In patients with limited neck extension and mouth opening due to reasons including previous radiation therapy in the head and neck area or cervical spine pathology, tracheal intubation with direct laryngoscopy (DL) are challenging because of the difficulty in aligning the oral, pharyngeal, and laryngeal axes in order to visualize the cords. In contrast, video-laryngoscopes (VL) only require alignment of the pharyngeal and laryngeal axes, which lie along much more similar angles when compared with the oral axis. Thus, VL make tracheal intubation easier to accomplish in these patients.

Good patient positioning also maximizes the chance of successful laryngoscopy and tracheal intubation. In difficult airway society 2015 guidelines, advantages of head-up positioning and ramping, which brings the patient's sternum onto the horizontal plane of the external auditory meatus (EAM), are highlighted. In the obese patient, the 'ramped' position should be used routinely because this improves the view during DL. This position is usually achieved by placing blankets or other devices under the patient's head and shoulders, but can also be achieved simply by configuring the operation room (OR) table into a back-up head elevated (BUHE) position. Significantly improved glottic views on DL have been reported with both obese and non-obese adult patients in BUHE position. However, the effect of this simple maneuver on laryngeal visualization with the VL in patients with limited neck extension and mouth opening has not been reported.

The investigators hypothesized that BUHE position might improve laryngeal views and make intubation easier compared to the supine position with the VL in patients with simulated difficult airway (application of a cervical collar to limit mouth opening and neck movement).The investigator investigated primarily the improvement in visualization of the glottis and, secondarily, the ease of tracheal intubation after alignment of the EAM and sternal notch.

Inclusion Criteria:

• patients of ASA physical status 1-2 who were scheduled for elective surgery under general anaesthesia requiring tracheal intubation

Exclusion Criteria:

• if they required rapid sequence induction; had a history of previous difficult direct laryngoscopy and required awake tracheal intubation; were unable or unwilling to provide informed consent; had uncontrolled hypertension; had a history of ischaemic heart disease without optimal control of symptoms; had a history of acute or recent stroke or myocardial infarction; had cervical spine instability or cervical myelopathy; had symptomatic asthma or reactive airway disease requiring daily pharmacological treatment for control of symptoms; or had a history of gastric reflux.