Ultrasound-measured cutaneous-epiglottic distance for predicting difficult laryngoscopy: an observational study

Ultrasound (US) allows for rapid bedside airway assessment. We aimed to evaluate the US-measured cutaneous-epiglottic distance (CED) in predicting difficult laryngoscopy (Cormack-Lehane grades 3‒4). We also evaluated the potential association between CED, sex, patient's body mass index (BMI), and the independent associations between CED and increased odds for Cormack-Lehane grades 3‒4 (secondary outcomes).

Patients aged 18‒70 years scheduled for elective surgeries under general anesthesia with tracheal intubation were included. Those with a BMI > 35 kg.m^-2 and/or previous history of difficult intubation were excluded. CED was measured with patients anesthetized before tracheal intubation. Age, sex, BMI, type of surgery, and number of attempts until successful tracheal intubation were recorded. Receiver operator characteristic (ROC) curve analysis was performed to evaluate CED's clinical relevance. Secondary analyses compared the association between CED and BMI in patients with Cormack-Lehane grades 1‒2 versus those with grades 3‒4. The relationship between CED and BMI was assessed using multiple linear regression. Binary logistic regression was employed for predicting Cormack-Lehane grades 3‒4 as a dichotomous outcome with CED and BMI as a covariate.

ROC curve analysis revealed an area under the curve of 0.899 (p < 0.001). The maximum CED cut-off point (by Youden index) was 25.6 mm. CED and BMI were positively correlated, and both were independently associated with an increased odds for difficult laryngoscopy [odds ratio for CED = 1.81, 95% confidence interval (CI) 1.35‒2.41; BMI = 1.30, 95% CI 1.05‒1.59].

US-measured CED has a high discriminatory capability for predicting lower (1‒2) and higher (3‒4) Cormack-Lehane grades during direct laryngoscopy. CED was positively correlated with BMI and was independently associated with higher odds for difficult laryngoscopy.