A Comparative Study to Evaluate Difficult Intubation Using Ratio of Patient Height to Thyromental Distance, Ratio of Neck Circumference to Thyromental Distance, and Thyromental Height in Adult Patients in Tertiary Care Centre

OBJECTIVE: Patients’ airway assessment is one of the foremost responsibilities of every anaesthesiologist. Several preoperative predictive methods have been studied by various authors to find the best difficult airway predictor. We conducted this study to compare 3 methods to predict the difficulty of laryngoscopic endotracheal intubation viz ratio of patient height to thyromental distance, ratio of the neck circumference to thyromental distance, and thyromental height in adult patients. METHODS: This prospective observational study was conducted on 330 adult patients, American Society of Anaesthesiologists (ASA) status I and II, aged 18-60 years of either sex, weighing 50-80 kg scheduled for elective surgeries under general anaesthesia. Patients’ height, weight, and body mass index were recorded, and thyromental distance, neck circumference, and thyromental height were measured preoperatively. Laryngoscopic view was graded according to the Cormack–Lehane grade. Predictive indices and optimal cutoff values were calculated using the receiver operating characteristic curve analysis. RESULTS: Difficulty in laryngoscopic endotracheal intubation was encountered in 12.42% of patients. The sensitivity, specificity, positive predictive value, negative predictive value, and area under the curve for thyromental height were 100%, 95.2%, 75.54%, 100%, and 0.982, respectively; for the ratio of patient height to thyromental distance the respective values were 75.6%, 72.7%, 28.18%, 95.45%, and 0.758 and for the ratio of the neck circumference to thyromental distance, the values were 82.9%, 65.4%, 25.37%, 96.42%, and 0.779, respectively. There was no statistically significant difference to predict the difficulty of laryngoscopic intubation between any of them (P < .05). CONCLUSION: Among these 3 parameters, thyromental height was found to be the best preoperative method to predict difficult laryngoscopic endotracheal intubation with the highest predictive indices and area under the curve. The ratio of the neck circumference to the thyromental distance method was found to be a more sensitive and useful method than the ratio of patient height to the thyromental distance method to predict the difficulty of laryngoscopic endotracheal intubation. KEYWORDS: Body mass index, endotracheal intubation, laryngoscopic, ROC curve, thyromental height