The effect of increased intracranial pressure during the appearance of pressure waves on the brainstem.

The effects of increased intracranial pressure (ICP) during the appearance of plateau waves or B-waves to the brainstem functions were investigated by evaluation of evoked potentials. The ICP and systemic blood pressure were continuously recorded in nine cases of intracranial hypertension. In the four cases demonstrating plateau waves in ICP recording, the latencies of the auditory brainstem evoked potentials (ABEP) measured during the appearance of plateau waves showed no significant differences compared to those measured during the interval phase between two plateau waves. In the five cases demonstrating B-waves in ICP recording, four cases showed significant (p less than 0.05) prolongation of the V wave of ABEP and three showed significant (p less than 0.05) prolongation of the P15 of somatosensory evoked potentials during the phase of increased ICP level with B-waves compared to those measured during the phase of decreased ICP level without B-waves, produced by external drainage of the cerebrospinal fluid or mannitol administration. The results indicated that during the appearance of plateau waves there were no significant changes of electrical activity in the brainstem, even though there was a significant reduction in cerebral perfusion pressure. It is suggested that in cases with the appearance of B-waves, an increase in ICP frequently affects the electrical activity in the brainstem.