Consciousness in deep hypothermic circulatory arrest: a feasibility study.

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.

Study at a glance

Abstract

Studies have not explored consciousness during deep hypothermic circulatory arrest (DHCA). However, as studies in cardiac arrest have identified a spectrum of consciousness, we sought to establish the feasibility of studying consciousness during DHCA. This was a prospective study across 10 hospitals with 36 DHCA patients undergoing thoracic aortic aneurysm repair or pulmonary endarterectomy. A tablet computer delivered audiovisual stimuli (images and names of three fruits) using headphones during each procedure as a potential test of implicit learning and explicit recall. We also established electroencephalography (EEG) and near-infrared spectroscopy (NIRS) to measure electrocortical markers of consciousness and cerebral oxygenation. Post-procedure interviews were carried out to test patients' ability to recall the audiovisual stimuli as well other explicit memories. 1) Feasibility of establishing tests of explicit recall and implicit learning, 2) Electroencephalography testing during DHCA. 1) Signs of explicit recall of memories or implicit learning, and 2) identification of electrocortical biomarkers of consciousness during DHCA. Overall, 29/36 (81%) had the tablet set up. All 36 had NIRS and EEG set up, but 9 (25%) had useable EEG data, and 23 (66%) NIRS data. Delta EEG waves were observed during circulatory arrest in 3/9 (33%) patients, while 1/9 (11%) had theta waves just prior to circulatory arrest. All others showed isoelectric pattern. 35/36 (97%) agreed to follow up interviews. None had explicit recall of the names of the three fruits, but 3/36 (9%) correctly guessed them as a potential sign of implicit learning and 3 (9%) recalled other memories including events around the procedure and themes consistent with a recalled experience of death. A spectrum of consciousness and awareness, including signs of implicit learning and electrocortical biomarkers of consciousness may be present during DHCA, despite absence of visible signs of consciousness. This can be further used to help explain the negative psychological outcomes that cardiac arrest survivors face.