During cardiac arrest and cardiopulmonary resuscitation (CPR), some patients show signs of consciousness and cognitive activity, including brain activity on EEG that resembles normal waking patterns despite severe oxygen deprivation. In a study of 567 in-hospital cardiac arrests, 11 of 28 survivors interviewed reported memories or perceptions suggesting consciousness during CPR. Four categories of experiences emerged: CPR-induced consciousness, post-resuscitation awareness, dream-like experiences, and transcendent recalled experience of death (RED). A separate group of 126 community survivors reinforced these categories and added delusions. Normal EEG activity (delta, theta, alpha) appeared for up to 35–60 minutes into CPR even with low cerebral oxygenation, suggesting that a network-level cognitive activity and lucidity may occur during cardiac arrest.
A spectrum of consciousness and awareness, including signs of implicit learning and electrocortical biomarkers, may be present during deep hypothermic circulatory arrest (DHCA), despite the absence of visible signs of consciousness. In a prospective study across 10 hospitals with 36 DHCA patients, 29 had a tablet set up to deliver audiovisual stimuli. All had EEG and NIRS monitoring, but only 9 had usable EEG data. Delta EEG waves were observed during circulatory arrest in 3 of those 9 patients. None had explicit recall of the three fruit names, but 3 of 36 correctly guessed them, suggesting implicit learning, and 3 recalled other memories, including themes of a death experience. This may help explain negative psychological outcomes in cardiac arrest survivors.