Abstract

Securing the airway for providing adequate oxygenation and ventilation is crucial in patients undergoing surgery requiring general anesthesia. The Modified Mallampati test has been traditionally used to predict difficult airway. The Thyromental Height test (TMHT) is an easy-to-do and non-invasive test. Increased anterior neck soft tissue thickness can impair the forward mobility of pharyngeal structures resulting in difficult laryngoscopy and intubation. Therefore we conducted this study to evaluate the predictive value of Thyromental height test (TMHT), Ultrasound guided anterior neck soft tissue thickness at the level of vocal cords (ANS-VC)and Modified Mallampatti test (MMT) in predicting difficult airway. Methodology : This prospective comparative study was done in a tertiary care hospital in India . Ethical committee approval and written informed consent was taken for the present study. 252 patients of either sex, age > 18 yrs, ASA I-II, who required general anaesthesia with endotracheal intubation for elective surgery were included in the study. Patients with malformation of the upper airway, pregnant women , patients coming for Emergency surgeries and patients who need awake intubation were excluded from the study. Preoperative airway assessment ( TMHT, ANS -VC , MMT) of all the patients was done by the same anaesthesiologist to avoid observer variability. All the patients were induced by a standard protocol. During laryngoscopy the cormack lehane grading was noted. Results: Preoperative airway evaluation parameters studied were modified mallampatti grading ( MMT) , thyromental height test (TMHT) and ultrasound guided anterior neck soft tissue thickness at the level of vocal cords (ANS-VC). According to MMT predicting difficult airway had a sensitivity of 31.8% and specificity of 91.3%. TMHT showed a sensitivity of 81.82% and specificity of 98.26% whereas ANS-VC showed a sensitivity of 90.91% and specificity of 98.7% in predicting difficult airway . Hence ANS-VC>0.23cm showed a slightly better predictability of difficult airway preoperatively. TMHT<5.5cm is also an equally good predictor whereas MMT has a very low sensitivity and PPV. Conclusion : Sonographic parameter ANS-VC >0.23cm is promising in predicting difficult airway. Along with this parameter the clinical parameter TMHT < 5.5 cm is equally good in predicting difficult airway compared to Modified Mallampatti test.

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