A brain stem test is a series of neurological examinations performed to assess the function of the brain stem, often to determine if brain death has occurred. These tests check for reflexes controlled by the brain stem.
What the Tests Involve
The tests typically include the following assessments:
- Pupillary Reflex: A light is shone into each eye to see if the pupils constrict (become smaller). Lack of reaction indicates the brain stem is not functioning.
- Corneal Reflex: The cornea (the clear outer layer of the eye) is gently touched with a cotton swab or tissue. A normal response is blinking. Absence of blinking suggests brain stem dysfunction.
- Oculocephalic Reflex (Doll's Eyes): The patient's head is turned from side to side. Normally, the eyes will move in the opposite direction. If the eyes remain fixed in their sockets, it suggests brain stem damage. Note: This test is not performed if there is any suspicion of neck injury.
- Oculovestibular Reflex (Cold Caloric Test): Cold water is injected into the ear canal. In a person with a functioning brain stem, this will cause the eyes to move slowly towards the irrigated ear, followed by a quick movement back. Absence of eye movement indicates brain stem dysfunction. Note: This test is not performed if there is any damage to the ear drum.
- Gag Reflex: Touching the back of the throat with a tongue depressor should elicit a gag reflex. Absence of this reflex suggests brain stem dysfunction.
- Cough Reflex: Suctioning the trachea (windpipe) should trigger a cough. Absence of coughing suggests brain stem dysfunction.
- Apnea Test: This test assesses whether the patient can initiate breathing when the carbon dioxide level in their blood rises. The patient is taken off the ventilator while being closely monitored for any respiratory effort. Failure to breathe, with a significant rise in carbon dioxide levels, is consistent with brain death.
Why Brain Stem Tests Are Performed
These tests are crucial in determining brain death, a legal and medical definition of death. When the brain stem ceases to function, the body loses its ability to regulate vital functions like breathing, heart rate, and blood pressure.
Important Considerations
Brain stem testing is a complex process and must be performed by qualified medical professionals. Certain factors can interfere with the accuracy of the tests, such as drug intoxication, hypothermia, and certain medical conditions. It's essential to rule out these factors before concluding brain death.
