Doctor at School of Veterinary Medicine of the University of Sao Paulo, Head of the Service of Hemotherapy of HEMOVET, Professor at the School of Veterinary Medicine of the University of Santo Amaro, São Paulo-SP, Brazil
Total Blood
Total blood is classified as fresh or stored. By definition, total blood is called fresh when it is refrigerated up to 24 hours after its collection. After this period, the total blood is called stored, kept refrigerated (2-6°C) for a storage period that varies according to the anticoagulant in the blood bag. Total blood, when refrigerated, loses some of its hemostatic characteristics within 24 hours.1 Hence, it is mainly indicated for anemia correction in hypovolemic patients. In general, the stored blood remains viable for a period of 35 days when maintained in CPDA-1 (citrate-phosphate-dextrose-adenine-1), which is the most common preservative solution in blood bags available in the market.1
Hemostatic Properties
Fresh total blood contains red blood cells, serum proteins, coagulation factors and platelets. The platelets gradually lose their viability when submitted to refrigeration.2 The deleterious effects of refrigeration on platelets have been well documented.3
Similarly, the activity of labile coagulation factors, such as Factor V (useful in the treatment of disseminated intravascular coagulation), factor VIII (essential for the treatment of Hemophilia A) and von Willebrand's factor (important in von Willebrand's disease therapy) progressively decreases in refrigerated total blood due to the proteolytic degradation.1
Indication
The main indication of fresh or stored total blood is acute hemorrhage, in which red blood cell and volume replacement are required. Otherwise, the indication of blood components is mandatory due to the benefits provided, when one can obtain a more adequate replacement of the deficient blood component. As mentioned before, fresh total blood is indicated for acute hemorrhages with concomitant hemostatic alterations, as it preserves its characteristics up to 24 hours after collection. However, in emergency situations, when the donor is a limiting factor, the correction of anemia is prioritized in anemic and thrombocytopenic patients, as it has been well established that hemostasis benefits from the prompt anemia correction; in this case, a red blood cell concentrate or stored total blood can be used.4-5
The administration of fresh total blood as therapy for non-anemic thrombocytopenic patients is contraindicated, due to the possibility of further worsening of the clinical picture. For these cases, the indication of platelet concentrate is mandatory.
The recommended dose is 20 mL/kg to elevate the hematocrit by 10%.1
Red Blood Cell Concentrate
The red blood cell concentrate is the first choice in the treatment of anemia in normovolemic patients, that is, most cases treated during the clinical routine, due to chronic hemorrhage, hemolysis or inefficient erythropoiesis.2,6 The advantage of this blood component is that it has the same amount of red blood cells of a total blood bag, with a smaller volume, benefiting patients that present concomitant cardiopathy or nephropathy.
The red blood cell concentrate is the first choice for the correction of other causes of anemia rather than acute blood loss, although total blood is frequently employed for this purpose. For instance animals with hemolytic anemia or decreased production of red blood cells present an increase in the compensatory intravascular volume due to the decrease in the availability of tissue oxygen, with the red blood cell concentrate being the best option.2 In general, 10 mL/kg of red blood cell concentrate is used to elevate the hematocrit by 10%.
Platelet Concentrate
The therapy with platelet concentrate is the first choice in the treatment of thrombocytopenic patients. The concentrate can be prepared by centrifuging or apheresis. The use of platelet concentrate allows the transfusion of large amounts platelets without the simultaneous transfusion of erythrocytes or plasma. Thus, the side effects associated with the transfusion of other unnecessary blood components are minimized, decreasing the risk of transfusional hemolytic reactions.5
The recommended dose is 1 unit of platelet concentrate for each 10 kg.
The transfusion of platelets can be therapeutic when the intention is stopping active bleeding or prophylactic. The latter, currently under use in veterinary practice, was disseminated mainly in humans, with the objective of prevent bleeding, especially before surgical procedures.5,7
Platelet Therapeutic Transfusion
The association of thrombocytopenia and active bleeding is the base for the decision of transfusing platelets to humans as well as animals5,7, regarding the therapeutic treatment. The clinical manifestations of bleeding normally occur when the platelet count is, at least, < 50,000/µl, being more common with counts < 30,000/µl. With counts < 5,000 platelets/µl, 90% of the patients present some type of bleeding and 60% present hemorrhage such as epistaxis, skin or mucosa hemorrhage and 30% present abundant hemorrhage. Critical bleeding in thrombocytopenic dogs normally presents manifestations in the gastrointestinal tract.
Prophylactic Transfusion of Platelets
The transfusional "trigger" refers to the hematologic value which, associated to clinical signs and symptoms, indicates the immediate administration of a blood component based on adverse consequences for the patient, if the transfusion is not performed. The trigger for the therapeutic transfusion of platelets is the critical bleeding, as mentioned before.7 However, this value is controversial and largely discussed in Medicine, regarding the prophylactic transfusion of platelet concentrate, differing in the clinical and surgical patients.
The most recent studies propose that the surgical patient receive around 50,000-100,000 platelets/μL in the perioperative period.5,7
Plasma Products
Fresh frozen plasma is obtained after the centrifuging of total blood and it must be frozen (- 20°C) up to 6 to 8 hours after collection to preserve its properties. This blood component maintains its viable characteristics for 1 year. It contains coagulation factors (including von Willebrand's), anti-thrombin III, albumin, immunoglobulins, proteins and antiproteases such as α1antitripsin and α2macroglobulins, as well as contributing to elevate the osmotic colloid pressure.1
After 1 year of storage, the fresh frozen plasma is called frozen plasma, characterized by the decrease in the activity of the labile coagulation factors (V and VIII); however, it preserves the activity of the vitamin-K dependent coagulation factors (II, VII, IX and X), as well as albumin and immunoglobulin. The frozen plasma remains viable for 5 years.2
The initial dose of fresh frozen plasma or frozen plasma is 10-30 mL/kg, which can be repeated if the hemorrhage persists.1,2
The main indications of the plasma products are: hereditary and acquired coagulopathies, acute pancreatitis and hypoalbuminemia.9
The cryoprecipitate is a white precipitate obtained through the slow defrosting of fresh frozen plasma at a temperature of 1 to 6°C, with subsequent centrifuging. It contains an elevated concentration of factor VIII, von Willebrand's and fibrinogen. Additionally, it contains the coagulation factors IX, XI and XIII. It is administered at a dose of 1 unit for each 10 kg and can be repeated as necessary for the bleeding control.1
References
1. Abrams-Ogg A. Practical blood transfusion. In: Day MJ, Mackin A, Littlewood JD, editors. BSAVA manual of canine and feline haematology and transfusion medicine. England: British Small Animal Association;2000.p.263-307;
2. Haldane S, Roberts J, Marks SL, Raffe MR. Transfusion medicine. Compendium of Continuing Education for the Practicing Veterinarian 2004; 26:502-518;
3. Allyson K, Abrams-Ogg ACG, Johnstone IB. Room temperature storage and cryopreservation of canine platelet concentrates. Am Journal Veterinary Research 1997. 58:1338-1347.
4. Callan MB. Red blood cell transfusions in the dog and cat. In: Feldman BF, Zinkl, J G, Jain NC, editors. Schalm's veterinary hematology. Philadelphia: Lippincott Williams & Wilkins; 2000, p. 833-848
5. Abrams-Ogg ACG. Triggers for prophylactic use of platelet transfusions and optimal platelet dosing in thrombocytopenic dogs and cats. The Veterinary Clinics of North America: Small Animal Practice 2003; 33:1401-1418.
6. Prittie JE. Triggers for use, optimal dosing, and problems associated with red cell transfusions. The Veterinary Clinics of North America Small Animal Practice 2003; 33:1261-1275.
7. Rebulla P. Trigger for platelet transfusion. Vox Sanguinis 2000; 78:179-182.
8. Rossi EC, Simon TL, Lewis DC. Disorders of platelet number. In: Day MJ, Mackin A, Littlewood JD. BSAVA manual of canine and feline haematology and transfusion medicine. England: British Small Animal Association; 2000. p.183-208.
9. Logan JC, Callan MB, Drew K, et al. Clinical indications for use of fresh frozen plasma in dogs: 74 dogs. Journal of American Veterinary Medical Association 2001; 218:1449-1455, 2001.