Predictors and prognostic value for in-hospital outcomes associated with postoperative anemia in cardiac surgery: a retrospective cohort study

Purpose Postoperative anemia after cardiac surgery is inconsistently managed and often untreated outside of transfusion thresholds. Despite the established association between preoperative anemia and adverse outcomes, the prognostic significance of postoperative anemia is inadequately characterized. In this study, we sought to analyze the predictors of postoperative anemia and its independent effect on in-hospital outcomes. Methods We conducted a single-centre retrospective cohort study of consecutive adult patients who underwent elective cardiac surgery at Toronto General Hospital (University Health Network, Toronto, ON, Canada) between 1 January 2016 and 31 December 2021. Postoperative anemia was defined as nadir hemoglobin < 100 g·L−1 on postoperative day (POD) 1. Multivariable regression modelled the predictors of postoperative anemia and its independent effect on acute kidney injury (AKI), length of stay (LOS), mortality, stroke, and a composite of ≥ stage 2 AKI, stroke, and mortality (secondary outcomes). We conducted sensitivity analyses in nonpreoperatively anemic and nontransfused subgroups. Results Among 4,633 patients (median [interquartile range {IQR}] age, 63 [53–71] yr; 1,384 [30%] female; 1,919 [41%] complex procedures), 2,232 (48%) were postoperatively anemic. Older age, female sex, lower body mass index, prior cancer, poor kidney function, unstable cardiac symptoms, preoperative anemia, procedure time, and intraoperative transfusions were independently associated with postoperative anemia. After adjustment, postoperative anemia was independently associated with AKI (adjusted odds ratio [OR], 1.67; 95% confidence interval [CI], 1.21 to 2.30; P < 0.01) and longer LOS (adjusted ratio of means [RoM], 1.05; 95% CI, 1.00 to 1.09; P < 0.05), but not mortality, stroke, or the composite outcome. Conclusions Postoperative anemia was common and independently associated with AKI and prolonged LOS after adjusting for preoperative anemia, intraoperative transfusion, and other confounders. Further research is needed to clarify underlying mechanisms and investigate opportunities for intervention.