S57 Novel measures for EEG monitoring in coma

Objectives In deep comatose states, the EEG appears discontinuous, consisting of bursts of activity on a flat electrical background referred to as the burst-suppression (BS) pattern. We aimed to develop a quantitative EEG measure that can be applied to both BS and continuous EEG coma. Methods We recoded EEG changes in response to intermittent photic or electrical nerve stimulation epochs lasting 1 min. The multi-channel EEG was reduced to a binary signal of alternating stimulus processing and default classes. A default class ratio could then be defined for continuous EEG by analogy with the suppression ratio of BS. A global EEG reactivity index was derived to measure the relative reduction in default class ratio during (effects) and immediately following stimulation (after-effects). Results We found that in patients with BS coma, the EEG reactivity index correlated with clinical coma evaluation and prognostication scales. The same reactivity index measured during BS induced by general anesthesia, was found to reflect the degree of brain injury in experimental rodent models. Ongoing studies indicate that the EEG reactivity index also correlates with the clinical severity of coma with continuous EEG. Discussion Our data suggest that during BS, the bursts reflect stimulus-evoked activity whereas the suppression reflects the missing default activity. Conclusions We propose a novel EEG reactivity index that can be measured in BS and continuous EEG coma alike. Significance Our EEG reactivity index could provide a continuous measure for monitoring recovery from coma and the post-comatose disorders of consciousness. This work was supported by grants of the Romanian National Authority for Scientific Research, CNCS – UEFISCDI, project number PN-II-ID-PCE-2011-3-0847, PN-II-PT-PCCA-2011-3.2-1290 and PN-III-P2-2.1-PTE-2016-0114 to MM.