BackgroundTo clarify the relationship between the PaO2/FiO2and 28-day mortality in patients with sepsis.MethodsThis was a retrospective cohort study regarding MIMIC-IV database. Nineteen thousand two hundred thirty-three patients with sepsis were included in the final analysis. PaO2/FiO2was exposure variable, 28-day mortality was outcome variable. PaO2/FiO2was log-transformed as LnPaO2/FiO2. Binary logistic regression was used to explore the independent effects of LnPaO2/FiO2on 28-day mortality using non-adjusted and multivariate-adjusted models. A generalized additive model (GAM) and smoothed curve fitting was used to investigate the non-linear relationship between LnPaO2/FiO2and 28-day mortality. A two-piecewise linear model was used to calculate the OR and 95% CI on either side of the inflection point.ResultsThe relationship between LnPaO2/FiO2and risk of 28-day death in sepsis patients was U-shape. The inflection point of LnPaO2/FiO2was 5.30 (95%CI: 5.21—5.39), which indicated the inflection point of PaO2/FiO2was 200.33 mmHg (95%CI: 183.09 mmHg—219.20 mmHg). On the left of inflection point, LnPaO2/FiO2was negatively correlated with 28-day mortality (OR: 0.37, 95%CI: 0.32—0.43,p< 0.0001). On the right of inflection point, LnPaO2/FiO2was positively correlated with 28-day mortality in patients with sepsis (OR: 1.53, 95%CI: 1.31—1.80,p< 0.0001).ConclusionsIn patients with sepsis, either a high or low PaO2/FiO2was associated with an increased risk of 28-day mortality. In the range of 183.09 mmHg to 219.20 mmHg, PaO2/FiO2was associated with a lower risk of 28-day death in patients with sepsis.