What are technical aspects of brainstem auditory evoked potential (BAEP) testing?

Updated: Oct 25, 2019
  • Author: Andrew B Evans, MD; Chief Editor: Selim R Benbadis, MD  more...
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An electrode is placed on each ear lobe and at Cz. The first 10 msec are averaged; 2000-4000 responses may be averaged. At least 2 separate trials should be performed. The recording montage is at least (and usually) a 2-channel montage: channel 1 is from the ipsilateral ear to the vertex, and channel 2 is from the contralateral ear to the vertex. Because of relative vertex positivity, the waveforms are recorded as upward deflections. The normal response is a series of waveforms within a 10-msec time window.

Clinically, the first 5 waves are used, with more significance placed on waves I, III, and V. Peak and interpeak latencies are measured, side-to-side differences are calculated, and wave I-V ratios may be used. Audiometry is very helpful and should be done within a reasonable interval after the BAEP study. This helps delineate any hearing loss that might influence the test results. Hearing loss in the 2000- to 4000-Hz frequency range is especially important in that it may delay the BAEP.

Recording a neonatal BAEP is technically different from recording an adult BAEP. The skin of a newborn is very sensitive; accordingly, special nonallergenic tape should be used to fix the electrode, and collodion or other irritant chemicals are to be avoided. To avoid collapse of the earlobe and obstruction of the auditory canal in premature babies, the earphone should be held slightly above the ear.

The earphone is best held by hand, and the recording preferably should be performed with the neonate asleep. This helps reduce those high-frequency EEG components that might interfere with BAEP recording. Because of the slower response, the sweep should be set at 15-20 msec and the low-frequency cutoff filter at 20-30 Hz.

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