September 25, 2016
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Detecting Hearing Loss in Children (cont.)

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Medical Editor:

How can hearing be assessed in a child who is unable to cooperate?

Some children are unable to cooperate for hearing evaluations, either due to their age or to a developmental delay (for example, a child with severe mental retardation). Currently, there are two different types of tests that are utilized for children who are unable to cooperate. The first is the frequency-specific auditory brainstem response (ABR) evaluation. An ABR is a physiological measure of the brainstem's response to sound. It tests the integrity of the hearing system from the ear to the brainstem. The test is performed by placing four to five electrodes on the child's head, after which a variety of sounds are presented to the child through small earphones. As the hearing nerve fires, the sound stimulus travels up to the brain. The electrical activity generated by the nerve can be recorded by the electrodes and presented as waveforms on a computer screen. The audiologist can then present different loudness levels of each sound and determine the softest levels at which the child can hear. The child can be tested using all the sounds of a conventional hearing evaluation (adult hearing evaluation).

The limitation of the ABR is the need for the child to be quiet and still. The electrical potential the computer is recording from the auditory nerve is very small. Any muscle movement, including something as small as an eye blink, can obliterate the hearing response; therefore, the infant or child must be sleeping during the test. Infants less than 3 months old can be tested during natural sleep. Children older than 3 months are typically sedated for about one hour (under the supervision of a physician) during the test. The most common oral sedative used is chloral hydrate.

The second type of test to objectively evaluate children is the otoacoustic emission (OAE) test. This test can be done as a supplement to the ABR or as an initial screen of hearing. An otoacoustic emission test measures an acoustic response produced by the inner ear (cochlea). The acoustic response measured is in essence the response produced by the inner ear as it bounces back out of the ear in response to a sound stimulus. The test is performed by placing a small probe that contains a microphone and speaker into the child's ear.

Otoacoustic Emissions (OAE) Photo - Hearing Loss in Children
Otoacoustic Emissions (OAE) Photo - Hearing Loss in Children

As the child sits or rests quietly, sounds are generated in the probe and responses that come back from the cochlea are recorded. Once the cochlea processes the sound, an electrical stimulus is sent to the brainstem. In addition, there is a second and separate sound that does not travel up the nerve but comes back out into the child's ear canal. This "byproduct" is the otoacoustic emission. The emission is then recorded with the microphone probe and represented pictorially on a computer screen. The audiologist can tell which sounds yielded a response/emission and the strength of those responses. If there is an emission present for those sounds critical to speech comprehension, then the child has "passed" the hearing screen. As a supplement to the ABR, the OAE serves as a crosscheck to either confirm normal hearing or verify the site-of-lesion for the hearing loss as the inner ear. OAE tests the integrity of the hearing organ for sound (the cochlea), but it does not evaluate the hearing beyond the cochlea. That is why the OAE is often paired with the ABR or with a behavioral test that can evaluate a child's responsiveness to sound.

The results from an ABR and an OAE evaluation can predict the child's hearing, determine if there is a loss, determine the type of hearing loss, and help with decisions regarding intervention. Intervention can include medical treatment, surgery, or hearing aids and therapy.

Medically Reviewed by a Doctor on 9/15/2016


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