BENEFITS, DANGERS

Artificial blood products known as hemoglobin-based blood substitutes are made from hemoglobin, the oxygen-carrying molecules in red cells.

When real blood passes through the lung, hemoglobin picks up oxygen and delivers it to tissues throughout the body.

The artificial products are made from hemoglobin extracted from blood cells of either cows or humans, chemically treated to make the molecules bigger or more stable.

The hope is that a blood substitute, in addition to having a long shelf life and not requiring refrigeration, would be able to be given to anyone, regardless of blood type.

Researchers suspect the products developed so far may be causing complications because they pick up a crucial substance in the body known as nitric oxide. That may cause blood vessels to constrict, increasing blood pressure and perhaps the risk of blood clots.

-- Rob Stein