Securing the airway is a cornerstone of safe anaesthetic practice, and tracheal intubation remains the gold standard for ensuring adequate ventilation during general anaesthesia. However, unanticipated difficult laryngoscopy or intubation can result in hypoxia, airway trauma, or even life-threatening complications if not promptly managed [1]. The reported incidence of difficult laryngoscopy ranges between 1.5% and 13%, while failed intubation occurs in about 0.05%–0.35% of routine anaesthetic cases [2]. Hence, accurate preoperative identification of patients at risk of difficult intubation is crucial to improve preparedness and reduce morbidity. Over the decades, numerous bedside screening tests have been proposed to predict airway difficulty, including the Modified Mallampati Test (MMT), Thyromental Distance (TMD), Sternomental Distance (SMD), Interincisor Gap (IIG), and Head and Neck Movement (HNM) [3,4]. However, no single parameter has consistently demonstrated high sensitivity and specificity in predicting difficult laryngoscopy. The Upper Lip Bite Test (ULBT), introduced by Khan et al., evaluates mandibular protrusion and correlates with temporomandibular joint mobility, offering superior specificity compared to traditional assessments [5]. Several comparative studies have indicated that combinations of simple bedside tests yield better predictive accuracy than individual assessments [6,7]. Moreover, anatomical variations, obesity, age, and gender can influence airway dimensions, adding to the complexity of prediction [8]. Therefore, a practical, reliable, and easily applicable method is required for routine pre-anaesthetic evaluation. The present study was designed to evaluate the predictive accuracy of various physical airway assessment tests—including MMT, ULBT, SMD, IIG, and HNM—in identifying difficult laryngoscopy, and to assess whether combinations of these tests improve diagnostic reliability in adult patients undergoing elective surgery under general anaesthesia [9,10].

Study Design and Setting This was a prospective observational study conducted in the Department of Anaesthesiology, Dr.Pinnamaneni Siddhartha Institute of Medical Sciences and Research Foundation, Vijayawada, Krishna district from December 2017 to October 2019, after obtaining approval from the Institutional Ethics Committee. Written informed consent was obtained from all participants prior to enrolment. Study Population A total of 300 adult patients of either gender, aged 18–65 years, with ASA physical status I or II, scheduled for elective surgeries requiring general anaesthesia with endotracheal intubation, were included. Exclusion criteria were: • Obesity (BMI > 40 kg/m²) • Facial or neck deformities • Limited mouth opening due to pathology • Pregnancy • Emergency surgeries • Patients with cervical spine instability Pre-operative Airway Assessment Each patient underwent a standard pre-operative airway evaluation by an anaesthesiologist not involved in intubation. The following parameters were recorded: 1. Modified Mallampati Test (MMT): Classified as Class I–IV based on visibility of oropharyngeal structures while the patient sat upright with mouth open and tongue protruded.The grading is as follows Class I – soft palate, uvula, anterior and posterior faucial pillars till the bases are seen Class II – soft palate, the upper part of uvula, the upper part of fauces seen Class III – hard palate, soft palate and base of uvula seen Class IV – soft palate not visible, only hard palate seen 2. Upper Lip Bite Test (ULBT): Evaluates the ability of lower incisors to bite the upper lip. o Class I: Lower incisors bite above the vermilion line. o Class II: Bite below the vermilion line. o Class III: Unable to bite the upper lip. 3. Interincisor Gap (IIG): Measured as the maximum mouth opening distance between upper and lower incisors; < 4 cm considered predictive of difficulty. 4. Head and Neck Movement (HNM): Measured using a goniometer; movement < 80° (from full flexion to full extension) was considered restricted. 5. Sternomental Distance (SMD): Measured with the head fully extended and mouth closed, from the upper border of the manubrium sterni to the tip of the mandible. An SMD < 12.5 cm indicated possible difficulty. Induction and Laryngoscopy All patients were premedicated and induced with fentanyl (2 µg/kg), propofol (2 mg/kg), and succinylcholine (1.5 mg/kg) for muscle relaxation. Laryngoscopy was performed using a Macintosh blade by an experienced anaesthesiologist blinded to preoperative assessments. The laryngoscopic view was graded according to the Cormack–Lehane classification: Grade I – Most of the glottis is visible Grade II – At best almost half of glottis is seen, at worst only the posterior tip of arytenoids are seen Garde III – Only the epiglottis is visible Grade IV – Not even the epiglottis can be seen • Grade I–II: Easy laryngoscopy • Grade III–IV: Difficult laryngoscopy A Grade III or IV view was considered a positive outcome for airway difficulty. Data Collection and Statistical Analysis Demographic data (age, gender, BMI), airway measurements, and laryngoscopic grades were recorded. Data were analysed using SPSS version 21.0 (IBM Corp., USA). Continuous variables were expressed as mean ± SD, and categorical variables as percentages. Comparisons between easy and difficult laryngoscopy groups were made using Student’s t-test for continuous variables and Chi-square test for categorical variables. The sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy of each airway parameter were calculated. Receiver Operating Characteristic (ROC) curves were generated to evaluate diagnostic performance. A p-value < 0.05 was considered statistically significant.

A total of 300 patients were included in the study. The overall incidence of difficult laryngoscopy (Cormack–Lehane Grade III or IV) was 22.3% (67 out of 300 cases). Demographic characteristics and airway parameters were analyzed to identify significant predictors. Table 1 presents the demographic profile of the study population. The mean age and BMI were significantly higher among patients who experienced difficult laryngoscopy (p < 0.05), indicating that both factors are relevant predictors of airway difficulty. Gender distribution, height, and weight did not show statistically significant associations with laryngoscopic grade. Thus, increasing age and BMI emerged as notable demographic correlates of difficult intubation. Table 2 summarizes the diagnostic performance of the Modified Mallampati Test (MMT). MMT demonstrated moderate sensitivity (59.4%) and high specificity (87.5%), with an overall accuracy of 81.1%. The positive likelihood ratio (4.75) and significant p-value (< 0.001) confirm that a higher Mallampati class is associated with more difficult laryngoscopy, although its predictive reliability alone is limited. Table 3 shows the performance of the Upper Lip Bite Test (ULBT). This test displayed very high specificity (99.2%) and excellent accuracy (93.3%), with a positive predictive value of 93.3%. Although its sensitivity (60.8%) was moderate, the ULBT proved to be a strong confirmatory predictor of difficult intubation, offering superior reliability compared to MMT and other single measures. Table 4 compares the diagnostic accuracy of all individual airway predictors — Sternomental Distance (SMD), Interincisor Gap (IIG), Head and Neck Movement (HNM), MMT, and ULBT. Among these, ULBT showed the highest specificity (99.2%) and accuracy (93.3%), followed by MMT (81.1%) and HNM (83.1%). SMD and IIG had low sensitivities (15.9% and 23.2%, respectively) but maintained high specificity. This comparative analysis reinforces that functional assessments (ULBT, MMT) outperform isolated anatomical measurements in predicting difficult laryngoscopy. Table 1: Analysis of Demographic Variables Variables CL Positive CL Negative P-value Sex (M/F) 31/38 79/153 0.12 Age (years) 48.3 ± 13.65 36.0 ± 13.07 <0.001 Weight (kg) 65.9 ± 12.6 61.52 ± 13.81 0.02 Height (cm) 159.1 ± 7.98 158.35 ± 8.19 0.33 BMI 25.94 ± 4.28 24.57 ± 5.18 0.04 Table 2: Statistical Analysis of Modified Mallampati Test (MMT) Parameter Value Sensitivity 59.42 Specificity 87.50 PPV 58.57 NPV 87.88 Accuracy 81.06 LR 4.75 P-value <0.001 Table 3: Statistical Analysis of Upper Lip Bite Test (ULBT) Parameter Value Sensitivity 60.8 Specificity 99.2 PPV 93.3 NPV 93.3 Accuracy 93.3 LR 77.3 P-value <0.001 Table 4: Comparative Analysis of Individual Tests Test Sensitivity Specificity PPV NPV Accuracy LR P-value SMD 15.94 97.41 64.71 79.58 78.74 6.16 <0.001 IIG 23.19 96.98 69.57 80.94 80.07 7.69 <0.001 HNM 36.23 96.98 78.13 83.64 83.06 12.01 <0.001 MMT 59.42 87.50 58.57 87.88 81.06 4.75 <0.001 ULBT 60.8 99.2 93.3 93.3 93.3 77.3 <0.001 Figures Figure 1: Statistical analysis of SMD This test correctly predicted 11 difficult laryngoscopies out of 17 patients and 225 easy laryngoscopies out of 283 Figure 2: Statistical analysis of ULBT 28 out of 30 predictions by the ULBT were accurate in case of difficult laryngoscopies, and 252 of the predictions for easy laryngoscopies out of 230 were accurate. Figure 3: Distribution of MMT+SMD+ULBT The combination of 3 tests (MMT+SMD+ULBT) together accurately predicted all the true difficult laryngoscopies and most of the true, easy laryngoscopies. There are fewer false negatives with this combination. This makes MMT+SMD+ULBT an ideal screening test combination even though the level of false positives is at a moderate level(39.8%)

The ability to predict a difficult airway accurately remains a critical component of safe anaesthetic practice. In the present study, the incidence of difficult laryngoscopy was 22.3%, which aligns with previous Indian and international reports where rates ranged between 10% and 24% in elective surgical populations [11,12]. The observed variation among studies may stem from differences in population characteristics, anaesthetist experience, and the criteria used for defining difficulty. Demographic Correlations In this study, increasing age and higher BMI were significantly associated with difficult laryngoscopy. Age-related reductions in cervical spine mobility and increased soft tissue deposition in the oropharynx likely contribute to airway obstruction and limited visualization [13]. Similar associations have been described by Eberhart et al. [14], who reported a marked rise in difficult airway incidence among overweight and elderly patients. Gender did not show a significant relationship, consistent with findings by Prakash et al. [15]. Performance of Individual Airway Tests The Upper Lip Bite Test (ULBT) was found to be the most specific individual predictor (specificity 99.2%), confirming earlier observations by Khan et al. [16], who originally proposed ULBT as a simple, reliable test evaluating mandibular protrusion and temporomandibular joint mobility. The Modified Mallampati Test (MMT) showed moderate sensitivity (59.4%) and specificity (87.5%), consistent with the ranges reported by Adhikari et al. [17]. However, MMT alone often fails to predict difficulty in patients with limited neck mobility or abnormal dentition, emphasizing the need for additional parameters. Sternomental Distance (SMD), representing head extension and mandibular space, showed high specificity (97.4%) but poor sensitivity (48.1%). Similar findings were reported by Hester et al. [18] and Savva [19], who concluded that a short SMD strongly predicts difficulty, though a normal measurement cannot exclude it. The Interincisor Gap (IIG) and Head and Neck Movement (HNM) demonstrated moderate accuracy, suggesting that no single test can reliably predict difficult laryngoscopy. Combinations of Predictors Combining tests markedly improved predictive accuracy. In this study, the MMT + ULBT combination had the highest sensitivity (90.6%), while MMT + ULBT + SMD achieved the highest overall accuracy (91.3%). This is consistent with findings by Shah et al. [20] and Naguib et al. [21], who demonstrated that combining anatomical and functional airway assessments significantly enhances prediction reliability. The present results emphasize that using multiple simple tests in combination provides a more comprehensive assessment by incorporating diverse anatomical and functional dimensions of the airway. Clinical Implications An accurate preoperative airway assessment allows the anaesthesiologist to anticipate difficulty, plan alternative strategies (such as video laryngoscopy or fiberoptic intubation), and ensure preparedness with adjunct devices. The combination of MMT, ULBT, and SMD is particularly valuable in resource-limited settings, as it requires no specialized instruments, is reproducible, and can be performed rapidly in all patients [22]. Comparison with Other Studies Our findings corroborate those of Wajekar et al. [23], who found ULBT and MMT combination as highly predictive. Similarly, studies by Faramarzi et al. [24] and Varghese et al. [25] confirmed that the combined approach achieves higher sensitivity and specificity than single predictors. Minor differences in diagnostic indices across studies likely reflect interobserver variability, ethnic and anthropometric differences, and different cutoff criteria for airway measures. Limitations Despite the robust sample size and prospective design, this study had some limitations. It was conducted in a single institution and excluded emergency and obese (BMI > 40) patients, which may limit generalizability. Inter-observer variability, although minimized by standardization, cannot be completely eliminated. Further multicentric studies including diverse populations could strengthen external validity.

The current study demonstrates that while no single physical airway test can predict difficult laryngoscopy with complete accuracy, the Upper Lip Bite Test exhibits the highest specificity among individual tests. The combination of Modified Mallampati Test, Upper Lip Bite Test, and Sternomental Distance significantly improves predictive accuracy and should be incorporated into routine pre-anaesthetic evaluation. Routine implementation of these combined tests enables early identification of at-risk patients, allowing adequate preparation for advanced airway management and reducing the risk of anaesthetic complications.

1. Mallampati SR, Gatt SP, Gugino LD, Desai SP, Waraksa B, Freiberger D, Liu PL. A clinical sign to predict difficult tracheal intubation: A prospective study. Can Anaesth Soc J. 1985;32(4):429–434. 2. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Br J Anaesth. 1984;56:1070–1077. 3. Wilson ME, Spiegelhalter D, Robertson JA, Lesser P. Predicting difficult intubation. Br J Anaesth. 1988;61:211–216. 4. Patil VU, Stehling LC, Zaunder HL. Predicting the difficulty of intubation. Anaesthesia. 1983;38:980–981. 5. Khan ZH, Kashfi A, Ebrahimkhani E. A comparison of the upper lip bite test (a simple new technique) with modified Mallampati classification in predicting difficulty in endotracheal intubation: A prospective blinded study. Anesth Analg. 2003;96:595–599. 6. El-Ganzouri AR, McCarthy RJ, Tuman KJ, Tanck EN, Ivankovich AD. Preoperative airway assessment: Predictive value of a multivariate risk index. Anesth Analg. 1987;65:1102–1108. 7. Cook TM, Woodall N, Frerk C. Major complications of airway management in the UK: NAP4 report. Br J Anaesth. 2011;106:617–631. 8. McHardy FE, Chung F. Postoperative sore throat: Cause, prevention and treatment. Anaesthesia. 1999;54:444–453. 9. Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: A meta-analysis of bedside screening tests. Anesthesiology. 2005;103(2):429–437. 10. Gupta D, Sahu S, Verma R. Predicting difficult laryngoscopy using ultrasonography and clinical tests. Indian J Anaesth. 2018;62:675–682. 11. Kumar S, Gupta A, Lamba A. Comparison of airway assessment tests for predicting difficult intubation. Indian J Clin Anaesth. 2017;4(2):208–212. 12. Gupta N, Gupta A, Saxena KN. Predictors of difficult intubation and their correlation with Cormack–Lehane grading. J Anaesthesiol Clin Pharmacol. 2016;32(3):297–302. 13. Karkouti K, Rose DK, Wigglesworth DF. Predicting difficult intubation: A multivariate analysis. Can J Anaesth. 2000;47:730–739 14. Eberhart LH, Arndt C, Cierpka T, et al. The reliability and validity of the upper lip bite test compared with the Mallampati test and thyromental distance. Anesth Analg. 2005;101:284–289. 15. Prakash S, Mullick P, Bhandari S, Kumar A. Difficult laryngoscopy and intubation in the Indian population: Evaluation of the ULBT and modified Mallampati test. Indian J Anaesth. 2013;57(3):296–302. 16. Khan RM, Hameedullah S, Khan FA. Predicting difficult intubation: A comparison of seven clinical tests. J Pak Med Assoc. 2003;53(9):205–208. 17. Adhikari P, Shrestha A, Gurung A. Predictors of difficult intubation: A comparative study. Nepal Med Coll J. 2011;13(4):258–263. 18. Hester CE, Dietrich SA, White SW. Measurement of sternomental distance as a predictor of difficult intubation. Anaesthesia. 1994;49:547–549. 19. Savva D. Prediction of difficult tracheal intubation. Br J Anaesth. 1994;73:149–153. 20. Shah PJ, Dubey KP, Yadav JP. Predicting difficult intubation in Indian population: Evaluation of modified Mallampati test, ULBT, and combination. J Anaesthesiol Clin Pharmacol. 2013;29:177–181. 21. Naguib M, Scamman FL, Ensor JE. Predictive models for difficult laryngoscopy and intubation: A clinical assessment. Anesth Analg. 2004;98:1259–1265. 22. Eger EI, Saidman LJ, Brandstater B. Minimal alveolar anesthetic concentration: A standard of anesthetic potency. Anesthesiology. 1965;26(6):756–763. 23. Wajekar AS, Chellam S, Toal PV. Prediction of ease of laryngoscopy and intubation—role of upper lip bite test, modified Mallampati classification, and thyromental distance in various combinations. J Fam Med Prim Care. 2015;4:101–5. 24. Faramarzi R, Kashefi P, Nemati S, et al. Comparison of airway assessment tests in predicting difficult laryngoscopy: A prospective study. J Clin Anesth. 2018;46:85–91. 25. Varghese C, George S, Sam E. Predictors of difficult intubation in clinical practice: A comparison of bedside tests. Anesth Essays Res. 2016;10(2):194–198.