Head extension angle required for direct laryngoscopy with the McCoy laryngoscope blade.

Abstract

To the Editor:—In patients with cervical spine injuries, laryngoscopy is usually difficult because of reduced mobility of the neck. Recently, new devices for laryngoscopy, such as the Bullard (Circon AMCI, Stamford, CT) and McCoy (Penlon Ltd., Abingdon, UK) laryngoscopes 1,2and the WuScope (Pentax Precision Instruments, Orangeburg, NY), 3have been available in cases of difficult laryngoscopy. Hastings et al. 4compared head extension and laryngeal view obtained with the Bullard, Macintosh (Penlon Ltd.), and Miller (Penlon Ltd.) laryngoscopes and concluded that the Bullard laryngoscope caused less head extension than a conventional laryngoscope. The McCoy laryngoscope is a modification of the Macintosh laryngoscope. The hinged tip controlled by a lever causes elevation of the epiglottis, thus facilitating visualization of the larynx. 2In the current study, we compared the McCoy and Macintosh laryngoscopes with regard to head extension angles required for direct laryngoscopy. Twenty adult patients (aged 24 ± 8 yr) with normal cervical spines who were scheduled to undergo elective oral and maxillofacial surgery with general anesthesia participated in this study after institutional review board approval and written informed consent. After intravenous administration of thiamylal and vecuronium, laryngoscopy was performed using the McCoy blade or the Macintosh blade at random in the same patient. The patient’s head was placed on a flat board in a neutral position so that the eye–ear plane (Frankfort horizontal plane) was perpendicular to the board. Then, head extension angle, based on the tilt of the eye–ear plane, was measured during laryngoscopy. In each trial, head extension angle was recorded in grade 1 (most of the glottis visible) and grade 2 (no more than the arytenoid cartilages visible) of the Cormack and Lehane classification of laryngoscopic view. 5Cricoid pressure was not applied. Head and neck stabilization was not used, but the laryngoscopist was not allowed to lift the patient’s head off the board during laryngoscopy.Values were expressed as mean ± SD. The differences in head extension angles produced by the two laryngoscope blades were analyzed using the Wilcoxon signed rank test. A P value of less than 0.05 was considered significant.Head extension angles required for arytenoid exposure were 15.4 ± 3.8° for the Macintosh blade and 9.3 ± 4.1° for the McCoy blade. The angles needed to obtain the best view of the vocal cords were 26.3 ± 3.6° for the Macintosh blade and 18.0 ± 4.4° for the McCoy blade. These results showed that the McCoy laryngoscope reduced the head extension angle required to visualize the arytenoid cartilages and vocal cords approximately 6–8° in comparison with the Macintosh laryngoscope (P < 0.0001). Several investigators reported that the McCoy laryngoscope improved the view of the larynx in patients with simulated cervical injuries. 6–8With regard to head extension angle, our study showed that the McCoy blade was more useful than the Macintosh blade in patients with limited neck extension.