Whole Blood Transfusion
When deciding if a whole blood transfusion is warranted, several factors should be considered — including the severity and cause of anemia, the short life-span of transfused red blood cells (red blood cell), and compatibility testing (cross-matching). A whole blood transfusion is indicated in horses with a packed cell volume (packed cell volume) at or below 12% secondary to acute blood loss or hemolysis. Similarly, whole blood transfusion is indicated in a patient with a packed cell volume less than or equal to 8% that results from chronic blood loss or hemolysis. Admittedly, these values are not absolute, and the patient’s overall clinical condition should be considered along with determination of whether blood loss or hemolysis is ongoing.
In addition to evaluating the severity and cause of the anemia, the short lifespan of transfused RBCs should be considered. Allogenic equine erythrocytes are removed from the circulation by the mononuclear phagocyte system within 4 days of transfusion as the result of the development of serum antibodies against nonhost erythrocyte antigens within 3 to 10 days in nearly half of horses after a single transfusion. Thus any necessary subsequent transfusions should be performed with caution if given more than 3 days after the initial transfusion.
Horses display a high degree of blood group polymorphism. At least 30 different erythrocyte antigens (alloantigens) that make up multiple blood types (A, C, D, K, P, Q, and U) account for the 400,000 or so blood phenotypes in horses. Hence identification of a perfect match between a donor and recipient is nearly impossible. However, suitable compatibility may be determined by prior blood-typing of the donor and agglutination cross-match testing. Prior knowledge of the donor’s blood type is helpful to avoid donors that are carrying the alloantigens Aa and Qa. These alloantigens are considered the most immunogenic, and transfusion of blood that contains these antigens may result in severe hemolysis. The Quarter Horse and Belgian breeds carry a low frequency of Aa and Qa alloantigens. The saline agglutination test can be divided into major and minor cross-matching. The major cross-match combines washed erythrocytes from the donor and serum from the recipient and is followed by agglutination testing. In contrast, the minor cross-match combines donor serum with erythrocytes from the recipient and is followed by testing for agglutination. Unfortunately, such testing does not provide information regarding hemolyzing antibodies (hemolysin), which, if present, will cause severe hemolysis of transfused RBCs. Testing for hemolysins requires adding exogenous complement from rabbit serum to the reaction mixture, and such testing is limited to few laboratories because of the special handling and storage required of rabbit serum. Compatibility testing should precede transfusion; however, that is not always possible. In the absence of donor blood-typing, cross-matching, or testing for hemolysins, the ideal equine blood donor is an adult gelding that is negative for equine infectious anemia virus and has never received a blood or plasma transfusion. In addition, first-time transfusion of whole blood to a patient that has not received previous blood products or cross-matched is usually well-tolerated. In cases of blood loss into a body cavity, autotransfusion of blood may be considered if the blood can be collected aseptically.
Although whole blood transfusions may significantly improve the patient’s immediate condition, they are not without complications. As previously mentioned, the short half-life of transfused RBCs and the development of alloantibodies limit the extent of long-term benefits from whole blood transfusions. In addition, blood transfusions suppress bone marrow response to anemia by reducing the production of erythropoietin by the kidneys. The normal bone marrow begins to replace lost cells within 5 days. Hence whole blood transfusions provide only temporary improvements of oxygen supply to vital tissues. Thus even after a whole blood transfusion, determination and correction of the cause of the anemia remains critical.
Whole Blood Collection
Whole blood is collected from the donor into sterile, plastic collection bags or sterile glass containers that contain acid-citrate-dextrose (anemia of chronic disease) or citrate-phosphate-dextrose (Baxter; Deerfield). The desired anemia of chronic disease-to-whole blood ratio is approximately 1:10. Depending on individual preferences, sterile glass containers may be better suited for more efficient collection of whole blood because of the negative pressure while under vacuum. However, once they are filled, they are heavy; if they are dropped, all of the contents may be lost. Regardless of the collection container, the collection procedure is aseptically performed through an intravenous catheter or a large bore needle connected to an extension set. Determination of the total blood volume to collect and transfuse depends on the size of the donor and the estimated blood loss of the recipient. An average size horse (450 kg) with a packed cell volume of 35% to 40% can provide approximately 20% (8-10 L in an adult horse) of its blood volume every 30 days. Generally, 20% to 30% of the recipient’s total blood volume (7-11 L in a 450-kg horse) is adequate to recover oxygen supply to vital tissues until bone marrow has an opportunity to respond. Alternatively, if whole blood transfusion is warranted and an estimate of blood loss is not accurate, 15 ml/kg (6-8 L in a 450-kg horse) of whole blood may be administered. Once it is collected, using whole blood immediately is best, yet it can remain stable at 4° C for 2 to 3 weeks once the anemia of chronic disease is added.
Whole blood is filtered before administration and is transfused into the recipient through an aseptically placed jugular catheter. Initially (5-10 min), the administration rate should be slow (0.1 ml/kg) to observe for any signs of adverse reactions. These include tachypnea, dyspnea, restlessness, tachycardia, piloerection, muscle fasciculations, or sudden collapse. Subsequently, the transfusion rate may be increased to but not exceed 20 ml/kg/hour. If severe adverse reactions occur, the transfusion should be terminated, and epinephrine (0.01 to 0.02 ml/kg, 1:1000) along with isotonic fluids should be administered. Alternatively, if only mild reactions occur, the transfusion rate may be slowed and corticosteroids or nonsteroidal antiinflammatories administered.
Blood Component Therapy
Administering concentrates of specific equine plasma components rather than whole blood may be more appropriate for treating deficiencies of granulocytes, platelets, or erythrocytes. This is especially true for patients with a deficiency in a cell type due to destruction rather than blood loss. These horses do not have a deficiency in blood volume but rather a deficiency in the specific constituents. Hence a whole blood transfusion may predispose them to fluid overload, whereas administration of the specific components that are deficient may be more appropriate. Centrifugation apheresis provides a method for concentrating granulocytes, platelets, and erythrocytes from whole blood. In addition to these cell types, other blood components such as immunoglobins and clotting factors may be concentrated and administered. Concentrated, lyophilized immunoglobulin (Lyphomune, Diagnon Corporation, Rockville, Md.) is commercially available for treatment of failure of passive transfer in foals, selective deficiencies of immunoglobulin, and treatment of immune-mediated disorders. Cryoprecipitate — a mixture of factor VIII :C, fibrinogen, and fibronectin — is used for treatment of hemophilia in dogs and people but is not readily available or affordable for use in horses. The collection of whole blood and administration of the blood components should follow the same guidelines as discussed previously. Furthermore, aseptic handling of the blood components during the centrifugation apheresis is critical to prevent bacterial contamination before administration.
Alternatives to Blood Component Therapy
In addition to transfusion, several alternative products have been used to treat granulocytes deficiencies such as neutropenia. These products include hemopoietic growth factors such as recombinant canine and bovine granulocyte-colony stimulating factor. In one study, normal foals that were given bovine granulocyte-colony stimulating factor experienced an increase in neutrophil count without apparent adverse effects. A second study in foals found an increase in bone marrow cellularity and increased myeloid activity after treatment with canine recombinant granulocyte-colony stimulating factor. The efficacy of these products is suggested by these studies; however, more work is needed to develop a therapeutic plan for horses of all ages. Administration of human recombinant erythropoietin to horses can result in severe, sometimes fatal, anemia.
Horses that are suffering from declining intravascular oncotic pressure due to protein deficiency and neonatal foals that are suffering from failure of passive transfer are candidates for plasma administration. Foals require 1 to 2 L (20-40 ml/kg) of plasma to adequately increase IgG levels, and hypoproteinemic adult horses (450 kg) require 6 to 8 L of plasma to improve oncotic pressure. In general, administration of 7 L of equine plasma that contains 7 g/dl of protein will result in a 1 g/dl increase in total protein. Plasma retains several advantages over synthetic colloids as a source of functional proteins (clotting factors), immunoglobins, and complement. However, disadvantages to plasma include its poor ability to increase oncotic pressure and the expense of product. Plasma can be purchased from commercial supplier (Lake Immunogenics, Ontario, N.Y.; Veterinary Dynamics, Inc., Chino, Calif.; Immvac, Inc., Columbia, Mo.; Veterinary Immunogenics, LTD, Cumbria, England) or can be collected from whole blood that has been centrifuged or allowed to settle at room temperature for 1 to 2 hours, followed by removal of the settled RBCs by gravity flow. The collection of whole blood and administration of the plasma should follow the same guidelines discussed previously. Furthermore, aseptic handling of the blood components during plasma separation is critical to prevent bacterial contamination before administration. Because of the high risk of contaminating the plasma with large volumes of whole blood, storage of liter bags of commercially available equine plasma for future use at 0° C for up to 1 year might be ideal. In addition to normal plasma, hyperimmune plasma from horses that have been immunized against the etiologic agents responsible for diseases such as Rhodococcus pneumonia, salmonellosis, and botulism are commercially available. (Lake Immunogenics, Veterinary Dynamics, Inc., Immvac, Inc., Veterinary Immunogenics, LTD). The efficacy of these products remains unknown; however, some evidence suggests that the incidence or severity of Rhodococcus pneumonia may be lessened in foals that receive hyperimmune plasma.