The effect of carbon dioxide on near-death experiences in out-of-hospital cardiac arrest survivors: a prospective observational study

Introduction: Near-death experiences (NDEs) are reported by 11-23% of cardiac arrest survivors. Several theories concerning the mechanisms of NDEs exist - including physical, psychological, and transcendental reasons - but so far none of these has satisfactorily explained this phenomenon. In this study, we investigated the effect of partial pressures of O-2 and CO2, and serum levels of Na and K on the occurrence of NDEs in out-of-hospital cardiac arrest survivors. Methods: A prospective observational study was conducted in the three largest hospitals in Slovenia. Fifty-two consecutive patients (median age 53.1 years, 42 males) after out-of-hospital cardiac arrest were included. The presence of NDEs was assessed with a self-administered Greyson's NDE scale. The initial partial pressure of end-tidal CO2, the arterial blood partial pressures of O-2 and CO2 and the levels of Na and K in venous blood were analysed and studied. Univariate analyses and multiple regression models were used. Results: NDEs were reported by 11 (21.2%) of the patients. Patients with higher initial partial pressures of end-tidal CO2 had significantly more NDEs (P < 0.01). Patients with higher arterial blood partial pressures of CO2 had significantly more NDEs (P = 0.041). Scores on a NDE scale were positively correlated with partial pressures of CO2 (P = 0.017) and with serum levels of potassium (P = 0.026). The logistic regression model for the presence of NDEs (P = 0.002) explained 46% of the variance and revealed higher partial pressures of CO2 to be an independent predictor of NDEs. The linear regression model for a higher score on the NDE scale (P = 0.001) explained 34% of the variance and revealed higher partial pressures of CO2, higher serum levels of K, and previous NDEs as independent predictors of the NDE score. Conclusions: Higher concentrations of CO2 proved significant, and higher serum levels of K might be important in the provoking of NDEs. Since these associations have not been reported before, our study adds novel information to the field of NDEs phenomena.