A COMPARATIVE STUDY OF UPPER LIP BITE TEST WITH OTHER PREDICTOR TESTS FOR PREDICTING DIFFICULTY IN INTUBATION AT A RURAL TERTIARY CARE HOSPITAL

Airway management is a critical responsibility of the anesthesiologist, and failure to anticipate a difficult airway remains a major cause of anesthesia-related morbidity and mortality. (1) Endotracheal intubation, though routinely performed, can become challenging in the presence of anatomical or functional variations of the airway. (2,3) Early and accurate prediction of difficult intubation allows appropriate planning, availability of alternative airway devices, and skilled personnel, thereby reducing complications such as hypoxia, airway trauma, and aspiration. (4)

Several bedside screening tests have been described to predict difficult laryngoscopy and intubation, including the Modified Mallampati classification, thyromental distance, inter-incisor gap, neck mobility, and the Wilson risk score. However, no single test has demonstrated high sensitivity and specificity when used alone. The Upper Lip Bite Test (ULBT) is a simple, quick, and noninvasive assessment that evaluates mandibular mobility and dentition, and has been proposed as a reliable predictor of difficult intubation. (5,6,7)

In rural tertiary care hospitals, limited resources, high patient load, and variable access to advanced airway equipment underscore the need for an effective and easily applicable predictive test. (8) Our study aims to compare the diagnostic accuracy of the Upper Lip Bite Test with other commonly used airway assessment methods in predicting difficult intubation, with the goal of identifying a practical and reliable tool suitable for routine pre-anesthetic evaluation in rural healthcare settings.

Table 1: Demographic Profile and Incidence of Difficult Intubation (n = 320)

Table 2: Distribution of Airway Predictive Tests

Table 3: Correlation of Airway Predictors with Difficult Laryngoscopy (C-L Grade III–IV)

Table 4: Diagnostic Accuracy of ULBT Compared with Other Airway Tests

Graph – ROC curves for airway predictive tests

Anticipation of a difficult airway remains a cornerstone of safe anaesthetic practice, particularly in settings where advanced airway equipment and subspecialty support may be limited. The present prospective observational study evaluated and compared the Upper Lip Bite Test (ULBT) with other commonly used bedside airway assessment tests for predicting difficult laryngoscopy and endotracheal intubation in a rural tertiary care hospital. The overall incidence of difficult laryngoscopy, defined as Cormack–Lehane (C-L) grade III or IV, was 10%, which is consistent with the incidence reported in previous studies, thereby validating the representativeness of the study population. (8,9,10)

In the present study, ULBT demonstrated a sensitivity of 65.6% and a remarkably high specificity of 98.6%, with an overall diagnostic accuracy of 95.9%. These findings suggest that although ULBT may miss a small proportion of difficult airways, a positive ULBT (Class III) is highly predictive of difficult laryngoscopy. This high specificity makes ULBT particularly useful as a screening tool to “rule in” difficult intubation, which is clinically valuable for planning airway management strategies. The high negative predictive value further indicates that patients classified as ULBT Class I or II are unlikely to pose difficulty during intubation.

When compared with other airway predictors, Modified Mallampati Score (MMS) showed higher sensitivity but significantly lower specificity. While MMS identified a larger proportion of difficult cases, it also falsely labeled many patients as difficult, reducing its positive predictive value. This limitation of MMS has been widely reported and may be attributed to interobserver variability, patient cooperation, and alteration of pharyngeal anatomy during phonation. In contrast, ULBT is less dependent on patient compliance and observer interpretation, contributing to its consistency and reliability. (11, 12)

Among the distance-based parameters, hyomental distance, thyrosternal distance, and mandibular length demonstrated high specificity and good overall accuracy, comparable to ULBT. These parameters reflect mandibular space, laryngeal position, and submandibular compliance, which are key anatomical determinants of laryngoscopic view. However, their practical applicability may be limited in routine clinical practice due to the need for precise measurement and patient positioning. ULBT, being a quick and equipment-free test, offers a practical advantage without compromising diagnostic performance.

The ratio of height to thyromental distance (RHTMD) showed moderate sensitivity and specificity in the present study. Although it incorporates patient anthropometry, its predictive ability was inferior to ULBT and certain distance-based measurements. Thyromental and sternomental distances also showed moderate diagnostic accuracy, reinforcing the concept that no single airway assessment test is sufficient to predict difficult intubation with absolute certainty.

The findings of this study support the concept that combining airway assessment tests may improve predictive accuracy. However, in resource-limited rural settings, reliance on a simple, rapid, and highly specific test such as ULBT may be particularly beneficial. The study reinforces ULBT as a valuable bedside tool that can be easily incorporated into routine preanaesthetic evaluation.

In conclusion, ULBT demonstrated superior specificity and high diagnostic accuracy compared to other commonly used airway predictors. Its simplicity, reproducibility, and reliability make it a useful screening test for anticipating difficult intubation, especially in rural tertiary care hospitals where early identification and preparedness are critical for patient safety.