Blood transfusions in small animal medicine have become more common and are now an integral part of advanced treatment. Often, the indication for blood transfusion occurs in the emergency or surgical setting. Situations that may require transfusion include life-threatening anaemia from acute haemorrhage, haemolysis, problems due to drugs or toxins, immune-mediated diseases, severe non-regenerative conditions and neonatal isoerythrolysis (NI), among others.

Advances in critical care medicine have moved transfusion medicine to the forefront of management in such cases. To ensure efficacious and safe transfusions, it is important to perform blood typing and cross matching, as incompatible transfusions can be life threatening.

Transfusions are indicated for anaemia, coagulopathy, and rarely for other conditions such as thrombocytopenia/-pathia, and hypoproteinaemia. However, the decision to transfuse is based upon the overall clinical assessment of a patient’s history and clinical signs, routine laboratory tests, underlying cause, and hence sound clinical judgment. And because of the inherent risks, transfusions should never be given without a clear indication and exhausting other alternatives.

The most common indication for a transfusion in dogs and cats are anaemias and depending on the type, degree and course of the anaemia a transfusion with blood products, such as stored packed red cells, fresh or stored whole blood, may be warranted. Animals with rapidly progressive anaemia need to be transfused much earlier, when the PCV is still around or above 20%, while patients with chronic anaemias may do well at lower haematocrits as long as they are not stressed. It should be noted that animals with per acute blood loss will not show a drop in PCV for hours until fluid shifts have occurred. Hence, other parameters, such as evaluation of mucous membranes and capillary refill time, are needed to assess the hypovolemia and need for blood transfusions. Fluid therapy may be all that is needed to restore vital organ perfusion in acute blood loss anaemias, while packed red blood cells (pRBCs) are considered, when there is evidence of tissue hypoxia. In other words the associated lowering of the PCV is no contraindication for fluid therapy to restore normovolemia. Furthermore, if an animal needs to undergo anaesthesia and surgery, generally the PCV should be at least 15-20% to assure proper oxygenation during the procedure. Red cell transfusions have proven life-saving in cases of immune-mediated haemolytic anaemia and there is no evidence that transfused red cells would be more rapidly destroyed than the patient’s erythrocytes or that they “add to the fire”, although some clinicians have questioned their value.

Blood donors should be young adult, lean, and good tempered animals, and weigh at least 23 kg for dogs (to donate 450ml) and 4 kg for cats (40ml); have no history of prior transfusion; have been regularly vaccinated and are healthy as determined by history, physical examination, and laboratory tests (complete blood cell count, chemistry screen, and faecal parasite examination every 6-12 months), as well as free from infectious diseases (testing depends on species/breed and geographic area but may include serology, antigen assays and PCR assays). Donors should receive a well-balanced, high performance diet, and may be supplemented twice weekly with ferrous sulfate (Feosal, 10 mg/kg), if bled every 4 weeks. Packed cell volume (PCV) and haemoglobin (Hb) should be >40% and >13 g/dl in canine donors and >30% and >10 g/dl in cats.

Canine donors are generally not sedated, while cats are regularly sedated. Some sedatives, such as acepromazine, interfere with platelet function and induce hypotension, hence they should not be used. Blood is collected aseptically by gravity or blood bank vacuum pump from the jugular vein over a 5 to 10 minute period.

Blood components are prepared from a single donation of blood by simple physical separation methods such as centrifugation generally within 8 hours from collection; thereby, fresh whole blood can be separated into packed red cells, platelet-rich plasma or concentrate, fresh frozen plasma, and cryoprecipitate and cryo-poor plasma. Blood component preparation is best accomplished by using plastic blood bags with satellite transfer containers in order to assure sterility. Fluctuations in storage temperature significantly alter the length of storage; thus, temperature controlled and alarmed blood bank refrigerators and freezers are ideal, but others are acceptable as long as the temperature is monitored and the refrigerator/freezer is not too frequently opened. Blood components that have been warmed to room or body temperature should not be re-cooled and cannot be stored again. Similarly, partially used or opened blood bags should be used within 24 hours because of the risk of contamination.

The Transfusion Steps:

Blood that has been refrigerated must be SLOWLY warmed to room temperature to avoid destruction of the cells.

Invert the bag gently to resuspend the cells, but again be careful since the cells are easily damaged.

Prepare the patient and equipment as you would for intravenous fluid therapy. The cephalic or jugular vein is most commonly used, although in neonates intraosseous administration may be the only feasible route.

A special giving set is used incorporating a nylon net filter to collect any aggregated cells or coagulation debris. A burette can also be incorporated to ensure accurate transfusion volumes. The Travenol blood administration set is suitable.

In very small patient’s blood may be mixed with normal saline to reduce its viscosity thus facilitating an easier passage through a fine catheter.