Thyromental Height - As a Predictor of Difficult Laryngoscopy

The fundamental responsibility of the anaesthesiologist and one of the most important steps in anaesthesia practice is the intubation and maintenance of the airway. The integral part of pre-anaesthetic evaluation to recognize a potentially difficult airway is the airway assessment. There are multitude of bedside screening tests which are helpful to predict a difficult airway but the accuracy is doubtful. Thus, pointing out a single reliable predictor of difficult intubation is important. Accordingly, this study aims to evaluate the practicality of thyromental height test alone as a sole predictor of difficult laryngoscopy in our present population. Ethical clearance was obtained and after taking an informed consent, a randomised prospective observational study was conducted on 315 adult patients who were posted for elective surgical procedures under general anaesthesia with endotracheal intubation. On the day before the surgery, airway was assessed and Thyromental height (TMHT) was measured. Laryngoscopy was performed intra-operatively and Cormack Lehane’s grading was noted. The evaluation of the accuracy of thyromental height in predicting difficult laryngoscopy was done by comparing the preoperative assessment data and laryngoscopy findings. In our study, the mean thyromental height observed was 5.4cm. Thyromental height at cut off of 50mm had a high negative predictive value of 94.1% and high sensitivity of 72.5%, but with low specificity of 64.2% (P value 0.000). When the cut off was emended to 48mm, sensitivity of the test decreased to 56.2% and specificity increased to 79.8% (P value 0.002).The conducted study demonstrates the usefulness of thyromental height. It substantiates the good sensitivity of thyromental height for predicting difficult intubation. But, the validation will require further studies in more diverse patient population.