Brain death is the permanent loss of brain activity. As a result, people cannot breathe or maintain the beating of the heart of any other vital function on their own, and they permanently lose all awareness and capacity for thought.
Brain death is the most severe form of unconsciousness. In the past, the idea of brain death was irrelevant because when the brain died, so did the rest of the body. That is, the person stopped breathing, and the heart stopped beating. However now, artificial means (such as ventilators and drugs) can temporarily maintain breathing and the heart's beating even when all brain activity stops. But eventually, even with help from artificial means, all the body's organs stop working. Nothing can keep the heart beating indefinitely once brain death occurs. A person with no brain activity (a brain-dead person) is considered legally dead.
There are specific criteria for diagnosing brain death. Doctors identify some of them during the physical examination:
Doctors also check certain other reflexes to confirm that the brain is not functioning. Doctors must also notify or attempt to notify the person's next of kin or a close friend.
In addition, doctors cannot diagnose brain death until they have checked for and corrected all treatable problems that could slow brain function and could thus be misdiagnosed as brain death. These problems include a very low body temperature, very low blood pressure, very high or very low levels of certain substances (such as sugar and sodium) in the blood, overdose of a sedative, and use of certain toxic drugs.
Doctors must also recheck the criteria 6 to 24 hours later to confirm the person's lack of response.
Only after confirming twice that the brain is not functioning and after checking for and correcting any problems present, can doctors diagnose brain death.
Occasionally, diagnostic tests are also done to confirm brain death, but these tests are usually not needed. After such tests are done, the criteria are checked again after 2 hours. These tests include
Imaging tests include angiography, CT angiography, single photon emission computed tomography (SPECT—which uses a radioactive molecule called a radionuclide to produce images of blood flow), and transcranial Doppler ultrasonography. Doctors may use EEG and imaging tests to rapidly confirm brain death after catastrophic head injuries (as may occur in motor vehicle accidents). Rapid confirmation of brain death makes organ donation possible.
After brain death is confirmed, all life support is stopped. No one who meets the criteria for brain death recovers. Family members may wish to be with the person at this time. They need to be told that one or more limbs may move when breathing assistance is ended or that the person may even sit up. These movements result from spinal reflex muscle contractions and do not mean the person is not really brain dead.
Last full review/revision March 2013 by Kenneth Maiese, MD