Optimal headrest height for the best laryngoscopic view: by anatomical measurements

We hypothesized that the oro-pharyngolaryngeal axes, occipito-atlanto-axial extension (OAA) angle and intubation distance would be influenced by the height of headrests.

Twenty patients were enrolled. The Macintosh 3 blade was used for direct laryngoscopy without a headrest or with the headrest of 6 or 12 cm high in randomized order, whereas a lateral radiograph of the neck was taken when the best laryngoscopic view was obtained. The following measurements were made: (1) the axis of the mouth (MA), the pharyngeal axis (PA), the laryngeal axis (LA), and the line of vision (LV). The various angles between these axes were defined: α angle between MA and PA, β angle between PA and LA, and δ angle between LV and LA. (2) Intubation distance, (3) mentovertebral distance, and (4) OAA angle.

Compared with 12-cm and no headrest, the δ angle decreased significantly with 6-cm headrest (19.4°/29.2°/29.2° in 6-cm/12-cm/no headrest, respectively; P < .001), and the intubation distance increased significantly (46.2/37.3/38.7 mm in 6-cm/12-cm/no headrest, respectively; P < .001). Mentovertebral distance was smallest (107.0/106.7/98.5 mm; P < .05) at 12-cm headrest. Occipito-atlanto-axial extension angle was largest significantly (40.7°/35.2°/34.5°; P < .05) at 6-cm headrest.

We conclude that compared with no or 12-cm headrest, 6-cm headrest could facilitate more alignment of these axes, increase the OAA angle, and enlarge the intubation distance.