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An international study published today in the New England Journal of Medicine sheds light on acute normovolemic hemodilution, also known as ANH, a blood conservation technique.

ANH involves removing a patient's blood before the patient goes on heart-lung bypass, and then reinfusing it toward the end of heart surgery. Long debated for its effectiveness, ANH does not appear to reduce the need for red blood cell transfusion, according to results of the global clinical trial.

However, study co-author Kenichi Tanaka, M.D., professor and chair of the Department of Anesthesiology at the University of Oklahoma College of Medicine, said the outcomes necessitate further scrutiny and may not be applicable to U.S. patients.

More than 2 million patients worldwide undergo heart surgery annually, and approximately 35% require at least one unit of red blood cells. However, blood transfusions can lead to complications, are costly, and are sometimes affected by shortages. Previous retrospective studies and meta-analyses have shown mixed results about whether ANH reduces the need for blood transfusions in heart surgery.

Although the study did not show that ANH decreased infusions, several factors should be taken into consideration, said Kenichi Tanaka, M.D., who co-led the United States' participation in the trial along with researchers from the University of Virginia. Altogether, the study recruited 2, 010 patients from 11 countries in Europe, Asia, South America and North America.

"This trial may reduce the interest in doing another large, randomized study, but I think it does not exclude the possibility that ANH could help some patients, " he said.

Tanaka pointed to several aspects that may make the study less applicable to the U.S., where about 20% of medical centers use ANH:

Tanaka is preparing to publish a retrospective study showing that ANH reduced the need for transfusions in a U.S. population.

"I plan to continue practicing ANH, " he said. "It is also an option for Jehovah's Witness patients whose beliefs stipulate they cannot receive blood transfusions (from donor blood). At the least, the study proved that there is no downside for ANH. I believe ANH can be part of a multi-pronged blood conservation strategy in the U.S., where blood product costs are very high."

More information: Fabrizio Monaco et al, A Randomized Trial of Acute Normovolemic Hemodilution in Cardiac Surgery, New England Journal of Medicine (2025). DOI: 10.1056/NEJMoa2504948  Journal information: New England Journal of Medicine