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.
This letter raises methodological concerns about a study claiming that low-dose S-ketamine during thoracic surgery reduces postoperative delirium and cognitive dysfunction in older adults. The authors point out that the study lacked details on how often delirium was monitored each day, relied solely on the Confusion Assessment Method for screening, did not report factors contributing to delirium in the ICU, and used a non-standard definition for cognitive impairment. They note inconsistencies with a recent randomized trial and argue these issues need clarification before accepting the conclusions.