A preanaesthetic checkup will be done for all the patients at least one day prior to surgery. A detailed history will be obtained followed by general physical and systemic examination. Physical characteristics such as age, height, weight and body mass index will be noted. Investigations will be done as per hospital protocol. After explaining the entire procedure to the patient a written informed consent will be taken.

Patients will fast overnight and will receive tablet alprazolam 0.25 mg night before and two hours prior to surgery. They will be randomly assigned to one of the two study groups by computer-generated randomisation using sealed opaque envelopes.

Group K- KingVision^® video laryngoscope with the channeled blade attachment will be used as an intubating aid in a simulated difficult airway.

Group M- McGrath^® MAC video laryngoscope will be used as an intubating aid in a simulated difficult airway.

In the operation theatre, standard monitors (electrocardiograph, non-invasive blood pressure and pulse oximeter) will be applied and baseline readings noted. Using18 gauge cannula vascular access will be secured. Anaesthesia will be induced with intravenous fentanyl 2µg/kg and propofol 2 mg/kg. After confirming that bag-mask ventilation is adequate, vecuronium bromide 0.1 mg/kg will be given intravenously for neuromuscular blockade. Once adequate muscle relaxation is achieved, the inter-incisor distance at maximal mouth opening will be measured. To simulate a difficult airway, an appropriately sized cervical collar will be applied. The inter-incisor distance will be again measured and noted (aiming at 25mm).

The anaesthesiologist inserting the study device would have received prior training on manikin and have used both the study devices before at least 10 times clinically. In group M, First laryngoscopy will be performed with the KingVision^® video laryngoscope, the laryngoscopic view will be graded and time taken to obtain an optimal laryngoscopic view (centralising the vocal cords in view) will be noted. The patient will be ventilated with 100% oxygen before introduction of the second device. The McGrath^® MAC video laryngoscope will be used to perform a second laryngoscopy. After noting the grade and time taken to obtain optimal laryngoscopic view, the trachea will be intubated using this second device and the time taken for tracheal intubation will be noted.

In group K, First laryngoscopy will be performed with the McGrath^® MAC video laryngoscope, the laryngoscopic view will be graded and time taken to obtain optimal laryngoscopic view noted. The patient will be ventilated with 100% oxygen before introduction of the second device. The KingVision^® video laryngoscope will be used to perform second laryngoscopy. After noting the grade and time taken to obtain optimal laryngoscopic view, the trachea will be intubated using this second device and the time taken for tracheal intubation will be noted.

Thus, while both airway devices will be used to perform laryngoscopy, the trachea will be intubated only once. Tracheal intubation will be done with tracheal tube of size 7.0 for females and 8.0 for males. Correct placement of tracheal tube will be confirmed by capnography and chest auscultation for bilateral breath sounds. Anaesthesia will be maintained using vecuronium bromide, nitrous oxide (66%), and isoflurane in oxygen. At the end of surgery, residual neuromuscular blockade will be reversed using injection neostigmine and glycopyrolate.

If the first attempt at tracheal intubation fails, then the patient will be ventilated using bag and mask and 100% oxygen to avoid desaturation. The duration of subsequent attempt will be added to the time to tracheal intubation.

Manoeuvres to facilitate tracheal intubation may be used as desired by the intubator and these will be noted.

Only two attempts will be allowed for tracheal intubation with either of the two devices. In case of failed intubation, the cervical collar will be removed and alternative airway management plan would be instituted.

The study will be terminated after two unsuccessful attempts, or upon occurrence of airway injury, bronchospasm, technical failure, or a reduction of oxygen saturation below 90%.

Patients will be monitored continuously throughout the surgical procedure. Readings of heart rate, systolic, diastolic and mean blood pressure and peripheral oxygen saturation will be noted immediately before induction as baseline, immediately after anaesthesia is induced, at insertion of First study device, at insertion of second study device, at intubation, and at one, three and five minutes’ post intubation.

Grading of laryngoscopic view will be done using the modified Cormack and Lehane grade  and the percentage of glottic opening.

Ease of intubation with each device, will be graded by the intubator on a scale from 0 (extremely easy) to 10 (extremely difficult).

The study data will be collected and analysed statistically.

McGrath^® MAC VL as compared to King Vision^® VL resulted in shorter TLV and TTI but had comparable first attempt intubation success.