some of these weaknesses. We would encourage further research to assess the effectiveness of the POGO score in everyday clinical practice.
The authors suggested that "prior laryngoscopy studies have been limited by poor methodology" (1) and we feel this study may have fallen into the same trap. It would be of great interest to have the results from an amended study that has rectified the limitations of this study. Can we also suggest a fourth recording of "blade activated with external laryngeal manipulation" to add completeness to a future larger study?
References
Department of Emergency Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA
In Response:
Drs. Stewart and Kessel have correctly noted some of the limitations of our study, specifically, the lack of blinding, the use of only one laryngoscopist, and the same sequence of testing. We had acknowledged these issues within our article. Of note, no laryngoscopy study on laryngeal view has ever been blinded. Although the imaging (recording) would have allowed this, our prior work on POGO scores suggested this was unnecessary and would not have affected the outcome because POGO scores have such strong interrater reliability (1,2). This study of the McCoy blade is the first study of this (or any) blade in which imaging was used to record the view, and then in systematic fashion review the videotaped images. All prior studies have depended on the momentary evaluation of the view by the laryngoscopist (neither blinded nor imaged).
Stewart and Kessel also raise the question of "accuracy" of POGO scores. This is a confusing concept because there is no gold standard measurement of laryngeal view to which POGO scores could be compared to determine accuracy. POGO scoring is designed to assess laryngeal view in a quantifiable fashion. Compared with Cormack-Lehane grading, POGO scoring has greater interrater agreement (1,2). In terms of the "significance" of the POGO scores and how much difference in POGO scores is meaningful, we agree that small changes might have no clinical significance. Our preliminary data suggests that differences of approximately 20%–25% result in incremental increases in the number of laryngoscopies needed for intubation (3). In our McCoy study, the mean differences of POGO scores with laryngeal manipulation and McCoy activation exceeded this value. Specifically, among the 16/33 patients in whom POGO score worsened with McCoy activation, the mean decrease was 38%.
Stewart and Kessel also suggest that we could have measured the laryngeal views recorded on videotape. Theoretically this would be advantageous because it would eliminate the estimation of POGO scoring. From a practical perspective, this would require using a fixed distance of laryngoscopy because the distance from the camera to the larynx would determine the size of the recorded image. Also, because of the variability of laryngeal apertures among patients, each patient would have to serve as their own control and measurements between patients could not be directly compared. Finally, it is uncertain how such measurement would be done. Should the maximal length of the laryngeal aperture be used, or some quantification of the area? In our 7 yr of experience with video imaging of laryngoscopy, cumulatively involving thousands of patients, the variability in laryngeal views recorded on videotape would make any standardized measurement impractical if not impossible. Even if achievable, we doubt such detailed measurement would have any clinical significance or practical advantage over POGO scoring.
Although POGO scoring of a laryngeal view in which the full larynx is not seen seems an awkward and "inaccurate" method, we have found it is actually easily understood and applied by a variety of laryngoscopists. We believe it is the best way of quantifying video images of laryngoscopy and strongly believe that imaging should become a standard part of laryngoscopy research.
References
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