The association of partial pressures of oxygen and carbon dioxide with neurological outcome after out-of-hospital cardiac arrest: an explorative International Cardiac Arrest Registry 2.0 study

BACKGROUND: Exposure to extreme arterial partial pressures of oxygen (PaO(2)) and carbon dioxide (PaCO(2)) following the return of spontaneous circulation (ROSC) after out-of-hospital cardiac arrest (OHCA) is common and may affect neurological outcome but results of previous studies are conflicting. METHODS: Exploratory study of the International Cardiac Arrest Registry (INTCAR) 2.0 database, including 2162 OHCA patients with ROSC in 22 intensive care units in North America and Europe. We tested the hypothesis that exposure to extreme PaO(2) or PaCO(2) values within 24 h after OHCA is associated with poor neurological outcome at discharge. Our primary analyses investigated the association between extreme PaO(2) and PaCO(2) values, defined as hyperoxemia (PaO(2) > 40 kPa), hypoxemia (PaO(2) < 8.0 kPa), hypercapnemia (PaCO(2) > 6.7 kPa) and hypocapnemia (PaCO(2) < 4.0 kPa) and neurological outcome. The secondary analyses tested the association between the exposure combinations of PaO(2) > 40 kPa with PaCO(2) < 4.0 kPa and PaO(2) 8.0–40 kPa with PaCO(2) > 6.7 kPa and neurological outcome. To define a cut point for the onset of poor neurological outcome, we tested a model with increasing and decreasing PaO(2) levels and decreasing PaCO(2) levels. Cerebral Performance Category (CPC), dichotomized to good (CPC 1–2) and poor (CPC 3–5) was used as outcome measure. RESULTS: Of 2135 patients eligible for analysis, 700 were exposed to hyperoxemia or hypoxemia and 1128 to hypercapnemia or hypocapnemia. Our primary analyses did not reveal significant associations between exposure to extreme PaO(2) or PaCO(2) values and neurological outcome (P = 0.13–0.49). Our secondary analyses showed no significant associations between combinations of PaO(2) and PaCO(2) and neurological outcome (P = 0.11–0.86). There was no PaO(2) or PaCO(2) level significantly associated with poor neurological outcome. All analyses were adjusted for relevant co-variates. CONCLUSIONS: Exposure to extreme PaO(2) or PaCO(2) values in the first 24 h after OHCA was common, but not independently associated with neurological outcome at discharge.