Title:
Ultrasonographic modification of Cormack Lehane classification for pre-anesthetic airway assessment.

Abstract:
The major drawback of Cormack Lehane classification for airway assessment is its dependence on invasive direct laryngoscopy and hence it is inapplicable for pre-anesthetic assessment of airway in patients with no prior history of tracheal intubation.
The purpose of the study was to compare and correlate the ultrasound view of the airway and the Cormack Lehane classification of the direct laryngoscopy. METHODS/STUDY PROCEDURES: The present study was conducted on patients scheduled for elective surgery and requiring general anesthesia with direct laryngoscopy and endotracheal intubation. In the pre-operative holding area, the following measurements were obtained with the oblique-transverse ultrasound view of the airway: (a) the distance from the epiglottis to the midpoint of the distance between the vocal folds, (b) the depth of the pre-epiglottic space, and (c) the total time taken by the operator to achieve the final ultrasonic image. The data was then compared with the Cormack Lehane classification during direct laryngoscopy in the operating room. Subsequently based on the correlation data, the ultrasonographic modification of Cormack-Lehane Classification was developed.
It was observed that there was a correlation of the distance between the epiglottis and the vocal cords (E-VC) with the Cormack Lehane Grading; correlation was strong negative with regression coefficient of -0.966 (95% CI -1.431 to -0.501; p = 0.0001). Subsequently, the correlation of the pre-epiglottis space (Pre-E) with the Cormack Lehane Grading was strong in positive direction with regression coefficient of0.595 (95% CI 0.261 to 0.929; p = 0.0008). Finally the ratio of Pre-E and E-VC distances with the Cormack Lehane Grading had the strongest positive correlation with regression coefficient of 0.495 (95% CI 0.319 to 0.671; p < 0.0001). Based on these statistical calculations and after rearranging the data, we found that prediction of Cormack Lehane (CL) grades can be adequately (67%-68% sensitivity) made by the ratio of Pre-E and E-VC distances (Pre-E/E-VC) {0 < [Pre-E/E-VC] < 1 approximately CL grade 1; 1 < [Pre-E/E-VC] < 2 approximately CL grade 2; and 2 < [Pre-E/E-VC] < 3 approximately CL grade 3}. The average time taken to complete the ultrasound examination of airway in the preoperative area was 31.7 +/- 12.4 seconds.
The non-invasive ultrasonographic modification of invasive Cormack Lehane classification for pre-anesthetic airway assessment can supplement the presently available noninvasive modalities of pre-anesthetic airway assessment including the Mallampati Classification.