Brain Death: Definition

Brain death is defined as an “Irreversible cessation of all functions of the entire brain, including the brainstem”. Brain death is a relatively new concept originating in the 20th Century with the advent of Mechanical Ventilation & Organ Transplantation. It led to a redefining of death- and this brain death concept was subsequently advanced through medical & legal frameworks. Ultimately, it lead to general (although not universal) acceptance that death of the brain was a sufficient condition for death of the individual. (1, 2)

Uniform Determination of Death Act (UDDA) was a draft state law that was approved for the United States in 1981 by the National Conference of Commissioners on Uniform State Law, in cooperation with the American Medical Association, American Bar Association, & President’s Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research. The act has since been adopted by most US states and is intended “to provide a comprehensive and medically sound basis for determining death in all situations.”

“An individual who has sustained either 1) irreversible cessation of circulatory & respiratory functions or 2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead.” (3)

Clinical determination of brain death involves 4 steps (4)

1. Clinical Evaluation (Prerequisites):

  • Establish irreversible & proximate cause of coma (hx, imaging, exam)
  • Exclude CNS Depressants & NMBs
  • Normal Temperature (>36°C)
  • Normal Systolic Blood Pressure (>100mmHg)
  • Single Neurologic Exam (2 exams in some states) after a ‘sufficient’ time period has passed since the injury (hours)
  • All physicians in most U.S. States can determine brain death although individual hospitals may require that it be a neurologist or neurosurgeon

2.  Neurologic Exam

  • Unresponsive coma
  • No CN reflexes
  • Apnea (PCO2 > 60mmHg, or >20 over baseline)

3.  Ancillary Testing (such as EEG, cerebral blood flow study); Note: Brain death is a clinical diagnosis and confirmatory testing is not mandatory
4.  Documentation: Time of Death; Checklist; Contact organ procurement organization


  1. “State beyond coma” [or coma dépassé; termed by French Neurologists] 1959
  2. A Definition of Irreversible Coma: A Report of the Ad Hoc Committee of the Harvard Medical School to Examine the Definition of Brain Death. JAMA. 1968 Aug 5;205(6):337-40.
  4. Wijdicks EF, Varelas PN, Gronseth GS, Greer DM; American Academy of Neurology. Evidence-based guideline update: determining brain death in adults: report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2010 Jun 8;74(23):1911-8. doi: 10.1212/WNL.0b013e3181e242a8.