Analysis of the forces and position required for direct laryngoscopic exposure of the anterior vocal folds

The sniffing position is traditionally considered optimal for direct laryng oscopic examination of the Vocal folds. This study examined head and neck p ositions associated with ideal exposure of the anterior glottal commissure with a variety of laryngoscopes. A prospective investigation was done in 20 patients by comparing the force required to expose the anterior vocal fold s by utilizing 3 head and neck positions with 3 different-sized tubular lar yngoscopes. The completeness of anterior glottal exposure was rated and the force required to achieve this exposure was measured with a strain gauge. Three positions relating the atlanto-occipital and cervicothoracic vertebra e were analyzed: 1) extension-extension, 2) sniffing: extension-flexion, an d 3) flexion-flexion. Head and neck position and laryngoscope size were bot h statistically significant factors for achieving complete anterior vocal f old exposure. Regardless of the laryngoscope, the number of patients in who m complete exposure could be achieved increased gradually when the position was changed from extension-extension to extension-flexion to flexion-flexi on. Complete exposure was inversely related to larger laryngoscope size. Ac cording to the data herein, the flexion-flexion position provides the best glottal exposure for endotracheal intubation in those patients who are anat omically predisposed to difficulty in direct examination of the glottis. Be cause this places the laryngoscope lumen in a vertical position, this posit ion is inappropriate for microlaryngoscopy. The study reinforced the concep t that the sniffing position is the optimal position for microlaryngoscopy because it enables the use of the largest-lumened laryngoscope. This facili tates ideal exposure of the anterior vocal folds, which is necessary for ph onomicrosurgery.