Ultrasonography of anterior neck soft tissue thickness at hyoid bone level vs thyrohyoid membrane level in predicting difficult laryngoscopy

Objective: To compare the effectiveness of ultrasonography of anterior neck soft tissue thickness at hyoid bone level vs thyrohyoid membrane level as a preoperative assessment tool to identify difficult laryngoscopy.
Materials And Methods: 100 patients who were to undergo elective surgery under general anaesthesia with endotracheal intubation were included in the study. Patients with no teeth and head and neck anatomical abnormality were excluded from study. In the pre operative room, clinical airway assessment which included Mallampatti's classification, inter incisor gap Neck circumference and thyromental distance were measured. The ultrasound was done to measure the thickness of soft tissues in the anterior neck at 2 levels
namely (a) hyoid bone and (b) thyrohyoid membrane. On the day of surgery anesthesia was provided to the patient according to the standard protocol. The Cormack-Lehane grading was recorded. Statistical analysis was done using the collected data.
Results: There was no statistical significance between the demographic variables like age (P=0.613), sex (P=0.670) and height (P=0.614) of the patients and the occurrence of difficult airway. Among the demographic variables, significant correlation was found between the weight (P=0.000) and difficult airway. The ultrasound measurements made at the 2 levels (a) hyoid bone and (b) thyrohyoid membrane showed significant results. The P values for each of the levels are P=0.000 and P=0.000 respectively. Among the 2 levels, the measurement made at thyrohyoid membrane level (skin to epiglottis thickness) was found to be highly sensitive (100%) and specific(99.3%). A cut-off point of 2.33cms was calculated using the Receiver Operating Characteristic curve (ROC curve). This cut-off point delineates difficult airway and difficult airway.
Conclusion: We concluded that ultrasound of anterior neck soft tissue at the thyrohyoid membrane level can be used as a reliable tool to identify difficult airway as compared with the ultrasound at the level of hyoid bone.