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 (Oxyglobin®). The hemoglobin is collected aseptically, filtered to removed 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.
In healthy animals, hemoglobin within RBC picks up oxygen from the lungs and deposits it in the tissues via the capillary microcirculation. Only a very small amount of oxygen can be carried dissolved in plasma. In an anemic animal, the hemoglobin within each red cell becomes fully saturated with oxygen, but tissue oxygenation is inadequate simply because fewer red cells are present. In hypotension, hypovolemia, or local tissue ischemia, oxygen delivery may be further impaired because of constriction or decreased perfusion of capillaries. If hemoglobin solution is given, the oxygen content of the plasma improves, and the delivery of oxygen becomes easier because the oxygen is already in contact with endothelium, and has only to diffuse into the tissues. Because the viscosity of the blood is lower after hemoglobin transfusion than it would be after a comparable volume of blood, perfusion of capillaries should be improved. One concern with hemoglobin solutions is that nitric oxide is scavenged and removed by the product. This might paradoxically cause vasoconstriction and decrease oxygen delivery to ischemic tissues.
Last full review/revision July 2011 by Susan M. Cotter, DVM, DACVIM (Small Animal, Oncology)