Evaluation of Hyomental Distance Ratio using ultrasound as a diagnostic predictor of difficult direct laryngoscopy and intubation

An unexpected difficult intubation can be highly challenging and significantly increases patient’s morbidity if not managed well . Identifying patients at risk for difficult laryngoscopy preoperatively is imperative to implement safer and more effective strategies during induction and airway management.  The hyo-mental distance (HMD) is the distance between the hyoid bone and the tip of the chin.  The hyo-mental distance ratio (HMDR) is the ratio between the hyo-mental distance (HMD) (the distance between the hyoid bone and the tip of the chin) at the extreme of head extension (HMDe) and the one in the neutral position (HMDn).  Patients of American Society of Anaesthesiologists Physical Status Class I, II, III scheduled to undergo elective surgeries under general anaesthesia will be selected based on the inclusion criteria. All enrolled patients will undergo ultrasonographic measurement hyo-mental distance in the pre-operative room prior to being shifted to the operating room. Ultrasound scanning of the submandibular region will be performed with a curvilinear transducer. We will measure the HMD between the hyoid bone and the posterior border of the symphyis menti in two positions, namely: neutral and maximum hyperextended. We define HMDR (hyo-mental distance ratio) as the ratio between the HMD in the maximum hyperextended position to that in the neutral position. During intraoperative laryngoscopy, Modified Cormack-Lehane grading will be recorded. Difficult intubation will be defined by the usage of any one or more of the following- The usage of BURP manoeuvre ,the use of adjuncts like bougie or stylet during the procedure ,the use of Macintosh 4 blade for intubation and the number of attempts to facilitate intubation and the duration of time taken from visualisation of vocal cords to successful intubation will be noted.