Prosen G, et al. - Dynamics of regional cerebral oximetry levels during out of hospital cardiac arrest (OHCA) resuscitation, specifically around the time of restoration of spontaneous circulation (ROSC) were described. It was noted that initial regional oximetry (rSO₂) levels during OHCA are generally undetectable by the time EMS teams initiate cardio-pulmonary resuscitation (CPR). A rise in rSO₂ levels was noted with CPR and these levels were noted to be higher during CPR in patients who later achieve ROSC. Significant, rapid, and sustained rise in rSO₂ minutes was noted among patients who achieve ROSC prior to attaining ROSC, and normalization of rSO2 levels was observed thereafter. During CPR, persistently low levels of rSO₂ seemed predicting poor neurologic outcomes.