Certain medical procedures can also injure the airways; these include tracheal intubation, bronchoscopy, and tracheotomy.[4] The back of the trachea may be damaged during tracheotomy.[22] TBI resulting from tracheal intubation (insertion of a tube into the trachea) is rare, and the mechanism by which it occurs is unclear.[23] However, one likely mechanism involves an endotracheal tube catching in a fold of membrane and tearing it as it is advanced downward through the airway.[24] When an endotracheal tube tears the trachea, it typically does so at the posterior (back) membranous wall.[9] Unlike TBI that results from blunt trauma, most iatrogenic injuries to the airway involve longitudinal tears to the back of the trachea or tears on the side that pull the membranous part of the trachea away from the cartilage.[24] Excessive pressure from the cuff of an endotracheal tube can reduce blood supply to the tissues of the trachea, leading to ischemia and potentially causing it to become ulcerated, infected, and, later, narrowed.[4]