ABSTRACT
Recognising a potential difficult airway at the time of preanaesthesia check-up,is very crucial. Several bedside screening tests have been used in clinical practice for predicting the difficult laryngoscopy/intubation. Aim: The study was undertaken to compare diagnostic value of Thyromental distance(TMD) and ratio of height to thyromental distance (RHTMD) in predicting a Cormack Lehane grade> or =3. Design: Prospective, comparative, observationl study Methods: 320 ASA 1 & 2 patients were subjected to pre-operative measurements of the thyromental distance (TMD)and ratio of height to thyromental distance (RHTMD) during the routine pre anaesthesia checkup. In the operating room, direct laryngoscopy performed with a Macintosh blade by an experienced anesthetist not aware of the pre-op measurements. Difficult laryngoscopy was defined as inadequate exposure of the glottis (Cormack-Lehane grade 3 or 4) under direct laryngoscopy with a blade of appropriate length, without any external pressure or other manoeuvre applied. The preoperative data of TMD & RHTMD and the laryngoscopic findings are correlated to evaluate the sensitivity, specificity,Positive predictive value, & Negative predictive value of each test according to standard formulae. Results: RHTMD had a better sensitivity(65.3% vs 59.2% for TMD) as well as a better specificity (50.6% vs 45.8 for TMD) and positive and negative predictive values. Conclusion: Among the tests studied, ratio of height to thyromental distance proved to be more accurate test for predicting difficulty larngoscopy.