Background: Preoperative airway assessment tests have been presented to help in anticipating a difficult airway. We conducted this study to compare five methods in prediction of difficult laryngoscopy: Neck circumference (NC), NC to thyromental distance ratio (NC/TMD), the ratio of height to thyromental distance (RHTMD), upper lip bite test (ULBT) and Mallampati test (MMT). These five methods are the most commonly used ones and have different powers for it. It was not clear which of these methods predicts difficult laryngoscopy better.
Materials and Methods: Six hundred consecutive patients participated in this study. NC, NC/TMD and RHTMD were measured, and ULBT and MMT were performed and recorded. The laryngoscopy view was graded according to Cormack and Lehane's scale (CLS) and difficult laryngoscopy was defined as CLS grades 3 and 4. Accuracy of tests in predicting difficult laryngoscopy was assessed using the area under a receiver-operating characteristic curve.
Results: The area under the curve in ULBT and RHTMD were significantly larger than that in TMD, NC and MMT. No statistically significant differences were noted between TMD, NC and MMT (all P > 0.05) (ULBT = RHTMD > NC/TMD > TMD = NC = MMT). RHTMD (>22.7 cm) exhibited the highest sensitivity (sensitivity = 64.77, 95% confidence interval [CI]: 53.9-74.7) and the most specific test was ULBT (specificity = 99.41%, 95% CI: 98.3-99.9).
Conclusion: RHTMD and ULBT as simple preoperative bedside tests have a higher level of accuracy compared to NC/TMD, TMD, NC, MMT in predicting a difficult airway.
Shah PJ, Dubey KP, Yadav JP. Predictive value of upper lip bite test and ratio of height to thyromental distance compared to other multivariate airway assessment tests for difficult laryngoscopy in apparently normal patients. J Anaesthesiol Clin Pharmacol 2013;29:191-5.
Safavi M, Honarmand A, Zare N. A comparison of the ratio of patient's height to thyromental distance with the modified Mallampati and the upper lip bite test in predicting difficult laryngoscopy. Saudi J Anaesth 2011;5:258-63.