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Conserving Red Cells

Blood dilution (hemodilution) is a practice to prevent loss of red blood cells. The patient has blood drawn before surgery and is immediately given intravenous fluids to make up for the drawn blood, which is saved to be reinfused after the operation.

"The idea," Fratantoni says, "is that during the operation any blood the patient loses will have been diluted, and therefore fewer red cells are lost. Following surgery, reinfusion of the removed blood provides a supply of normally concentrated red cells."

Directed Donations Safer?

In directed donations, friends or family donate blood for a specific patient. Such donors must go through all the standard donor screening and testing procedures. Several states have passed laws establishing directed donation as a procedure that must be followed when requested, except in an emergency.

Some people may feel it's always safer to receive blood from a relative or friend than from the general blood supply, but experts say this is not necessarily the case.

"In fact, the track record on directed donations is mixed," Fratantoni says. "Studies have shown that relatives or friends, feeling pressured to donate, sometimes hide information during screening that they wouldn't under other circumstances, so that they give blood when they shouldn't." (Since the blood is tested the same as all other donations, blood that tests positive for infection or other problems will not be used.)

While matching a patient's blood type may be easier when the donor is a relative rather than someone else, such patients have a high risk of developing graft-versus-host disease, a complication due to the donor and recipient's sharing certain tissue-type substances. In this disease, lymphocyte white blood cells from the transfused blood multiply and react against the recipient's tissues.

When the donor and recipient are both from the general U.S. population, the probability of their sharing a tissue-type substance is very low. Not zero, Fratantoni says, but "somewhere between rare and extremely uncommon."

In the United States, the risk of graft-versus-host disease with blood from a blood relative is about 1 in 7,000 (or higher, depending on the data used). The closer the relatedness, the greater the risk. In a parent-child relationship, the risk is double that in a relationship between grandparent, uncle or aunt.

To reduce the risk, the American Association of Blood Banks recommends irradiating blood derived from all donors who are blood relatives of the recipient. Irradiation suppresses proliferation of lymphocytes contained in the transfused blood. Blood treated this way must meet special FDA licensing requirements, such as permanent labeling that it has been irradiated.

For the Future

A look to the future may envision the ultimate alternative to homologous transfusion to be artificial blood. As blood is extremely complex, however, the dream of a true substitute may never be realized.

Even so, one important blood function has been reproduced artificially: bloodstream transport of life-giving oxygen, the substance all tissues need to survive.

The ideal artificial blood oxygen carrier would pick up oxygen in the lungs and deliver it to all tissues, have a long shelf life with stability at room temperature, be compatible with all blood types, and present no risk of infection, immune reaction, or other health problem.

In 1989, FDA licensed the first artificial oxygen carrier, Fluosol, which used substances called "perfluorochemicals" to temporarily transport oxygen to the heart during coronary artery balloon angioplasty. But the product carried limited amounts of oxygen and had other drawbacks. The manufacturer recently stopped production.

Fratantoni says that two new investigational perfluorochemicals have advantages over Fluosol, including greater oxygen solubility and the capability to be stored at room temperature without being reconstituted before infusion.

Researchers are also experimenting with modifying normal red blood cells so that the cells can be freeze-dried, stored at room temperature, and then reconstituted and infused without concern for blood type.

One modification, by a process called "polymerization," permits high concentration and increases circulation time. Using another technique that encapsulates red cells with a fatty membrane, researchers have supported oxygen requirements in animals with too few red cells to sustain life.

But a major problem with perfluorochemical and red cell oxygen carriers is that the bloodstream retains them only six to 36 hours. Normal red cells survive 100 to 120 days.

There also is an ethical consideration to testing artificial oxygen carriers in human studies in which some participants would get the real biologic while others receive a placebo (dummy) infusion.

According to Thomas Zuck, M.D., director and professor of Hoxworth Blood Center of the University of Cincinnati Medical Center, in Transfusion Medicine in the 1990's: "If whole blood or red cells that are known to be effective are available, it would be difficult to contend that participating in blood substitute clinical trials for acute hemorrhage would benefit recipients."

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