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 spectroscopy (NIRS). 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 (rSO 2 ) with NIRS, invasive blood pressures, end-tidal CO 2 (etCO 2 ) and arterial blood gas samples. Moderate and severe hyperoxia were defined as arterial oxygen partial pressure (paO 2 ) 20.0–39.9 and ≥40 kPa, respectively. Intra-arrest factors correlated with the NIRS value, rSO 2, were assessed with the Spearman's correlation test. Results Of 80 recruited patients, 73 (91%) patients had rSO 2 recorded during CPR, and 46 had an intra-arrest paO 2 analysed. ROSC was achieved in 28 patients, of whom 20 had paO 2 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 rSO 2 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 paO 2 (r = 0.13, p = 0.41), paCO 2 (r = 0.18, p = 0.22) or etCO 2 (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.