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  • Updated 01.08.2024
  • Released 05.09.1994
  • Expires For CME 01.08.2027

Brain death/death by neurologic criteria



“Brain death,” or death by neurologic criteria (BD/DNC) is the common term for the determination of human death by showing the permanent cessation of all clinical brain functions. It has been accepted as a legal definition of death in the United States and throughout the world. BD/DNC must be determined by careful neurologic examination showing apnea, cranial nerve areflexia, and unresponsiveness that is permanent and caused by a structural lesion that accounts for the clinical findings. Tests showing the absence of intracranial blood flow can establish the diagnosis and should be used whenever any doubt arises over the clinical examination or if portions of it cannot be performed safely or adequately. In this article, the author discusses the need for uniformity in BD/DNC determination, updates to the 2023 American Academy of Neurology BD/DNC guidelines, the use of ancillary tests in BD/DNC, and several reports on specific topics, including BD/DNC in pregnancy, declaring BD/DNC in the setting of drug intoxication, BD/DNC in the setting of hypothermia or extracorporeal membrane oxygenation, the legal positions on BD/DNC, and portrayals of BD/DNC in the popular media.

Key points

• BD/DNC is human death determined by establishing the permanent cessation of all clinical and physiologic functions of the brain.

• BD/DNC is the legal standard for human death throughout the Western world and most of the developing world.

• The essential criteria for BD/DNC are complete unresponsiveness (coma), brainstem areflexia, apnea, and permanence.

• Tests showing the absence of intracranial circulation can confirm BD/DNC in cases in which the examination findings are drawn into question or the complete examination cannot be performed.

Historical note and terminology

"Brain death," or death by neurologic criteria, is the commonly accepted name for human death determined by clinical evaluation showing the permanent cessation of all clinical functions of the entire brain. The concept of BD/DNC originated with observations made by French neurologists in the late 1950s that patients with irreversible structural brain lesions maintained on ventilators showed an unprecedented depth of coma, cranial nerve areflexia, and apnea, a state they termed “coma dépassé,” meaning a “state beyond coma” (81). Their key findings included deep coma, lack of spontaneous breathing, inability to vary heart rate and blood pressure in response to appropriate stimuli, polyuria, and subsequent cardiac arrest days later. In a landmark paper in 1968, an ad hoc Harvard Medical School committee proposed the first definition of BD/DNC, which required the presence of coma (no response to external stimuli), no spontaneous movements or spontaneous breathing, lack of brainstem reflexes, and an isoelectric EEG (01). Since that time, guidelines for the determination of BD/DNC have been published, and the “Uniform Determination of Death Act” has been adopted by most states in the United States, establishing BD/DNC as a legal definition of death (102).

The term “brain death” is misleading because it incorrectly implies that only the brain has died and not the person. This term alone may be responsible for much of the confusion by the public and by some professionals. Yet because the term “brain death” has been generally accepted, it is likely to remain in common use. A more appropriate term is “death by neurologic criteria.” This article will use “BD/DNC” to accommodate both terms.

The prevalence of BD/DNC practice is expanding internationally. A 2002 survey of BD/DNC practices worldwide disclosed the accepted practice of BD/DNC determination in 80 countries surveyed. Practice guidelines were available in 70 of these countries; legal standards were in effect in 55 countries. Although there was widespread agreement on the concept of BD/DNC, differences were detected in the clinical practices of determining BD/DNC (133; 48). A detailed survey of international BD/DNC practices in 91 countries showed legal provisions in 70% and found that the presence of institutional BD/DNC protocols correlated highly with the presence of an organized organ transplantation network (126). Subsequent studies have demonstrated advances in the acceptance and practice surrounding BD/DNC in the United States and throughout the world (41; 66).

The terminology in this area is confusing. The old terms "cerebral death" and "neocortical death" should be abandoned because they incorrectly imply that the destruction of the cerebrum or neocortex alone is sufficient for death. The term "brainstem death" has been used in the United Kingdom to acknowledge that most of the bedside tests demonstrating the absence of clinical brain functions examine brainstem functions specifically (93). However, the term "brainstem death" adds confusion to an already confused terminology (80; 142) and should not be used in place of "brain death." Public surveys show persistent confusion about the meaning of the term brain death and its distinction from the persistent vegetative state (118; 72). Similarly, surveys of American neurologists disclosed an inadequate understanding of BD/DNC (54). Several countries continue to use the term “brainstem death” despite the confusion it introduces (119).

The concept of "whole BD/DNC" embodies the most useful and widely accepted criterion of death (04; 05; 07). Except for the United Kingdom, all BD/DNC clinical and ancillary tests in current use are based on the “whole brain” criterion of death, which requires that the clinical functions of all portions of the brain, including the brainstem, must have ceased irreversibly.

The American Academy of Neurology updated its evidence-based practice parameter for determining BD/DNC in 2023, combining adult and pediatric guidance into one document (02; 68). This was a joint effort with the Society of Critical Care Medicine, the American Association of Pediatrics, and the Child Neurology Society. This was a huge advance in the field, providing updated guidance for special circumstances, including BD/DNC in the setting of hypothermia, primary posterior fossa injury, pregnancy, and extracorporeal membrane oxygenation, among others. This came on the heels of the World Brain Death Project, published in JAMA in 2020 (41), a joint effort of 27 international societies to provide worldwide guidance and criteria.

There remains variability in how physicians determine BD/DNC. A study of the BD/DNC determination policies of the top 50 neurology departments in the United States revealed a disturbing pattern of non-uniformity (43). The authors found significant variations from accepted guidelines or from each other in many areas: who can perform the testing; whether more than one examination is required and the duration of the interval between examinations; the preconditions for testing (eg, establishing an underlying cause and requiring the exclusion of reversible metabolic or toxic factors, hypothermia, and shock); the techniques for testing brainstem function; whether and how to perform apnea testing; and whether and which ancillary electrophysiologic or neuroimaging tests are used. Similar results of practice variability were found in a later survey of 68 hospitals in the United States (113). A 2016 survey of 508 BD/DNC hospital policies in the United States showed significant noncompliance with the American Academy of Neurology standards, particularly by not excluding hypotension and hypothermia, and in the details of apnea testing and ancillary tests (44). The most recent survey showed progress in increasing the uniformity of BD/DNC determination guidelines among the leading United States medical centers in compliance with the American Academy of Neurology’s 2010 standards (128). The new AAN guidelines were published in 2023, and we can expect a follow-up study to look at variability in the coming years.

Not all scholars accept the conceptual validity of BD/DNC. A few physicians, philosophers, and theologians continue to hold that patients clinically determined to be BD/DNC are not truly dead (115; 116; 117). Some of these opponents to BD/DNC have argued that BD/DNC is not an entirely coherent concept, but these arguments have not persuaded medical or public policy bodies to stop recognizing BD/DNC as human death. BD/DNC continues to be an accepted legal standard of death throughout the majority of the Western and undeveloped world, and its practice is increasing in prevalence. In its analysis, the United States President’s Council on Bioethics acknowledged certain conceptual shortcomings in the concept of BD/DNC but recommended that BD/DNC continue to serve as a legal definition of death for the United States (President’s Council on Bioethics 2008).

The highly publicized BD/DNC cases in the United States sparked much public and scholarly commentary concerning whether they were truly dead and what the law stipulated (13; 08; 67). These discussions culminated in the identification of areas of uncertainty and the further work needed on BD/DNC (08).

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