BACKGROUND: The unexpected difficult endotracheal intubation is a significant contributor to mortality and morbidity in clinical practice. Although there are many methods to predict difficult intubation, modified Mallampati test (mMT) and airway score were popular tests. The authors wanted to compare upper lip bite test (ULBT) with those two tests and also explored the possibility that ULBT could be a good sole predictor for difficult intubation.

METHODS: 322 patients who were ASA I or II, aged > 16yr were enrolled in this study. Three residents visited patients to obtain airway measurements such as 1) ULBT, 2) mMT, 3) airway score (inter-incisor gap, mMT, thyromental distance, head & neck movement, history of difficult intubation, buck teeth). They were not involved in the intubation of patients they evaluated. The accuracy, specificity, positive and negative predictive values were calculated from the data of three tests, and three tests were compared with patient's laryngoscopic view grade according to Cormack & Lehane criteria by using Chi-square test.

RESULTS: The incidence of Cormack & Lehane grade III, IV was 14.6% (not applied external laryngeal pressure). ULBT showed significantly higher specificity, positive predictive value than mMT, but sensitivity was lower than other tests. There were significant correlations between ULBT class III and Cormack & Lehane laryngoscopic grade III, IV (P<0.001).

CONCLUSIONS: ULBT is good for predicting difficult intubation as a simple, single test. But because of it's low sensitivity, it seems better to incorporate ULBT as a factor of airway score tests for more reliable prediction.