<unk>  is a form of hypoxia (reduced supply of oxygen), specifically involving the brain; when the brain is completely deprived of oxygen, it is called<unk>  anoxia. There are four categories of<unk> ; they are, in order of increasing severity: diffuse<unk>  (DCH), focal<unk>  ischemia,<unk>  infarction, and global<unk>  ischemia. Prolonged hypoxia induces neuronal cell death via apoptosis, resulting in a hypoxic brain injury. Cases of total oxygen deprivation are termed "anoxia", which can be hypoxic in origin (reduced oxygen availability) or ischemic in origin (oxygen deprivation due to a disruption in blood flow). Brain injury as a result of oxygen deprivation either due to hypoxic or anoxic mechanisms are generally termed hypoxic/anoxic injuries (HAI). Hypoxic ischemic encephalopathy (HIE) is a condition that occurs when the entire brain is deprived of an adequate oxygen supply, but the deprivation is not total. While HIE is associated in most cases with oxygen deprivation in the neonate due to birth asphyxia, it can occur in all age groups, and is often a complication of cardiac arrest.
Cerebral hypoxia
Silent hypoxia
Histotoxic hypoxia
Pseudohypoxia
Hypoxia 
Anoxia
Oxygen toxicity
Nitrogen narcosis