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What is the Difference Between a Coma and Brain Death?

Answer: A lot.

UPDATE: If you have family or loved ones currently in the hospital and you are discussing the potential to donate and save lives, click here.


A coma is a deep state of eyes-closed unconsciousness where a person is not able to respond to people or the environment around them. In a coma, a patient is alive and there is some brain activity. Depending on the severity of the injury, recovery time varies. A coma can be temporary or permanent.

Patients in a coma might have brain stem responses, spontaneous breathing and/or non-purposeful motor responses. Coma has three possible outcomes: progression to brain death, recovery of consciousness, or evolution to a state of chronically depressed consciousness, such as a vegetative state.

Patients in comas are not considered for organ, eye, or tissue donation.

Brain Death

Brain Death is death. No brain function exists. Brain death results from swelling in the brain; blood flow in the brain ceases and without blood to oxygenate the cells, the tissue dies. It is irreversible. Once brain tissue dies, there is nothing that can be done to heal it.

The brain performs many functions, including thought, movement and all the neurological functions that allow the body to maintain blood pressure, heart rate, body temperature, hormones, breathing, etc. When a person deteriorates to brain death, the body’s entire system stops. You cannot breathe, your heart cannot beat and your body cannot function once your brain dies. Massive artificial medical measures must be started to maintain organ function (such as ventilated support), but these interventions are only a temporary measure.

Brain Death Testing

Brain death is a very conservative diagnosis and is only made when there is no doubt in the findings. Brain death is a rare event that occurs in one out of every 200 hospital deaths (CDC study, 1986).

Physicians will perform a series of tests to determine if brain death has occurred. These tests would confirm: the patient has no response to verbal or visual command, the patient is flaccid; pupils are unreactive and fixed; has no oculocephalic, gag, oculovestibular or corneal reflexes; and there is no spontaneous respiration.

Even after confirmation of these tests, many physicians request additional, tests before pronouncing brain death. These commonly include the electroencephalogram (EEG) and the cerebral blood flow (CBF) study.

The EEG measures brain voltage in microvolts. It is so sensitive that the static electricity in a person’s clothes will give a squiggle on the EEG (a false positive). All positive responses suggest brain function. The patient in the deepest coma will show some EEG electroactivity, while the brain-dead patient will not.

The cerebral blood flow (CBF) study involves the injection of a mild radioactive isotope into the blood stream. By placing a radioactivity counter over the head, one can measure the amount of blood flow into the brain. If there is no blood flow to the brain, the brain is dead. A negative cerebral flow study is indisputable evidence of a dead brain.

Only after brain death has been confirmed and the time of death noted, can organ donation become a possibility.

Donation After Brain Death

Families of a brain dead patient must, by federal regulations, be provided the option of organ donation. If the family declines donation, the mechanical ventilator, medications and fluids are discontinued, after which the heart stops. If the family says yes to donation, the regional organ procurement organization (LifeSource in MN, ND, SD) is involved. The donor’s body is kept functioning by artificial means, such as ventilated support until the recovery of organs and tissue for life-saving transplant.

If you support donation it is important to document your decision. This removes the burden off of your loved ones to make the decision once you have passed away.

Register online as a donor.

Learn more about the donation process.