Introduction

Important advances have occurred in veterinary transfusion medicine over the past 20 years. The major innovation has been the application of blood component technology to canine and feline blood. A 1996 survey of AAHA member hospitals indicated the predominant blood product transfused was whole blood. Another survey performed at Tufts University School of Veterinary Medicine demonstrated an increased use of packed red blood cells and a concomitant decrease in fresh whole blood usage during the 5 years studied. Fresh frozen plasma usage increased as well. In the USA, blood components are the products available from commercial veterinary blood banks, but the variety of available products make choosing the optimal product confusing. Commercial veterinary blood banks are being developed worldwide and more veterinarians will face this difficult decision making process. To improve the ability of veterinarians to use blood components effectively, this pair of lectures (Transfusions Without Red Blood Cells) will discuss the various components available for use in veterinary patients. The discussion will include product composition, clinical use, dosage and most common adverse events associated with each product.

Component therapy is considered the optimal method of transfusion since it allows specific hemotherapy: red blood cells in patients or plasma to provide deficient coagulation factors. The use of whole blood in anemic patients wastes the plasma, which could be used to control hemorrhage in a dog with anticoagulant rodenticide toxicity. A dog with anemia secondary to chronic renal failure does not require coagulation factor replacement and only needs a red blood cell transfusion. The plasma from this unit of blood can be used for a different dog with a bleeding disorder. By transfusing only the component required to treat the disorder, the risk of adverse reaction is decreased while maintaining efficacy. Although manufacturing blood components requires advanced planning, collecting blood on demand and transfusing fresh blood makes adequate screening for transfusion transmitted infectious diseases extremely difficult.

Although there have been many advances in veterinary transfusion medicine, there is currently not a consensus regarding the size of a "unit" of blood. For this discussion a unit of canine whole blood will be the blood plus the anticoagulant collected from 1 dog into a standard blood bag which contains approximately 450 ml of blood and 63 ml of anticoagulant preservative solution. A "unit" of a component is the volume of a product produced from 1 unit of whole blood. This information will not apply to blood from all blood banks and the reader is referred to the product insert for information regarding a particular blood banks products. Because feline blood is collected in such a small volume and there is a lack of appropriate sized multi-bag systems, it is not typically processed into components, but it is possible to do so.

Volume in various units of canine red blood cell containing products.

Available blood products containing red blood cells.

*The dosage of any blood product is simply a guideline for the initial transfusion. All transfusions are given "to effect" meaning until the RBC count is high enough to adequately improve the recipient's oxygenation or adequate coagulation factors have been transfused to correct the hemorrhagic process.
#Transfusion associated circulatory overload = TACO is most common with WB transfusions, but can occur with any transfusion.
**WBC's and platelets in stored blood products are not functional, but may contribute to adverse events following transfusion.

Whole Blood (WB) is blood collected from the donor, plus the anticoagulant. A standard blood bag contains 63 ml of anticoagulant and is designed to collect 450 ml of WB. It is probably the most commonly used product in veterinary practice since a practitioner can produce whole blood simply, without any expensive equipment. Even in institutions equipped to prepare blood components, whole blood is typically used to transfuse cats. Feline units of blood are usually 40-50 ml of blood plus 5-9 ml of anticoagulant preservative solution. Ideally, WB would rarely be used in the dog as component therapy conserves blood and allows more dogs to be transfused from one unit of donated blood. WB would be most appropriate in pediatric transfusions when an entire unit of blood would be wasted to obtain10 or 20 ml to transfuse a small puppy or kitten. WB could be used for patients experiencing hypovolemic anemia from hemorrhage, but packed red blood cells and crystalloid or colloid solutions will achieve the same effect. The initial dosage of whole blood is 10-20 ml/kg.

Packed red blood cells are available in multiple formulations. Each has advantages and disadvantages, but the clinical indication for administration is the same for each: a clinically symptomatic anemia. All packed red blood cell products are appropriate products to treat anemia caused by blood loss, hemolysis or bone marrow failure. Signs of anemia include: tachycardia, weakness, tachypnea, and collapse. In both dogs and cats, transfusions are most commonly administered for the treatment of blood loss anemia, although hemolysis and decreased red cell production are also causes.

Packed red blood cells (pRBC) in CPDA or ACD are the cells and a small amount of plasma, which remain after the plasma and anticoagulant, are removed. The PCV is approximately 80%, making pRBC very viscous. Normal (0.9%) saline is the only solution that should be added to any blood product and can be done with pRBC to improve flow. To improve flow rate when transfusion pRBC 50-100 ml of saline can be added to 1 unit if the patient is not at risk for volume overload. The initial dosage of packed red blood cells is 6-10 ml/kg.

Packed red blood cells in additive solution are processed similarly to pRBCs, but after the red blood cells are separated from the plasma 100 ml of an additive solution are added to the red blood cells. PCV is 55-60%. This preserves the red blood cell function longer than the traditional anticoagulants ACD or CPDA and it eliminates the need to add saline to the pRBC to decrease viscosity and improve flow. The fresh frozen plasma obtained from this process is exactly the same as FFP produced from multi-bag systems containing CPDA. The initial dosage of additive solution p RBC's is 9-15 ml/kg.

Leukoreduced packed red blood cells are specially processed through a filter which reduces the WBC to <5x10⁸/unit while maintaining 85% of the original RBC count. Removal of WBC decreases the risk of febrile non hemolytic transfusion reactions.

Are they in additive solution The initial dosage of leukoreduced pRBC's is 15ml/kg.

Adverse events associated with red blood cell containing products are similar for all products. The most common reaction is fever, which is not related to an acute hemolytic transfusion reaction, but is believed to be due to cytokines contained in the transfused blood or from antibodies against RBC, WBC or platelets. Leukoreduction is performed in an attempt to decrease the risk of fever induced by WBC contained in packed red blood cells. Because WB contains a large volume of plasma, the risk of transfusion associated circulatory overload (TACO) is greater than with packed red blood cells, pRBC should be substituted for WB in normovolemic anemia, especially with in patients with underlying cardiovascular disease. The most serious adverse event associated with administration of any blood product containing red blood cells is an acute hemolytic transfusion reaction. Acute hemolytic transfusion reactions occur in <1% of cats and dogs. Although rare, this reaction carries a high fatality rate due to the immune reaction resulting from recipient antibodies against the donor red blood cells. Pretransfusion blood typing and crossmatching are performed in an attempt to prevent this potentially fatal reaction. Clinical signs of an acute hemolytic reaction include vomiting, diarrhea, fever, collapse, and hemolysis of the transfused red blood cells.

References

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3.  Henson MS, Kristensen AT, Armstrong PJ, et al. Feline blood component therapy: retrospective study of 246 transfusions. J Vet Int Med 1994;8:169.

4.  Howard A, Callan B, Sweeny M, et al. Transfusion practices and costs in dogs. J Am Vet Med Assoc 1992;210:1697-1701.

5.  Kerl ME, Hohenhaus AE. Packed red blood cell transfusions in dogs: 131 cases (1989). J Am Vet Med Assoc 1992:1495-1499.

6.  Klaser DA, Reine NJ, Hohenhaus AE. Red blood cell transfusions in cats: 126 cases (1999). J Am Vet Med Assoc 2005;226:920-923.

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8.  Wardrop KJ, Owen TJ, Meyers KM. Evaluation of an additive solution for preservation of canine red blood cells. J Vet Int Med 1994;8:253-257.