Ethnic considerations in the upper lip bite test: the reliability and validity of the upper lip bite test in predicting difficult laryngoscopy in Koreans.

BACKGROUND: Several methods have been used to predict difficult tracheal intubation. Among recently suggested methods, the upper lip bite test (ULBT) could serve as a good predictor. Soft tissue and skeletal hard tissue profiles are affected by many factors including ethnicity. We aimed to assess the clinical utility of the ULBT in Koreans while considering ethnic differences. METHODS: Three-hundred-forty-four Korean patients undergoing general anesthesia with orotracheal intubation were included. Preoperatively, we recorded the patient's Modified Mallampati (MMT) classification, ULBT ratings, and the Cormack-Lehane grade. RESULTS: The area under the receiver operating characteristic (ROC) curve (AUC) was lower for the ULBT than the MMT (95% confidence interval: 0.0697-0.191, p < 0.0001). The ULBT showed high accuracy (73.83%) and specificity (98.04%). On the other hand, the ULBT showed significantly lower sensitivity (4.49%). Only nine of 344 Korean patients could not bite their upper lip; among them, only three presented a difficult laryngoscopic view. CONCLUSIONS: One factor related to the low sensitivity is the low incidence of a grade III ULBT in Koreans. In Asians, the scarcity of a grade III ULBT is explainable as a result of anteriorly displaced temporomandibular joints and redundant lip soft tissues. Despite its high specificity, the low sensitivity and AUC of the ULBT mean that the test results should be interpreted cautiously in Koreans. Ethnic differences should be considered when evaluating parameters related to soft tissues such as the ULBT. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01908218, Date of registration JUL 2013.

Estimation of the length of the nares-vocal cord.

The nasal route is preferred for fiberoptic intubation. Placing a lubricated endotracheal tube through the nostril can guide the fiberoptic scope towards the larynx. It would be helpful for optimal visualization of the vocal cord when the scope is passed through the endotracheal tube if the length of nares-vocal cord (NV length) could be predicted and the tip of the endotracheal tube could be placed close to the vocal cord. In this study we measured the NV length and examined the relationship between the NV length and various external measurements. Using a fiberoptic scope, the NV lengths were measured in 50 male and 45 female patients scheduled to undergo elective surgery under general anesthesia. In addition, the distances from the lateral border of the nares to tragus of the ear (NE distance) and to the angle of the mandible (NM distance) were measured. The age, height, and weight of all the patients were recorded. The NV length of the males was 18.3 +/- 0.8 cm, and that of the females was 16.3 +/- 0.7 cm. The relationship between the NV length and body height (P < 0.001, r = 0.755) and the NE distance (P < 0.001, r = 0.636) showed a significant correlation but NM distance did not (P = 0.075). The length of the NV cord can be predicted using the body height or the NE distance.