Near-death experiences: Can chemistry explain them?

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The phenomenon known as ‘near-death experience’ is the stuff of hospital dramas, a dramatic conceit for movies about do-overs and for a (I guess lucky) few of us, a mysterious peephole to ‘the other side.’

The phenomenon is very real: By various estimates, 11% to 23% of those who had experienced cardiac arrest and lived to tell about it report some unique cognitive experience -- an overwhelming feeling of transcendence, doors opening, beckoning light, a thumbnail life-review -- that broadly fits the description. (The Internet yields a bounty of personal accounts as well, so it must be real!)

But their observations are not very well explained -- not, at least, by standard earthly measures.

A study appearing this week in the open-access British journal Critical Care offers an intriguing blood-chemistry analysis of the phenomenon, which may point to further avenues of research.

Researchers from University of Maribor’s School of Medicine in Slovenia followed 52 patients in Slovenia who had suffered out-of-hospital cardiac arrests, were resuscitated after they had ceased breathing and lost a pulse, and survived. Eleven of the 52 patients -- aged on average 53 years and 42 of whom were male -- reported having had a near-death experience. The researchers compared the 11 patients whose recalled experiences measured at least a seven on a possible 33-point scale measuring near-death experience (yes, there is such a thing).

Near-death experiences were significantly more likely to have been recalled by survivors who, within five minutes of their arrival at the hospital, had higher concentrations of carbon dioxide in arterial blood and higher blood-potassium levels, the Slovenian physicians found. At least as important is what factors were not associated with a higher likelihood of a patient having had the near-death experience: Researchers found no link between near-death experience and patients’ religious belief, fear of death, education level, age, sex, time elapsed until resuscitation or drugs administered during resuscitation. They also looked for links to patients’ sodium levels -- another critical piece of blood chemistry -- and found none.

The mystery of near-death experiences, of course, is very far from answered here. One thing we don’t know -- and I’d venture to claim will never be known -- is how many and which of the heart attack victims that failed to survive also had a near-death experience before dying. One 2007 study found that low blood levels of potassium in patients with heart failure, for instance, is associated with a higher risk of death. Possibly, patients with higher carbon dioxide and potassium levels who had had near-death experiences were simply more likely to survive to recount the sensation.

And then there’s the simple fact that many people have described cognitive disturbances that could readily be mistaken for near-death experiences when they were not (technically) near death: fighter pilots have described such experiences under the influence of high G-forces; patients anesthetized for surgery have reported similar experiences -- as have, of course, psychotic patients. There’s a fine overview of all the vagaries of the near-death experience here.

So, have you had a near-death experience? Please share!

-- Melissa Healy