A prospective observational evaluation of an anatomically guided, logically formulated airway measure to predict difficult laryngoscopy.

CONTEXT: Difficulty during tracheal intubation is the most common cause of serious adverse respiratory events for patients undergoing anaesthesia. Current traditional bedside predictors of difficult laryngoscopy have poor sensitivity. A simple method to accurately predict difficult laryngoscopy could greatly improve patient safety.

OBJECTIVES: This study examined a novel bedside predictor of difficult laryngoscopy that calculates a ratio of measurements directly affecting the ability to achieve the necessary line of vision (NLV) from the larynx to the operator (NLV ratio).

DESIGN: This was a prospective observational study.

SETTING: A single tertiary care surgical centre.

PATIENTS: We enrolled 2046 patients scheduled for elective surgery under general anaesthesia with anticipated tracheal intubation.

INTERVENTION: Prior to surgery, patients had their NLV ratio and standard airway measures recorded. The anaesthesiologist who performed the intubation was blind to the airway assessment and recorded the best view of the larynx according to the Cormack and Lehane scale. Difficult laryngoscopy was defined as a grade 3 or 4 view.

MAIN OUTCOME MEASURE: The main outcome measure was the sensitivity and specificity of the NLV ratio measurement for predicting difficult laryngoscopy.

RESULTS: Receiver operating characteristics curve analysis of the NLV ratio revealed an optimal sensitivity of only 41% and specificity of 77%.

CONCLUSION: Although our novel measurement performed similarly to traditional bedside predictors of difficult laryngoscopy, the sensitivity was too low for the test to be clinically useful. Numerous factors which may be very difficult to predict at the bedside probably contributed to the poor performance of this novel measurement.