brain death [AS, bragen + death] , an irreversible form of unconsciousness characterized by a complete loss of brain function while the heart continues to beat. The legal definition of this condition varies from state to state. The usual clinical criteria for brain death include the absence of reflex activity, movements, and spontaneous respiration requiring mechanical ventilation or life support to continue any cardiac function. The pupils are dilated and fixed. Because hypothermia, anesthesia, poisoning, or drug intoxication may cause deep physiological depression that resembles brain death, these parameters must be within normal limits prior to testing. Diagnosis of brain death may require evaluating and demonstrating that electrical activity of the brain is absent on two electroencephalograms performed 12 to 24 hours apart. Brain death can be confirmed with electroencephalograms showing a complete lack of electrical activity (a flat line) or vascular perfusion studies showing a lack of blood flow to the brain. Also called irreversible coma. Compare coma, sleep, stupor.
