A two-dimensional model of anatomic relationships during laryngoscopy.

Abstract

The view obtained during direct laryngoscopy is only seen by a single anesthesiologist. The inability of instructors to observe the view poses problems for teaching the technique. The anatomic interactions affecting laryngoscopy are largely internal, hampering efforts to understand why some patients are unexpectedly difficult to intubate. In response, we have constructed a full scale, adjustable, two-dimensional model showing the head and neck in the sagittal plane. In this article, we validate the mannequin and test how various conditions or changes in equipment affect the laryngoscopic view. Model parameters were compared with literature values. Glottic exposure was evaluated over a range of jaw lengths and interincisor gaps for Macintosh 3, Miller 2, and Macintosh 4 blades. Thirty segmental airway distances and 10 angles were within 1 standard deviation from published values. Spine and jaw mobilities approximated normal range of motion. Glottic exposure decreased steeply for mouth openings below a threshold. A larger mouth opening was required to obtain a view when the mandible was short. None of the blades exposed the glottis when mouth opening was narrow, 2.4 cm. The Macintosh 4 blade was closest to success, within 7 mm of viewing the posterior cords. The model reflects an average 16-yr-old male patient in size, proportion, and mobility. It can be used to explicate how anatomic relationships affect laryngoscopy. An objective assessment is necessary to determine the model's utility for teaching and as a tool for researching the mechanisms responsible for laryngoscopic difficulty.