The direction of transfusion practice has been one of steady movement from whole blood to fractions designed for specific therapy and most recently toward products produced by recombinant DNA technology. The limits of this progression are not yet defined. Progress in developing red cell substitutes illustrates the extent of this problem. The search for a practical replacement for the red cell that would allow stable storage, provide adequate oxygen delivery, and be free of significant toxicities has been long and filled with substantial obstacles. Hemoglobin-based substitutes are now the most promising, but problems of purification, modification to permit adequate unloading of oxygen, and control of potential toxicity represent major roadblocks to eventual use.
Perfluorocarbons improve oxygen delivery by increasing solubility in plasma.
The effectiveness of these compounds is limited by their poor solubility in plasma and the requirement for high oxygen tension for effectiveness. These considerations have resulted in licensure of Fluosol-DA only for oxygen delivery during coronary angioplasty when the balloon is inflated. Despite these substantial obstacles, the search for a clinically useful product persists because it would clearly be useful when red cells are unavailable or cannot be used because of a patient's religious convictions. However, this effort may eventually be limited by the recognition that the improved safety of natural products and the excessive cost of a substitute make its use practical only in a very narrow range of indications. Similar considerations could limit efforts to find an artificial platelet.