Accuracy of airway ultrasound parameters to predict difficult airway using the LEMON criteria as a reference: A cross-sectional diagnostic accuracy study.

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.