Evoked Potentials (EPs) Tests

What are evoked potentials (EP)?

Your child is having a test called evoked potentials (EPs). There are three main types of EPs and a couple of subtypes:

  • Visual EPs (VEP), including flash VEP and pattern VEP
  • Somatosensory EPs (SEP), including upper limb SEP and lower limb SEP
  • Brainstem auditory EPs (BAEP)

The meaning of each type of test is explained later in this fact sheet.

Sometimes all three types of EPs will be done at the same time. Other times, only one of these tests will be done. Your child's doctor will decide which test or tests need to be done.

Visual evoked potential (VEP) tests

A visual evoked potential test checks the nerves that go from the eye to the visual cortex. The visual cortex is the part of the brain that lets you see things.

During a VEP test

There are two types of VEP test: a "flash" test and a "pattern" test. Your child may be having both tests. How the tests are done changes a bit depending on how old your child is and how well your child can see.

During the test, small metal circles filled with cream and covered with gauze are put on your child's head. These metal circles are called electrodes.

For a flash visual evoked potential test, your child will wear goggles that put tiny red lights over the eyes. Your child will see red flashes first in one eye and then in the other eye, and finally in both eyes. While your child sees these flashes, the electrodes record the way the brain responds. The flash is very bright, so your child can see it even with his eyes closed. Your child will be able to see the flash through his eyelids.

For a pattern visual evoked potential test, your child will sit in a chair in front of a television screen. The television screen will show a checkerboard pattern that moves between black and white squares. Your child will be asked to stare at a dot in the middle of the screen while the electrodes record the way the brain responds. During this test, your child will need to stay still and focus on the screen.

Somatosensory evoked potential (SEP) tests

A somatosensory evoked potential test checks the nerves that go from the upper limb (wrist) or lower limb (ankle) to the somatosensory cortex. The somatosensory cortex is the part of the brain that lets you feel things when you touch them.

During a SEP test

Your child will lie comfortably on his or her back on a bed. To make sure your child keeps still during the test, he or she may be given a medicine called chloral hydrate. This is a mild sedative that will help your child relax.

During the test, small metal circles filled with cream and covered with gauze are put on your child's head. These metal circles are called electrodes.

For the upper limb SEP, electrodes are put on your child's head, neck , and shoulder.

For the lower limb SEP, electrodes are also put on your child's back and behind the knee.

Your child will feel a tingle or buzzing from a special bar-shaped electrode at the wrist or ankle. We will test each arm or leg by itself.

This test will not hurt your child. But he or she may find the tingling or buzzing a little bit uncomfortable.

Brainstem auditory evoked potential (BAEP) tests

A brainstem auditory evoked potential test checks the nerve from the ear to the brainstem. The brainstem is part of the brain that links the spinal cord to the rest of the brain. The brainstem controls heart beat, breathing, wakefulness, and messages to and from the brain to other parts of the body. This test tells us how well the nerves that connect the ears and the brain are working.

This test is also used to check hearing problems in children who cannot take a regular hearing test.

During a BAEP

Your child will lie comfortably on his or her back on a bed during the test. To make sure your child keeps still during the test, he or she may be given a medicine called chloral hydrate. This is a mild sedative that will help your child relax.

Small metal circles filled with cream and covered with gauze are attached to your child's head and ears. These metal circles are called electrodes.

Your child will wear earphones on both ears. Through the earphones, your child will hear rapid clicking sounds, first in one ear and then in the other ear. The electrodes will record how your child's brain reacts to these sounds.

An EP test takes less than an hour

If your child needs all three types of EPs, this may take 1 1/2 to 2 hours.

Preparing for an evoked potential test

You do not need to do anything to prepare your child for an evoked potential test, unless your child cannot lie very still for about 30 minutes.

If your child cannot lie still for 30 minutes, your child may need a mild sedative. A sedative is a medicine that will calm your child so that he or she can lie still for the test.

If your child needs a sedative, he or she cannot have any solid food for 8 hours before the test. Your child can have milk or formula up to 6 hours before the test and breast milk up to 4 hours before the test. Your child may drink clear liquids such as apple juice or water, or eat Jell-O up to 2 hours before the test.

Please check on your child carefully for about 6 hours after the test. Give your child only small sips of clear liquids, such as water and apple juice. Your child can have a regular meal if he feels like eating. When your child is fully awake, he can return to his or her usual activities.

There are no side effects from evoked potential tests

There are no side effects from evoked potential tests. If your child needs a sedative, he or she might be sleepy, grumpy, and unsteady for about 4 to 6 hours after the test.

Key Points

  • Evoked potential tests check how well messages travel through different nerves to the brain.
  • There are three types of EPs: visual EPs (VEP), somatosenory EPs (SEP), and brainstem auditory EPs (BAEP).
  • If your child cannot be still during the test, he or she may have to take a sedative.
  • The tests take about 30 to 45 minutes each and are not painful.

Elizabeth Pang, PhD

Roy Sharma, RET

Jennifer Boyd, RN, MHSc, CNN(C)

11/6/2009
 




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