Incidence of hyperoxia and factors associated with cerebral oxygenation during cardiopulmonary resuscitation

Background: High oxygen levels may worsen cardiac arrest reperfusion injury. We determined the incidence of hyperoxia during and immediately after successful cardiopulmonary resuscitation and identified factors associated with intra-arrest cerebral oxygenation measured with near-infrared Methods: A prospective observational study of out-of-hospital cardiac arrest patients treated by a physician-staffed helicopter unit. Collected data included intra-arrest brain regional oxygen saturation (rSO2) with NIRS, invasive blood pressures, end-tidal CO2 (etCO2) and arterial blood gas samples. Moderate and severe hyperoxia were defined as arterial oxygen partial pressure (paO2) 20.0-39.9 and 40 kPa, respectively. Intra-arrest factors correlated with the NIRS value, rSO2, were assessed with the Spearman's correlation test. Results: Of 80 recruited patients, 73 (91%) patients had rSO2 recorded during CPR, and 46 had an intra-arrest paO2 analysed. ROSC was achieved in 28 patients, of whom 20 had paO2 analysed. Moderate hyperoxia was seen in one patient during CPR and in four patients (20%, 95% CI 7-42%) after ROSC. None had severe hyperoxia during CPR, and one patient (5%, 95% 0-25%) immediately after ROSC. The rSO2 during CPR was correlated with intra-arrest systolic (r = 0.28, p < 0.001) and diastolic blood pressure (p = 0.32, p < 0.001) but not with paO2 (r = 0.13, p = 0.41), paCO2 (r = 0.18, p = 0.22) or etCO2 (r = 0.008, p = 0.9). Conclusion: Hyperoxia during or immediately after CPR is rare in patients treated by physician-staffed helicopter units. Cerebral oxygenation during CPR appears more dependent, albeit weakly, on hemodynamics than arterial oxygen concentration.