Alvedia

The red blood cell membrane is covered proteins and complex carbohydrates and hence is antigenic. Patients recognise these foreign antigens as non-self when they receive a transfusion and stimulate antibody production.

Blood types in dogs

Canine blood groups are classified by the Dog Erythrocyte Antigen (DEA) system. Currently there are 6 recognised DEAs (1.1, 1.2, 3, 4, 5 and 7) and dogs can be either positive or negative (i.e. A+ or A-) for each group. At present there are easily available tests for DEA 1.1 only. There are no naturally occurring alloantibodies to1.1. or 1.2 and so these blood types will not typically cause an acute reaction to a recipients first transfusion. However if a DEA 1.1 negative dog receives a DEA 1.1 positive transfusion antibodies will be formed and a second transfusion with DEA 1.1 positive blood will cause a haemolytic transfusion reaction. This sensitization typically takes 1-2 weeks to occur as it requires the production of antibodies. Antibodies are also formed to the other blood types. As it is only possible to type dogs for DEA 1.1 cross matching should always be carried out when a recipient has been previously transfused.

Blood types in cats

Three blood types have been described in cats; A, B and AB which is thought to be rare. Cats have preformed antibodies to other blood types and administration of the incorrect type can result in rapid and fatal consequences. All cats MUST be blood typed before a transfusion and should only receive type specific blood.

Anticoagulant-preservative solutions

Generally anticoagulants used for blood collection include either heparin or citrate. The citrate solutions contain agents that act to preserve the red blood cells. Preservative solutions such as Adsol are now widely used. These allow red blood cells to be stored for up to 35 days and protect them against trauma.

Blood collection

Typically dogs do not require anything more than gentle restraint. Blood may be taken under gravity or gentle vacuum, it is useful to be able to weigh the blood during collection so that the quantity taken is known (1ml blood weighs 1.06g). The minimum amount that may be taken into a human collection bag is 300ml and the maximum 495ml. Cats typically require sedation, after placement of a cephalic catheter we use 2-3mg/kg ketamine and 0.25mg/kg midazolam i/v immediately prior to collection. Blood is taken from the jugular vein using a 19G butterfly winged catheter attached to a 20ml syringe prefilled with anticoagulant (CPDA at 1:7-1:9, i.e 3ml of CPDA in every 20ml syringe). It is easier to take blood into 3x20ml syringes.

Blood products

Whole blood can be made into a number of products. These include packed red blood cells, fresh frozen plasma, frozen plasma, cryoprecipitate and platelet rich plasma.

Red blood cell products

Whole blood is ideal to replace lost blood as it replaces the lost cells, coagulant factors and volume deficit. It should be considered when there is severe anaemia with ongoing blood loss or there is haemorrhage as a result of coagulation deficits, e.g. anticoagulant rodenticide toxicity. Packed red blood cells are useful for cases of euvolaemic anaemia, e.g. immune mediated haemolytic anaemia. They can also be used concurrently with colloids or crystalloid for acute haemorrhage.

Plasma products

Fresh frozen plasma is separated from whole blood less than 8 hours after collection and frozen at -30°C. It contains all coagulation factors, including the labile factor VIII and von Willebrands factor. It also contains normal levels of albumin and other plasma proteins such as a2-macroglobulin. Fresh frozen plasma has therefore been advocated for use in pancreatitis and DIC although there is ongoing discussion as to how useful it is in these cases. It is most useful in coagulopathies in particular those caused by specific factor VIII deficiency or von Willebrands disease. Both liquid plasma and frozen plasma retain adequate levels of the stable coagulation factors which include vitamin K dependent factors II, VII, IX and X. Typically 20ml/kg is required to correct a coagulopathy. Plasma has been historically used for hypoalbuminaemia however this tends to be an extremely expensive and plasma consuming endeavour as a high proportion of the albumin is translocated from the blood stream to the interstitium.

Administration

Blood products should be warmed to room temperature prior to administration. They may be given via any vein but should not be administered with any other drugs or fluid other than saline. All blood products should be given via a filter to remove clots and platelet aggregates. Standard blood giving sets are available for dogs, for cats an in line filter should be used due to the small volumes involved. Animals should be closely monitored for acute transfusion reactions during administration. In the emergency situation however this is sometimes not possible. A maximum rate of 22ml/kg/hr is recommended with the aim to deliver products over 4-6 hours to prevent bacterial contamination.

Transfusion reactions

Reactions are classified into immunological and nonimmunological, acute and delayed.

Immunological reactions

Immunological reactions are due to RBCs, plasma protein, white cells and platelet antigens. Red blood cell incompatibility reactions are most important and result in haemolysis. With acute haemolytic reactions non-specific signs such as pyrexia, weakness, tachypnoea, tachycardia, salivation, vomiting or diarrhoea may be seen as well as more specific signs of haemoglobinuria or haemoglobinaemia. In cats acute haemolysis may present as an anaphylactoid reaction with recumbency, hypotension, bradycardia and apnoea. This may be extremely severe and due to the rapidity of onset may occur without visible haemolysis. Delayed haemolytic reactions are more common in dogs. There are no acute signs but the PCV typically deteriorates over 3-5 days.

Non-immunological reactions

These include transfusion associated sepsis, hyperammonaemia, dilational coagulopathy, pretransfusion haemolysis and citrate intoxication. They are uncommon but can be associated with incorrect handling of blood products. Every effort should be made to ensure blood is taken and stored correctly.

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