Patients undergoing cardiac surgery frequently require allogeneic red-cell transfusions, which carry inherent risks and costs. A new study has investigated whether acute normovolemic hemodilution (ANH), a blood-conservation technique, can reduce the need for these transfusions. The findings from the large, randomised ANH trial (NCT03913481) suggest the technique does not significantly lower the rate of allogeneic red-cell transfusion in this patient population.¹

ANH is an intraoperative procedure involving the collection of a patient's autologous whole blood immediately before the initiation of cardiopulmonary bypass. The patient's circulating volume is maintained with crystalloid replacement fluid. The collected autologous blood is then reinfused after the patient is weaned from bypass, aiming to reduce the need for donor blood. Other blood conservation techniques are also used in this setting.²

The ANH trial was a multinational, single-blind, randomised controlled study conducted across 32 centres in 11 countries. The trial enrolled 2,010 adult patients scheduled for cardiac surgery requiring cardiopulmonary bypass. Patients were randomly assigned to either the ANH group (n=1,010), which involved the withdrawal of at least 650 ml of whole blood, or the usual care group (n=1,000).

The primary outcome was the proportion of patients who received at least one unit of allogeneic red cells during their hospital stay. Secondary outcomes included death from any cause within 30 days or during the index hospitalisation, bleeding complications, ischemic complications, and acute kidney injury.

The trial did not meet its primary endpoint. Data showed that 27.3% of patients (274 of 1,005) in the ANH group received an allogeneic red-cell transfusion, compared with 29.2% (291 of 997) in the usual-care group (relative risk, 0.93; 95% confidence interval, 0.81 to 1.07; P=0.34).¹

Regarding secondary outcomes, surgery for postoperative bleeding occurred in 3.8% of patients in the ANH group and 2.6% in the usual-care group. Mortality rates were similar between the groups, with death within 30 days or during hospitalisation occurring in 1.4% of the ANH group and 1.6% of the usual-care group. Overall safety outcomes were comparable between the two arms of the study.

This large-scale trial demonstrates that the use of ANH in adults undergoing cardiac surgery did not result in a statistically significant reduction in the number of patients requiring allogeneic red-cell transfusions. The ANH Study Group concluded, “Among adults undergoing cardiac surgery, ANH did not reduce the number of patients receiving allogeneic red-cell transfusion.”¹ These findings challenge the perceived benefit of this blood-conservation strategy in this specific clinical context.

References

1. Monaco F, Lei C, Bonizzoni MA, et al. A Randomized Trial of Acute Normovolemic Hemodilution in Cardiac Surgery. N Engl J Med. 2025;393:450-460. https://doi.org/10.1056/NEJMoa2504948

2. Ozgodek HB, Aydin ME, Oksuz DA, et al. Acute Normovolemic Hemodilution Versus Norepinephrine Infusion During Autologous Blood Donation in Coronary Artery Bypass Graft Surgery: A Prospective Randomized Study. J Cardiothorac Vasc Anesth. 2025. https://doi.org/10.1053/j.jvca.2025.06.053

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