Brain-stem auditory evoked potential monitoring in experimental diffuse brain injury

The time course of brain-stem auditory evoked potential (BAEP) changes was investigated using an impact-acceleration trauma model in 23 spontaneously breathing rats. Intracranial pressure (ICP), arterial blood pressure and respiratory rate were monitored. The experiments were terminated at four hours after trauma. No significant changes in intracranial pressure (ICP) occurred following the impact. After a short increase, blood pressure returned to baseline values within 5 min. Transient apnea was not followed by prolonged respiratory depression. Diffuse closed head injury (CHI) did not result in general, unidirectional changes of peak latencies or amplitudes of auditory evoked responses. Most BAEP changes developed slowly reaching a maximum at 1 to 4 hours after the injury. In the absence of ICP changes, this pattern reflects secondary ischemia in sensitive brain-stem areas rather than direct traumatic lesions or hypoxia due to respiratory depression.