INTRODUCTION
A blood transfusion is indicated in the following cases:

• Acute haemorrhage.
• Acute haemolysis.
• Chronic anaemia.
• Profound hypoproteinaemia.
• Colostrum deprived neonates.

Diseases that may require blood transfusion therapy include:

• Bone marrow disease (fresh blood).
• Septicaemia (fresh blood).
• Platelet defects (fresh blood).
• Poisoning (fresh blood for Warfarin, or serum).
• Haemophilia (fresh or frozen plasma containing missing factors).
• Von Willibrand's Disease (fresh blood or plasma).

The purposes of a transfusion are provision of oxygen transport or clotting factors. Whole blood, plasma or packed cells may be used depending upon the reason for the transfusion. Plasma is a useful fluid in cases of hypovolaemia and hypoproteinaemia. Packed red blood cells are used when red cell replacement is indicated (these are re-suspended in an isotonic solution which does not contain calcium since this reacts with the citrate anticoagulant).

BLOOD DONORS - GENERAL INFORMATION

A donor animal must meet the following criteria:

• Large adult but not obese.
• Fit and healthy.
• Not have been previously transfused themselves.
• FeLV, FIV and haemobartinella negative in the case of cats.
• Have a PCV of at least 40% in dogs & 35% in cats.
• Docile disposition.
• Speyed if female (to negate the influence of oestrogens on platelets).

ACP should be avoided to sedate donor animals since this lowers blood pressure.

Unmatched blood is fairly safe in the case of a first transfusion but with subsequent transfusions, the blood should be cross matched.

The 8 dog blood groups are as follows:

DEA 1.1, DEA 1.2 and DEA 7 negative are the most useful donors since they provide universal blood which prevents the formation of antibodies against these determinants in the transfused recipient.

DEA 1.1 and DEA 1.2 positive are the only blood groups to cause potentially severe reactions.

DEA stands for Dog Erythrocyte Antigens. Previously, blood groups were classified with a letter system; A1, A2, B, C, D, F, Tr, He.

The 3 cat blood groups are as follows:

Most domestic short-haired and domestic long-haired cats are type A. The Abyssinian, Birman, British short haired, Somali, Devon Rex, Himalyan and Scottish Fold are type B.

COLLECTION OF BLOOD FROM THE DONOR

1. Ask an assistant to restrain the animal.
2. Clip the hair from the jugular area.
3. Apply antiseptic solution and spirit.
4. Inject local anaesthetic peri-venously (in a 1ml syringe with 25g sterile needle).
5. Wait a few minutes for the local anaesthetic to take effect.
6. A second assistant should now be on hand to hold the blood collection bag as low as possible and gently mix the blood as it is collected with the anticoagulant.
7. Access the jugular with a 16g sterile needle and attach a commercial blood collection pack (some collection packs have an integral needle). 10-20mls/kg may be collected from dog, whilst a maximum of 40mls may be collected from a cat.
8. Having collected the blood, remove the needle from the jugular and apply a cold compress to the area to prevent the formation of a haematoma.
9. Reassure the donor animal and offer food and water.
10. The donor animal must avoid strenuous exercise for 24 hours. Also ensure that a tight collar is not worn.

Commercial blood collection packs are usually designed for the collection of 500mls of blood. CPD (Citrate phosphate dextrose) is the preferred anticoagulant.

BLOOD STORAGE
Fresh blood is preferred, since stored blood does not possess an active clotting mechanism (thus making stored blood unsuitable for cases such as Warfarin poisoning). Fresh blood cells also have a much longer life span.
If necessary, blood can be stored at 4°C for up to 3 weeks with acid citrate dextrose and up to 4 weeks with citrate phosphate dextrose.
Whole blood should never be frozen; however plasma may be frozen for up to 6 months at -70°C. Plasma deteriorates rapidly unless it is frozen.  

THE TRANSFUSION

1. Blood that has been refrigerated must be SLOWLY warmed to room temperature to avoid destruction of the cells.
2. Invert the bag gently to resuspend the cells, but again be careful since the cells are easily damaged.
3. 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.
4. 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.
5. In very small patients blood may be mixed with normal saline to reduce its viscosity thus facilitating an easier passage through a fine catheter.
6. Monitor the patient very closely watching for any signs of febrile, allergic or haemolytic reactions. Transfusion patients are critical care patients and will require intensive nursing according to the veterinary surgeon's instructions. Cats are sensitive to citrate - citrate toxicity may cause hypocalcaemia.

COMPLICATIONS
Problems associated with blood transfusions include:

• Allergic reactions (e.g. Facial oedema, pruritis, uticaria).
• Ammonia accumulation in stored erythrocytes.
• Febrile reactions (fever of haemolytic, immunologic or infectious cause).
• Haemolytic reactions (may be due to mishandling of the blood or immune mediated).
• Hypothermia.
• Transmission of disease from the donor blood to the recipient.