Quantitative electroencephalographic evaluation of non-fatal and fatal traumatic coma

Diffuse axonal injury (DAI) is an important cause of morbidity and mortality after traumatic brain injury (TBI), and its severity is therefore a major determinant of outcome. There have been suggestions that the extent of DAI may be reflected in quantitative measures of cerebral function, including the electroencephalogram (EEG) and brain-stem auditory evoked potentials (BAEPs). It has therefore been proposed that these quantitative methods of analysis may provide objective predictors of outcome following TBI. We prospectively investigated the relationship between quantitative EEG and BAEP measures and outcome, in 60 comatose patients (47 male and 13 female; age range 1-80 years, mean 36.4) after severe, closed head injury (post-resuscitation Glasgow Coma Scale (GCS) of 8). The Spearman correlation coefficients (rs) have been calculated for quantitative EEG measures (mean regional power and interhemispheric coherence) and BAEPs with patient outcome on the Glasgow Outcome and Disability Rating Scales at 6 months and 1 year. The measures most significantly correlated with outcome (P < 0.001) are over the left hemisphere, beta activity power (amplitude squared) in the fronto-central and centro-temporal regions, and alpha activity power in the centro-temporal region. We found no correlation between interhemispheric coherence (a statistical measure of cross-correlation in the frequency domain) and outcome at either 6 months or 1 year post-injury. In 10 fatalities, we examined the relationship between interhemispheric EEG coherence prior to deaths and the histopathological severity of DAI, in concordant regions. The only significant correlation between DAI and interhemispheric coherence is seen in the alpha band at the temporo-occipital site (rs = -0.79, P = 0.007). Our data indicate that there is regional information in EEG power spectra over the left hemisphere, which could be used in prognostic predictions for patients in coma after severe TBI. We were unable to demonstrate a correlation between interhemispheric coherence and outcome, or any clear and consistent evidence of a relationship between interhemispheric coherence and the severity of DAI.