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WHAT IS EVOKED POTENTIAL TESTING?

 

There are 3 types of evoked potential tests: visual, brainstem auditory, and somatosensory.

 These tests are used to check the nerve signals your brain and spinal cord (parts of your nervous system) receive from other parts of your body. The signals tell us what you see, hear, or feel during the tests. They can also be used to check for vision and/or hearing problems. While these tests are being performed the technologist will look at wavy lines (waveforms) on a screen or on paper. These lines show the activity in your brain and other parts of your body. These waveforms will be studied to help determine your test results, and a report will be sent to the doctor who ordered the tests.

Remember:  

        The visual evoked potential test may be used to check for vision problems.

        The brainstem auditory evoked potential test may be used to assess your hearing.       

    The somatosensory evoked potential test may be used to check your nervous system.

PREPARING FOR YOUR TEST:

  • Prepare as instructed. Shower or bathe, and wash and dry your hair, but don't use lotion, oil, powder, or hairstyling products because your skin and hair should be clean and free of excess oil.

  • Wear loose clothes. Be aware that you may be asked to change into a hospital gown.

  • Bring or wear any eyeglasses or contact lenses you use.

  • Your testing may last from 30 minutes to 4 hours, depending on how many tests you're scheduled for.

  • Be sure to allow extra time to find a parking space, walk to the area and be checked in.

  • Arrange for someone to drive you home, if needed.

 

 

LET THE TECHNOLOGIST KNOW

For your safety and for the success of your test, tell the technologist:

  • If you are allergic to any medications

  • What medications you take

  • You may also be asked questions about your overall health.

DURING YOUR TEST

Testing is done in a quiet room. The technologist will explain how your test or tests will be done. Sometimes the lights in the room may be dimmed.

VISUAL EVOKED POTENTIAL (VEP)

You will sit a few feet from a screen (like a TV monitor or computer screen). The technologist will attach small metal disks (electrodes) to your scalp using water-based gel or paste, or glue. You will gaze at a dot at the center of the screen. With one eye covered, you will watch a checkerboard pattern reversing on the screen. The test will then be repeated with the patch over your other eye.

BRAINSTEM AUDITORY EVOKED POTENTIAL (BAEP)

You will be seated in an exam chair. The technologist will attach the same electrodes to your head and on or behind your ears with gel or paste. You will then wear headphones that are like the ones you would listen to a stero with. You will hear clicking sounds or tones first in one ear, then in the other. You will also hear a constant noise through the headphones. This noise can be a hum or “hiss” (white noise). 

 

SOMATOSENSORY EVOKED POTENTIAL (SSEP)

This test is done while you lie back in a reclining chair or lie down on an exam table. Electrodes will be placed on parts of your body, such as your head, spine, arms, or legs. The technologist will apply mild electrical currents to the nerves in your wrists or ankles. You may feel your muscles “twitch” or itch. But there is not enough electricity to hurt or harm you. Many people discribe it as “like when a arm that’s “asleep” “wakes up””.

 AFTER YOUR TEST

Before you leave, all electrodes will be removed, and your hair will be cleaned enough for you to return to your normal routine. If you took medication to help you relax for any test, arrange to have someone drive you home.

Your doctor will let you know when your test results are ready, you will not hear directly from the technicians- the results will go to your doctor’s office.