Hyperangulated video laryngoscopes have blade shapes with a curvature more acute than a standard Macintosh blade. Commercial products include the GlideScope, Storz D-Blade, and McGrath X blade. In the course of teaching use of these devices, I have often been told, “I had a great view but had trouble delivering the tube.”
Hyperangulated blades look around the curvature of the tongue very well, but their perspective on the larynx, looking upward at it from the base of the tongue, can lead to difficulty in tube delivery. If the blade is inserted too deeply, the video-imaging element gets very close to the larynx, and the view will be great, but the angle of approach is consequently very extreme. This creates difficulty with tube delivery through three mechanisms. First, it steepens the up angle to the larynx; second, it shortens the tube delivery area (distance from blade tip to larynx); and third, it reduces the area on the screen for observing tube delivery. Operators must be careful that they look in the mouth when inserting a hyperangulated stylet, then carefully observe it coming into view on the monitor. Jamming a rigid hyperangulated stylet into the posterior pharynx (off screen) can cause injury to the soft palate, tonsils, or hypopharynx.
George Kovacs, MD, MHPE, an emergency physician from Halifax, Nova Scotia, and director of the Airway Interventions & Management in Emergencies (AIME) courses, recently showed me a simple way to determine if the angle of approach using a hyperangulated blade is excessive. I have labeled this “Kovacs’ sign” and now incorporate it into my instruction with hyperangulated blades (see Figures 1 and 2). If the blade is overinserted, the cricoid ring becomes visible between the vocal cords. This indicates a very steep angle of approach and will likely make tube introduction difficult. Conversely, when the angle of approach is not so steep, the cricoid ring is not seen, there is more room between the blade tip and the larynx, and there will be more space on the inferior aspect of the monitor to observe tube delivery.