ULTRASOUND BASED ASSESSMENT OF TONGUE THICKNESS, SKIN TO HYOID BONE DISTANCE AND SKIN TO EPIGLOTTIS DISTANCE IN PREDICTING DIFFICULT LARYNGOSCOPY IN ADULT PATIENTS.

Difficult intubation is an emergency situation and an important procedural step during anaesthesia, and failure to anticipate difficult intubation can have serious consequences like local injury, hypoxia, need of putting surgical airway, arrhythmia, cardiac arrest and death. The incidence of difficult laryngoscopy and tracheal intubation still ranges between 1.5%-13%.

An accurate pre-operative assessment therefore provides comprehensive planning and management for reducing the risk of unanticipated difficult airway. However, common clinical evaluation measurements (e.g. the modified Mallampati test, thyromental distance, inter-incisor distance, cervical mobility, sex, body mass index, etc.) have limited value with unsatisfactory sensitivity and specificity.

Tongue thickness assessed by USG gives us an internal characteristic of a patients upper airway and helps us in predicting difficult laryngoscopy. It will be determined by placing curvilinear ultrasound probe one end against top of the mandible and other end to the sternum.

Skin to epiglottis distance tells us about width of anterior soft tissue of neck at the level of thyrohyoid membrane. It will be determined by placing linear probe at thyrohyoid membrane level, the distance from skin to epiglottis midway between the hyoid bone and thyroid cartilage is measured.

Skin to hyoid bone distance tells us about the anterior soft tissue thickness of neck at the level of hyoid bone. The hyoid bone is identified by placing the linear ultrasound probe transversely over the hyoid bone. It appears as curved echogenic structure with a bright posterior air mucosal interface and hyperechoic pre-epiglottic space. At hyoid bone level, the minimal distance from skin to hyoid

bone will be measured.

However, difficult airway is not determined by a single anatomical factor, and the sensitivity and specificity of a single index for airway prediction are not ideal. Also, there is a paucity of data on the role of ultrasound measurement of combination of airway parameters in predicting difficult laryngoscopy in adult patients.

The purpose of this study is to evaluate the role of ultrasound based assessment of tongue thickness, skin to hyoid bone distance and skin to epiglottis distance in predicting difficult laryngoscopy in adult patients.