Ratios of Height-to-Thyromental Distance and Height-to-Sternomental Distance as Predictors of Difficult Airway in Patients Posted for General Anaesthesia

Abstract

Background: Preoperative airway assessment and anticipation of a difficult airway is of utmost critical value in anesthesiology as failure to secure airway can lead to morbidity and mortality. The study evaluated ratio of height-to-thyromental distance (RHTMD) and ratio of height-to-sternomental distance (RHSMD) as predictors of a difficult airway.

Methods: The prospective observational study evaluated 131 adult participants scheduled for elective surgery under general anesthesia. In addition to the preoperative airway assessment, RHTMD and RHSMD were calculated. Correlation of these ratios with the Cormack-Lehane grading of glottis visualisation on direct laryngoscopic view following induction of anesthesia was analyzed. The optimal cut-off point for RHTMD and RHSMD were identified using receiver operating characteristic curve analysis.

Results: The incidence of difficult intubation was 14.50%. The cut-off values for RHTMD and RHSMD were ＜ 21.50 (sensitivity 85.25%, specificity 100.00%) and ＜ 10.50 (sensitivity 84.21%, specificity 96.42%) respectively for predicting difficult airway. The area under the curve with 95% confidence interval for RHTMD was 0.875 (0.730-1.000) and that for RHSMD was 0.890 (0.777-1.000).

Conclusion: RHTMD was found to be a better predictor of difficult intubation and restricted laryngoscopic view compared to RHSMD.