Evaluation of Thyromental Height Test for Predicting Difficult Laryngoscopy in Morbid Obese Patients Candidate for Bariatric Surgery: An Observational Study

Upper airway management in morbid obese patients undergoing bariatric surgery is a major challenge during induction of anesthesia. Bed side Thyromental Height Test (TMHT) is an easy and valid predictor for prediction of difficult airway in non‑obese patients, but its precision in morbid obese patients haven’t been evaluated yet. The purpose of present study is to find the accuracy of TMHT for the prediction of difficult laryngoscopy in morbid obese patients undergoing bariatric surgery. The present prospective observational study was performed on 95 morbid obese patients at Sina hospital during 2020. Preoperative exams of patients include the assessment of Mallampati classification, thyromental height, thyromental, sternomental and interincisor distances. After induction of anesthesia, the laryngoscopy view was evaluated using the Cormack Lehane classification, and the relationship between these tests to prediction of difficult laryngoscopy view based on the Cormack Lehane degrees (grades 3,4) were evaluated. A total of 95 morbid obese patients with a mean BMI of 44.7±5.6 kg/m2.were included in the study. 67.3% of them were women. The incidence of difficult laryngoscopy (C & L III, IV) was 16.8%. TMHT less than 56.5 mm, with 98% positive predictive value and 93% accuracy was the best predictor of difficult intubation in these patients. The accuracy of thyromental, sternomental and interincisor distance, with cut off value less than 51.5 mm, 89.5 mm, 41.5 mm respectively was less than TMHT in prediction of difficult laryngoscopy in morbid obese patients. In morbid obese patients with a BMI greater than 40, thyromental height less than 56.5 mm with 98% positive predictive value and 93% accuracy is the best predictor for difficult laryngoscopy view.