Blood levels of carbon dioxide may be linked to near death experiences after heart attack

By Dr. Ananya Mandal, MDApr 9 2010

Near death experiences have often been described as “seeing life flash before one’s eyes” or “intense feelings of joy and peace.” Now researchers claim that levels of Carbon Dioxide or CO₂ may be the causal link for these sensations. They believe that the CO₂ alters the levels of certain chemicals in the brain and makes it see lights at the ends of tunnels or dead loved ones.

This finding was reported in a small study in people who had survived a heart attack. The study was undertaken by Dr Zalika Klemenc-Ketis and colleagues from the University of Maribor in Slovenia and published online in the peer-reviewed medical journal Critical Care.

According to the study near death experiences or NDEs are reported by up to 23% of people who survive a heart attack, but there is little explanation for the mechanisms behind them. They go on to describe the experiences of 52 people who had a heart attack outside of a hospital setting and who were admitted to the intensive care units in one of three main hospitals between January 2008 and the end of June 2009. These adults were all defined as clinically dead on admission i.e. their breathing and effective heart activity had stopped from which they had recovered later. They answered a questionnaire about their experience and their medical records were reviewed.

The researchers recorded the CO₂ in their exhaled air, amount of CO₂ and oxygen as well as sodium and potassium in blood, this information was taken from blood samples within 5 minutes of admission. 11 of these 52 patients had an NDE. Patients with higher levels of CO₂ in their exhaled air and in their blood had more near death experiences. High levels of potassium and CO₂ in blood were also linked with NDEs. Since this study involved too few patients the results cannot be absolute according to researchers. However larger studies may shed more light on this phenomenon. Dr Sam Parnia, a senior research fellow at the University of Southampton who is conducting a study on NDEs in cardiac failure patients in Britain and America, said that the research was “quite interesting — albeit a very small study”. He said that high levels of CO₂ could mean that blood was going back to the brain adding that this could mean patients remember their NDEs. “This may explain why [patients] have better recall of the experience, it doesn’t mean the CO₂ was causing the experience…These observations may indicate that those patients who had improved resuscitation had better brain recovery and hence better recall and less amnesic effects of brain injury, which seems to be what limits people’s ability to recall their near death experiences.”