Mehran Sotoodehnia1, Najmeh Abbasi1, Razman Arabzadeh Bahri1, Atefeh Abdollahi1, Alireza Baratloo2

1Prehospital and Hospital Emergency Research Center, Tehran University of Medical Sciences, Tehran, Iran
2Research Center for Trauma in Police Operations, Directorate of Health, Rescue and Treatment, Police Headquarter, Tehran, Iran

Keywords: Airway management, difficult airway, intratracheal intubation, LEMON score, prediction, ultrasonography


OBJECTIVES: Ultrasound (US) airway indexes were frequently compared with other scoring systems such as Mallampati score and Cormack − Lehane classification system, but to the best of our knowledge never with LEMON. Here, in this study, we evaluated the accuracy of some recommended airway US parameters in terms of screening difficult airway using the LEMON criteria as a reference.

METHODS: This was a cross-sectional diagnostic accuracy study in which people with at least 18 years old coming to the emergency departments for any reason who had consent for participation, were enrolled with the simple random sampling method. Hyo mental distance (HMD), skin to epiglottis distance (EP), and peri epiglottic space to epiglottis to vocal cord ratio (PEP/E. VC) were the US indexes that were calculated in all participants. Using a preprepared checklist, measured US parameters were recorded. For each participant, the LEMON score variables were also assessed and recorded, and the cutoff point for considering as a difficult airway case, based on LEMON score, was 2. Demographic characteristics of the participants were also registered.

RESULTS: A total of 299 cases with a mean age of 41.1 years (95% confidence interval [CI]: 39.3–42.9), were participated. Based on LEMON score ≥2, 20 participants (6.7%) were categorized in difficult airway group. Comparison of the PEP/E. VC (P = 0.007) and EP distance (P = 0.049) of the participants based on LEMON score showed a statistically significant difference; but comparison of the means of HMD in the two groups was not statistically significant (P = 0.144). The median of EP of the participants was 7.70 mm (interquartile range [IQR]: 6.70–9.40). The best cutoff point of EP distance for evaluating a difficult airway was 12.27 mm and more with the sensitivity of 35% and the specificity of 86.96% (accuracy = 0.614; 95% CI: 0.492–0.736). The median of PEP/E. VC was 1.01(IQR: 0.79–1.23). The best cutoff point of PEP/E. VC for evaluating a difficult airway was 0.88 and less with the sensitivity of 70% and the specificity of 67.38% (accuracy = 0.701; 95% CI: 0.583–0.818).

CONCLUSION: As per our results, PEP/E. VC and EP distance measured with sonography can be used in distinguishing the difficult airway, using the LEMON criteria as the reference. However, further studies are needed to use PEP/E. VC and EP distance as a part of reliable indexes.

How to cite this article: Sotoodehnia M, Abbasi N, Bahri RA, Abdollahi A, Baratloo A. Accuracy of airway ultrasound parameters to predict difficult airway using the LEMON criteria as a reference: A crosssectional diagnostic accuracy study. Turk J Emerg Med 2023;23:38-43.

Ethics Committee Approval

The study proposal was approved by the ethical committee of Tehran University of Medical Sciences (code: IR.TUMS.MEDICINE. REC.1399.025) at 2019‑12‑14 (available via the URL: https://ethics. Conducting this study did not impose any additional cost, neither to the participants nor to the health system.

Author Contributions

The conception and design of the work by MS, NA, AA and AB; Data acquisition by NA and RB; Analysis and interpretation of data by MS, RB and AB; Drafting the work by NA and RB; Revising it critically for important intellectual content by MS, AA, and AB; all the authors approved the final version to be published; AND agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work.

Conflict of Interest

None declared.

Financial Disclosure



We would like to express our commitment to the Prehospital and Hospital Emergency Research Center affiliated to Tehran University of Medical Sciences.