Hypercapnia and hypokalemia in near-death experiences

A commentary on a study linking hypercapnia and hypokalemia to near-death experiences (NDEs) urges caution. The original study found a correlation, but the commentary notes that hypercapnia may simply indicate better cardiac output and perfusion pressure, which reduces amnesia during cardiac arrest, making patients more likely to remember events and report NDEs. Contradictory evidence from other studies, including one finding lower carbon dioxide levels during NDEs and a prospective study of 63 cardiac arrest survivors finding no association, along with the small sample size and unclear link between blood and brain carbon dioxide levels, suggest the findings require further research.

Study at a glance

Abstract

Klemenc-Ketis and colleagues’ novel report of hyper capnia and hypokalemia associated with near-death experiences (NDEs) [1] was somewhat surprising, as Sabom [2] had previously reported lower than normal carbon dioxide levels measured at the time of a patient’s NDE, and Parnia and colleagues, in a prospective study of 63 cardiac arrest survivors, had found no signifi cant association of either potassium or carbon dioxide with NDEs [3]. Klemenc-Ketis and colleagues’ conclusion that hypercapnia plays a role in provoking NDEs is one possible interpretation of the correlation they found. It is also plausible that hypercapnia is simply an indicator of another factor that may be linked causally to NDE reports. For example, the authors noted that hypercapnia indicates better cardiac output and perfusion pressure, which would reduce the amnesia that is usually seen in cardiac arrest, so that patients would be more likely to remember what happened during the arrest. Th e association between NDEs and hypercapnia may thus indicate simply that patients who are able to recall more of their cardiac arrest also report more NDEs. Gliksman and Kellehear reviewed studies showing that levels of carbon dioxide in the blood are not necessarily accurate estimates of levels in the brain [4], which further complicates the interpretation of the current fi ndings. Th e small sample size of this study, the contradictory evidence from other studies, and the unclear association between levels of carbon dioxide in the blood and in the brain suggest caution in interpreting the fi ndings and suggest the need for further research.