Perioperative Outcomes of Acute Normovolemic Hemodilution in Cardiac Surgery

Acute normovolemic hemodilution (ANH) is a blood conservation strategy used in cardiac surgery, but its efficacy in reducing allogeneic blood transfusion remains debated. This systematic review and meta-analysis updates the existing evidence by incorporating recent randomized controlled trials (RCTs) to provide a contemporary assessment of ANH's impact on perioperative transfusion outcomes. We searched PubMed/MEDLINE, Scopus, and Cochrane Central up to August 2025 for RCTs comparing ANH to standard care in adult cardiac surgery. Primary outcomes were the number of allogeneic red blood cell units transfused, the rate of allogeneic blood transfusion, and estimated total blood loss. Data were pooled using random-effects models, and subgroup analyses were performed by type of surgery. Thirty-one RCTs involving 4426 patients (ANH = 2242, control = 2184) were included. ANH significantly reduced the rate of allogeneic blood transfusion (risk ratio 0.75, 95% confidence interval [CI] 0.66-0.87; P < 0.0001), the number of allogeneic red blood cell units transfused (standardized mean difference -0.42, 95% CI -0.64 to -0.20; P = 0.0001), and estimated total blood loss (standardized mean difference -0.42, 95% CI -0.63 to -0.21; P < 0.0001). Substantial heterogeneity was observed. Subgroup analysis demonstrated that benefits were most consistent in patients undergoing coronary artery bypass grafting. In patients undergoing cardiac surgery, particularly coronary artery bypass grafting, ANH reduces exposure to allogeneic blood transfusion and decreases perioperative blood loss. Despite significant heterogeneity across studies, these findings support the inclusion of ANH within multimodal blood management protocols. Further large, high-quality RCTs with standardized protocols are warranted to confirm its role in modern practice.