Blood transfusion

Published on 11/04/2015 by admin

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9

Blood transfusion

Principles of blood transfusion

The ability to safely transfuse blood and blood products revolutionised outcomes from major trauma. It also enabled extraordinary advances in areas of surgery involving heavy blood loss such as arterial reconstruction, open-heart surgery and organ transplantation.

Nevertheless, blood transfusion carries a range of potential hazards, including transfusion reactions, transmission of infection, clerical errors leading to incompatible transfusion, and potential immunosuppression in cancer patients. For replacing blood loss, stored blood has the advantage over gelatin and electrolyte solutions that it remains within the vascular compartment, although most ‘blood’ for transfusion consists of concentrated red cells with platelets and clotting factors removed. Potentially lethal side-effects mean that a decision to transfuse blood or blood products must be based on clear indications and after considering alternatives (see Reducing the need for bank blood transfusion, p. 120). The types of transfusion components available and the general indications for their use are summarised in Box 9.1.

Box 9.1   Types of transfusion and indications for their use

Whole blood

Very rarely used because of the demand for separate blood components. Whole blood carries greater risks of adverse reactions owing to the presence of leucocytes

Packed or concentrated red cells (the most common transfusion product)

For use in substantial haemorrhage and severe anaemia. Whole blood is collected then centrifuged to separate the red cells (and platelets and plasma). Packed/concentrated red cells are then suspended in a preservative solution ready for reinfusion. A bag of red cells is approximately 300 ml and raises the haemoglobin concentration by approximately 1 g/dl

Human albumin solution, available as 4.5% and 20% solutions

Albumin is expensive and is derived from human donor blood. In terms of efficacy, mortality and cardiorespiratory function, there is little evidence that albumin solutions are better than plasma substitutes or normal saline for resuscitating patients with traumatic or septic shock or requiring large perioperative volume replacement

Transfusion of albumin solutions should probably be restricted to patients with hypoproteinaemic oedema with nephrotic syndrome or with ascites in chronic liver disease. Other uses are difficult to justify in the absence of scientifically proven benefit

Fresh-frozen plasma (FFP)

Plasma is separated from fresh whole blood and then frozen. FFP contains near normal amounts of all clotting factors and other plasma proteins. It should be blood group compatible when possible and should not be used simply for volume replacement. FFP is often used to replace clotting factors exhausted during major haemorrhage (due to a combination of consumption of clotting factors by attempted haemostasis and the lack of clotting factors in transfused blood). This is likely when blood loss exceeds 1.5 times the blood volume, and the loss has been replaced rapidly with red cells and crystalloids or colloids. Clotting studies usually demonstrate a coagulopathy

FFP is also used to replace deficiencies of coagulation factors when there is continued bleeding and the necessary specific factor concentrates are unavailable. This may occur in liver disease, thrombotic thrombocytopenic purpura (TTP) and acute disseminated intravascular coagulation (DIC)

Platelet concentrates

Used for platelet exhaustion during major haemorrhage (e.g. ruptured abdominal aortic aneurysm) and in thrombocytopenia. Indicated if the platelet count is < 50 × 109/L, or massive blood loss is occurring. Platelets should be avoided in autoimmune platelet disorders except in the presence of life-threatening haemorrhage

Cryoprecipitate, fibrinogen and other specific clotting factor concentrates

Used for various specific coagulation deficiencies, e.g. severe hypofibrinogenaemia, haemophilia. These should only be used in consultation with a haematologist

Plasma substitutes

These are solutions of macromolecules with colloid osmotic pressure and viscosity characteristics similar to plasma. Gelatin solutions (e.g. Haemaccel, Gelofusine) and etherified starch solutions (e.g. hetastarch) are used for initial restoration of circulating volume in haemorrhage or burns and to maintain volume, blood pressure and renal perfusion intraoperatively where blood transfusion is not indicated

Laboratory aspects of blood transfusion

Blood grouping and compatibility testing

Transfusion of ABO incompatible blood may be fatal. Transfusion practice aims to minimise this risk and involves two steps: first, determining the patient’s ABO and Rhesus groups; second, screening the patient’s blood (and each unit of donor blood) for antibodies. Traditionally, each unit of group-compatible donor blood has been directly cross-matched against the patient’s serum to ensure compatibility. Fortunately, in donor blood shown to be antibody-free, 97% is completely compatible with a group-matched recipient and can safely be transfused without cross-matching. Thus grouped and antibody screened blood can be supplied quickly from a prepared pool, rather than individually cross-matching it. This saves time and money and most hospitals are adopting this practice.

After transfusion of about 10 units of blood, the patient’s antibodies are so depleted that group-compatible blood can safely be given safely. In an emergency (e.g. obstetric haemorrhage) where group-compatible blood is unavailable, group O, Rh-negative blood can be given with comparative safety.

Storage and useful life of blood

Blood and blood products have exacting requirements for preserving their quality. Their usefulness is easily impaired if handled inappropriately.

Packed red cells are stored between 2°C and 6°C, and have a shelf life of 35 days. Improved preservative solutions mean red cell quality deteriorates little during storage but pH changes occur and potassium leaches from the cells. The latter is only significant in neonates undergoing exchange transfusion or in patients with renal failure.

To ensure vitality, blood should be retained in the designated blood refrigerator until just before use. Blood removed for more than 30 minutes and not transfused should be returned to the laboratory for disposal because of the risk of bacterial proliferation. As soon as it becomes clear that blood products will not be required, the laboratory should be informed so they can be made available for other patients. Empty blood packs should be retained for 48 hours for examining and testing in the event of a transfusion reaction.

Blood transfusion in clinical practice

Blood transfusion and elective surgery

Attitudes to transfusion in elective surgery are becoming more conservative. Blood is expensive and its use carries risks. In elective surgery, patients fall into one of three categories: transfusion not anticipated (e.g. hernia repair), transfusion possible but unlikely (e.g. cholecystectomy), and transfusion probable (e.g. major arterial reconstruction). For patients in the second category, blood should be sent for ABO and Rhesus grouping and antibody screening, and serum retained for compatibility testing if required later (‘group and save’). For patients in the third category, an appropriate number of units is requested for the operation; many hospitals operate a maximum blood ordering schedule (MSBOS) to ensure appropriate ordering. The blood is prepared a day or so before operation. If the antibody screen is negative and criteria for electronic cross-match are met, a serological cross-match is unnecessary and group-specific blood can be immediately issued. If a further transfusion is required more than 72 hours later, a new blood sample must be tested for new antibodies.

To prevent the disaster of giving blood to the wrong patient, transfusion blood samples must be scrupulously labelled in the presence of the patient. Immediately before transfusion, the label of each unit of blood must be checked against the identity and blood group of the patient (along with any compatibility slip).

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