Ultrasound Guided Measurement of Anterior Neck Tissue for the Prediction of Difficult Airway: A Prospective Observational Study.

Objectives: To determine that ultrasound (US) measurements of anterior neck soft tissue thickness at hyoid bone, thyrohyoid membrane, and anterior commissure levels can be used to predict difficult laryngoscopy.

Materials & methods: The present study included 100 patients of age group 18-60 years undergoing elective surgery under general anaesthesia. It was a prospective observational study which included patients with ASA physical status I and II. Excluded patients were with facial and neck deformities, neck trauma, or those undergoing surgery of the larynx, epiglottis and pharynx. Comparison analysis was performed using t-test for continuous variables and chi-square or Fisher exact test for non-continuous variables. Correlation analysis performed using Pearson test.

Results: There were 39 out of 100 patients categorised as difficult laryngoscopy. Thickness at hyoid bone (DSHB), thyrohyoid membrane (DSEM) and anterior commissure (DSAC), MMS (modified Mallampati score), and BMI (body mass index) were greater in the difficult laryngoscopy group (p < 0.001). TMD (thyromental distance) was less in the difficult laryngoscopy group (p < 0.001). There was a strong positive correlation between DSEM and DSAC (r = 0.784). Moderate positive correlation was between DSEM and DSHB (r = 0.559), DSEM and MMS(r=0.437). The area under curve (AUC) of DSHB, DSEM, DSAC, TMD and MMS is >0.7. The optimal cut-off values for DSEM, DSHB, DSAC and TMD were 1.34 cm, 0.98 cm, 1.68 cm and 6.59 cm, respectively, in predicting difficult airway.

Conclusion: Ultrasound measurement of soft tissue thickness at hyoid bone, thyrohyoid membrane, and anterior commissure of vocal cord are good independent predictors for difficult laryngoscopy. When combined with traditional screening tests it improves the ability to predict difficult laryngoscopy.