No Substitute for Real Blood

While donating blood is a noble gesture, there are a couple of problems. There is never enough donated blood and the blood that is acquired does not last long in storage. As engineers, the natural conclusion is to develop a blood substitute. However, this has been proven difficult.
Charles Natanson and Public Citizen teamed up to compare the effects of using donated blood versus blood substitutes. Their findings were frightening. Those who received blood substitutes were at a higher risk for heart attacks and death.
One theory as to why this is happening is that the hemoglobin in the blood substitute binds to nitric oxide, which causes the platelets to stick, increasing the risk of clots.
However, not all scientists are in agreement. Some argue that there is not a statistical difference between deaths caused by regular blood transfusions and those using blood substitutes. There is an agreement that more research should be done in this field.

http://sciencenow.sciencemag.org/cgi/content/full/2008/428/1