Airway management is a critical aspect of anaesthesia practice, with many incidents arising from challenges in maintaining or securing the airway1-3. One of the most significant challenges anesthesiologists’faces ismanaging an unpredictable and difficult airway during intubation, a situation that can arise unexpectedly and demands prompt and precise action. Accurate preoperative airway assessment plays a pivotal role in identifying patients at risk of difficult airway scenarios, allowing clinicians to implement tailored strategies for optimal management. Failure to properly manage the airway is a leading cause of adverse outcomes, including patient morbidity and mortality4.Encountering an unexpected difficult laryngoscopy is a challenge that nearly every clinician has faced at some point, even when pre-procedural airway assessments suggest otherwise. The prevalence of difficult laryngoscopy in the general population is estimated to range from 1.5% to 13%, underscoring its unpredictability and the complexity of airway management5-7.

A variety of clinical criteria have been developed to evaluate a patient's airway prior to the induction of anesthesia. These include assessments such as mouth-opening measurement, Mallampati classification, jaw protrusion test, neck extension evaluation, thyromental distance measurement, and the upper-lip bite test8. Furthermore, studies have indicated that these methods have low sensitivity and often lack sufficient negative predictive value, meaning they are not consistently reliable in ruling out the possibility of a difficult airway9-11.

Among the parameters used to predict airway difficulty, the laryngeal inlet's appearance during direct laryngoscopy is considered a significant indicator. This is most effectively described using the Cormack-Lehane (CL) grading system, which categorizes the laryngeal view obtained during laryngoscopy. While the CL grade is a reliable predictor of difficult intubation, its utility is limited to patients already under anaesthesia since it requires direct laryngoscopic visualization of the airway. As a result, it cannot be employed during pre-anaesthetic airway evaluations 12-13.According to the Cormack-Lehane (CL) classification, difficult laryngoscopy corresponds to grades 2b, 3a, 3b, and 4. The incidence of difficult laryngoscopy is reported in the literature to range between 5% and 10% 1-2.

In recent years, ultrasound technology has gained significant recognition as a valuable tool in the field of anesthesia. Its non-invasive nature, simple, bedside technique coupled with its ability to provide real-time imaging of airway structures, has made it an increasingly favored method for enhancing preoperative airway assessments 14-15.

Aim:

To evaluate the ultrasonographic measurement of skin to epiglottis distance in correlation with Cormack- Lehane grading as a predictor of difficult laryngoscopy.

Objectives:

1. To estimate diagnostic accuracy of Ultrasonographic Distance from Skin to Epiglottis (DSE) measurement as a predictor of difficult laryngoscopy.
2. To evaluate the preoperative ultrasonographic measurement of the Distance from Skin to Epiglottis (DSE) as a predictor of difficult laryngoscopy by analyzing its correlation with the Cormack-Lehane grading system.

We conducted an observational study on 400 adult patients of either sex undergoing elective surgery under general anesthesia between August 2023 and January 2025 at Department of Anaesthesiology, Government Medical College, Srinagar after ethical committee approval. Patients aged 18 years and older with ASA grade I-III and willing to participate in this study were included.

Patients with anatomical abnormalities affecting the airway, restricted neck movements, limited mouth opening, edentulism, cervical tumours, goiter, morbid obesity (BMI >35), Pregnant patients, patients having MPS grade III & IV, patients having tracheostomy tubes were excluded.

Detailed pre-anesthetic history and physical examination including airway evaluation were done one day prior to surgery. Modified Mallampati score (MPS), thyromental distance (TMD), maximum mouth opening and neck mobility were recorded.

After clinical examination and airway assessment, all participants underwent Ultrasonographic evaluation to determine the DSE. The measurements were taken at the thyrohyoid membrane, positioned midway between the hyoid bone and the thyroid cartilage using a high frequency linear transducer probe (L38) operating at a frequency of 5-10 MHz (SonoSite M-Turbo) with assessments performed in the transverse plane while applying varying angles of cephalad and caudal tilting. Participants were placed in a supine position with their head and neck aligned neutrally, and no pillow was used to maintain consistency. To reduce potential errors caused by breathing, participants were instructed to close their mouths and breathe slowly during the procedure. The epiglottis was identified at the thyrohyoid membrane level as a curvilinear hypoechoic structure. Its posterior margin appeared as a brighter linear air-mucosa interface, and its anterior margin was outlined by the hyperechoic pre-epiglottic space. Measurements were taken from the skin surface to the midpoint of the epiglottis through the thyrohyoid membrane.

The patients were then transferred to the operationtheatreand placed under continuous monitoring using standard equipment. Following the administration of general anaesthesia, direct laryngoscopy was performed by a trained anaesthesiologist using an appropriately sized curved Macintosh blade. The Modified Cormack–Lehane grading system was used to assess the view. Cormack-Lehane grades I and IIa were classified as easy laryngoscopy, while grades IIb, IIIa, IIIb and IV indicated difficult laryngoscopy. Once the laryngoscopic assessment was complete, patients were intubated with the appropriately sized endotracheal tube, and the surgical procedure proceeded as planned.

A total of 400 participants (220 females, 180 males) were included in this study out of which the majority of participants (48.5%) were classified under CL Grade I, with 194 individuals, indicating a good view of the glottis. The second most frequent grade was Grade IIa, comprising 41% of participants (164 individuals). Grades IIb, IIIa, IIIb and IV had lower frequencies with 3.5% (14 individuals), 2.0% (8 individuals), 3.0% (12 individuals), and 2.0% (8 individuals), respectively. Regarding the DSE values majority of participants (89.5%) had a distance of ≤ 2 cm, with a frequency of 358 individuals, while 10.5% of participants had a distance greater than 2 cm, totaling 42 individuals. The mean distance from the skin to the epiglottis was found to be 1.56 cm, with a standard deviation of ±0.39 cm. The range of distances observed in the study was 2.23 cm, with the minimum being 0.73 cm and the maximum 2.96 cm. The median distance was 1.5 cm, with an interquartile range (IQR) of 0.44 cm. The mean distance for easy laryngoscopy was 1.49 ± 0.31 cm, while for difficult laryngoscopy, the mean distance was 2.23 ± 0.35 cm. The P value was statistically significant.

Out of total 90% had easy laryngoscopy and the remaining 10% had difficult laryngoscopy. Among patients with a distance of ≤ 2 cm, 344 had easy laryngoscopy and only 14 had difficult laryngoscopy, suggesting a strong correlation between a shorter distance and easier intubation. In contrast, for patients with a distance greater than 2 cm, 15 had easy laryngoscopy and 27 had difficult laryngoscopy, indicating that a longer distance from the skin to the epiglottis is more likely to be associated with difficult laryngoscopy. The P value of <0.05 indicates that the association between the DSE and difficult laryngoscopy is statistically significant.

On Receiver Operating Curve (ROC) Curve Analysis of Distance Skin to Epiglottis (DSE) in Predicting Difficult Laryngoscopy the area under the curve (AUC) for DSE is 0.961, with a 95% confidence interval ranging from 0.94 to 0.98, which indicates excellent diagnostic accuracy. The P value of <0.05 suggests that the relationship between DSE and predicting difficult laryngoscopy is statistically significant. The sensitivity of DSE in predicting difficult laryngoscopy is 68.3%, indicating, it correctly identifies 68.3% of the cases with difficult laryngoscopy. The false positive rate (1-specificity) is 4.5%, indicating that 4.5% of easy laryngoscopy cases are incorrectly identified as difficult based on DSE. These results highlight the high accuracy of DSE as a predictor for difficult laryngoscopy.

In our study no statistically, significant correlation was found between age, gender, height, weight, BMI, MPS and difficult laryngoscopy.

Table 1: Distribution of study participants based on Cormack-Lehane Grading system.

Table 2: Distribution of study participants based on Ultrasonographic Distance from Skin to Epiglottis.

Table 3: Association between Distance from skin to epiglottis and difficulty of laryngoscopy.

Table 4: Bivariate analysis between DSE and difficulty of laryngoscopy.

Table 5: ROC Curve Analysis of Distance Skin to Epiglottis (DSE) in Predicting Difficult Laryngoscopy.

Over the past decade, Ultrasound has become an essential tool in operating theatres and critical care settings for both diagnostic and therapeutic purposes. Its application in airway management, however, is a relatively recent development16. While several conventional methods exist for predicting difficult laryngoscopy, none are entirely sensitive or specific, and no standardized parameters have been universally established. Among the various methods, Ultrasonographic derived Skinto Epiglottis distance has shown promise in predicting difficult laryngoscopy, with significant findings reported in several studies17-20.

This study was conducted to evaluate the predictive accuracy of the Ultrasonographic measured SkintoEpiglottis Distance (DSE) in identifying difficult laryngoscopy. The analysis was performed using a Receiver Operating Characteristic curve to assess the diagnostic performance of DSE. At a cutoff value of 2 cm, our study demonstrated that DSE had a sensitivity of 68.3% in predicting difficult laryngoscopy, with an area under the curve (AUC) of 0.961 and a p-value < 0.05, indicating strong statistical significance. Additionally, the false positive rate was low at 4.5%, reinforcing the reliability of DSE as a valuable predictive marker for airway difficulty. These findings highlight the clinical utility of Ultrasonographic measurements in preoperative airway assessment, offering an objective and non-invasive tool for improving patient safety and optimizing airway management strategies. Study conducted by Pinto J et al reported a sensitivity of 64.7% with DSE cutoff value of 27.5mm in predicting difficult laryngoscopy4. Abdelhady BS et alfound that a DSE cutoff value of >1.85 cm yielded a sensitivity of 80% and an AUC of 0.75921. In another study, Nazir I et al identified a cutoff value of 17.7 mm, which predicted difficult laryngoscopy with a sensitivity of 78.9%, an AUC of 0.772, and a statistically significant p-value13. Falcetta S et al determined that a DSE cutoff of 2.54 cm achieved a sensitivity of 82% 16.Asystematic review conducted by Sotoodehnia M et al confirmed that increased skin thickness at the epiglottis is associated with difficult laryngoscopy22. Supporting this further, Aruna et al. found that the Skinto Epiglottis distance was the most sensitive (75%) and specific (63.6%) ultrasound measurement for predicting a difficult glottic view compared to other ultrasound parameters23.

These findings suggest that ultrasonographic measurement of DSE can serve as an effective adjunct in airway assessment, aiding in the preoperative prediction of difficult laryngoscopy.

Limitation

Future multicentric research combining multiple ultrasonographic parameters would be more informative in predicting difficult airway.

The findings in this studyestablishes the effective role of Ultrasound in airway assessment, highlighting its potential to enhance perioperative planning and improving patient safety by providing an objective, non-invasive, and reliable airway evaluation method.

Conflict of interest: Nil

Funding: Nil

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