Initial collection yields fresh whole blood (FWB) and is defined as such for up to eight hours after collection. FWB provides red blood cells (RBCs), white blood cells, platelets, plasma proteins and coagulation factors. Certain components in blood are more fragile than others and will become less effective with time and ambient temperature change. To achieve full benefit of all components when needed, FWB should be administered immediately after collection. FWB is used in actively bleeding, anemic animals with thrombocytopenia or thrombopathia, anemia with coagulopathies, and massive hemorrhage.
After collection, whole blood must be processed into components or refrigerated at 1–6° C within 8 hours. After 24 hours' storage of whole blood, platelet function is lost and the concentration of labile coagulation factors decreases (factor V and factor VIII). The product is then defined as stored whole blood (SWB) and provides RBCs, the more stable coagulation factors, and other plasma proteins (i.e., albumin, globulins). The length of time a unit of whole blood can be stored under refrigeration depends on the anticoagulant-preservative solution used in collection. With the advantages in the use of blood components so well documented in both human and veterinary medicine, as well as the improved availability of these products as a result of commercial blood banks, the use of whole blood is no longer considered the treatment of choice. However, SWB can be used in patients that require oxygen-carrying support and intravascular volume expansion.
The use of whole blood, fresh or stored, is not recommended in severe chronic anemia. Chronically anemic patients may have a reduced red cell mass but have compensated over time by increasing their plasma volume to meet their total blood volume. Administration of whole blood may expose these patients to the risk of volume overload, especially in patients with pre-existing cardiac disease or renal compromise.
Packed Red Blood Cells
Packed red blood cells (PRBCs) can be harvested from a unit of whole blood after centrifugation at 4° C, and stored at 1–6° C for approximately one month (definitive storage time is determined by the anticoagulant-preservative solution used in collection). In patients that require oxygen-carrying support, PRBC is the component of choice for increasing red cell mass. Decreased red cell mass may be caused by decreased bone marrow production, increased destruction of red blood cells, or surgical or traumatic bleeding. Although it seems logical that blood loss should be replaced with whole blood, replacing blood volume with PRBCs and crystalloid or colloid solutions is often adequate therapy for the majority of acutely bleeding patients.
Transfusion of PRBC is not recommended in patients that are well compensated for their anemia (e.g., chronic renal failure). The decision to perform red cell transfusion should never be based solely on hematocrit or hemoglobin levels. Patients should be properly evaluated and PRBC administration based primarily on clinical status (e.g., respiratory compromise, tachycardia, poor pulse quality, lethargy).
Platelet-rich plasma (PRP) is harvested from a unit of FWB less than eight hours old and not cooled below 20° C; refrigerated platelets do not maintain function or viability as well as platelets stored at room temperature. In human medicine, platelets are routinely stored at room temperature under constant agitation for up to five days; however, studies have shown that, even at room temperature, function begins to be compromised after 24 hours. Attempts have been made to freeze platelets to achieve a longer shelf life, but these techniques have not been validated for animals.
PRP may be administered following centrifugation, or the platelets may be concentrated by further centrifugation and removal of most of the supernatant plasma. Under optimal conditions, platelets prepared from a single unit of FWB administered to a 30 kg dog would be expected to result in an increase in the patient’s platelet count of 10,000/µl.
The major indication for platelet transfusion is to stop severe, uncontrolled or life-threatening bleeding in patients with significantly decreased platelet number and/or function. Patients experiencing massive hemorrhage may require platelet support to compensate for excessive consumption during hemostasis and the dilution factor associated with volume replacement therapy. In veterinary medicine, platelet preparation is difficult in regard to the volume needed to measurably increase platelet numbers in larger breed dogs. In some patients, however, cessation of bleeding following platelet transfusion has been achieved without a measurable increase in platelet number. Due to the impracticality associated with production of this component in the required volume necessary for significant impact, specific storage requirements, and the short shelf life, in veterinary medicine we routinely treat thrombocytopenia/thromobpathia with active bleeding with FWB through which the patient will receive both platelets and red blood cells. In situations of platelet destruction, such as immune-mediated thrombocytopenia (IMT), the survival of transfused platelets is a matter of minutes rather than days; however, platelet transfusion may still be warranted if the patient is acutely bleeding into a vital structure (i.e., brain, myocardium, lung).
In addition to water and electrolytes, plasma contains albumin, globulins, coagulation factors and other proteins. Plasma is primarily used for its coagulation factor value; it does not contain functional platelets. Most coagulation proteins are stable at 1–6°C, with the exception of factors V and VIII. To maintain adequate levels of all factors, plasma must be harvested from a unit of FWB and frozen at -18° C or below within eight hours from the time of initial collection. This product is referred to as fresh frozen plasma (FFP). FFP will retain its coagulation factor efficacy for a period of 12 months provided it is maintained at the appropriate temperature. FFP can be used to treat most coagulation factor deficiencies (e.g., disseminated intravascular coagulation, liver disease, anticoagulant rodenticide toxicity, hereditary coagulopathies) and potentially other conditions (e.g., acute pancreatitis). FFP is not recommended for use as a blood volume expander or for protein replacement in animals with chronic hypoproteinemia.
If FFP is not used within 12 months, it can be relabeled as frozen plasma (FP) and stored for an additional four years. Also, plasma may be separated from a unit of whole blood at anytime during its recommended storage time. If frozen at -18° C or below, this component is also called FP and may be kept for up to five years. FP has varying levels of the more stable coagulation factors, as well as albumin, but does not contain functional platelets or the labile coagulation factors V and VIII.
Cryoprecipitate (CRYO) is the cold-insoluble portion of plasma that precipitates after FFP has been slowly thawed at 1–6° C (refrigerator). The precipitated material contains concentrated amounts of von Willebrand factor, factor VIII, fibrinogen and fibronectin. Following production, CRYO can be frozen at -18° C or colder and has a shelf life of one year from the original date of whole blood collection. CRYO can be used in patients with suspected or diagnosed von Willebrand disease or hemophilia A (factor VIII deficiency). FFP or FWB may also be used to treat these patients based on product availability.