Abstract: Objective To analyze the risk factors for difficult airway in laryngoscopy and mask ventilation. Methods A total of
300 patients receiving general anesthesia with tracheal intubation were examined preoperatively for height, thyromental and
sternomental distance (TMD), range of neck movement, inter-incisor distance, and modified Mallampati class. Intubation
Difficult Score was used to identify a difficult laryngoscopy. Difficult airway was defined as either difficult laryngoscopy or
difficult mask ventilation. The association between the airway characteristics and difficult airway was analyzed by logistic
regression analysis, and the cut-off values for the height-to-TMD ratio was determined by the ROC curve. Results and
Conclusion Eight airway characteristics were identified to contribute to a difficult airway, including (OR [95% CI]) the
height-to-TMD ratio (3.58[1.95-8.46]), modified Mallampati class (3.34 [1.82-7.14]), BMI (3.07 [1.64-6.69]), history of a previous
difficult airway (2.79 [1.28-5.25]), a thick neck (2.15 [1.04-4.37]), range of neck movement (1.98 [0.96-3.89]), sternomental and
angulus mandibulae distance (1.46 [0.67-3.04]), and inter-incisor distance (1.01 [0.49-2.54]). The optimal cut-off value for the
height-to-TMD ratio was 22.8 for predicting a difficult airway.