In the U.S., an ad hoc committee at Harvard Medical School published a pivotal 1968 report to define irreversible coma. The Harvard criteria gradually gained consensus toward what is now known as brain death. In the wake of the 1976 Karen Ann Quinlan controversy, state legislatures moved to accept brain death as an acceptable indication of death. Finally, a presidential commission issued a landmark 1981 report — Defining Death: Medical, Legal, and Ethical Issues in the Determination of Death. — that rejected the "higher brain" approach to death in favor of a "whole brain" definition. This report was the basis for the Uniform Determination of Death Act, which is now the law in almost all fifty states.
Today, both the legal and medical communities use "brain death" as a legal definition of death. Using brain-death criteria, the medical community can declare a person legally dead even if life support equipment keeps the body's metabolic processes working. The first nation to adopt brain death as a legal definition of death was Finland in 1971. In the United States, Kansas enacted a similar law earlier.
Similarly, Islamic views on brain death are mixed.
The 1981 federal report, Defining Death, found that Catholic and Protestant theologies did not object to brain death criteria. Indeed, Dennis Horan, president of the pro-life group Americans United for Life, stated:
Legislation limiting the concept of brain death to the irreversible cessation of total function of the brain, including the brain stem, is beneficial and does not undermine any of the values we seek to support.
More recently, the findings of the 1981 President's Commission Report have been questioned. The new attack on brain death criteria has been multi-pronged. First, the view that brain death marks the end of the integrated unity of the human organism has been questioned. Alan Shewmon has argued that the body as a whole is the central integrator of the organism rather than the brain. He appeals to, among other reasons, brain dead pregnant women who have lived up to 200+ days and given birth to healthy children, as well as to a brain dead boy who lived over fourteen years on a ventilator and with basic nursing support. Others have argued that there is insufficient evidence that the entire brain is dead in a brain dead individual. Some brain dead individuals have continuing EEG activity and others maintain normal or near-normal body temperature, implying continuing hypothalamic function.
In Catholic medical ethics, Pope Pius XII stated that death is determined by medical experts and it "does not fall within the competence of the Church. Advocates of brain death criteria have claimed that this implies that the church is bound to support the view of the medical community on this issue. More recently, the Pontifical Academy of Science has upheld Catholic doctrine. Nevertheless, there was some Catholic dissent on neurological criteria for death. In addition, a volume consisting of essays by opponents of brain death criteria who participated in a 2005 conference at the Pontifical Academy of Sciences was published in 2006 by a publisher outside the Vatican.
In 2008, an article of the Osservatore Romano expressed the wish that the debate on brain death be re-opend because of new developments in the medical world. Anyway, Vatican spokesman said that the article presented a personal opinion of the author and "did not reflect a change in the Catholic Church's position".
It is important to distinguish between brain death and states that may mimic brain death (e.g., barbiturate intoxication, alcohol intoxication, sedative overdose, hypothermia, hypoglycemia, coma or chronic vegetative states). Some comatose patients can recover, and some patients with severe irreversible neurologic dysfunction will nonetheless retain some lower brain functions such as spontaneous respiration, despite the losses of both cortex and brainstem functionality. Thus, anencephaly, in which there is no higher brain present, is generally not considered brain death, though it is certainly an irreversible condition in which it may be appropriate to withdraw life support.
Note that brain electrical activity can stop completely, or drop to such a low level as to be undetectable with most equipment. This includes a flat EEG during deep anaesthesia or cardiac arrest. However, the EEG is not required in the United States, but is considered to have confirmatory value.
The diagnosis of brain death needs to be rigorous to determine whether the condition is irreversible. Legal criteria vary, but it generally requires neurological exams by two independent physicians. The exams must show complete absence of brain function, and may include two isoelectric (flat-line) EEGs 24 hours apart. The widely-adopted Uniform Determination of Death Act in the United States attempts to standardize criteria. The patient should have a normal temperature and be free of drugs that can suppress brain activity if the diagnosis is to be made on EEG criteria.
Alternatively, a radionuclide cerebral blood flow scan that shows complete absence of intracranial blood flow can be used to confirm the diagnosis without performing EEGs.
Most organ donation for organ transplantation is done in the setting of brain death. In some nations (for instance, Belgium, Poland, Portugal and France) everyone is automatically an organ donor, although some jurisdictions (such as Singapore) allow opting out of the system. Elsewhere, consent from family members or next-of-kin is required for organ donation. The non-living donor is kept on ventilator support until the organs have been surgically removed. If a brain-dead individual is not an organ donor, ventilator and drug support is discontinued and cardiac death is allowed to occur.