Chicago: Donated blood quickly loses some of its life-saving properties as an important gas dissipates, US researchers said on Monday, in a finding that explains why many patients fare poorly after blood transfusions.

Researchers at Duke University Medical Centre found that nitric oxide in red blood cells is key to transferring oxygen in the blood to tissues. This gas appears to break down almost immediately after red blood cells leave the body, leaving much of the blood stored in blood banks impaired, said Duke’s Dr Jonathan Stamler in the Proceedings of the National Academy of Sciences.

“If you don’t have nitric oxide in there, you can’t get oxygen into the tissues,” he said. But if you restore this gas, banked blood appears to regain this ability, Stamler said. “The medical community, for the past few years, has been struggling with this issue of blood not being quite as good as we’d hoped,” he said.

He noted that many studies have shown patients who receive blood transfusions have higher incidents of heart attacks, heart failure, stroke and even death. “This is not a new issue. It has been a long struggle,” he said. While researchers had understood that banked blood is not the same as the blood in the body, the exact difference was not well understood.

“I think we have a good explanation and I think we have a solution,” Stamler said. He measured levels of nitric oxide in stored human blood obtained from a commercial supplier and found that the levels started dropping quickly. But if the nitric oxide was restored at any point, the red blood cells were again able to open blood vessels and deliver oxygen to tissues, he said. He tested the blood with added nitric oxide both in the lab and in dogs, and found the flow was restored.

Led by Dr Timothy McMahon, a second team at Duke University - whose study appears in the same journal - documented the depletion of nitric oxide in banked blood. “We were surprised at how quickly the blood changes,” he said. “We saw clear indications of nitric oxide depletion within three hours.” Both researchers called for clinical trials to study exactly who might benefit from banked blood.

They said researchers should study ways to safely add nitric oxide back into banked blood to see how this might improve its effectiveness. “In principle, we now have a solution to the nitric oxide problem. But it needs to be proven in a clinical trial,” Stamler said.