If in doubt, take it out. Obstruction of tracheal tube by prominent aortic knuckle.
D000402:Airway Obstruction / Q000209:etiology*; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging; D006801:Humans; D007431:Intraoperative Complications / Q000209:etiology; D007442:Intubation, Intratracheal; D008297:Male; D008875:Middle Aged; D011859:Radiography