Postoperative anemia is highly prevalent among patients undergoing cardiac surgery and is associated with delayed functional recovery, increased morbidity, and impaired long-term outcomes. Preoperative iron deficiency is common in this population and contributes to inadequate erythropoietic recovery after surgery. Functional iron deficiency frequently develops even in patients without preoperative deficiency due to blood loss, hemodilution, and inflammation-mediated disruption of iron homeostasis. Despite this clinical burden, standardized strategies for postoperative anemia management have not been established.

This prospective, randomized, double-blind, placebo-controlled clinical trial evaluates whether early postoperative intravenous iron supplementation improves long-term anemia outcomes in patients undergoing cardiac surgery with cardiopulmonary bypass. Adult patients with preoperative anemia (hemoglobin <13 g/dL) or iron deficiency (ferritin <100 ng/mL or transferrin saturation <20%) will be screened. Eligible participants with postoperative day (POD) 1 hemoglobin <10 g/dL will be randomized in a 1:1 ratio to receive either ferric derisomaltose (20 mg/kg, maximum 1,000 mg) or a matched placebo administered intravenously over 30 minutes on POD 1. All perioperative management outside the intervention follows current institutional standards.

The primary outcome is the incidence of anemia at 6 months following surgery. Secondary outcomes include perioperative hemoglobin trends, functional recovery assessed by cardiopulmonary exercise testing and the 6-minute walk test at 6 months, transfusion requirements, postoperative complications including MAKE-90 and STS major morbidity, and changes in biomarkers of erythropoiesis and iron metabolism (erythroferrone, erythropoietin, hepcidin, and iron profile). Blood samples for biomarker analysis are collected at predefined perioperative timepoints.

Ferric derisomaltose allows high-dose single-session iron repletion with a favorable safety profile and minimal risk of anaphylaxis when administered slowly. Prior studies in cardiac surgery and heart failure populations support its efficacy and safety at doses up to 20 mg/kg. The intervention is expected to facilitate erythropoietic recovery, reduce the duration of postoperative anemia, and improve long-term functional status. The trial aims to generate evidence to inform postoperative anemia management strategies in cardiac surgery patients.

Inclusion Criteria:

• Adults aged ≥19 years scheduled to undergo cardiac surgery requiring cardiopulmonary bypass Preoperative anemia defined as hemoglobin <13.0 g/dL, or preoperative iron deficiency defined as ferritin <100 ng/mL or transferrin saturation <20% Ability to understand the study information and provide written informed consent prior to surgery

Postoperative day 1 hemoglobin <10.0 g/dL on the first CBC following surgery (required for final enrollment)

Exclusion Criteria:

• Emergency surgery Preoperative major organ failure requiring intensive care unit management Active infection prior to surgery, including sepsis Active bleeding prior to surgery Pregnancy or breastfeeding Use of erythropoiesis-stimulating agents or intravenous iron therapy within 3 months prior to surgery Iron overload defined as ferritin ≥500 ng/mL or transferrin saturation ≥45% Aplastic anemia Hemolytic anemia Hemochromatosis or hemosiderosis Decompensated liver cirrhosis, acute hepatitis, or alcohol dependence Known hypersensitivity to intravenous iron formulations Participation in another clinical trial that may influence outcomes Inability to understand or provide informed consent due to language barriers, illiteracy, or cognitive impairment

Double-blind; participants, care providers, investigators, and outcome assessors remain blinded until study completion.