Access or Anatomy (obesity, poor landmarks, or otherwise poor access)
Radiation (or other tissue deformity or scarring)
Tumor (including intrinsic airway tumor)
Adapted from: Brown III CA, Walls RM. Identification of the difficult and failed airway. In: The Walls Manual of Emergency Airway Management, 5th ed, Brown III CA, Sakles JC, Mick NW (Eds), Wolters Kluwer, Philadelphia 2018.
