Lack of oxygen supply to the brain, usually as a result of either diminished blood flow (e.g., in traumatic childbirth or cardiopulmonary arrest) or diminished oxygenation of the blood (e.g., in high-altitude exposures or patients with advanced cardiopulmonary disease). If nothing is done to treat this condition, irreversible anoxic damage to the brain begins after 4 to 6 minutes and sooner in some cases. If basic resuscitation measures are begun before the end of this period, the onset of cerebral death may be postponed.