[Head extension during laryngoscopy for obtaining a best glottic view: comparison of the McGrath and Macintosh laryngoscopes]

Camera eye in the McGrath video-laryngoscope blade is located closer to the larynx, which may allow reduction of the head-neck movement during laryngoscopy compared with a conventional laryngoscope. We compared the degree of head extension during laryngoscopy with McGrath laryngoscope and that with Macintosh laryngoscope.

Fifty patients without cervical spine abnormality were randomized into two groups: laryngoscopies with Macintosh laryngoscope and that with McGrath laryngoscope. Each patient wearing goggles mounted with a goniometer lay supine with the head in the neutral position. After general anesthesia and muscle relaxation were obtained an experienced anesthesiologist obtained the best glottic view using either laryngoscope, and change in the angle of goggles (head extension angle) during laryngoscopy was measured. In addition, we compared the head extension angle with extension angle of the cervical spine between the occiput and the fourth cervical vertebra (C0-4) measured radiologically in 7 healthy volunteers.

Head extension angles with Macintosh and McGrath laryngoscopes were 18.2 ± 4.3 degrees and 9.6 ± 2.7 degrees, respectively (P < 0.0001). There was a strong relationship between head extension angle and C0-4 extension angle measured radiologically in the volunteers (r = 0.92, P < 0.0001).

The McGrath laryngoscope may be a reasonable technique of choice for intubation when minimal cervical spine movement is indispensable because of reduction of head extension during laryngoscopy compared with the conventional laryngoscopy.