Description of device included in the study: Imago V-Blade® and Glidescope®

The Imago V-Blade® was equipped with a wireless video assisted stylet within the 90° angled disposable blade. Endotracheal intubation with Imago V-Blade® did not require a rigid stylet because it has a designed channel on the right for placement of the tracheal tube. This videolaryngoscope is inserted into the mouth in the midline, without displacing the tongue laterally, and advanced slowly until the epiglottis comes into view. The tip of the blade is then positioned in to the vallecula indirectly elevating the epiglottis for vocal cords exposure (Fig. 2). It is important to place the glottic opening in the centre of the monitor.

Laryngeal view from the Imago V-Blade® used in this study. The left panel show the glottis view with the tip of the blade inserted into the vallecular. The middle panel shows the placement of the endotracheal tube in front of the vocal cords with the tip of the blade slightly elevating the epiglottis. The right panel shows the passage of the endotracheal tube though the vocal cords keeping the tip of the blade into the vallecula

The Glidescope® is a rigid video-laryngoscope with a 60° angled blade connected by cable to a monitor. The tracheal tube used with the Glidescope® was pre-loaded with the manufacturer’s pre-configured stylet because the Glidescope® does not have a tracheal tube channel. The Glidescope® is introduced into the middle of the oral cavity, without tongue displacement, gliding along the palate and the posterior pharynx until their tip is inserted into the vallecula or posterior to the epiglottis, if the epiglottis obscures the glottis.

Anesthesiologists A and B, with 10 years of experience in conventional endotracheal intubation but without experience in video assisted intubation, were given didactic instruction on the proper use of the Imago V-Blade® and Glidescope®. As training, anesthesiologists A and B each performed 60 intubations with the assigned videolaryngoscope in a manikin with three difficult airway scenarios: 20 intubations in a normal manikin without modifications, 20 intubations in a manikin with the tongue insufflated with 110 ml of air, 20 intubations in a manikin with cervical immobilization. The anesthesiologist C, with more than 100 clinical intubations with both devices, supervised the training.