European Journal of Cardiovascular Medicine

Airway management is a cornerstone of anesthetic practice and one of the most critical determinants of patient safety in the perioperative setting. The ability to secure the airway rapidly and effectively through tracheal intubation is vital, as failure to do so can result in catastrophic outcomes such as hypoxia, brain injury, or death. The term “difficult airway” broadly encompasses difficulties with face-mask ventilation, supraglottic airway device placement, endotracheal intubation, or surgical airway access. Among these, the difficulty with laryngoscopic intubation is of greatest concern to anesthesiologists. Therefore, predicting a difficult airway preoperatively has been a subject of extensive clinical research and is of immense practical relevance.^[1]

Despite decades of investigation, unanticipated difficult intubations continue to challenge anesthesiologists. The incidence of difficult laryngoscopy varies from 1.5% to 13%, while failed intubation is reported in approximately 0.05% to 0.35% of elective surgical patients. In obstetric populations, the rate of failed intubation can be even higher due to physiological and anatomical changes of pregnancy. The Cormack-Lehane (CL) grading system, introduced in 1984, remains the gold standard for describing laryngeal view during direct laryngoscopy. Grades III and IV are generally considered “difficult laryngoscopy,” requiring multiple attempts, adjunctive devices, or alternative airway strategies. Because the CL grade can only be determined after induction of anesthesia and laryngoscopy, preoperative predictors are crucial to anticipate such scenarios.^[2]

Numerous bedside screening tests have been described for prediction of difficult laryngoscopy, such as the Mallampati classification, thyromental distance, inter-incisor gap, sternomental distance, upper lip bite test, and neck mobility assessment. Each of these evaluates specific anatomical or functional features that may affect visualization of the glottis. However, no single test has shown sufficient sensitivity or specificity to serve as a definitive predictor. Consequently, guidelines recommend combining multiple predictors to improve diagnostic accuracy. The American Society of Anesthesiologists (ASA) and other airway management societies emphasize the need for systematic airway assessment to minimize the risks associated with unanticipated difficulty.^[3]

The Modified Mallampati Test (MMT) is among the most widely used screening tools. It assesses the visibility of oropharyngeal structures with the patient seated, mouth open, and tongue protruded without phonation. Higher classes (III and IV) have been associated with difficult intubation. However, interobserver variability and poor predictive value when used alone limit its reliability. The thyromental distance (TMD), measured from the mentum to the thyroid notch with the neck extended, reflects the mandibular space available for tongue displacement. A shorter distance (<6.5 cm) suggests a potentially difficult laryngoscopy. Similarly, reduced inter-incisor distance (<3.5 cm), short sternomental distance (<12.5 cm), and restricted head extension have all been implicated as predictors.^[4]

The upper lip bite test (ULBT), introduced later, involves the ability of the lower incisors to bite the upper lip. It indirectly evaluates mandibular mobility and the relative alignment of the maxillary and mandibular structures. Several studies have found it to be a better single predictor compared with MMT, though its applicability is limited in edentulous patients. Other adjunctive assessments such as body mass index (BMI), presence of beard, receding mandible, macroglossia, and cervical spine deformities also contribute to the risk stratification.^[5]

Aim

To evaluate the association between preoperative difficult airway predictors and Cormack-Lehane grades in surgical patients undergoing general anesthesia.

Objectives

1. To assess the prevalence of difficult laryngoscopy (Cormack-Lehane grade III/IV) in the study population.
2. To evaluate the predictive accuracy of commonly used airway assessment tests (Mallampati, thyromental distance, sternomental distance, inter-incisor gap, upper lip bite test, and neck mobility).
3. To analyze the correlation between individual and combined predictors with observed Cormack-Lehane grades.

Source of Data

The study population comprised patients scheduled for elective surgical procedures under general anesthesia with endotracheal intubation, Department of Anaesthesiology, BAVMC, Pune at tertiary care teaching hospital.

Study Design

This was a hospital-based cross-sectional observational study.

Study Location

The study was conducted in the Department of Anaesthesiology, BAVMC, Pune at a tertiary care teaching hospital attached to a medical college.

Study Duration

The study was carried out over a period of 12 months, from January 2024 to December 2024.

Sample Size

A total of 160 patients were enrolled in the study based on predefined inclusion and exclusion criteria.

Inclusion Criteria

• Adult patients aged 18-65 years.
• ASA physical status I and II.
• Patients scheduled for elective surgery requiring endotracheal intubation under general anesthesia.
• Patients who provided informed written consent.

Exclusion Criteria

• Patients with known airway pathology (tumors, infections, congenital anomalies).
• Patients with limited mouth opening due to trauma, lockjaw, or temporomandibular joint ankylosis.
• Patients requiring rapid sequence induction, awake intubation, or emergency surgeries.
• Patients with cervical spine injury or instability.
• Pregnant women.

Procedure and Methodology

All enrolled patients underwent a standardized preoperative airway assessment by the investigator. The following predictors were measured and documented:

• Modified Mallampati Classification (Class I-IV).
• Thyromental Distance (TMD): measured in centimeters with the head fully extended.
• Sternomental Distance (SMD): measured from sternum to mentum with head extended.
• Inter-Incisor Distance (IID): maximum mouth opening measured in centimeters.
• Upper Lip Bite Test (ULBT): classified as Class I-III.
• Neck Mobility: assessed as normal, restricted extension, or fixed.
• Additional factors: BMI, presence of beard, short neck, or receding mandible.

After preoxygenation and induction with standard anesthetic agents, laryngoscopy was performed using a Macintosh blade by an anesthesiologist with at least three years of experience to minimize inter-observer variability. The laryngeal view was graded according to the Cormack-Lehane classification (Grade I-IV) during the first laryngoscopic attempt. External laryngeal manipulation (BURP maneuver) was allowed, and its requirement was documented. Difficult laryngoscopy was defined as CL Grade III or IV.

Sample Processing

Data from airway assessments and laryngoscopic grades were recorded in predesigned case record forms. Each patient was assigned a unique identification number to ensure confidentiality.

Statistical Methods

Data were entered into Microsoft Excel and analyzed using SPSS (version 27.0). Descriptive statistics were used to summarize baseline characteristics. Categorical variables were expressed as numbers and percentages; continuous variables as mean ± standard deviation. Association between predictors and CL grades was tested using Chi-square test or Fisher’s exact test. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for each predictor. Logistic regression analysis was performed to identify independent predictors of difficult laryngoscopy. A p-value <0.05 was considered statistically significant.

Data Collection

All relevant data were collected prospectively during the study period, starting from preoperative assessment to intraoperative laryngoscopy findings. The data were compiled, validated, and prepared for statistical analysis

Table 1. Association between difficult airway predictors and Cormack-Lehane grade III/IV (n = 160)

Table 1 shows the association between preoperative difficult airway predictors and the occurrence of difficult laryngoscopy defined as Cormack-Lehane grade III/IV. Among 160 patients, Mallampati class III/IV was present in 54 patients (33.8%), of whom 31.5% had difficult laryngoscopy, compared with only 13.2% in the lower Mallampati classes. This association was statistically significant (RR = 2.38, OR = 3.01, p = 0.0066). A similar trend was observed with a thyromental distance <6.5 cm, where 31.9% of exposed patients had difficulty compared with 14.2% of those with normal distance (RR = 2.25, OR = 2.85, p = 0.0098). Sternomental distance <12.5 cm also showed nearly doubled risk (RR = 1.96, OR = 2.37, p = 0.0409). An inter-incisor gap <3.5 cm was strongly associated, with 39.3% of these patients experiencing difficulty compared with 15.2% in those with adequate gap (RR = 2.58, OR = 3.57, p = 0.0042). Similarly, upper lip bite test class III, limited neck extension, receding mandible, and short neck were all significantly associated with difficult laryngoscopy (p < 0.05). High BMI (≥30 kg/m²) showed a higher prevalence of difficulty (30.3% vs. 16.5%) but did not reach statistical significance (p = 0.0897).

Figure 1

Table 2: Prevalence of difficult laryngoscopy (Cormack-Lehane grade III/IV) in the study population (n = 160)

Table 2 presents the prevalence of difficult laryngoscopy in the study cohort. Out of 160 patients, 31 (19.4%) had Cormack-Lehane grade III/IV with a Wilson 95% CI of 13.9-26.5%. When stratified by sex, males had a higher prevalence (22.9%) compared with females (15.6%), although the difference was not statistically significant (p = 0.289). By age group, prevalence increased slightly with age: 15.5% in patients <40 years, 20.9% in those aged 40-59 years, and 22.9% in patients ≥60 years, but no significant association was observed (p = 0.5384). In terms of BMI, prevalence was 13.9% in normal-weight patients, 20.0% in overweight patients, and 30.3% in obese patients. Although there was a rising trend with BMI, this also did not reach statistical significance (p = 0.167).

Figure 2

Table 3: Predictive accuracy of preoperative airway assessment tests for difficult laryngoscopy (n = 160)

Table 3 outlines the predictive accuracy of individual airway assessment tests. Mallampati class III/IV had the highest sensitivity (54.8%, 95% CI: 37.8-70.8%) with good specificity (87.6%, 95% CI: 80.3-92.6%) and an excellent negative predictive value (93.4%). Thyromental distance <6.5 cm showed slightly lower sensitivity (48.4%) but comparable specificity (85.3%) and NPV (91.6%). Sternomental distance <12.5 cm had lower sensitivity (38.7%) but maintained good specificity (84.5%). Inter-incisor gap <3.5 cm demonstrated high specificity (84.8%) and the highest positive predictive value among tests (39.3%). Upper lip bite test class III performed similarly with sensitivity 45.2% and specificity 85.7%. Limited neck extension, receding mandible, and short neck all had modest sensitivities (25-39%) but retained acceptable specificities (>83%). BMI ≥30 kg/m² had low sensitivity (32.3%) and was not statistically significant (p = 0.0897).

Figure 3

Table 4A: Multivariable logistic regression of predictors for difficult laryngoscopy

Table 4A presents the results of multivariable logistic regression after adjusting for potential confounders. Mallampati class III/IV remained a strong independent predictor (aOR = 2.71, 95% CI: 1.29-5.70, p = 0.008). Similarly, thyromental distance <6.5 cm (aOR = 2.12, p = 0.043), inter-incisor gap <3.5 cm (aOR = 2.87, p = 0.014), upper lip bite test class III (aOR = 2.29, p = 0.031), and limited neck extension (aOR = 2.24, p = 0.045) all showed statistically significant independent associations. BMI ≥30 kg/m² demonstrated a modest increase in risk (aOR = 1.78) but was not statistically significant (p = 0.149).

Figure 4A

Table 4B: Combined predictor count and risk gradient

(χ² for trend = 9.86, p = 0.0017)

Table 4B highlights the combined effect of multiple predictors. Patients with 0-1 predictors had only a 9.0% incidence of difficult laryngoscopy. This increased significantly to 24.6% in those with 2-3 predictors (RR = 2.74, 95% CI: 1.16-6.47) and further to 40.0% in those with ≥4 predictors (RR = 4.42, 95% CI: 1.82-10.77). The chi-square test for trend was highly significant (χ² = 9.86, p = 0.0017), indicating a dose-response relationship.

Figure 4B

In this cross-sectional cohort of 160 adults, the overall prevalence of difficult laryngoscopy (Cormack-Lehane [CL] III/IV) was 19.4% (Table 2). This point estimate is higher than the 1-13% range frequently reported for difficult laryngoscopy in mixed elective populations, and toward the upper bound of what older series described for “difficult glottic view” rather than failed intubation per se. Differences likely reflect the definition of “difficulty” (strict CL III/IV), operator standardization, and the enrichment of risk markers in our surgical case mix. Comparable fluctuations are evident across meta-analyses and hospital registries when different operational definitions are used.

Individual predictors. In keeping with prior evidence, several preoperative bedside tests were significantly associated with difficult laryngoscopy in univariable analyses (Table 1): Mallampati III/IV (RR 2.38; OR 3.01), thyromental distance (TMD) <6.5 cm (RR 2.25; OR 2.85), inter-incisor gap (IID) <3.5 cm (RR 2.58; OR 3.57), upper lip bite test (ULBT) class III (RR 2.38; OR 3.12), limited neck extension (RR 2.18; OR 2.75), receding mandible (RR 2.11; OR 2.70), and short neck (RR 2.07; OR 2.66) were all statistically significant (p<0.05). The magnitude and direction of these associations mirror the aggregated effects reported in classic by Yuan J et al.(2024)^[6] and El-Tawansy A et al.(2024)^[7], which consistently show that tests reflecting oropharyngeal space (Mallampati), mandibular space (TMD, IID), mandibular mobility/alignment (ULBT, retrognathia), and cervical extension carry the most signal for difficult laryngoscopy. The ULBT in particular has repeatedly exhibited favorable discrimination as a single bedside test, a pattern reproduced here (OR ~3.1), aligning with Patel JD et al.(2025)^[8] who originally reported superior performance versus Mallampati.

Diagnostic performance. No single test in our dataset achieved both high sensitivity and high specificity (Table 3), a finding that is remarkably consistent with the literature. Mallampati III/IV displayed the highest sensitivity (54.8%) with good specificity (87.6%) and a high NPV (93.4%), making it useful for “ruling out” difficulty when low. IID <3.5 cm offered the highest PPV (39.3%) among the tests, emphasizing its rule-in value when markedly reduced. The performance of TMD and SMD was intermediate, again paralleling earlier reports that their predictive value is real but modest when used in isolation. Practically, these data reinforce the longstanding guidance that no single screening test suffices; combining complementary predictors improves clinical utility. Patel JD et al.(2025)^[8]

Multivariable effects and cumulative burden. After adjustment, Mallampati III/IV (aOR 2.71), IID <3.5 cm (aOR 2.87), TMD <6.5 cm (aOR 2.12), ULBT class III (aOR 2.29), and limited neck extension (aOR 2.24) remained independently associated with CL III/IV (Table 4A). This pattern underscores a common mechanistic thread: limited oropharyngeal visualization, inadequate mandibular space, and restricted atlanto-occipital extension synergistically impair the laryngoscopic line of sight. The dose-response across combined-predictor strata was pronounced (9.0% vs 24.6% vs 40.0% difficult; p-trend = 0.0017; Table 4B), echoing the composite risk frameworks and scoring approaches proposed in earlier observational work (e.g., Wilson score, Samsoon-Young modification of Mallampati), where accumulated abnormalities sharply escalate the odds of difficult laryngoscopy. Krishnamoorthy DG et al.(2025)^[9]

Anthropometry. Obesity (BMI ≥ 30 kg/m²) showed a higher crude prevalence of difficult laryngoscopy (30.3%) with non-significant adjusted effect (aOR 1.78, p=0.149). This nuance is consistent with large perioperative datasets: while BMI is a robust determinant of difficult mask ventilation, its independent association with difficult laryngoscopy attenuates when craniofacial and neck mobility variables are co-modeled. Yirga S et al.(2025)^[10] In other words, BMI may act as a proxy for correlated anatomic constraints; once those are directly measured (IID, ULBT, TMD, neck extension), BMI’s residual independent signal diminishes.

Context with prior evidence and practice. The present findings align with core principles in airway assessment: (i) visualization predictors (Mallampati, ULBT) and space/mobility predictors (IID, TMD, neck extension) are the most informative; (ii) specificity and NPV are generally higher than PPV and sensitivity for single tests; and (iii) risk rises steeply as abnormalities accumulate. These convergent signals support guideline-endorsed strategies favoring multimodal assessment and pre-emptive planning, ensuring the availability of video laryngoscopy, external laryngeal manipulation, and adjuncts in patients who “stack up” multiple high-risk features. Cangiani LH et al.(2025)^[11]

Implications. For day-to-day practice, a streamlined composite using Mallampati, IID, TMD, ULBT, and neck extension can be operationalized at the bedside within minutes. Patients in the ≥ 2-predictor strata (Table 4B) merit a heightened readiness posture (skilled assistance, Plan B devices open, consideration of ramping/positioning optimization). Future work could explore combined/weighted scores calibrated on local populations and modern adjuncts (e.g., video laryngoscopy as first-pass in high-risk phenotypes), while validating cutoffs that may vary by craniofacial anthropometry across regions. Gupta A et al.(2025)^[12]

This cross-sectional study demonstrated that several bedside airway assessment tests, including Mallampati classification, thyromental distance, inter-incisor gap, upper lip bite test, and neck extension, were significantly associated with difficult laryngoscopy defined by Cormack-Lehane grade III/IV. The findings confirm that no single predictor offers sufficient accuracy in isolation, but the risk of difficulty increases substantially with the accumulation of multiple predictors. These results support the routine use of a composite, multimodal preoperative airway assessment to anticipate and plan for potential intubation challenges, thereby improving perioperative safety.

LIMITATIONS

1. Single-center design limits generalizability; the results may not be applicable to different populations with varied craniofacial or anthropometric profiles.
2. Sample size (n=160), though adequate for primary analysis, may not be large enough to detect small effect sizes for less common predictors such as short neck or receding mandible.
3. Observer bias could not be fully excluded, as airway assessments were performed by a single investigator and laryngoscopic grading involved subjective interpretation.
4. Only conventional direct laryngoscopy was used; adjunct techniques such as video laryngoscopy, which may alter glottic visualization, were not evaluated.
5. The study excluded emergency, obstetric, and pediatric populations, so findings cannot be extrapolated to these high-risk groups.

1. Abdel Aziz GM, Mohamed HA, Hasan AM. Prediction of Difficult Airway Using Sonographic Assessment of Pre-Epiglottic Space Versus Mallampati Grading in Correlation to Cormack Lehane Grading. Zagazig University Medical Journal. 2024 Dec 1;30(9):4724-35.
2. Nagabhushanam K, Chalapathy P, Emeema B, Charan MV. Correlation of Ultrasonographic Airway Assessment with Cormack-Lehane Grading in Adult Patients. European Journal of Cardiovascular Medicine. 2024 Apr 1;14(2).
3. Sadaf S, Afzal W, Kousar R. Comparison of four airway assessment tools to predict difficult endotracheal intubation: A cross-sectional study to facilitate early-year residents in anesthesia training. The Professional Medical Journal. 2025 Sep 4;32(09):1103-9.
4. Shakeel MA, Khan SA, Shah SQ, Yasin B, Bhalli AH, Hajra MM. Neck Circumference as Sole Predictor of Cormack-Lehane Score and Difficult Intubation. Pakistan Armed Forces Medical Journal. 2025 Jul 31;75:S718.
5. Taboada M, Almeida X, Cariñena A, Costa J, Carmona-Monge J, Agilda A, Barreiro L, Castillo J, Williams K, Segurola J, Álvarez J. Complications and degree of difficulty of orotracheal intubation in the Intensive Care Unit before and after the establishment of an intubation protocol for critically ill patients: a prospective, observational study. Revista Española de Anestesiología y Reanimación (English Edition). 2024 Jan 1;71(1):17-27.
6. Yuan J, Ye H, Tan X, Zhang H, Sun J. Determinants of difficult laryngoscopy based on upper airway indicators: a prospective observational study. BMC anesthesiology. 2024 Apr 24;24(1):157.
7. El-Tawansy A, Elnajar AM, Mahmoud HA, Amin MI, Bedewy AA. Validity of Airway Ultrasound in Correlation with Cormack-Lehane Grading in Obese Patients: A Cross-Sectional Study. Anesthesiology and Pain Medicine. 2024 Mar 24;14(2):e142701.
8. Patel JD, Chaudhary PD, Chandak AA. A Prospective Observational Study on the Incidence and Predictors of Difficult Airway in Patients Undergoing Elective Surgeries Under General Anesthesia. Journal of Heart Valve Disease. 2025 Jul 16;30:113-7.
9. Krishnamoorthy DG, Devendra Prasad KJ, Rajesh K, Nikhil Reddy Y, Aravind SR. Unlocking Airway Predictability: The Role of Ultrasound in Assessing Cormack-Lehane Grade Through Anterior Neck Soft Tissue Thickness at the Level of Vocal Cords and Hyoid Bone. Journal of Intensive Care Medicine. 2025 Jul;40(7):798-806.
10. Yirga S, Samuel H, Markos Z, Yohannes W. Comparison of modified Mallampati test with and without phonation for prediction of difficult laryngoscopy and intubation among adult surgical patients: cross-sectional study. Annals of Medicine and Surgery. 2025 Jan 1;87(1):85-92.
11. Cangiani LH, Alves RL, Mizubuti GB, e Lima RM, e Lima LH. Evaluation of the cutaneous-epiglottic distance obtained by ultrasound in predicting difficult laryngoscopy in adult patients: an observational study. Brazilian Journal of Anesthesiology (English Edition). 2025 May 9:844637.
12. Gupta A, Srinivasan G. Evaluation of Airway Parameters to Predict Difficult Laryngoscopy in Paediatric Patients Undergoing Surgery. Indian Journal of Critical Care Medicine: Peer-reviewed, Official Publication of Indian Society of Critical Care Medicine. 2025 May 31;29(Suppl 1):S237.