Doctors hope to soon have artificial blood or blood replacements available. Blood replacements being studied include oxygen-carrying chemicals (such as perfluorocarbon emulsions) and cell-free hemoglobin-the portion of the red blood cell that carries oxygen. There are several advantages to blood replacements.

• Blood replacement products can be stored for long periods of time. Human blood must be used within a few weeks of being donated.
• Blood replacement products can be stored at room temperature. Human blood must be kept refrigerated until used.
• There is no risk of a transfusion reaction caused by mismatched blood type.
• Blood replacement products can be sterilized, eliminating the risk for infection.

The blood replacement products being tested still have problems. For example, blood replacement products can interfere with blood tests, are more quickly removed from the body, and are less efficient oxygen carriers.

Several of these products are being developed, but their use, after they are approved, will probably be limited to emergencies involving severe blood loss caused by serious accidents.