The investigators hypothesized that the use of the King Vision™ and the Airtraq® VL would reduce the time to DLT intubation compared with the GlideScope® and Macintosh in simulated easy and difficult airways. The investigators have considered to assess the efficacy of each device in manikins before considering to evaluate them in patients undergoing thoracic procedures.

Twenty-one staff anaesthesiologists who had limited prior experience in using the VLs for DLT intubation participated in this randomised crossover study. Following a brief demonstration and two practice attempts, participants were volunteered to insert a DLT using the Macintosh, GlideScope®, Airtraq®, and King Vision™ on two high-fidelity easy and difficult airway simulators in a computer-generated randomized sequence. The primary endpoint, time to DLT intubation, as well as, the views obtained at laryngoscopy, ease of intubation, numbers of laryngoscopy attempts and optimisation manoeuvers, and failure to intubation; defined as an attempt took longer than 150 seconds, were recorded.

Several regional surveys demonstrated that most thoracic anesthesiologists are using the double-lumen endobronchial tubes (DLT) as the first-choice lung separation technique. DLT, when compared with single lumen tracheal tube, can be more difficult to insert in patients with difficult airways. The videolaryngoscopes (VL) have the potential to facilitate the placement of the DLTs for lung separation in patients with predicted or unanticipated difficult airway.

The use of GlideScope® (Verathon Inc., Bothell, WA, USA), a VL with an angulated blade, has been associated with variable times to DLT intubation according to the prior experience of the operators, despite superior visualization of the glottis The channeled Airtraq® (Prodol Meditec S.A., Vizcaya, Spain) and standard non-channeled blade of the King Vision™ (Ambu, Ballerup, Copenhagen, Denmark), may offer additional benefits for DLT intubation in patients with limited mouth opening or restricted neck movement, in whom the use of traditional VL like as the Glidescope® could be difficult. This is because of the larger outer diameter, the distal curvature and the increased rigidity of the DLT. Of note, the longer times to DLT intubation with the use of different VL could be shortened with building up the operator's experience.

To the best of the investigators knowledge, the comparison of the effects of the Macintosh, GlideScope®, Airtraq®, and King Vision™ VL on the time to DLT intubation in simulated easy and difficult airways has not yet been studied.

Two high-fidelity simulators (Airway Management Trainer, model AA-3100, Laerdal, Kent, UK) were prepared to simulate easy and difficult airway situations, as described by Marshall et al. and Wang et al. The "easy" airway was established with the manikin in a neutral position. The "difficult" airway setting was obtained by placing an Oasis Elite™ Prone Head Rest, Adult (140 mm in height) (Covidien, Mansfield, MA) under the occiput and securing the head position with adhesive tape, object to replicate cervical-collar use. Positioning was confirmed after each attempt to ensure consistency.

Inclusion Criteria:

• Staff anesthesiologists
• Signed consent
• Limited experience in using videolaryngoscopes for inserting double lumen tubes

Exclusion Criteria:

• Decline to sign the consent
• Non receiving the prior training demonstration
• Non practicing once with each device tested on each simulator scenario