Near death experiences (NDEs), reported to include sensations such as life flashing before the eyes, feelings of peace and joy, and apparent encounters with mystical entities, may be caused by raised levels of carbon dioxide in the blood. Researchers writing in BioMed Central's open access journal Critical Care investigated the unexplained events in 52 cardiac arrest patients.

Zalika Klemenc-Ketis worked with a team of researchers from the University of Maribor, Slovenia, to examine patients who reported NDEs. She said, "Several theories explaining the mechanisms of NDEs exist. We found that in those patients who experienced the phenomenon, blood carbon dioxide levels were significantly higher than in those who did not."

Of the 52 patients, 11 reported NDEs. Their occurrence did not correlate with patients' sex, age, level of education, religious belief, fear of death, time to recovery or drugs given during resuscitation. They were more common in people who had previously experienced NDEs. According to Klemenc-Ketis, "Our study adds new and important information to the field of NDE phenomena. The association with carbon dioxide has never been reported before, and deserves further study."