Blood Transfusions Notes

Blood transfusions

1. Introduction

A transfusion is intravenous therapy with whole blood or blood products.

Blood products include blood components, such as packed red blood cells or plasma. Oxyglobin is a chemically modified haemoglobin of bovine origin.

The aims of blood transfusions are:

• To replace what is lacking.

• To support patients whilst investigations are being carried out or whilst treatment is initiated.

• To aim for a clinical improvement rather than a normal PCV

• Post transfusion PCV of 25-30% in dogs

• Or 20% in cats

Indications for blood transfusion are:

• Evidence for circulatory collapse.

• A rapid drop in PCV to <20% in dogs or <15% in cats.

• An absolute PCV of 15-20%, depending on historical and presenting clinical signs.

• A PCV of <12%.

• Clear evidence of reduced oxygen carrying capacity.

2. Blood and blood products

It is important to select the most suitable product for transfusion based on what is required.

Products available include:

• Products containing everything – whole blood products

• Products containing cells – packed RBC, platelets*, WBC*

• Products containing plasma proteins – plasma and its fractions

• Products containing none of the above – oxygen carrying solutions.

*Currently commercially unavailable in the UK.

1. Fresh whole blood (FWB)

Fresh whole blood is unaltered blood from a suitable donor. It should be harvested aseptically into a closed collection system. A single unit is ~450ml. It must be transfused within 8 hours or must be refrigerated after collection (making it stored whole blood - SWB).

It contains all blood products included red blood cells, platelets, white blood cells and labile and non-labile clotting factors.

It is the most common agent transfused in practice, and is appropriate for animals that are haemorrhaging as a result of coagulopathies, thrombocytopaenia or due to trauma/surgical complications.

2. Stored whole blood (SWB)

Fresh whole blood that is not transfused within 8 hours can be refrigerated (<4C) and stored, becoming stored whole blood. The storage life of SWB is around 3-5 weeks depending on the anticoagulant used.

SWB lacks platelets, white blood cells and labile clotting factors.

Once a transfusion has begun, it must be completed within 4 hours.

3. Packed red cells (PRC)

Packed red cells are prepared from whole blood by centrifugation. The whole blood is collected into a system where there is an extra bag for the plasma to be separated. The red cells are then re-suspended in a small volume of plasma and nutrient such as SAG-M (sodium chloride, adenine, glucose and mannitol).

PRC is concentrated relative to whole blood (with a PCV of 70-80%) and can be administered with saline, although this is no longer considered necessary.

The shelf life of PRC is 3-6 weeks depending on the preservative used (SAG-M provides 6 weeks of shelf life).

PRC is useful in transfusions to treat anaemia due to haemolysis, chronic disease or erythropoietic failure where patients are volume deplete. PRC can also be used in conjunction with colloidal solution in animals requiring whole blood if this is unavailable.

4. Autologous transfusion

There are various types of autologous transfusion, including

• Harvesting blood from the patient ready for later transfusion when anticipating haemorrhage.

• Harvest of blood from acute cavity haemorrhage due to trauma/coagulopathies.

The benefit of autologous transfusion is that it reduces the potential for exposure to allogenic blood, reduces the risk of new infectious disease, reduces the chance of transfusion reactions and is immediately available.

Scavenging systems are available but are not essential – surgical suction catheters, dialysis catheters or needles can be used as long as sterility is in place. Cavity blood drawn into sterile syringes can be driven back into the patient using an in-line filter or placed aseptically into emptied fluid bags and delivered bia a blood-giving set.

Risks of autologous transfusion include sepsis and dissemination of neoplasia.

1. Platelet rich plasma (PRP)

PRP is prepared from fresh whole blood at specialist centres. It is difficult to prepare due to the platelets, whose activity must be minimised at all stages.

The lifespan of PRP is 5 days. It must be stored at room temperature and not refrigerated.

It is most useful in treating life-threatening haemorrhage due to thrombocytopaenia or pathia. The major advantage is the reduction in volume required to increase platelet numbers compared to using FWB.

2. Platelet concentrate (PC)

Platelet concentrate is prepared from PRP. A small volume of around 35-70ml of PRP is frozen to provide PC.

It has similar features to PRP – it must be stored at room temperature for 4-5 days and once opened must be used within 4 hours.

The indications for PC use are the same as for PRP but the volume is even less and therefore of greater benefit from limited volume expansion.

3. Fresh frozen plasma (FFP)

FFP is harvested from fresh whole blood within 8 hours of collection.

If frozen and stored at <20C, it is stable for up to 12 months. Once defrosted or after being freshly collected, it must be used within 5 days.

It provides maximal concentrations of all factors. Indications for FFP use include treatment of acquired or inherited coagulopathies, DIC, pancreatitis and liver disease. The dose rate is 6-10ml/kg q12h and up to 20ml/kg for severe coagulopathy.

It should not be used for albumin replacement or as colloidal therapy due to the volume required to increase the plasma oncotic pressure and albumin concentration.

4. Stored plasma/frozen plasma (non-FFP)

This is FFP which is more than 1 year old, or FFP that has been thawed, or separated from whole blood more than 8 hours after collection.

Non-FFP can be used up to 5 years from the preparation if it is frozen and stored at <20C.

Some factor activity is lost, particularly labile clotting factors, but vitamin K dependent clotting factors are active. It is indicated for use to treat...

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