Intracranial and Cerebral Perfusion Pressures in Relation to Auditory Brainstem Responses and Initiation of Secondary Brainstem Damage

Abstract

The authors investigated the relationship between supratentorial intracranial pressure (ICP) and serial changes in auditory evoked brainstem responses (ABR). Of 122 cases of brain death evaluated over a 5-year period, serial ABRs were observed in 28, excluding patients with posterior fossa lesions. When an increase of ICP to 35-40 mmHg was sustained for an average of 10.1 hours, wave V was prolonged. Wave V was lost when the ICP exceeded 40 mmHg. Waves I and III were undetectable above an ICP of 60 mmHg and below a cerebral perfusion pressure (CPP) of 30 mmHg.
The results indicate that evaluation of secondary brainstem damage by ABR should be initiated when an increase in ICP to within the critical zone of 35-40 mmHg lasts for more than 10 hours and that vigorous efforts should be made to decrease the ICP below this level. Both low CPP and high ICP were involved in the loss of wave I, indicating that both ischemia and displacement of the brainstem were important pathophysiological factors.