Brainstem auditory evoked potentials.

Brainstem auditory evoked potentials (BAEPs) have obtained widespread clinical application in assessing neurologic and audiologic problems. Seven waves (I-VII) are usually recorded in the first 10 ms following broad-band and high-intensity clicks. Latencies of waves I, III, and V, interpeak latencies of I-III, III-V, and I-V, and the amplitude ratio of wave V to wave I are common parameters evaluated for assessing clinically relevant abnormalities of BAEPs. Usually two-channel recordings are obtained: vertex (Cz) to ipsilateral ear and Cz to contralateral earlobe derivation. Evaluating different components in the two derivations helps their identification, particularly when the BAEPs are abnormal. Several technical and subject-related factors affect the amplitude and latencies of BAEP components besides lesions and dysfunctions involving the peripheral auditory structures and brainstem auditory pathways. BAEPs have maximal clinical utility in evaluating comatose patients, in patients with suspected demyelinating disorders, posterior fossa tumors, or in audiologic evaluation, especially in infants. They are also used for intraoperative monitoring of eighth-nerve and brainstem function during different types of posterior fossa surgery.