Validity of Preoperative Assessment of Neck Circumference to Thyromental Height Ratio as a Reliable Predictor of Difficult Laryngoscopy in Obese Adult Patients Undergoing Elective Surgery Under General Anaesthesia

Background: Difficult laryngoscopy is a major challenge in anaesthetic practice, especially in obese patients, when airway anatomy can change. Traditional airway evaluation measures, such as Mallampati scores, have limited predictive capabilities. Recently, the neck circumference-to-thyromental height (NC/TMH) ratio has been proposed as a potential anthropometric indicator of challenging laryngoscopy. The proposed study focused on evaluating the accuracy of the NC/TMH ratio as a predictor of challenging laryngoscopy in obese adult patients undergoing elective surgery under general anaesthesia. Material and Methods: This was a prospective observational study involving 60 obese adult patients with body mass index 30 kg/m2 and above, aged between 18 and 65 years old, who had been planned to undergo elective surgeries under general anaesthesia. Airway examination performed before surgery included measurement of neck circumference (NC) and thyromental height (TMH), after which the NC/TMH ratio was estimated for each patient. The Mallampati classification was done. The Intubation Difficulty Scale (IDS) was used to characterize intubation as being easy (IDS <5) or difficult (IDS >5) during the laryngoscopy. Statistical analysis involved comparisons between groups and receiver operating characteristic (ROC) curve analysis to assess predictive accuracy. Results: Of the 60 patients, 45 (75%) had an easy intubation, and 15 (25) had a difficult intubation. The neck circumference (38.85 0.92 cm) and thyromental height (7.45 0.58 cm) of the patients were significantly lower in the easy intubation group (37.42 1.05 cm and 8.21 0.68 cm, respectively) than in the difficult intubation group (p = 0.001). The NC/TMH ratio of the difficult intubation group (5.22 ± 0.28) was considerably higher than that of the ease intubation group (4.56 ± 0.31; p < 0.001). The ROC analysis revealed good predictive ability of the NC/TMH ratio (AUC = 0.898), with an optimal cut-off of 4.85, sensitivity of 94.29, and specificity of 71.11. By comparison, the Mallampati score was poor at predicting (AUC = 0.208). Conclusion: The NC/TMH ratio appears to be a simple, reliable, and extremely sensitive predictor of difficult laryngoscopy in obese patients. It demonstrated superior predictive accuracy compared with the Mallampati classification. Incorporating the NC/TMH ratio into routine preoperative airway assessment may improve identification of patients at risk for difficult intubation.

Keywords: Difficult laryngoscopy, Neck circumference, Thyromental height, NC/TMH ratio, Obesity, Airway assessment, General anaesthesia.