During deep anesthetic coma, the electroencephalographic (EEG) becomes discontinuous. This activity pattern comprised of bursts of activity lasting a couple of seconds on a “flat”, suppressed, background is referred to as burst-suppression (BS). Apart for surgical anesthesia, prolonged EEG depression to BS levels is increasingly used as target for medically-induced coma for neuroprotection after brain injury as well as in the treatment of status epilepticus. In these situations, the BS state is fully reversible. Nevertheless, BS activity can also occur as a result of pathologic conditions, such as cerebral ischemia/hypoxia, in which case it frequently associated with an ominous prognosis. The distinction between pathologic BS and fully reversible BS cannot be satisfactorily made by monitoring solely the “spontaneous” BS.
Figure: Cortical EEG recordings showing anesthetic BS patterns in rat during flash stimulation (STIM) aquired with the CERMO device (Moldovan et al 2014, unpublished)
An increasing wealth of evidence suggests that the bursts can be triggered by somatosensory stimuli which can therefore “drive” the BS patterns, a phenomenon termed BS reactivity. Nevertheless, the relationship between external stimuli and burst generation was found not to be 1:1, which confounds the reliability of BS reactivity testing.
At ComaEEG we currently work to develop a better understanding of BS reactive behavior using experimental studies during BS coma in rodents (Project UEFISCDI PN-II-ID-PCE-2011-3-0847, contract 110/2011) as well as to develop a clinical monitoring device for BS reactivity (Project UEFISCDI PN-II-PT-PCCA-2011-3.2-1290, contract 129/2012).
Table: Roadmap of the ComaEEG projects 2011-2016
Status report (Updated: December 2014)
Our main finding to date is that the “unreliability” of BS reactivity testing is in fact the result of a dynamic BS reactive behavior which is reproducible and can be reliably predicted by mathematical modeling. This behavior is similar in humans and rodents, does not depend on the stimulus used (optic, electric etc) or the anesthetic used (gas or injectable). Ongoing experimental studies of neurovascular coupling and cortical excitability modulation indicate that alterations of BS reactive behavior can be used to asses cortical integrity during coma. These findings encourage us to proceed with testing the potential of reactive BS behavior monitoring in the clinical setting using the CERMO device. Further details on the scientific production resulting from the ComaEEG projects can be found in the research section.