Classification<unk>  is typically grouped into four categories depending on the severity and location of the brain's oxygen deprivation: Aneurysm in a<unk>  artery,one cause of hypoxic anoxic injury (HAI). # Diffuse<unk>  – A mild to moderate impairment of brain function due to low oxygen levels in the blood. # Focal<unk>  ischemia – A stroke occurring in a localized area that can either be acute or transient. This may be due to a variety of medical conditions such as an aneurysm that causes a hemorrhagic stroke, or an occlusion occurring in the affected blood vessels due to a thrombus (thrombotic stroke) or embolus (embolic stroke). Focal<unk>  ischemia constitutes a large majority of the clinical cases in stroke pathology with the infarct usually occurring in the middle<unk>  artery (MCA). # Global<unk>  ischemia – A complete stoppage of blood flow to the brain. #<unk>  infarction – A "stroke", caused by complete oxygen deprivation due to an interference in<unk>  blood flow which affects multiple areas of the brain.<unk>  can also be classified by the cause of the reduced brain oxygen: * Hypoxic hypoxia – Limited oxygen in the environment causes reduced brain function. Divers, aviators, mountain climbers, and fire fighters are all at risk for this kind of<unk> . The term also includes oxygen deprivation due to obstructions in the lungs. Choking, strangulation, the crushing of the windpipe all cause this sort of hypoxia. Severe asthmatics may also experience symptoms of hypoxic hypoxia. * Hypemic hypoxia – Reduced brain function is caused by inadequate oxygen in the blood despite adequate environmental oxygen. Anemia and carbon monoxide poisoning are common causes of hypemic hypoxia. * Ischemic hypoxia ( or "stagnant hypoxia") – Reduced brain oxygen is caused by inadequate blood flow to the brain. Stroke, shock, cardiac arrest and heart attack may cause stagnant hypoxia. Ischemic hypoxia can also be created by pressure on the brain.<unk>  edema, brain hemorrhages and hydrocephalus exert pressure on brain tissue and impede their absorption of oxygen. * Histotoxic hypoxia – Oxygen is present in brain tissue but cannot be metabolized by the brain tissue. Cyanide poisoning is a well-known example.
Cerebral hypoxia
Silent hypoxia
Histotoxic hypoxia
Pseudohypoxia
Hypoxia 
Anoxia
Oxygen toxicity
Nitrogen narcosis