A grading system for direct laryngoscopy

We have followed with interest the recent article by Dr Yentis and Lee [1] and subsequent letter by Dr Cook [2] on laryngeal grading. As each of these authors point out, the Cormack and Lehane grading system has numerous problems; grades are ambiguous between grades 1 and 2, and these grades apply to 95–99% of laryngeal views. Dr Cook correctly explained in his letter the ambiguity of the original definitions and discordance between the drawings and descriptions of grades in the original articles [3, 4]. Cohen et al. have pointed out the confusion amongst British anaesthetists at correctly defining Cormack/Lehane (CL) grades [5]. Not only is there ambiguity between grades 1 and 2, but there is also ambiguity within these grades. Benumof, for example, has noted that a grade 1 view includes anywhere from 1 to 100% visualisation of the vocal cords [6]. Numerous authors, including Drs Yentis and Lee, have attempted to subcategorise grades 1 and 2 [1, 7–9]. We believe there is a more critical deficiency with CL grading and modifications of CL grading as proposed by Drs Yentis and Lee. The visual restrictions inherent to laryngoscopy cause laryngeal sighting to occur with only one eye [10]. Therefore, two people cannot simultaneously sight the same laryngeal view. CL grading has never been validated between observers. Historically, no studies have addressed whether two people seeing the same laryngeal view simultaneously agree with the assignment of CL grades. In the process of testing an imaging system for direct laryngoscopy, we discovered that CL grading was inadequate at categorising the laryngeal images we obtained [11]. As with prior studies, we found that almost all views fell into grades 1 or 2, and distinguishing between these grades was difficult. To better describe the laryngeal views recorded with the imaging system we devised the percentage of glottic opening (POGO) score [12]. The POGO score represents the percentage of glottic opening seen, defined by the linear span from the anterior commisure to the interarytenoid notch (Fig. 1). A 100% POGO score is a full view of the glottis from the anterior commisure to the interarytenoid notch. A POGO score of 0 means that even the interarytenoid notch is not seen. The POGO score replaces CL grades 1 and 2 with a continuous numerical value. Unlike CL grading, POGO score is not dependent upon visualisation of the vocal cords. We have found that shadowing by the epiglottis frequently causes the vocal cords to be poorly visualised even though the glottic opening is clearly delineated. The descriptive nature of the POGO score is easily understood with minimal explanation, and does not require memorisation of numerical and alphabetical categories. The percentage of glottic opening (POGO) score for laryngeal grading. The POGO score represents the linear span from the anterior commissure to the interartytenoid notch. We have recently conducted two studies on the validity of POGO scoring as compared with CL grading [12, 13]. The participants, anaesthetists and emergency physicians, were asked to grade laryngeal views obtained with the imaging system using both CL grades and POGO scoring. We measured both intra- and inter-observer reliability. CL grading and POGO scoring were found to have good intrareliability. Between observers, however, there was very poor agreement with CL grading and very good agreement with POGO scoring. POGO scoring does not distinguish between CL grades 3 (epiglottis) and 4 (tongue) views, as each would have a score of 0. This could be addressed descriptively, however. We are currently assessing the correlation between POGO scores and ease of intubation, as well as evaluating POGO scoring using dynamic images of laryngoscopy. Although further studies are needed, POGO scoring has numerous advantages over CL grading for laryngoscopy research and clinical application. It is a validated, continuous numerical method that is more sensitive than CL grading, and easy for all to understand and apply.