Analysis of the Forces and Position Required for Direct Laryngoscopic Exposure of the Anterior Vocal Folds

Abstract

The sniffing position is traditionally considered optimal for direct laryngoscopic examination of the vocal folds. This study examined head and neck positions 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 folds by utilizing 3 head and neck positions with 3 different-sized tubular laryngoscopes. 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 vertebrae were analyzed: 1) extension-extension. 2) sniffing: extension-flexion, and 3) flexion-flexion. Head and neck position and laryngoscope size were both statistically significant factors for achieving complete anterior vocal fold exposure. Regardless of the laryngoscope, the number of patients in whom complete exposure could be achieved increased gradually when the position was changed from extension-extension to extension-flexion to flexion-flexion. Complete exposure was inversely related to larger laryngoscope size. According to the data herein, the flexion-flexion position provides the best glottal exposure for endotracheal intubation in those patients who are anatomically predisposed to difficulty in direct examination of the glottis. Because this places the laryngoscope lumen in a vertical position, this position is inappropriate for microlaryngoscopy. The study reinforced the concept that the sniffing position is the optimal position for microlaryngoscopy because it enables the use of the largest-lumened laryngoscope. This facilitates ideal exposure of the anterior vocal folds, which is necessary for phonomicrosurgery.

Preoperative clinical predictors of difficult laryngeal exposure for microlaryngoscopy: The laryngoscore

“…In group B (n 5 156), 78 (50%) patients were in class 0 (median score, 3; range, 0-9), 41 (26%) patients were in class I (median score, 3; range, 0-8), 18 (12%) patients were in class II (median score, 5; range, 3-11), 13 (8%) patients were in class III (median score, 6; range, 3-11), and six (4%) patients were in class IV (median score, 7; range, [3][4][5][6][7][8][9][10]. No statistically significant difference was observed in the distribution of patients among different classes between the two institutions.…”

“…In fact, if the entire glottis is not appropriately visualized through direct laryngoscopy due to suboptimal laryngeal exposure, misdiagnosis, incomplete resection, or inadvertent injury to teeth and pharyngolaryngeal soft tissues can be easily encountered. 7 Moreover, the preoperative assessment of adequate laryngeal exposure is of paramount value both in benign and preneoplastic/neoplastic conditions. In routine phonosurgical procedures, for example, DLE should prompt the novice to seek the assistance of more expert colleagues.…”

Laryngoscopy — its past and future

“…Czermak (1858) used this same position for indirect mirror laryngoscopy and Kirstein, 30 years later used it for DL. 11 It was Chevalier Jackson who used the sniffing posture in the recumbent patient (1913), elevating the head and extending the neck while using his left hand to hold the laryngoscope and his right hand to perform surgery. Killian devised a suspension laryngoscope, which freed up the operator's hands to perform surgery, however, it placed the patient in a position of extensionextension.…”

Myths and Realities: The “Difficult Airway” and Alternative Airway Devices in the Emergency Setting

“…3 Exaggerated head elevation with neck flexion permits better laryngeal exposure with less force. 4 Decades after Jackson and others pioneered laryngology, advancements in general anesthesia led to the formation of anesthesiology as a medical specialty and tracheal intubation became commonly performed. While tube-shaped laryngoscopes continued to be used by laryngeal surgeons, new designs were developed specifically for the placement of rubber breathing tubes.…”

“…Examples include external laryngeal manipulation (by the laryngoscopist's right hand), increasing head elevation (if not contraindicated), and effective use of straight blades (paraglossal placement fully to the right of the tongue). [2][3][4]20 Simple laryngoscopy adjuncts, such as the gum elastic bougie and the lighted stylet, also deserve our attention. Nasal intubation and surgical airways, despite their decreasing frequency in EDs, remain lifesaving procedures.…”