A proposal for a new scoring system to predict difficult ventilation through a supraglottic airway

The aim of this study was to propose and validate a new clinical score to predict difficult ventilation through a supraglottic airway device. The score was proposed from our previously reported derivation data, and we prospectively validated the score in 5532 patients from November 2013 to April 2014. Predictive accuracy of the score was compared by the area under the receiver operating characteristic (ROC) curve (AUC). We assigned point values to each of the identified four risk factors: male, age >45 yr, short thyromental distance, and limited neck movement, their sum composing the score. The score ranged between 0 and 7 points. The optimal predictive level of the score was determined using ROC curve analysis. The AUC of the score was 0.75 (95% CI 0.66 to 0.84) in the validation data set, and was similar to that in the derivation data set (0.80; 95% CI 0.75 to 0.86). In derivation and validation data sets, the incidence of low risk categories (scores 0–3) was 0.42% vs 0.32% and of high risk categories (scores 4–7) was 3% vs 1.7% respectively. A score 4 or greater is associated with a six to seven fold increased risk of difficult ventilation through a supraglottic airway device. The new score for prediction of difficult ventilation through a supraglottic airway device is easy to perform and reliable, and could help anaesthetists plan for difficult airway management.