Thyromental Height Test as a New Method for Prediction of Difficult Intubation Using Videolaryngoscopy

Successful and fast intubation are crucial for the safety of general anaesthesia. Failed intubation and acute hypoxia remain among the major contributing factors of anaesthesia related deaths. Difficult intubation prevalence in literature is very inconsistent and varies between 1.5-20% of cases in general population, to even 50% in obese Thai population.

There is a number of anthropometric scales and tests used for predicting difficult intubation. However, none of them appears to be sensitive and specific enough to effectively predict difficult intubation.

Recently, simple and non-invasive test predicting difficult intubation was introduced-thyromental height test (TMHT). It shows promise as a more effective substitution for frequently cited anthropometric measures. It is based on the height between the anterior border of the thyroid cartilage and the anterior border of the mentum, measured while the patient lies in the supine position with closed mouth The main objective of the trial is to assess the clinical usefulness of TMHT in prediction of difficult intubation using videolaryngoscopy and double lumen endotracheal tubes in patients scheduled for elective thoracic surgical procedures. The secondary aim is to evaluate usefulness of other commonly used predictive tests associated with difficult intubation.

During routine, preoperative anaesthetic visit thyromental height, thyromental distance, sternomental distance and Mallampati scale score are assessed. Then, during videolaryngoscopy and intubation, score in Cormack-Lehane scale and occurrence of difficult intubation are noted.