Brain death is the permanent loss of brain activity. As a result, people cannot breathe or maintain other vital functions on their own, and they permanently lose all awareness and capacity for thought.
Brain death means that the brain stops functioning. People do not respond to any stimuli. No treatment can help, and once the diagnosis is confirmed, a person is considered legally dead.
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.
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 the following:
Doctors typically recheck the criteria 6 to 24 hours later to confirm the person's lack of response.
After confirming twice that the brain is not functioning and after checking for and correcting any problems present, doctors diagnose brain death. No additional testing is needed.
Occasionally, doctors use certain diagnostic tests to help confirm brain death. The tests are typically done only to make organ donation possible—for example, after catastrophic head injuries (as may occur in car crashes). These tests can be done instead of testing a person's breathing, which requires several tests. Testing whether a person can breathe is undesirable because each test deprives organs of oxygen, risking further damage to organs that are intended for donation. The tests include
Electroencephalography (EEG—a recording of the brain’s electrical activity): This test shows no brain waves when a person is brain dead.
Imaging tests that detect blood flow to the brain: No blood flows to the brain when a person is brain dead.
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.
No one who meets the criteria for brain death recovers. After brain death is confirmed, all life support is stopped. 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 (sometimes called the Lazarus sign). These movements result from spinal reflex muscle contractions and do not mean the person is not really brain dead.