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 responsibility 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 three methods to predict difficulty of laryngoscopic endotracheal intubation viz Ratio of patient Height to Thyro-Mental Distance (RHTMD), Ratio of Neck Circumference to Thyro-Mental Distance (RNCTMD) and Thyro-Mental Height (TMHT) in adult patients.

Methods: This prospective observational study was conducted on 330 adult patients, ASA staus I and II, aged 18-60 years of either sex, weighing 50-80 kg scheduled for elective surgeries under general anaesthesia. Patient's height, weight, Body Mass Index (BMI) was recorded and thyromental distance, neck circumference, TMHT were measured preoperatively. Laryngoscopic view was graded according to Cormack- Lehane (CL) Grade. Predictive indices and optimal cut-off values were calculated using ROC curve analysis.

Results: Difficulty in laryngoscopic endotracheal intubation was encountered in 12.42% patients. The sensitivity, specificity, positive predictive value, negative predictive value and Area Under Curve (AUC) for TMHT were 100%, 95.2%, 75.54%, 100%, 0.982; for RHTMD were 75.6%, 72.7%, 28.18%, 95.45%, 0.758 and for RNCTMD were 82.9%, 65.4%, 25.37%, 96.42%, 0.779 respectively. There was no statistically significant difference to predict difficulty of laryngoscopic intubation between any of them (P < .05).

Conclusions: Among these 3 parameters, TMHT was found to be the best preoperative method to predict difficult laryngoscopic endotracheal intubation with highest predictive indices and AUC. The RNCTMD was found to be more sensitive and useful method than RHTMD to predict difficulty of laryngoscopic endotracheal intubation.