by Christine Jenkins, D.V.M.
Hemoglobin based oxygen carriers (HBOCs) are fluids that contain hemoglobin and have the ability to deliver oxygen. The hemoglobin source can be bovine, human (from old stored blood) or recombinant. The hemoglobin is either cross-linked or polymerized to prolong the half-life and decrease the toxicity. Oxyglobin?which is made by Biopure, is the solution with which most veterinarians are familiar. Oxyglobin?s polymerized bovine hemoglobin.
There are many uses for these products. Most are familiar with its use in hemolytic anemias cases where it can carry oxygen without red cell antigens. However, due to a high oncotic pull and usual normovolemia, administration must be slow. Fifty percent (50%) of the hemoglobin in these solutions become methemoglobin within 24 hours. Because they lose the ability to carry oxygen, further transfusions may be necessary.
HBOCs can also be used for treating hemorrhagic shock. Not only is cross matching unnecessary, which is an advantage as time is usually critical, but it also allows the loss of the HBOC until the hemorrhage can be stopped. After which, cross-matched blood transfusions can be given, thereby restoring lost red blood cells and clotting factors. This decreases the amount of blood transfusions given and their subsequent risks. HBOCs, colloids and crytalloids can be used to restore intravascular volume. They also have the ability to bind nitric oxide (a potent vasodilator) resulting in a “pressor effect” often needed in cases of shock. The “pressor effect” causes blood vessels to constrict and facilitates clot formation at the hemorrhage site.
Hemoglobin moieties are smaller than red blood cells. Their size allows them to deliver oxygen in collapsed or constricted capillaries where a red blood cell may not be able to pass. These solutions can also deliver oxygen past microthrombi inhibiting red blood cells and may be beneficial in ischemic conditions such as gastric dilatation volvulus and mesenteric volvulus.
There are numerous areas of HBOCs use currently under investigation. These include use in other forms of shock (septic, etc.), stroke potential, ischemic heart disease and chemotherapy. Hemoglobin based oxygen carries are not the magic “cure all” treatment but do have unique properties that may prove beneficial. Unlike other blood products, they are easily stored, have a long shelf life and do not require large, expensive blood banking capabilities. There is a very real need for hemoglobin based oxygen carrying solutions in today’s practice and certainly, more uses will be discovered in the future.