Thyomental distance is a good difficult airway indicator: Truth or a misconception- A prospective observational study

Abstract

Unanticipated difficult intubation can be a true challenge to any anaesthesiologist. The most widely used determinant till date in almost every airway study is Thyromental distance[TMD]. We aimed to determine if a TMD above the average values could indicate difficult intubation.70 patients were selected in this prospective observational study who require general anesthesia with endotracheal intubation for their respective surgeries. Patients who fulfilled the inclusion criteria were enrolled in the study and informed written consent was taken.Routine pre-anesthetic check up was done. Thyromental distance was measured [thyroid notch to the lower border of the mandibular mentum-head fully extended] using a rigid ruler. Intraoperatively: After following standard general anaesthesia protocol, patients were intubated by anesthesiologist with atleast 2 years of experience and blinded to the study. The ease (0-5) / Difficulty (>5) in intubation was assessed with Intubation difficulty scale(IDS). Data was analysed using SPSS Software 16. Data was expressed in terms of frequency and percentage. In a total of 70 patients, 18.6% of the patients had difficult intubation. It was observed that 50 patients had a TMD >=7.5 cm out of whom, 7 patients were difficult to intubate. 12 patients had TMD<6.5 cm out of which 6 patients had an IDS of >5 indicating difficult intubation. Sensitivity, specificity, PPV, NPV were calculated. Categorical Pearson chi square test was done for TMD>7.5 vs IDS and it showed a p value of 0.017 (p<0.05).We observed that a long TMD (TMD>=7.5cm) could be a difficult airway indicator just like a short TMD (TMD<=6.5). Therefore, our findings suggest that thyromental distance may not have a significant role as a standalone pre-operative indicator of a difficult airway and its reliability as a useful parameter in predicting difficult intubation is questionable.