Reversibility of Cerebral Function Assessed by Somatosensory Evoked Potentials and its Relation to Intracranial Pressure

Abstract

The critical value and duration of intracranial pressure (ICP) causing cerebral function damage was evaluated in six head injury patients by monitoring the first negative cortical component (N20) of the somatosensory evoked potential (SEP). The SEP was elicited by stimulating the median nerve, and N20 (C3' or C4'-Fz on the affected side) and N13 (C2S-Fz) were monitored serially with a signal processor. The auditory brainstem response (ABR) was simultaneously recorded on the affected side (A1 or A2-Cz). A reversible loss of N20 occurred 7 times in six cases. In all cases, the N20 was restored by emergency decompression or hyperosmolar therapy. The minimum ICP at which N20 disappeared was 30 mmHg, and the N20 was restored when decompression was performed within 4.5 hours. However, when the disappearance persisted for more than 1.5 hours, the N20 latency was markedly prolonged after restoration. These changes appeared before the ABR showed definite abnormalities. These results show that the cerebral function may be damaged when ICP exceeds 30 mmHg, and that emergency decompression is required within 4.5 hours, preferably within 1.5 hours, to restore cerebral function. This critical ICP and duration should be of clinical value in patient management.