Correlation between Ultrasound Measured Distance from Skin to Epiglottis and Epiglottis to Mid-Vocal Cord with Cormack-Lehane Classification for Predicting Difficult Intubation

Difficult tracheal intubation is an important challenge for anesthesiologists. Many anatomical parameters are available for evaluating the ease of tracheal intubation. Cormack-Lehane (CL) grade is one that can reliably predict a difficult intubation but it is an invasive procedure and can be performed in an anesthetised patient so it is not useful during pre-anesthetic airway evaluation. Prediction of the CL grading before operation can help in better airway management during induction of anesthesia.
The aim of this study was to find a correlation between ultrasound measured distance from skin to epiglottis and from epiglottis to mid-vocal cord with Cormack-Lehane grading in patients undergoing general anesthesia for predicting difficult intubation.

In a cross-sectional study, 60 ASA class I - III patients aged 18 - 70 years who were scheduled for tracheal intubation under general anesthesia were included. Before anesthesia, an ultrasound view of the airway was obtained and the distance from skin to the epiglottis and from the epiglottis to the mid-point between the ends of vocal cords were all recorded. The ultrasound measurements were then compared with the CL grade during direct laryngoscopy under general anesthesia.

Thirty-six patients had CL grade I, twenty-one had CL grade II and three had CL grade III. It was observed that the correlation between CL grade and distance from skin to epiglottis (DSE) with cutoff value 21mm(with an accuracy of 99%, a sensitivity of 100%, and a specificity of 82% ; P=0.0001) and from epiglottis to mid vocal cord distance (EMVD) with cutoff value 13.38(with an accuracy of 99%, a sensitivity of 100%, and a specificity of 85% ; P=0.01) and the ratio of DSE/EMVD with cutoff value 1.64(with an accuracy of 95%, a sensitivity of 100%, and a specificity of 91%; P=0.004) was significant for predicting of difficult intubation in patients with BMI>25.

Our study revealed good correlation between DES/EMVC ratio and Cormack-Lehane grade, therefore sonographic measurement criteria may be helpful in airway evaluations before anesthesia for predicting difficult intubation.