CT in a person after generalized hypoxia. The brain requires approximately 3.3 ml of oxygen per 100 g of brain tissue per minute. Initially the body responds to lowered blood oxygen by redirecting blood to the brain and increasing<unk>  blood flow. Blood flow may increase up to twice the normal flow but no more. If the increased blood flow is sufficient to supply the brain's oxygen needs then no symptoms will result. However, if blood flow cannot be increased or if doubled blood flow does not correct the problem, symptoms of<unk>  will begin to appear. Mild symptoms include difficulties with complex learning tasks and reductions in short-term memory. If oxygen deprivation continues, cognitive disturbances, and decreased motor control will result. The skin may also appear bluish (cyanosis) and heart rate increases. Continued oxygen deprivation results in fainting, long-term loss of consciousness, coma, seizures, cessation of brain stem reflexes, and brain death. Objective measurements of the severity of<unk>  depend on the cause. Blood oxygen saturation may be used for hypoxic hypoxia, but is generally meaningless in other forms of hypoxia. In hypoxic hypoxia 95–100% saturation is considered normal; 91–94% is considered mild and 86–90% moderate. Anything below 86% is considered severe.<unk>  refers to oxygen levels in brain tissue, not blood. Blood oxygenation will usually appear normal in cases of hypemic, ischemic, and hystoxic<unk> . Even in hypoxic hypoxia blood measures are only an approximate guide; the oxygen level in the brain tissue will depend on how the body deals with the reduced oxygen content of the blood.
Cerebral hypoxia
Silent hypoxia
Histotoxic hypoxia
Pseudohypoxia
Hypoxia 
Anoxia
Oxygen toxicity
Nitrogen narcosis