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.
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