Unexpected difficult intubation is probably the result of inadequate preoperative examinations of the airway. The purpose of this study is to indicate that the oropharyngeal classification (OPC) and several tests may be predict difficult intubation in Korean.

In each of 462 adults the OPC was determined in sitting position. In supine position, hyomental distance (HD) and sternomental distance (SMD) with head in neutral, and thyromenal distance (TD), SMD and inter-incisors distance (DI) on mouth opening with the head fully extended were measured. The laryngoscopic grades were determined at the time of induction. We defined the cases of intubation trials > or = 3 times in patients with laryngoscopic grade 3 and 4 as difficult intubation. The datas were analyzed with Mann-Whitney and Kruskal-Wallis test.

14 patients had difficulty in intubating (3.03%) and 1 of 14 was failed to intubate (0.22 %). Assignment to either OPC > or = 3 and DI < or = 4.1 cm had relative high sensitivity, specificity and negative predictive value (NPV) to predict difficult intubation. Of various combinations, OPC > or = 3 and HD < or = 5.5 cm had high sensitivity, specificity, and NPV. When DI and HD < or = 4 cm were employed, combination of OPC and HD/DI resulted in increasing sensitivity and positive predictive value (PPV).

Based on the results and performance indexes of patients in this study, we concluded that assignment to OPC, DI and HD, consider either alone or combinations, be valuable tests to predict difficult intubation before anesthesia in Korean.