Notes supplied by Nadja Sigrist, DrMedVet, FVH(Small Animals), DACVECC.

Introduction

Administration of blood products is often life saving; however, side effects and complications may occur. Generally, problems associated with transfusions can be avoided by carefully selecting blood donors and choice of blood product, using appropriate collection, storage and administration techniques, and performing blood typing or a cross-match. However, administration of transfusions will always have side effects such as leucocyte-related immunosuppression and risk of nosocomial infection, and the risk of a transfusion reaction can never be eliminated completely.

Choice of Blood Product

Blood products should be administered following a clear indication. Replacement of the deficient blood component(s) only is preferred but may not be possible in an emergency situation or in private practice. Babesiosis, ehrlichiosis, anaplasmosis, leishmaniasis and dirofilariasis can be transmitted by blood transfusion and donor dogs should test negative for these infections. Cats should have been tested for feline leukaemia virus (FeLV), feline immunodeficiency virus (FIV) and haemobartonellosis.

The blood product is examined for signs of bacterial contamination (brown colour, gas bubbles). Human blood older than 15 days has been associated with splanchnic vasoconstriction in septic patients, pneumonia, multiple organ failure and mortality.

Blood Collection and Storage

Blood collection should be aseptic from the jugular vein over a 5–10-minute period by means of a needle which is connected to a sterile bag with anticoagulant. The commercially available three-bag systems are easiest to use since they not only ensure sterile withdrawal and processing, but also contain the necessary anticoagulant and nutrient solution, so that the blood products are maximally durable. If blood is collected for immediate transfusion (whole blood or autotransfusion), it can be anticoagulated by addition of sodium citrate (1 part of 3.8% sterile anticoagulant for 9 parts of whole blood) or heparin (625 U per 50 ml blood) and collected in a sterile way using a large-bore needle, infusion tubing and a sterile bag.

Blood products should be kept refrigerated (packed red blood cells (pRBCs), whole blood) or frozen (plasma, platelet concentrate, cryoprecipitate).

Administration of Blood Products

Plasma should be thawed slowly, and excessive warming should be avoided in all blood transfusions. Blood products should be infused with a filter (170 µm pores). Leucocyte reduction filters may be used to decrease adverse reactions to white blood cell (WBC) components; however, they are expensive. If additional infusion solutions are given over the same infusion line, calcium-free and isotonic solutions (0.9% NaCl) should be used and sterility has to be maintained when connecting bags to infusion lines and catheters. No other additives or medications should be given over the same line. Whole blood or pRBC should not be given by means of an (older) infusion pump, since the erythrocytes may be destroyed in the pump. All transfusions should be given slowly in the first 30 minutes, and heart rate, respiration and temperature checked frequently in order to be able to recognise transfusion reactions in time.

Blood products should be administered in an appropriate dosage. The dose depends on the patient's condi­tion, haematocrit and desired haematocrit. The dose of blood required to reach the desired haematocrit (usually chosen around 20%) is: 2x desired haematocrit increase x kg bodyweight for whole blood; and 1.5 x desired haematocrit increase x kg bodyweight for pRBCs. Plasma is administered at a dose of 10–15 ml/kg.

Blood Group Typing and Crossmatching

Ideally, all erythrocyte transfusions should be cross-matched. The erythrocytes are washed and donor erythrocytes are incubated with recipient plasma. If macroscopic or microscopic agglutination arises, then antibodies are present against a component of the other blood and the donor is not compatible with the receiver.

Since dogs do not have naturally occurring antibodies against another blood group, the first transfusion is usually not a problem. In dogs which have already had a blood transfusion earlier in their life and dogs that have ever been pregnant, a cross-match is mandatory. If cross-matching is not a possibility, then at least the DEA 1.1 group should be determined using the commercially available blood group testing cards. Dogs have at least 13 different blood groups. Transfusion reactions are usually due to incompatibilities of DEA 1.1, DEA 1.2 or DEA 7, the ideal blood donor is therefore negative for these blood groups. DEA 1.1- negative dogs should receive only DEA 1.1-negative blood, DEA 1.1-positive dogs can receive either positive or negative blood.

Cats have only one blood group system: A, B or AB. Blood group testing is mandatory in cats, because cats have natural antibodies against the other blood group and transfusion reactions can be lethal. Ninety-nine percent of cats are type A; type B is particularly seen in British Short-hair and Devon Rex breeds. Type AB is extremely rare, but these cats can receive type A blood safely.

Transfusion Reactions

A transfusion reaction can be due to immunological or metabolic factors. Immunological reactions include acute haemolytic transfusion reaction (type II), acute hypersensitivity (type I), platelet or leucocyte sensitivity, delayed haemolysis, post-transfusion purpura and immunosuppression. Haemolytic transfusion reactions and acute hypersensitivity are feared most but can be prevented by a cross-match.

In any case, the transfusion is stopped and the patient is evaluated. Fever and haemolysis are treated with steroids if severe, while diphenhydramine is indicated with acute hypersensitivity reactions associated with urticaria and swelling.

Non-immunological transfusion reactions include erythrocyte trauma leading to haemolysis, intravascular fluid overload, bacterial contamination, citrate intoxication (hypocalcaemia) and hypothermia, and can be avoided by the above principles.