Monitoring severe head injury: a comparison of EEG and somatosensory evoked potentials

We report on our experience with long-term monitoring of the EEG power spectrum and somatosensory evoked potentials (SSEPs) in 103 patients with severe closed head injury (Glasgow Coma Scale-GCS < or = 8). Patients were monitored for an average of 5 days post injury and monitoring was terminated when they died, regained consciousness or their intracranial physiologic parameters (primarily intracranial pressure-ICP) were stable for 2-3 days. Patients were treated according to a standard protocol that included mechanical ventilation, sedation, and neuromuscular blockade. At 7 of 9 twelve hour time intervals post injury, SSEPs were significantly (p < .05) different between outcome groups using the Glasgow Outcome Score collapsed to 3 categories. The percent slow (delta) activity in the EEG was not significantly different between outcome groups at any time point, post injury. The total power in the EEG power spectrum differed only at the last time epoch post injury (108 hr.). Based on the superior prognostic capabilities of the SSEP, we routinely base critical management decisions on SSEP values. We have not been able to rely on EEG parameters for these same decisions due to the lack of clear distinction between good and poor prognosis groups based on common EEG parameters.