Shafna K T*, Vayal Peedeyakkal Lubaiba and P Vineetha
Aim
Ultrasonography is a non-invasive bedside device for predicting difficult airways. This study aims to evaluate whether ultra-sonographic airway parameters such as the ratio of Pre-Epiglottis space (Pre-E) depth to the distance measured from epiglottis to midpoint of distance present between the Epiglottis Vocal Cords (E-VC), a ratio of Hyomental Distance(maximal/neutral) (HMDR(m/n)) and Tongue Thickness (TT) could be used in predicting Difficult Airway (DA).
Materials and Methods
After getting research and ethical committee approval, Pre-E/E-VC ratio had been measured using a linear USG probe and HMDR(maximal/neutral) ratio and TT were measured using a curved probe preoperatively on the day of surgery. Cormack Lehane grading was noted during direct laryngoscopy after general anesthesia induction. The predictive value of each parameter was measured by employing Negative Predictive Value (NPV), sensitivity, Positive Predictive Value (PPV), as well as specificity. ROC analysis had been done to identify each parameter’s cut-off value to predict difficult airway.
Results
Out of the three airway parameters studied in 210 patients, Pre-E/E-VC ROC analysis revealed a threshold of >0.73, sensitivity 80%, specificity 85.1%, PPV 51.8% and NPV 95.5%. HMDR(maximal/neutral) showed a sensitivity of 97.1%, specificity 72% and a cut-off of ≤ 1.21. Tongue thickness with a cut-off of ≥ 5.2cm showed lowest sensitivity 60% and specificity 55.4%.
Conclusion
This study concluded that ultra-sonographic airway parameters are useful in predicting difficult airway preoperatively. HMDR(m/n) has a maximum sensitivity of 97.1% and specificity of 72%, while Pre-E/E-VC has a maximum specificity of 85.1% and sensitivity of 80%. A threshold of HMDR(m/n) ≤ 1.2 as well as Pre-E/E- VC of ≥ 0.73 could be utilized should anticipate a DA.
