This is a prospective, single-blinded observational study done with the clearance of Ethical Committee. Informed written consent of 260 patients of either sex, aged 18–65 years, American Society of Anesthesiologist Status I and II undergoing elective surgical procedures under general anesthesia were enrolled for the study. Uncooperative and unwilling patients, history of burns involving head and neck, trauma and airway surgeries, tumor or mass in the neck or airway, patients with restricted mobility at neck and mandible, patients with inability to sit, edentulous or need awake intubation, pregnant females, and patients with body mass index (BMI) ≥35 were excluded from the study. All patients were examined preoperatively to assess airway parameters, the day before surgery by the same anesthesiologist to avoid interobserver variability.
Height and weight were recorded and BMI calculated. Height was measured in centimeters from vertex to heel with the patient standing.
The oropharyngeal view was assessed using:

MMT:[17 (link)] Sampson and Young's modification of Mallampati test recorded oropharyngeal structures visible upon maximal mouth opening. Each patient when seated was asked to open mouth maximally and to protrude the tongue without phonation. The view was classified as Grade 0 - epiglottis visualized, Grade 1 - good visualization of palate, fauces, uvula, and tonsillar pillars, Grade 2 - pillars obscured by the base of the tongue but the soft palate, fauces, and uvula visible, Grade 3 - soft palate and base of the uvula visible, and Grade 4 - soft palate not visible

RHTMD:[18 (link)] TMD was measured from the bony point of the mentum to thyroid notch while head was fully extended and mouth closed. RHTMD was calculated as RHTMD = height (in cm)/TMD (in cm) and graded as Grade 1 <23.5 and Grade 2 ≥23.5

Upper lip bite test:[19 (link)] ULBT was done to assess the range of freedom of the mandibular movement and the architecture of the teeth concurrently. It was done by assessing the ability of the patient to touch the vermilion line of upper lip with lower incisors. This test was graded as Class 1 - If the lower incisors could bite the upper lip above the vermilion line, Class 2 - If the lower incisors could bite the upper lip below the vermilion line, and Class 3 - If the lower incisors could not bite the upper lip

IIG:[19 (link)] It was assessed by asking each patient to open the mouth to maximum extent. The distance between upper and lower incisor at the midline is measured, which is usually >3.5 cm

TMD:[15 (link)] TMD was measured from the bony point of the mentum whereas the head is fully extended and mouth closed using a rigid ruler. The distance was rounded to nearest 0.5 cm and graded as Class 1: >6.5 cm, Class 2: 6–6.5 cm, and Class 3: <6 cm

SMD:[15 (link)] SMD was measured from sternal notch to the mentum in centimeter with head fully extended on the neck with the mouth closed which is normally >12.5 cm

Horizontal length of the mandible:[15 (link)] It was measured from angle of the mandible to the mentum. A length of ≥9 cm was considered normal

Maximum range of HNM:[11 (link)] was noted as Grade 1 ≤80° or Grade 2 ≥80°. The patient was first asked to extend the head and neck fully, where a pencil was placed vertically on the forehead and then while the pencil was held firmly in position, the head and neck were flexed.

The airway assessment parameters which predicted difficult laryngoscopy are listed in Table 1.
Patients were kept nil orally for 8–10 h preoperatively. In operation theater, intravenous (IV) line was secured with 18-gauge IV cannula and Ringer's lactate infusion was started. Electrocardiogram, noninvasive blood pressure, and peripheral oxygen saturation monitor were connected to the patient, and basal heart rate, blood pressure, and oxygen saturation were recorded. Patient was premedicated with injection glycopyrrolate 0.01 mg/kg, injection midazolam 0.05 mg/kg, injection fentanyl 2 μcg/kg intravenously, and preoxygenated with 100% oxygen. Induction of anesthesia was done with injection propofol 2 mg/kg body weight intravenously and injection vecuronium 0.1 mg/kg IV was administered once mask ventilation confirmed. Laryngoscopy was done using Macintosh blade Size 3 or 4 by an experienced anesthesiologist who was blinded to preoperative airway assessment details, and the view was classified as per Cormack-Lehane's Scale:[20 ] Grade 1 - vocal cords visible, Grade 2 - only posterior commissure or arytenoids visible, Grade 3 - only epiglottis visible, and Grade 4 - none of the above visible without any external laryngeal manipulation.
Cormack and Lehane Grade 1 and 2 was considered as easy visualization whereas Grade 3 and 4 was considered as difficult visualization. A maximum of three attempts were allowed with conventional laryngoscope. In case of failure of first two attempts, third attempt was by another senior experienced anesthesiologist. If there was failure to intubate at third attempt, alternate measures such as use of supraglottic device, bougie was done as per the discretion of attending anesthesiologist. External laryngeal manipulation was used to improve visualization after first attempt. Use of additional gadgets/maneuvers during intubation was noted. Oxygenation was ensured in between attempts at intubation. Intubation was done with appropriate sized endotracheal tubes. Confirmation of intubation was done by bilateral auscultation of lung fields and capnography. Number of attempts at intubation was noted. Maintenance of anesthesia was done with oxygen, nitrous oxide, and isoflurane. At the end of surgery, isoflurane disconnected, and after adequate respiratory efforts, injection neostigmine and injection glycopyrrolate were administered to reverse neuromuscular blockade. Patient was extubated after adequate recovery and shifted to the postanesthesia care unit.