OKLAHOMA CITY – 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:
- U.S. centers did not begin enrolling patients in the study until at least half of all participants had been enrolled. He estimates that less than 5% of participants are from the United States.
- U.S. patients are typically larger than patients from other countries and, paradoxically, larger body size is protective against surgical bleeding and the need for transfusions.
- Smaller patients have less blood to give during ANH. This means a smaller volume is available to treat anemia and bleeding that can occur while the patient is on a heart-lung bypass machine.
- There was no standardized protocol for ANH or transfusion in the trial. Countries like the United States are more likely to use special clotting factor concentrates in combination with ANH, which has been shown to reduce the need for transfusions.
- In supplemental information not included in the study, patients receiving ANH showed a slight trend toward better overall survival rates compared to those who received transfusions only.
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."
