Comparative evaluation of sternomental and hyomental distance–based dynamic airway indices for predicting difficult laryngoscopy in obese surgical patients: A prospective observational study

Abstract Background and Aims: Obesity is associated with higher incidences of difficult laryngoscopy, and static airway predictors often underperform in this population. This study evaluated the accuracy of four dynamic airway indices: sternomental distance ratio and displacement (SMDR and SMDD), hyomental distance ratio (HMDR), and a novel index, hyomental distance displacement (HMDD), for predicting difficult laryngoscopic view (DLV) in obese surgical patients. Material and Methods: Eighty obese adults (body mass index [BMI] >30 kg·m⁻²) scheduled for elective surgery under general anesthesia were enrolled. Measurements of SMD and HMD were obtained in neutral and extended head positions using a digital Vernier caliper. Direct laryngoscopy was performed, and the best laryngeal view was graded using the modified Cormack–Lehane classification. Pearson correlation, receiver operating characteristic (ROC) curve analysis with bootstrap resampling, and univariate logistic regression were performed. Results: DLV was observed in 38 patients. SMDD and SMDR demonstrated high inverse correlations with DLV ( r = −0.82 and −0.78, respectively). Optimal threshold values for predicting a DLV were as follows: SMDD ≤6.07 cm (areas under the ROC curve [AUC]: 0.993; 95% confidence interval [CI]: 0.975–1.000), SMDR ≤1.58 (AUC: 0.985; 95% CI: 0.958–0.999), HMDR ≤1.34 (AUC: 0.986; 95% CI: 0.953–0.998), HMDD ≤1.41 cm (AUC: 0.980; 95% CI: 0.943–0.995). All indices demonstrated high sensitivity and specificity at these thresholds. Conclusions: Dynamic airway indices demonstrated good discriminatory ability for predicting DLV in obese patients. These simple bedside tools may serve as useful adjuncts to routine airway assessment.