Timing matters: association of persistent postoperative anemia with adverse outcomes in cardiac surgery

OBJECTIVE: To investigate the dynamic impact of anemia at different perioperative timepoints (preoperative, postoperative day 1, 3, and 7) on adverse events in patients undergoing cardiac surgery. METHODS: This single-center retrospective cohort study included 315 adult patients who underwent cardiac surgery between January 2020 and June 2025. Anemia was defined according to World Health Organization (WHO) criteria. Baseline characteristics, perioperative indicators, and postoperative outcomes were compared between the preoperative anemia and non-anemia groups. Multivariable logistic regression models were used to assess the independent association of anemia at different timepoints with three pre‑specified primary outcomes: increased postoperative hospital stay, pulmonary infection, and low cardiac output syndrome (LCOS), after adjusting for potential confounders. RESULTS: Results: The prevalence of preoperative anemia was 48.6% (153/315). For the three pre‑specified primary outcomes, compared to the non‑anemia group, the preoperative anemia group had significantly higher rates of postoperative pulmonary infection (32.03% vs. 17.28%, p = 0.003) and increased postoperative hospital stays (median 10.0 [IQR 9.0-15.0] vs. 10.0 [7.0-12.0] days, p = 0.026). Multivariable analysis revealed that anemia on postoperative day 7 was an independent risk factor for increased postoperative hospital stays (OR = 3.033, 95% CI: 1.547-5.946, p = 0.001) and pulmonary infection (OR = 2.526, 95% CI: 1.235-5.167, p = 0.011). Furthermore, anemia on postoperative day 7 was a strong independent predictor of low cardiac output syndrome (LCOS) (OR = 8.494, 95% CI: 2.316-31.156, p = 0.001), whereas anemia on postoperative day 1 was associated with a lower risk of LCOS (OR = 0.146, 95% CI: 0.041-0.517, p = 0.003). RBC transfusion was associated with a reduced risk of adverse outcomes. CONCLUSION: Postoperative anemia, particularly persistent anemia on postoperative day 7, is an independent risk factor for increased postoperative hospital stays, pulmonary infection, and LCOS in cardiac surgery patients. Dynamic monitoring of postoperative hemoglobin levels is crucial for risk stratification and individualized blood management. However, the modest sample size (n = 315) limits the precision of estimates for infrequent outcomes, and these findings therefore require validation in larger studies.