Comparison of thyromental height and sonographic hyomental distance ratio in predicting difficult intubation in adults undergoing elective surgery under general anaesthesia.

Being competent in airway management is an indispensable skill for every anaesthesiologist. Inability to deal with it exposes a patient to the risk of injury and death. Difficult airway is defined as a clinical situation in which a conventionally trained anaesthesiologist experiences difficulty with ventilation of the upper airway with bag and mask or endotracheal intubation or both. The search for predictors of a difficult airway has been ongoing since the very first intubation was performed. Many morphological parameters have been suggested for the same. These include the modified Mallampatti test (MMT), upper lip bite test (ULBT), inter incisor gap (IIG), degree of neck movement, sternomental distance (SMD) and thyromental distance (TMD). These conventional tests are simple, take minimum time, are comfortable for the patient, reproducible and can be measured manually without the need of any equipment. In spite of these benefits, none of these tests, when used individually, is conclusive on its own. So, the anaesthesiologist has to perform all these tests to get a better prediction rate for the presence of a difficult airway. Thyromental height (TMH) and sonographic hyomental distance ratio (HMDR) are both newly proposed tests for predicting a difficult airway. Thyromental height is the height between the anterior border of the thyroid cartilage and the anterior border of mentum. It is measured with the patient lying supine with his/her mouth closed. A cut off value of 5 cm has been considered as a good correlative predictor of difficult airway. Hyomental distance ratio (HMDR) is the ratio of the hyomental distance (the distance between the hyoid bone and the tip of the chin) at the extreme of head extension (HMDe) and in the neutral position (HMDn). Cut off value of sonographic hyomental distance ratio of 1.2 has been shown to predict a difficult airway.There is limited research on the above said parameters i.e thyromental height and sonographic hyomental distance ratio in comparison to each other so as to predict difficult airway in patients scheduled to undergo general anaesthesia. Therefore, the present study aims to compare these two tests amongst themselves as well as with the conventional tests like MMT, TMD and SMD to determine the method of airway assessment that has the highest sensitivity and specificity.