Brain-stem auditory-evoked potentials in post-comatose patients after severe closed head trauma.

Brain-stem auditory-evoked potentials (BAEPs) were recorded in 35 post-comatose patients after severe closed head trauma. Compared to the normal BAEPs obtained from 30 normal controls, significant individual abnormality could be detected in only 2 patients. This abnormality consisted of lateral asymmetry, but not prolonged interpeak latencies or abnormal amplitude ratios. Further, no differences were found between groups as regards interpeak latencies. A significant reduction of BAEP amplitudes was seen in the patient group, being most pronounced in the 13 patients with hearing loss. It is concluded that the BAEP does not sufficiently reveal brain-stem lesions expected to persist after severe closed head trauma, presumably because the structures generating waves IV and V are not permanently affected. The amplitude reductions observed may be explained by the diffuse cochlear damage known to occur concurrently with head trauma.