Clinical Effectiveness of Acute Normovolemic Hemodilution in Cardiac Surgery: A Systematic Review and Meta-analysis

Acute normovolemic hemodilution (ANH) is endorsed by contemporary patient blood management guidelines as a cost-effective strategy for reducing allogeneic transfusion in cardiac surgery. However, evidence remains inconsistent due to protocol variability and limited statistical power in earlier trials. This systematic review and meta-analysis seek to evaluate the clinical effectiveness of ANH in adult patients undergoing cardiac surgery.

A comprehensive search of four databases was performed up to October 2025 to identify randomized controlled trials (RCTs) and matched cohort studies comparing ANH with standard intraoperative care. The primary outcome of interest was the incidence of allogeneic red blood cell (RBC) transfusion. Data were pooled using DerSimonian-Laird random-effects models, expressed as risk ratios (RR) or mean differences (MD) with 95% confidence intervals (CI).

Nineteen studies (15 RCTs, four cohorts) involving 9418 patients were included. ANH significantly reduced the incidence of allogeneic RBC transfusion compared with control (27.6% vs 31.5%; RR = 0.85, 95% CI [0.75-0.96], P = .01). The transfusion reduction was more evident in crystalloid-based protocols (RR = 0.72, 95% CI [0.54-0.96], P = .026) and on-pump surgeries (RR = 0.86, 95% CI [0.76-0.97], P = .01). Matched cohort analyses also confirmed the benefit (RR = 0.87, 95% CI [0.81-0.94], P = .001), whereas RCT-only analysis showed a nonsignificant difference (RR = 0.81, 95% CI [0.64-1.02], P = .07). No significant differences were found in hematocrit, hemoglobin, fresh frozen plasma transfusion, renal dysfunction, myocardial infarction, stroke, or mortality.

ANH significantly reduces the need for allogeneic transfusions while maintaining a favorable safety profile for patients undergoing cardiac surgery.