In caring for sick animals, all veterinarians eventually find themselves faced with a patient that has anemia of such severity as to require a blood transfusion.  Access to blood products has improved in the past few years.  Veterinary blood banks can supply canine, feline, and even ferret blood within 24 hours via overnight mail.  For animals that need blood more immediately, however, veterinarians have to be more resourceful.  Canine blood is usually obtained from another donor dog, often a young, healthy large-breed dog owned by a member of the veterinary staff, such as a technician, receptionist, or doctor.  Sometimes, the client of a dog requiring a transfusion offers the services of one of their other dogs in an attempt to provide the life-saving blood that their sick dog requires.  Obtaining feline blood can be more of a challenge, as the demand for feline blood products is much greater than the supply.  Some veterinary clinics utilize a so-called “hospital cat”.  This invariably turns out to be a cat that was either abandoned by a client or left on the doorstep of the hospital. Rather than being surrendered to a local shelter, these cats, through their sweet dispositions, manage to win over the hearts of the hospital staff, becoming adopted mascots of sorts.  They live a life of relative luxury at the hospital, entertaining clients and staff alike.  Occasionally, they get called into duty, donating blood to a desperately ill patient in time of need. Unfortunately, most cats can donate only small volumes of blood (35 to 50 milliliters) every four weeks at maximum.

In human medicine, there has been an increased demand for blood and blood products.  This demand has been driven by the need to support procedures with heavy transfusion requirements, such as total hip replacement, organ transplantation, and coronary bypass surgery.  The need for blood for sophisticated procedures, coupled with the risk of viral transmission via transfusion, has led to a quest for a blood substitute in human medicine.  This endeavor has been beneficial for veterinary medicine.  In 1998, the Food and Drug Administration approved the use of Oxyglobin.  Manufactured by Biopure Corporation, Cambridge, Massachusetts, Oxyglobin is the first “blood substitute” approved for use in the dog. 

Hemoglobin is an iron-containing molecule found in red blood cells that is responsible for binding oxygen.  Oxyglobin is a purified hemoglobin solution.  It has the ability to deliver oxygen from the lungs to the tissues.  Because Oxyglobin does not contain red blood cells, white blood cells, platelets, or clotting factors, the term “blood substitute” is somewhat of a misnomer.  The preferred term is “hemoglobin based oxygen carrier”, often abbreviated as HBOC.

As with any therapeutic product, there are both advantages and disadvantages to its use.  Advantages include the fact that blood-typing and cross-matching is not required before administration.  Adverse transfusion reactions occur because the red blood cells of the donor are incompatible with those of the recipient.  Oxyglobin contains hemoglobin only; red blood cells and membranes are removed during ultrapurification, eliminating the need for typing and cross-matching and eradicating the occurrence of adverse transfusion reactions.  Another advantage is the long shelf life: Oxyglobin can be stored for 36 months without refrigeration.

Oxyglobin has some disadvantages that veterinarians and clients need to be aware of.    When administered, Oxyglobin expands the total blood volume, and close monitoring is necessary to prevent development of pulmonary edema (fluid in the lungs) and pleural effusion (fluid in the chest cavity), both signs of fluid overload.  The distinct purple color of Oxyglobin will temporarily impart an unusual color to the gums and the urine.  Some blood parameters may be affected after administration of Oxyglobin, temporarily affecting our ability to use these parameters as a diagnostic or monitoring tool.  Despite these shortcomings, Oxyglobin has become a useful product in canine transfusion medicine.

As a veterinarian, I was certainly thrilled when news of the availability of this product was announced.  As a cat specialist, however, the first thing I focused on was the labeling: Oxyglobin is approved for use in dogs only.  Despite the label, when faced with a cat that is imminent danger of dying from severe anemia and with compatible cat blood not readily available, my colleagues and I have found ourselves cautiously reaching for the Oxyglobin.  As with any off-label usage, we inform our clients that the product is not approved for use in cats, warn them of the potential risks and benefits as best we can, and obtain their written consent before proceeding.  With no reason to suspect that Oxyglobin would work differently in cats compared to dogs, but with limited experience using the product in cats, I  still find myself asking the basic questions: is Oxyglobin useful in cats?  Is it effective?  Is it safe? According to a recent article in the Journal of the American Veterinary Medical Association, the answer to these questions is a qualified “yes”.  The article, entitled “Use of a Hemoglobin-based Oxygen Carrier Solution in Cats”, details the results of a review of the medical records of 72 cats that received Oxyglobin.  Ninety-seven percent of the cats receiving the Oxyglobin were anemic and most often received it because compatible blood wasn’t available.  Thirty-seven of 43 cats that were monitored very closely showed improvement in at least one evaluation parameter, such as increased body temperature, blood hemoglobin concentration, blood pressure, appetite and activity.  A significant number of cats, however, showed adverse events following administration of Oxyglobin, including discoloration of mucous membranes and urine, vomiting, pleural effusion, and pulmonary edema.  Overall, 49 cats, all severely ill, died or were euthanized, however, 23 cats survived and were discharged to their owners.  The authors concluded that administration of a hemoglobin-based oxygen carrier solution may provide temporary support to anemic cats, however, they remain somewhat reluctant to recommend routine usage in cats pending further investigation of some of the complications that may be associated with its use, such as pulmonary edema and pleural effusion.

One exciting possibility that is currently being investigated is the use of Oxyglobin in non-anemic patients with other disorders requiring increased oxygen delivery to tissues, for example, restoring oxygen supply to tissues that have suffered oxygen deprivation.  This may have application for cats with aortic thromboembolism, a devastating complication that sometimes develops  in cats with hypertrophic cardiomyopathy, a disease of the heart muscle. 

We still have much to learn about the clinical use of hemoglobin-based oxygen carriers.  Studies in which HBOCs are compared to blood are difficult to interpret because HBOCs do not have many of the properties of blood and cannot be considered to be equivalent to transfusion with red blood cells.  It would be like comparing apples and oranges.  It would be even more difficult to perform studies comparing HBOCs to no transfusion at all, as it would be ethically questionable to deny a pet a transfusion when medically necessary.  We can, however, continue to make observations regarding which species might benefit from these products, and which diseases and conditions might improve with their use.  Hopefully, HBOCs will allow us to treat a myriad of diseases for which current therapy is limited.