Variance of interburst intervals in burst suppression.

Each EEG performed over a 3 year period at the University of Michigan with a diagnosis of generalized burst-suppression (BS) was reviewed. Ten EEGs from 10 patients with hypoxic-ischemic encephalopathy (HIE-BS) and 21 records from 8 patients with pentobarbital induced burst-suppression for treatment of status epilepticus (SE-BS) were reviewed. For each EEG, the mean duration of 40 interburst intervals (IBIs) as well as their coefficient of variability were calculated. We found that in the SE-BS group the coefficient of variability of IBI duration was highly correlated with the logarithm of mean IBI duration while in the HIE-BS group, there was no significant correlation between these 2 variables. This suggests that the underlying mechanism causing BS is different in the 2 groups and might be related to a uniform and progressive affection of similar brain structures in the SE-BS group and a more patchy and variable pathology in the HIE-BS group.