Background Current predictors for evaluating difficult endotracheal intubation had poor accessibility or sensitivity at the emergency department, so we evaluated the incidence and predictive factors, then built an easy-to-use predictive formula. Methods This was a 17-month prospective observational study. For the 110 patients, difficult airway was defined as Cormack & Lehane classification grade III and IV at first attempt of intubation. The univariate associations between patient

more »

... s and difficult endotracheal intubation were then analyzed, and the significantly associated factors were included in a multivariate binary logistic regression model then a predictive formula was generated. Generalized association plot (GAP) was used to show the relationship between each variable. Results The incidence of difficult intubation in our study was 35.5%. In the difficult airway group, significantly higher rates (p < 0.05) of high body mass index (BMI); double chin; thick, short neck; Mallampati difficulty; smaller inter-incisors distance; smaller thyromental distance; and upper airway obstruction were noted. Finally, a predictive formula for difficult intubation was successfully established by the combination of four predictors: BMI (odds ratio [OR] = 1.270), thyromental distance (OR = 0.614), upper airway obstruction (OR = 4.038), and Mallampati difficulty (OR = 5.163). A cut-off score of 4 provided the best sensitivity (79.5%) and specificity (81.7%)(95% CI: 0.794 to 0.938). Conclusions Our predictive formula could be used by emergency physicians to quickly identify and carefully manage patients with potentially difficult intubation. Early expert consultation could be sought when necessary.