Cerebral tissue oximetry levels during prehospital management of cardiac arrest - A prospective observational study

Introduction: Near-infrared spectroscopy (NIRS) enables continuous monitoring of regional oximetry (rSO₂). The aim of this study was to describe dynamics of regional cerebral oximetry levels during out of hospital cardiac arrest (OHCA) resuscitation, specifically around the time of restoration of spontaneous circulation (ROSC).

Methods: This prospective observational study was performed in the prehospital setting during cardio-pulmonary resuscitation (CPR) of OHCA patients. In the three-year study period, two-hundred eighty OHCA's were responded to; rSO₂ was continuously measured throughout CPR and after attaining ROSC.

Results: Final data analysis included 53 patients. Continuous rSO₂dynamics were described and data was compared amongst ROSC (22 cases) and no-ROSC (31 cases) groups. Initial rSO₂levels were below 15% (not detectable) in both groups. With ongoing CPR, rSO₂levels were higher in the ROSC group (median 22% vs. 14% in no-ROSC group, p = 0.030). Until ROSC, rSO₂levels were higher throughout CPR before ROSC (mean maximal value 47% at ROSC vs. 31% no-ROSC, p < 0.01). Furthermore, we found a pattern of significant, rapid and sustained rise in rSO₂levels minutes prior to ROSC and normalization thereafter.

Conclusions: Initial rSO₂levels during OHCA are generally undetectable by the time EMS teams initiate CPR. With CPR, rSO₂levels rise and are higher during CPR in patients who later achieve ROSC. Patients who achieve ROSC exhibit significant, rapid, and sustained rise in rSO₂minutes prior to attaining ROSC, and normalization of rSO₂ levels thereafter. Persistently low levels of rSO₂ during CPR likely portend poor neurologic outcomes.