Blood Substitutes

Because of problems associated with finding compatible donors and disease transmission by transfusion, the search for a red cell substitute has been ongoing for >50 yr. An ideal substitute would carry and deliver oxygen like red cells, be easy to produce in large quantities, be nonantigenic, and persist in the circulation at least long enough for resuscitation.

One hemoglobin-based oxygen carrier of bovine origin is currently licensed for use in dogs. The hemoglobin is collected aseptically, filtered to remove all red cell stromal elements, and polymerized to allow the product to persist in the circulation for a half-life of ~36 hr. This product has been shown to carry and deliver oxygen efficiently, can be used immediately without need for typing or crossmatching, and has a 3-yr shelf life at room temperature. Because the structure of the hemoglobin molecule is similar between species, bovine hemoglobin is minimally antigenic. Although currently licensed for use only in dogs, it has been used in cats, horses, llamas, birds, and people. Its colloidal effects are especially useful in resuscitation after trauma with acute blood loss. Because the cost of hemoglobin solution is often higher, and duration of effect is shorter than that of blood, the main value of hemoglobin is in emergency situations when blood is not immediately available. Volume overload is a potential risk if hemoglobin is given too rapidly. Another concern with hemoglobin solutions is that nitric oxide is scavenged and removed by the product. This paradoxically might cause vasoconstriction and decrease oxygen delivery to ischemic tissues.