Comparison of Four Methods for Predicting Difficult Laryngoscopy: A Prospective Study of Validity Indexes

Background: Considering that a simple yet valid airway predictor is basically preferred to a multivariable test with the same level of validity, we designed a study to compare the validity indexes of the TMHT, as a single variable test, with that of Wilson, Arne, and Naguib tests. Methods: 270 consecutive ASA physical statues I and II patients aged ≥16 years, candidate to receive general anesthesia for elective surgeries, were enrolled in the study. All patients preoperatively were evaluated using four airway predictor tests including Wilson, Arne, Naguib, and Thyromental height test (TMHT). Cut-off points to predict a difficult laryngoscopy were extracted from previous published studies for each test. Based on each predictor, all patients were classified into either easy or difficult. Based on Cormack-lehane scoring system, as the gold standard, all patients during laryngoscopy were categorized into two groups of “easy, grades I, II” and “difficult, grades III, IV”. Finally, validity indexes for each test were calculated and compared to one another. Results: The incidence of difficult laryngoscopy according to Cormack-lehane grading was 17.4% (47/270). The predicted rates of difficult laryngoscopy were 47 (17.4%), 2 (0.7%), 10 (3.7%) and 61 (22.6%) for TMHT, Wilson, Arne and Naguib respectively. Based on Chi-square test, the TMHT as well as the Naguib could significantly predict difficult laryngoscopy. However, the highest rate of sensitivity, positive predictive value, negative predictive value, and accuracy belonged to TMHT. Conclusion: Both TMHT and Naguib are acceptable predictors of difficult laryngoscopy while the TMHT is a more accurate predictor of difficult laryngoscopy than the other multivariable models.