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 (N
20) of the somatosensory evoked potential (SEP). The SEP was elicited by stimulating the median nerve, and N
20 (C3' or C4'-Fz on the affected side) and N
13 (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 N
20 occurred 7 times in six cases. In all cases, the N
20 was restored by emergency decompression or hyperosmolar therapy. The minimum ICP at which N
20 disappeared was 30 mmHg, and the N
20 was restored when decompression was performed within 4.5 hours. However, when the disappearance persisted for more than 1.5 hours, the N
20 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.
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