Decreased Nitric Oxide Levels in Banked Blood Associated with Adverse Outcomes |
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Several studies have shown that blood transfusions increase the risk for myocardial infarction, heart failure, stroke and death. Although differences between banked blood and red blood cells in vivo have been recognized, the mechanisms resulting in these adverse outcomes have not been delineated.
In two studies published online in the Proceedings of the National Academy of Sciences, Duke University Medical Center researchers suggested that shortly after blood is collected, its nitric oxide content becomes depleted leading to impaired vasodilation and decreased tissue perfusion (PNAS.2007;104(43):17058-17068). They further proposed that as a result of banked blood's inability to dilate small blood vessels, red blood cells may build up and further obstruct larger vessels, resulting in more ischemia. This scenario was suggested as a possible explanation for the adverse outcomes seen in ischemic patients following blood transfusion.
Nitric oxide levels begin to decline rapidly within three hours after collection and are reduced by 70% during the first day of storage. Levels are undetectable by day 21. Based on these findings, the researchers suggested that even "fresh" blood may lead to adverse clinical outcomes. The reduction in nitric oxide directly correlated with stored red blood cell's inability to promote vasodilation. Nitric oxide depleted blood transfusions led to decreased coronary blood flow in canines. However, when stored red blood cells were replenished with nitric oxide prior to transfusion, coronary perfusion increased. These differences in blood flow were most noticeable during hypoxemic states.
Although adding nitric oxide to stored red blood cells prior to transfusion looks like a promising solution, the authors acknowledged that a large-scale randomized clinical trial in humans is needed to determine whether adding nitric oxide back to stored blood before transfusion or preventing nitric oxide depletion would actually improve patient outcomes. The Duke University studies once again demonstrated that blood transfusions have risks as well as benefits.
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