Fig. 1

Transillumination-assisted technique and midline approach technique. Note: In intubation using the transillumination-assisted technique, the Bonfils optical stylet (a) with a preset tracheal tube was slowly inserted into the upper respiratory tract along the midline. If a centered bright spot was visible in the cricothyroid membrane region of the neck (b), it might indicate that the laryngoscope tip was located near the glottis, where the vocal cords, annulus tracheae, and other structures were visible (c). If the laryngoscope tip was deviated to one side, the spot was more focal and darker (d), where sinus piriformis, glossoepiglottic folds, and other structures were visible (e)