Hyperoxemia after reperfusion in cardiac arrest patients: a potential dose–response association with 30-day survival

Background Hyperoxemia may aggravate reperfusion brain injury after cardiac arrest. The aim of this study was to study the associations between different levels of hyperoxemia in the reperfusion period after cardiac arrest and 30-day survival. Methods Nationwide observational study using data from four compulsory Swedish registries. Adult in- and out-of-hospital cardiac arrest patients admitted to an ICU, requiring mechanical ventilation, between January 2010 and March 2021, were included. The partial oxygen pressure (PaO 2 ) was collected in a standardized way at ICU admission (± one hour) according to the simplified acute physiology score 3 reflecting the time interval with oxygen treatment from return of spontaneous circulation to ICU admission. Subsequently, patients were divided into groups based on the registered PaO 2 at ICU admission. Hyperoxemia was categorized into mild (13.4–20 kPa), moderate (20.1–30 kPa) severe (30.1–40 kPa) and extreme (> 40 kPa), and normoxemia as PaO 2 8–13.3 kPa. Hypoxemia was defined as PaO 2 < 8 kPa. Primary outcome was 30-day survival and relative risks (RR) were estimated by multivariable modified Poisson regression. Results In total, 9735 patients were included of which 4344 (44.6%) were hyperoxemic at ICU admission. Among these, 2217 were classified as mild, 1091 as moderate, 507 as severe, and 529 as extreme hyperoxemia. Normoxemia was present in 4366 (44.8%) patients and 1025 (10.5%) had hypoxemia. Compared to the normoxemia group, the adjusted RR for 30-day survival in the whole hyperoxemia group was 0.87 (95% CI 0.82–0.91). The corresponding results for the different hyperoxemia subgroups were; mild 0.91 (95% CI 0.85–0.97), moderate 0.88 (95% CI 0.82–0.95), severe 0.79 (95% CI 0.7–0.89), and extreme 0.68 (95% CI 0.58–0.79). Adjusted 30-day survival for the hypoxemia compared to normoxemia group was 0.83 (95% CI 0.74–0.92). Similar associations were seen in both out-of-hospital and in-hospital cardiac arrests. Conclusion In this nationwide observational study comprising both in- and out-of-hospital cardiac arrest patients, hyperoxemia at ICU admission was associated with lower 30-day survival.