The auditory brainstem response (ABR) is an evoked potential that originates at the auditory nerve (Cranial Nerve VIII). This test is used to assess the auditory system’s function from the cochlea through the brainstem. The response is identified by “peaks” that occur typically between 1 and 15 milliseconds from the stimulus onset. The ABR peaks are measured and marked traditionally as I, II, III, IV, and V. Each peak has an expected latency to be considered “normal”. Delayed or missing peaks are consistent with abnormal auditory function.
The amplitudes and latencies (both absolute and inter-peak) are used to diagnose certain auditory pathologies.
ABR testing is traditionally used to help determine the degree of hearing loss in pediatric or difficult to test populations. It is also used for testing the auditory pathway as related to acoustic neuromas and some nervous system abnormalities.
The patient should be relaxed or sleeping in a quiet environment. It is preferable that the patient lie down during the procedure to facilitate a calm and comfortable environment. The electrode sites must be prepared and cleaned in order to obtain acceptably low skin impedance. It is recommended to have impedance values be 3kΩ or lower. The impedance values between one another should be balanced or similar in value.
The electrodes must be placed as indicated below. The must be a few centimetres between each electrode. The same electrode placement for ABR is used for ASSR allowing for easy switching between the test types.
Check the impedance on the preamplifier and place the transducers. Make sure the patient is relaxed prior to starting the test. You can monitor this by watching the EEG Window on the top right of the recording window.
The Eclipse comes with pre-programmed protocols so the system is ready to use immediately. Protocols can be created or modified easily to fit your clinical needs. Consult your Additional Information to learn how to create or modify a protocol. The procedure discussed on the next page is simply a suggested process to be used as a guideline.
Waveforms can be marked during a recording or afterwards from the Recording or Edit sheet. Waveforms can be marked manually or automatically. To mark a waveform automatically, use the Suggest Waveform marker.
This feature will place markers within the latency ranges that may be entered in the Latency template. To mark a selected waveform manually, choose the appropriate marker or select 1-5 on the keyboard. Now drag the mouse to the correct position on the waveform and click to place the marker (or push Enter). The same function is available if you right click in the graph area with the curve selected.
HINT If you hold down Crtl key while using the Arrow keys the Waveform Marker will jump from peak to peak!
HINT You can use the digital filters to “clean up” noisy data even after a completed test or run! You’ll find this feature on the bottom of the Edit sheet.
The system has an option to load default latency data during installation. You may also create your own (consult your Additional Information for instruction). While marking waveforms manually, a shaded area will appear indicating such latency data to assist with marking.
Once the waveforms are marked, choose the Latency sheet. The shaded area indicates the range of the latency data.
Choose the Report Icon
When complete, choose Save and Exit.