Brain death

The concept that a person may be considered dead when the brain is no longer functioning as determined by technology.

Condition in which the nerves in the brain stem have died, and the person can be certified as dead, although the heart may not have stopped beating.

Total cessation of all activity in the brain, generally measured by lack of electrical signals on electroencephalograph readings taken over a period of at least 12 to 24 hours, even though heart and lungs may still continue to function (with machine assistance). The time period is important, because some conditions, such as some kinds of poisoning or drug reactions, can suppress brain activity. Brain death (sometimes called irreversible coma) has been variously defined and interpreted in different states and settings, but generally the patient has ceased to have reflexes, movements, and independent breathing. The definition of death has become important in several areas, notably the question of whether a patient should be maintained in a ventilator and whether the patient’s organs might be used for transplants. Often organs for transplants are taken after the brain is dead but while the heart and lungs are still functioning, since blood supply to organs is important if the transplant is to have the best chance to succeed.

Irreversible unconsciousness with total loss of brain function, usually determined by loss of reflex activity and respiration and fixed, dilated pupils while the heart continues to beat. In the United States, legal definitions of brain death vary from state to state, but usually electrical activity of the brain must be shown to be absent on at least two electroencephalograms taken 12 to 14 hours apart.

Irreversible cessation of all functions of the entire brain, including the brain stem. This definition of death was developed by Harvard Medical School in 1968. While brain death is diagnosed by a careful clinical examination, the diagnosis is confirmed by a variety of tests that determine an absence of reflexes, unresponsiveness to stimuli, a lack of spontaneous respiration or movement, and the absence of electrical activity of the brain as indicated by a flat electroencephalogram (EEG). In addition, it must first be determined that nothing is suppressing the person’s responses, such as hypothermia (cold body temperature) or drugs (for example, excessive phenobarbital levels can result in a coma and suppression of EEG activity). If after 24 hours there is no change in a person’s status, he or she is declared dead. This definition of brain death allows for the certification of death even if the lungs and heart continue to function with machine assistance but electrical activity in the brain has ceased. After brain death has been determined, the person’s organs can be donated.

The cessation of brain function. The criteria for concluding that the brain has died include lack of response to stimuli, lack of all reflexes, absent respirations, and an isoelectric electroencephalogram that for at least 30 min will not change in response to sound or The cessation of brain function. The criteria for concluding that the brain has died include lack of response to stimuli, lack of all reflexes, absent respirations, and an isoelectric electroencephalogram that for at least 30 min will not change in response to sound or pain stimuli. Other criteria that are sometimes used include loss of afferent cerebral evoked potentials, loss of isotope uptake during brain scans, or absence of cerebral perfusion on Doppler sonography. Before making this diagnosis, two physicians, including one experienced in caring for severely brain damaged patients, should examine the patient. It is inadvisable for physicians associated with transplant procedures to participate in the review. The patient’s body may be kept “alive” briefly by life-support devices if the patient is an organ donor.