EEG patterns in hypoxic encephalopathies (post-cardiac arrest syndrome): fluctuations, transitions, and reactions.

In patients with coma resulting from hypoxic encephalopathy (e.g., after cardiac arrest), the EEG may reflect the severity of brain dysfunction, although the exact relationship among the EEG changes, the extent of neuronal damage, and consequent prognosis is still under study. Many prognostications are based on particular EEG patterns at a time point, such as burst suppression or generalized periodic discharges, but with sequential, repeated, or with prolonged or continuous EEG monitoring, it has become increasingly clear that more information might be gleaned from EEG pattern changes over time. Short-term fluctuations (as opposed to permanent transitions), or preserved reactions to exogenous stimuli, have to be differentiated. This review presents many of the typical postanoxic EEG patterns, along with their evolution over time. This preliminary report illustrates the temporal dynamic changes of EEG over time. It is hoped that it will act as a starting point for prospective and systematic investigation to test whether EEG evolution and transitions add diagnostic and prognostic value.