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What Are the Different Types of Brain Stem Tests?

By Nicole Etolen
Updated May 17, 2024
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Physicians use brain stem tests to determine the overall level of functioning within that region of the brain. The brain stem controls several functions vital to survival, including breathing, heart rate, and consciousness. The most common test is the brain stem auditory evoked response test. In the United Kingdom, where brain stem death is considered major criteria for determining if a person is technically alive or dead, additional tests must be performed before declaring a person dead.

The brain stem auditory evoked response test uses a series of sounds to evoke a response within the brain stem. During the procedure, the patient wears a set of headphones through which the sounds are delivered. Electrodes attached to the scalp and earlobes measure the brain stem's response to these sounds. The main purpose of the test is to determine the overall functioning of the nervous system and diagnose hearing problems.

Some countries, such as the United Kingdom, define death as an irreversible loss of consciousness as well as an irreversible loss of the ability to breathe. Since the brain stem places a major role in both functions, if it is damaged beyond repair, patients often fit the definition of death. Before a patient can be declared dead, a series of brain stem tests must be carried out. These tests are performed by two different doctors several hours apart.

Before the doctors can begin the brain stem tests, certain criteria must be fulfilled. First, a patient’s presumed brain stem death must have a cause, such as an accident or illness that affects this region of the brain. Second, coma cannot be the result of something potentially reversible, such as a drug overdose or a metabolic disorder. After these two main criteria are met, brain stem functions tests can begin.

The first of the brain stem tests involves shining a light, typically a pen light, into a patient’s eyes. When the brain stem stops functioning, the pupils appear fixed and dilated. Typically, this test is done without any special equipment aside from the light. In rare cases, however, patients still exhibit signs of pupil activity despite meeting all other criteria for brain stem death, and special imaging scans or brainwave testing equipment may be used to determine the cause of the abnormal reaction.

Testing the cornea’s reaction to irritation by rubbing it with some sort of coarse material, such as a piece of gauze, is typically the next step in the series of brain stem tests. In a patient with a functioning brain stem, this highly sensitive part of the eye would evoke a pain response when touched with gauze. Additional tests to measure the pain response include firmly pinching the nose and prodding the forehead. The gag reflex, which is controlled by the brain stem, is also measured by inserting a tube down the patient’s throat.

The final test for determining brain stem death involves removing the patient from life support for a brief period of time to see if the patient spontaneously starts breathing without assistance. Several hours later, these tests must be repeated a second time by a different senior physician to confirm results. If the patient fails the second time, the doctor can legally declare death.

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