What blood substitutes are available?
Blood substitutes are substances that are characterized by their ability for oxygen transport, volume expansion, and lack of red cell mass. These products include perfluorocarbons and hemoglobin solutions. Some of these products are currently undergoing clinical trials, and their utility remains controversial. A comparison of blood and blood substitutes is shown in Table 52.5.
Perfluorocarbons are synthetic substances that have a high oxygen solubility. The emulsified form of perfluoro-carbons is surrounded by surfactant, and is administered by the IV route to patients in the presence of high levels of inspired oxygen. The oxygen-carrying emulsion is capable of unloading oxygen to the tissues. Problems encountered with the first-generation perfluorocarbons (e.g., Fluosol DA-20) included a short half-life, pulmonary toxicity, and complement activation. The second-generation perfluoro-carbons have a greater oxygen-carrying capacity. Clinical trials with these compounds are in progress.
Hemoglobin solutions have been developed from human, animal, and recombinant sources. Problems associ-ated with these solutions include renal damage, systemic toxicity, short half-life, and increases in mean arterial and pulmonary artery pressures. A group of hemoglobin solu-tions, referred to as stroma-free hemoglobin, have emerged and have fewer side-effects reported. The stroma-free hemo-globin solutions contain a modified hemoglobin molecule that results in a longer half-life, larger molecule size, and less filtration by the kidneys compared with earlier hemoglobin solutions. Some of these solutions are in clinical trials, and issues remain concerning their safety and efficacy.