Evaluation of the predictive value of tongue height to oral cavity height ratio and anterior neck soft tissue measurements for difficult laryngoscopy in patients with unanticipated difficult airway: A prospective observational study.

Background and aims: Effective airway assessment prevents intubation failure. Despite the limited sensitivity of standard tools, ultrasonography (USG) offers promise, especially in predicting difficult laryngoscopies. Our study aims to evaluate tongue-to-oral height ratio (TTOHR) and anterior neck soft tissue measurements on airway USG to predict difficult laryngoscopy.

Methods: This prospective observational study enroled 120 patients posted for elective surgery under general anaesthesia, without anticipated difficult airways. The skin to hyoid bone distance (SHBD), skin to epiglottis distance (SED), skin to thyrohyoid membrane distance (STHMD), and TTOHR were measured on USG. Modified Cormack-Lehane (CL) grading at laryngoscopy was the primary outcome. Statistical analysis included ROC curve analysis, multivariable logistic regression, and evaluation of predictive models combining multiple USG parameters.

Results: The incidence of difficult laryngoscopy and intubation was 11.6% and 6.6%, respectively. The highest diagnostic performance was observed for SED, with an area under the curve (AUC) of 0.95 [95% confidence interval (CI): 0.91, 0.98], a cut-off value of 1.87 cm, a sensitivity of 100%, a specificity of 89%, and a diagnostic accuracy of 90%. STHMD followed with an AUC of 0.94 (95% CI: 0.88, 0.99), a cut-off of 1.58 cm, a sensitivity of 90%, a specificity of 86%, and a diagnostic accuracy of 84%. TTOHR showed an AUC of 0.92 (95% CI: 0.78, 1.00), with a cut-off value of 0.80, a sensitivity of 92%, a specificity of 98%, and the highest diagnostic accuracy of 97% (95% CI: 0.96, 1.00). Various models, tested using three or four parameters, showed AUC values ranging from 0.96 to 0.97. A model containing TTOHR, SHBD, and STHMD was identified as a best-fit model for predicting difficult laryngoscopy.

Conclusion: SED, STHMD, and TTOHR individually showed substantial diagnostic accuracy, with AUCs ranging from 0.92 to 0.95. Analysis of models combining parameters outperformed individual measurements, with statistically significant contributions from TTOHR and SHBD.