How Brain Death Is Diagnosed

Death by Neurologic Criteria

Brain death is a clinical and legal definition of death. Sometimes, when a person is declared brain dead, their heart may still be still beating and their chest may rise and fall with every breath from the ventilator. The skin might be warm and a person who is brain dead may appear to be resting.

These physical functions may be present in a person who is brain dead because the physical damage is actually hidden in the brain, rather than visible on the body.

Brain cells do not effectively regenerate. This makes it difficult for the brain to recover from injury. Serious brain damage can occur due to a stroke, heart attack, or head trauma. When brain cells undergo permanent damage, they cannot be replaced. Major loss of brain function results in brain death.

patient on ventilator in hospital bed
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Declaring Brain Death

Brain death means that a qualified physician, typically a neurologist, did an extensive physical examination and documented brain death criteria.


Before brain death is pronounced, three clinical criteria must be met:

  • Unresponsiveness
  • Absence of reflexes
  • Apnea (inability to breathe without a ventilator)

Brain Death Testing

Brain death testing falls into three main categories:

  • Physical examination
  • Apnea testing
  • Other testing, also known as ancillary testing

Physical Examination

The physical examination is done to determine the level of responsiveness. If the examination shows a lack of responsiveness, the physical exam would proceed to check for certain reflexes.

Someone who is brain dead will not have any brainstem reflexes. For example, a person in a coma who is not brain dead would blink or move their head if their eye is irritated with a piece of a cotton ball. A person who is brain dead cannot blink, flinch or try to move away if the doctor touches their eye with a fuzzy piece of cotton. Therefore, if there is no blink reflexes, that implies that the brainstem is not functioning properly.

Another type of physical testing is the cold caloric. This test is done by using a syringe of ice-cold water and injecting it into the ear canal. A patient who is brain dead will have no response to this type of stimuli, but an individual who has brain function will have a response, which can range from eye movement to vomiting. 

Apnea Testing

A patient who is sick enough for brain death testing will be on a ventilator and cannot breathe without a ventilator. In order to test to see if the breathing reflex is intact or absent, the ventilator is removed in a procedure called an apnea test.

Typically, an arterial blood gas (ABG) is drawn immediately prior to the beginning of the apnea test, when the ventilator is removed. Oxygen may be given during the apnea test, but the ventilator cannot be used.

Most people, even those who have severe illnesses, will attempt to draw a breath when a ventilator is removed, but someone who is brain dead will not take a breath during apnea testing.

When a person is brain dead, the brain is unable to send the signal to breathe and breathing does not happen without the support of a ventilator.

Other Brain Death Testing

After completing the physical assessment, the physician may elect to order additional testing. While it is typical for both a physical assessment and an apnea test to be done, some people who are not brain dead cannot tolerate apnea testing. Often, in those cases, a flow study will be done. These studies are done to see if blood is traveling to the brain through the bloodstream. If the study shows that no blood is reaching the brain, the test is consistent with brain death.

Some physicians will use an EEG, or electroencephalogram, which is a test that measures brain waves. A person who is brain dead will have a "flat" EEG, as brain waves will be absent.

Atropine, a prescription medication that causes the heart rate to increase, can also be administered as an ancillary test for brain death because it is not effective in brain dead individuals. If the heart rate increases notably after the medication is given, this suggests that a person is not brain dead.

Brain Death Pronouncement

When a person is pronounced brain dead, this means that they are legally dead. Their death certificate will reflect the date when brain death was pronounced, not when their heart stops at a later time.

In the United States, if a person is pronounced brain dead and meets certain medical criteria, organ donation may be an option. In many cases, the individual has already made their decision to donate and has indicated their choice on their driver's license or in their will.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Wijdicks EF, Varelas PN, Gronseth GS, Greer DM. Evidence-based guideline update: determining brain death in adults. Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2010;74(23):1911-8. doi.10.1212/WNL.0b013e3181e242a8

  2. American Academy of Neurology, AAN Summary of evidence-based guideline for caregivers and families of patients: Determining brain death in adults.

  3. American Academy of Neurology. Practice guideline update: disorders of consciousness.

  4. Lewis A, Bernat JL, Blosser S, et al. An interdisciplinary response to contemporary concerns about brain death determination. Neurology. 2018;90(9):423-426. doi.10.1212/WNL.0000000000005033

Additional Reading
  • Practice Parameters: Determining Brain Death In Adults. American Academy of Neurology. 

By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.