Unanticipated difficulty during endotracheal intubation remains a major cause of anesthesia-related morbidity and mortality, with complications ranging from hypoxia and arrhythmias to cardiac arrest.^[1,2] Accurate preoperative prediction of difficult visualization of the larynx (DVL) is therefore essential for effective airway management and improved patient safety. Several bedside screening tests such as the Modified Mallampati classification (MPC), thyromental distance, and sternomental distance have been traditionally used to predict difficult laryngoscopy. However, these tests often show limited sensitivity and specificity and depend on patient cooperation and proper positioning, which may not always be feasible—particularly in critically ill or supine patients.^[3–6]   In 2013, Kamranmanesh et al. introduced the Acromio–Axillary–Suprasternal Notch Index (AASI) as a novel, objective, and position-independent predictor of DVL.^[7] AASI measures the relative depth of the neck into the thorax and can be assessed easily in the supine position. Early studies reported high diagnostic accuracy for AASI, but evidence remains limited, especially among diverse populations.^[8,9,10] The present study was designed to evaluate the diagnostic accuracy of AASI in predicting difficult visualization of the larynx in adult patients undergoing elective surgery under general anesthesia. We aimed to determine the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of AASI and to compare its performance with the Modified Mallampati classification.

Methodology

Study Design and Setting

A prospective observational study was conducted in the Department of Anaesthesiology, in a superspeciality medical college hospital from September 2022 to September 2023, after obtaining Institutional Research committee (IRC No: 378/08/2022) and Ethics Committee approval (IEC No: 47/623/09/2022).

Participants

Adult patients (18–70 years, ASA physical status I–II) scheduled for elective surgeries under general anesthesia with endotracheal intubation were included by consecutive sampling. Patients with head, neck, or thoracic deformities; cervical spine abnormalities; prior head and neck surgery; history of difficult airway; obesity (BMI > 30 kg/m²); obstetric cases; or inability to open the mouth were excluded.

Sample size

Consecutive sampling was done- consecutive cases meeting the eligibility criteria was included in the study. Sample size was calculated using sensitivity and specificity. Highest sample size was found to be 131.

Measurement of AASI

With the patient in the supine position and arms resting alongside the body, a vertical line (A) was drawn from the acromion process to the upper border of the axilla at the level of the pectoralis major. A perpendicular line (B) was extended from the suprasternal notch to intersect line A. The segment above the intersection was designated as line C. The Acromio–Axillary–Suprasternal Notch Index (AASI) was calculated as C/A.

Fig 1: Measurement of AASI

Airway Assessment and Laryngoscopy

Preoperative airway assessment included the Modified Mallampati classification (MPC). Following induction of general anesthesia with standard agents, laryngoscopy was performed in the sniffing position using a Macintosh blade by an anesthesiologist blinded to the AASI values. The laryngeal view was graded according to the modified Cormack–Lehane (CL) scale. Grades I–IIa were classified as easy visualization of the larynx (EVL) and grades IIb–IV as difficult visualization (DVL).

Statistical Analysis

Data were analyzed using SPSS version 25. Receiver operating characteristic (ROC) curve analysis was used to determine the diagnostic accuracy of AASI and identify the optimal cutoff value for predicting DVL. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated.  A  p-value < 0.05 was considered statistically significant.

Results

Age distribution

131 patients were enrolled for this study whose age group ranges from 21(minimum) to 70 (maximum) . Majority were of the age group 41-50 years (28.2%) and least patients from the age group 61- 70 years (9.9%). We noticed that majority patients had EVL, but in  elderly (61-70) and younger (21-30)groups , EVL and DVL both had roughly the same prevalence.

Table 1: Age distribution

Fig 2: Age distribution

Fig 3: Age v/s DVL , EVL

Table 2: Age v/s DVL , EVL

Gender distribution

Out of 131  patients in total,  63 (48.1% ) were females and 68 (51.9%) were males. Our study is consistent with other studies which state that the incidence of difficult airway is more in males than in females. In this study incidence of DVL  in males was 39% and in females was 26%.

Table 3: Gender distribution

Fig 4: Gender distribution

Table 4: Gender v/s EVL, DVL

Fig 5: Gender v/s EVL, DVL

BMI Distribution

BMI of the patients ranged from 18 to 29.1. BMI > 30 were not included in the study since obesity in itself is a predictor of difficult airway. None of the patients were underweight ( BMI < 18). 86 patients(65% ) were found to have normal weight. 45 patients (34%) were overweight. We studied BMI in these patients and  do not  see much increase in DVL with increase in BMI. This is probably because the effects of BMI on DVL is more apparent in the Obese ( BMI >30)

Table 5: BMI distribution

Table 6: BMI v/s DVL. EVL

Fig 6: BMI distribution

Fig 7: BMI v/s DVL. EVL

ASA status distribution

ASA physical status I and II were included in the study. 48 patients were ASA I (36.6%) and 83 patients were ASA II (63.4%). We do not see any evident co-relation between ASA physical status and DVL,

37.5 % of ASA I had DVL while 31.3 % of ASA II patients had DVL.

Table 7: ASA distribution

Fig 8: ASA distribution

Table 8: ASA v/s DVL, EVL

Fig 9 : ASA v/s DVL, EVL

Mallampatti class distribution

Modified Mallampatti classification revealed classes I,II,III and IV among the patients. 37 patients (28.2%) were class I, 65 (49.6%) were class II, 28 (21.4%) were class III and 1 patient was class IV. As expected MMC class I and II  had high fraction of EVL .However only one patient was found to have MMC class IV .However a significant fraction of MMC I and II were found to have DVL

Table 9: MMC distribution

Fig 10: MMC distribution

Table 10: MMC v/s DVL, EVL

Fig 11: MMC v/s DVL, EVL

CL Grade distribution

Cormack Lehane grading on direct laryngoscopy was recorded as grade I, IIA,IIB, IIIA,IIIB and IV. 54 patients(41.2%) had grade I, 33 patients (25.2%) had grade II A, 14 patients (10.7%) had grade IIB, 19 patients (14.5 %) had grade IIIA and 6 patients (4.6%) had IIIB and 5 patients (3.8%) had grade IV. We see a steady decline in frequency of patients at higher CL grades. The main focus of this study is to establish the co-relation between Line C/A and CL grading. We calculate the average line C for each grade of CL. We see a clear co relation between CL grade and Line C. We see that the mean of Line C increases with the CL grade, starting with Grade II B, which is the grade where difficult air way starts. The difference between the mean line C of each grade and the previous grade, is significant compared to the standard deviation of the line C values. The AASI value increases steadily with increase in CL grade. Due to the positive correlation between the AASI value and the CL grade, the AASI value can be used to predict difficulty in airway in patients. Patients with AASI greater than 0.469 are classified as difficult airway patients, whereas those with AASI lesser than 0.469 are classified as easy airway patients. This is because an AASI value of 0.469 corresponds to a CL grade of II B, which is the onset of difficulty in airway, as per literature.

Table 11: CL grade distribution

Fig 12:  CL grade distribution

Table 12: CL grade v/s  DVL, EVL

Fig 13: CL grade v/s  DVL, EVL

Table 13: CL grade V/S AASI

AASI

AASI values ranged from 0.2 to 0.83. The mean AASI value was 0.43 and standard deviation was 0.1. AASI value increases steadily with increase in CL grade. Due to positive correlation between AASI and CL grade , AASI can be used to predict difficult airway in patients.

Patients with AASI > 0.469 are classified as difficult airway patients and AASI < 0.469 are classified as easy airway. This is because AASI value of 0.469 corresponds to CL grade II b, which is the onset of difficult airway.

Fig 14: AASI v/s DVL, EVL

Table 14: AASI distribution

Fig 15: AASI distribution

Fig 16:  ROC curve of AASI, Line A , Line C for Difficult Visualization of Larynx.

Table 15: ROC curve of AASI, LINE A and LINE C for Difficult Visualization of Larynx.

Prevalence of DVL was 33.6%- 44 out of 131 patients had DVL. Optimum cut off value  of AASI for DVL is 0.469. AUC of AASI  is 0.86. Sensitivity of AASI was 72.73. Specificity of AASI was 87.36. Positive predictive value was 74.4 .Negative predictive value was 86.4

Discussion

Accurate preoperative prediction of a difficult airway is essential for patient safety during anesthesia.^{[15,16,17,18]} In this study, the Acromio–Axillary–Suprasternal Notch Index (AASI) demonstrated good diagnostic accuracy in predicting difficult visualization of the larynx (DVL), with an AUC of 0.86 and an optimal cutoff value of 0.46. Patients with higher AASI values were significantly more likely to experience DVL during direct laryngoscopy.

Our findings are consistent with those of Kamranmanesh et al., who first proposed the AASI and reported high sensitivity and specificity for predicting difficult laryngoscopy.^[7] Similar results were observed by Nasr and Anvari, who found an AUC of 0.857 and comparable predictive values.^[11] The present study thus supports the reproducibility of AASI across populations and reinforces its potential as a reliable bedside screening tool. Unlike conventional predictors such as the Modified Mallampati classification (MPC), AASI does not depend on patient cooperation or sitting posture, making it particularly useful for evaluating critically ill or immobilized patients.

While the Mallampati and other bedside tests (e.g., thyromental distance, sternomental distance, upper lip bite test) remain valuable, their combined sensitivity and specificity are limited.^[12,13,14] AASI, in contrast, provides an objective, measurable index that reflects the anatomical relationship of the thorax and neck — factors often contributing to difficult laryngoscopy. Its use in the supine position is an additional advantage, particularly in emergency and intensive care settings.

This study has certain limitations. Laryngoscopic grading may vary with operator technique, neck position, and laryngoscope size. The sample size, although adequate for primary analysis, was confined to ASA I–II patients, limiting generalizability to higher-risk populations. Future research should include larger, multicenter cohorts and assess the additive value of AASI when combined with existing predictive models.

Conclusion

The Acromio–Axillary–Suprasternal Notch Index (AASI) is a simple, reproducible, and position-independent predictor of difficult laryngoscopy. An AASI cutoff value of approximately 0.46 effectively distinguishes between easy and difficult visualization of the larynx. Given its ease of measurement in the supine position, AASI may complement traditional predictors such as the Modified Mallampati classification, especially when patient cooperation is limited. Further large-scale validation is recommended before routine clinical adoption.

Acknowledgements: The authors sincerely thank the patients who participated in the study, as well as the operation theatre staff and anesthesia technicians for their valuable support throughout the research.

Source of financial support: Nil

Conflict of interest: There are no conflicts of interest

Authors contribution: TAE concept, design, definition of intellectual content, literature search, clinical studies, experimental studies, data acquisition, data analysis, statistical analysis, manuscript preparation, manuscript editing and manuscript revision. LSM definition of intellectual content, literature search, clinical studies, experimental studies, data acquisition, data analysis, statistical analysis, manuscript preparation, manuscript editing and manuscript revision, manuscript review and is guarantor. SS  literature search, clinical studies, experimental studies, data acquisition, data analysis,  manuscript preparation, manuscript editing and manuscript revision, manuscript review .SUR definition of intellectual content ,overall supervision and guidance, manuscript review .

CTRI Number: CTRI/2024/02/062357

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