Highlight
- Acute normovolemic hemodilution (ANH) is significantly associated with reduced transfusion rates of red blood cells and other blood components in adult cardiac surgery.
- Higher volumes of ANH (≥650 mL) further strengthen its blood conservation effect, lowering transfusion odds by up to 64%.
- Despite its safety and cost-effectiveness, ANH utilization remains below 20% in the United States cardiac surgical population.
- ANH contributes to substantial reductions in blood product use and associated acquisition and activity-based costs.
Study Background
Cardiac surgery, notably operations involving cardiopulmonary bypass (CPB), remains the single highest consumer of allogeneic blood components in the United States. Perioperative blood transfusions, although lifesaving, carry well-documented risks including transfusion reactions, immunomodulation, increased infections, and longer hospital stays. Acute normovolemic hemodilution (ANH) is a blood conservation strategy where a patient’s blood is removed and simultaneously replaced with crystalloid or colloid solutions at the beginning of surgery, reducing red cell loss during CPB and surgery. The withdrawn autologous blood is reinfused after bleeding risk decreases. However, despite its theoretical and demonstrated benefits globally, ANH is underutilized in the U.S., with less than 20% adoption particularly in cardiac surgery. Given increasing challenges in blood supply sustainability, vulnerability to shortages, and escalating costs, reassessing ANH’s clinical effectiveness and cost impact is imperative.
Study Design
This retrospective propensity score-matched cohort analysis utilized data from the Society of Thoracic Surgeons (STS) Adult Cardiac Surgery Database (version 4.20.2), encompassing operations from July 2020 to September 2023. The study population included 16,795 adult patients (≥18 years) undergoing coronary artery bypass grafting (CABG), valve surgeries, or combined procedures with CPB. The exposure of interest was documented use and volume of ANH, as captured in the database.
Primary outcome was defined as any intraoperative or postoperative transfusion of blood components (red blood cells [RBCs], platelets, plasma, cryoprecipitate). A secondary analysis stratified the ANH volume effect using a cutoff of 650 mL to assess a dose-response relationship. Additional outcomes included number of transfused units, bleeding-related surgical reexplorations, intensive care unit length of stay, and economic evaluations related to blood product acquisition and procedural activity costs.
Propensity score matching accounted for baseline differences, particularly given that ANH patients had fewer preoperative anemias and higher baseline hematocrit, potentially confounding interpretation.
Key Findings
Among the entire cohort, ANH was applied in 14.7% (2,463 cases), reflecting its relatively modest adoption despite endorsement in guidelines. Patients selected for ANH tended to be less anemic preoperatively; mean hematocrit was 2.5% higher on average compared to controls (95% CI 2.3-2.7, P < 0.001).
After propensity matching, 2,282 patient pairs were analyzed. Transfusion exposure was significantly reduced in the ANH group with 31.2% receiving any blood product versus 36.4% in controls (P < 0.001). Logistic regression revealed that ANH use decreased the odds of transfusion by 27% (OR 0.73; 95% CI 0.60-0.89). The volume-stratified analysis demonstrated dose dependence: ANH volumes ≥650 mL yielded a 47% to 64% reduction in blood component transfusions covering RBCs and non-RBC components.
Quantitatively, cumulative reductions reached 167 fewer units of erythrocytes and 295 fewer platelet units transfused compared to non-ANH counterparts. Importantly, these reductions translated to meaningful savings in blood acquisition and activity-based procedural costs. No significant increase in bleeding reexploration rates or ICU length of stay was observed, supporting the safety of ANH.
Expert Commentary
ANH represents a pragmatic, physiologically sound, and low-cost method for minimizing allogeneic blood exposure during complex cardiac surgeries. The volume-dependent transfusion benefit aligns with the mechanism whereby greater blood withdrawal induces more effective hemodilution and preservation of patient red cell mass when reinfused.
Despite its demonstrated efficacy, barriers to wider ANH implementation remain complex and multifactorial, including practitioner unfamiliarity, workflow integration challenges, perceived logistic burdens, and institutional priorities. The STS database’s real-world evidence contributes to accumulating data that should incentivize clinicians and centers to re-examine their blood management protocols.
While this study’s retrospective observational design cannot prove causality and residual confounding may exist, the large sample size, rigorous propensity matching, and consistency of effect across blood product types strengthen external validity. Future prospective randomized trials or pragmatic implementation studies would be valuable to confirm these findings and address operator-level adoption barriers.
Conclusion
In summary, ANH demonstrates a clear, volume-dependent association with reduced perioperative use of both RBC and non-RBC blood components in adult cardiac surgery requiring CPB. It is a safe, cost-effective strategy that can alleviate pressure on blood supplies and reduce transfusion-associated risks. However, its underuse in U.S. cardiac surgery settings reflects a significant opportunity gap in perioperative blood management. Greater awareness, education, and institutional support are needed to optimize blood conservation efforts and improve patient outcomes.
References
Tanaka KA, Stewart KE, Vandyck KB, Burkhart HM, Garwe T, Kertai MD, Butt AL, Mazzeffi MA. Acute Normovolemic Hemodilution in Adult Cardiac Surgery. JAMA Surg. 2025 Sep 3:e253238. doi: 10.1001/jamasurg.2025.3238. Epub ahead of print. PMID: 40900582; PMCID: PMC12409644.