Sternomental Distance Ratio as a Predictor of Difficult Laryngoscopy: A Prospective, Double-Blind Pilot Study

No single test has shown to be an accurate predictor of difficult laryngoscopy.

This study aims to evaluate the effectiveness of the ratio of the sternomental distance (SMD) in neutral and full neck extension position SMD ratio (SMDR) as a predictor of difficult laryngoscopy and any need of assisted intubation.

Prospective, double-blind pilot study.

This study included 221 consecutive adult patients scheduled to undergo elective surgery under general anesthesia. Physical and airway characteristics, SMDR, difficult laryngoscopy (using Cormack/Lehane [C/L] scale), and any kind of assisted intubation were assessed.

The optimal cutoff point for SMDR was identified using receiver operating characteristic (ROC) analysis. The association between SMDR and the intubation method was evaluated through multiple logistic regression analysis.

A SMDR below 1.55 led in 33% of the cases to assisted intubation and 33%-53% of C/L III-IV glottic views for McCoy and Macintosh blades, respectively. On the other hand, SMDR above 1.9 led to no C/L IV glottic views for both blades and 4% and 11% C/L III views glottic views for McCoy and Macintosh, respectively. The best sensitivity and specificity cutoff point as defined by the ROC curve was identified for an SMDR value of 1.7 (area[s] under the curve: 0.815; 95% confidence interval: 0.743-0.887). Assisted intubation rates were significantly higher in patients with an SMDR inferior to 1.7 (30.5% compared to 3.5%, P < 0.001).

SMDR is a simple, objective, and easy to perform test. The present study indicates that SMDR may be helpful in predicting difficult laryngoscopy and assisted intubation.