 Damage to the brain ( such as from a massive stroke , non @-@ penetrating head injury , intoxication or poisoning ) may result in a depressed level of consciousness . When this becomes severe to the point of stupor or coma ( defined as a score on the Glasgow Coma Scale of less than 8 ) , dynamic collapse of the extrinsic muscles of the airway can obstruct the airway , impeding the free flow of air into the lungs . Furthermore , protective airway reflexes such as coughing and swallowing may be diminished or absent . Tracheal intubation is often required to restore patency ( the relative absence of blockage ) of the airway and protect the tracheobronchial tree from pulmonary aspiration of gastric contents . 
