Blood transfusions are often administered to horses as a treatment for acute life-threatening hemorrhage, hemolytic anemia, or anemia caused by erythropoietic failure.1 The purpose of a transfusion is to restore oxygen delivery to tissues by increasing the oxygen-carrying capacity of blood through restoring blood volume, increasing hemoglobin concentration in blood, or a combination of both. The choice between transfusion of whole blood or PRBCs is influenced by the type of anemia (normovolemic vs hypovolemic) and products available for transfusion. For instance, whole blood is preferred for animals with hemorrhagic disease,2 whereas for horses with anemia attributable to hemolytic disease or erythropoietic dysfunction, transfusion of PRBCs is often sufficient to improve tissue oxygenation while minimizing the likelihood of volume overload.3,4 There is limited information on the usefulness of transfusion of whole blood or PRBCs for improving oxygen delivery or clinical signs in horses with naturally developing anemia. Furthermore, there is limited empirical information on the clinical and clinicopathologic abnormalities that prompt transfusion of blood to adult horses.
Evidence-based guidelines for the decision to perform a transfusion have not been reported for equine medicine and critical care of horses. Consequently, recommendations of transfusion triggers for large animals are based on recommendations developed for humans, dogs, and cats. Identifying the indications for transfusion is not simple, and because of the risk to recipients and cost of the procedure, blood transfusion should be performed only when indicated. Conversely, the severe adverse effects of anemia mean that animals should not be denied a transfusion when it is needed. The PCV may be used as a guide5; however, there is no variable for which a single value is a transfusion trigger, and the decision to provide a transfusion should not be made on the basis of Hct, hemoglobin concentration, or RBC count alone. Rather, the decision to provide a transfusion should be made on the basis of a holistic evaluation of an animal, which would include the medical history, physical abnormalities, and clinicopathologic data. However, we are not aware of any reports on objective clinical or clinicopathologic abnormalities in anemic horses that subsequently received a transfusion of whole blood or PRBCs, except in animals with experimentally induced anemia.6 Additionally, the efficacy of transfusion for improving these variables in horses has not been reported.
An important concern when performing a blood transfusion is the risk to a recipient. Acute reactions vary in severity from mild urticarial skin reactions to acute anaphylaxis and may even result in death.5 Development of alloantibodies in a recipient and subsequent problems with repeat transfusions or development of neonatal alloimmune hemolytic anemia in progeny of female recipients is a concern.5 To our knowledge, the incidence of these adverse events has not been recorded for large animals.
The purposes of the study reported here were to identify the clinical and clinicopathologic abnormalities in horses with severe hemorrhagic anemia, hemolytic anemia, or anemia attributable to erythropoietic failure; to determine the effect of transfusion of whole blood or PRBCs on those variables; and to describe the incidence and type of adverse reactions in horses receiving a transfusion of whole blood or PRBCs.
Recombinant human erythropoietin
Equine infectious anemia
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