The term brain death is defined as "irreversible unconsciousness with complete loss of brain function," including the brain stem, although the heartbeat may continue. Demonstration of brain death is the accepted criterion for establishing the fact and time of death. Factors in diagnosing brain death include irreversible cessation of brain function as demonstrated by fixed and dilated pupils, lack of eye movement, absence of respiratory reflexes (apnea), and unresponsiveness to painful stimuli. In addition, there should be evidence that the patient has experienced a disease or injury that could cause brain death. A final determination of brain death must involve demonstration of the total lack of electrical activity in the brain by two electroencephalographs (EEGs) taken twelve to twenty-four hours apart. Finally, the physician must rule out the possibilities of hypothermia or drug toxicities, the symptoms of which may mimic brain death. Some central nervous system functions such as spinal reflexes that can result in movement of the limbs or trunk may persist in brain death.
Until the late twentieth century, death was defined in terms of loss of heart and lung functions, both of which are easily observable criteria. However, with modern technology these functions can be maintained even when the brain is dead, although the patient's recovery is hopeless, sometimes resulting in undue financial and emotional stress to family members. French neurologists were the first to describe brain death in 1958. Patients with coma depasse were unresponsive to external stimuli and unable to maintain homeostasis. A Harvard Medical School committee proposed the definition used in this entry, which requires demonstration of total cessation of brain function. This definition is almost universally accepted.
Brain death is not medically or legally equivalent to severe vegetative state. In a severe vegetative state, the cerebral cortex, the center of cognitive functions including consciousness and intelligence, may be dead while the brain stem, which controls basic life support functions such as respiration, is still functioning. Death is equivalent to brain stem death. The brain stem, which is less sensitive to anoxia (loss of adequate oxygen) than the cerebrum, dies from cessation of circulation for periods exceeding three to four minutes or from intracranial catastrophe, such as a violent accident.
Difficulties with ethics and decision making may arise if it is not made clear to the family that brain stem death is equivalent to death. According to research conducted by Jacqueline Sullivan and colleagues in 1999 at Thomas Jefferson University Hospital, roughly one-third to one-half of physicians and nurses surveyed do not adequately explain to relatives that brain dead patients are, in fact, dead. Unless medical personnel provide family members with information that all cognitive and life support functions have irreversibly stopped, the family may harbor false hopes for the loved one's recovery. The heartbeat may continue or the patient may be on a respirator (often inaccurately called "life support") to maintain vital organs because brain dead individuals who were otherwise healthy are good candidates for organ donation. In these cases, it may be difficult to convince improperly informed family members to agree to organ donation.
Ad Hoc Committee of the Harvard Medical School. "The Harvard Committee Criteria for Determination of Death." In Opposing Viewpoint Sources, Death/Dying, Vol. 1. St. Paul, MN: Greenhaven Press, 1984.
"Brain (Stem) Death." In John Walton, Jeremiah Barondess, and Stephen Lock eds., The Oxford Medical Companion. New York: Oxford University Press, 1994.
Plum, Fred. "Brain Death." In James B. Wyngaarden, Lloyd H. Smith Jr., and J. Claude Bennett eds., Cecil Textbook of Medicine. Philadelphia: W.B. Saunders, 1992.
Sullivan, Jacqueline, Debbie L. Seem, and Frank Chabalewski. "Determining Brain Death." Critical Care Nurse 19, no. 2 (1999):37–46.
ALFRED R. MARTIN