1. Hypocalcaemia. Transfused blood contains citrate which binds the patient's ionised calcium. Usually this is not a problem as the healthy liver can metabolise (to bicarbonate) the citrate in one unit of blood in 5 minutes. Where transfusion rates are rapid, however, excessive calcium binding may itself lead to hypotension, and also to tetany. To avoid citrate toxicity it has been common practice to give Ig of calcium chloride (or4 g calcium gluconate) for every 4 units of blood administered. It is recommended, as belter practice, to avoid the administration of calcium unless there are clinical or biochemical indications (e.g. by the assessment of the ionised calcium levels).
2. Hyperkalemia. This is not usually a problem unless very large amounts of blood are transfused. It is more usual to find hypokalaemia as the metabolic activity of the red cells begins and the tissues begin to lake up potassium. Attempts at correction are only indicated if the serum electrolytes or the HCG are disturbed.
3. Acid/base disturbances. Alter large transfusions any residual disturbance is dependent on the quality of tissue perfusion, the rate of administration, and the effectiveness of citrate metabolism in the liver. The need for correction is determined by regular serum sampling.
4. Defects of clotting. It has been suggested that 8 units of platelet concentrate and 2 units of fresh frozen plasma should be transfused routinely with every 12 units of packed red blood cells ( I unit (50 mL) of platelet concentrate should raise the platelet count by 10 000). Nevertheless, during the administration of large replacements it is preferable that there should be regular monitoring of the platelet count, prothrombin time, partial prothromboplastin time and fibrinogen levels, and appropriate replacements given only where clearly indicated. (Fresh frozen plasma should be given if the prothrombin or partial prothromboplastin exceed 1.5 times the control levels. Cryoprecipitate (1.0-1.5 units) is given for fibrinogen levels less than 0.8 g/L.)
5. Transmission of disease. The risks of HIV and hepatitis B transmission are small (said to be in the order of I in 200 000 in the US), but are higher in the case of Hepatitis C (c. I in 5000). Septic reactions are rare, but commoner with platelet concentrates which are stored at room temperature.
6. Reactions. Acute haemolytic reactions from mismatched blood require immediate cessation of blood administration and a full investigation, which should include a haematocrit to check for the presence of haemolysis, culture of the patient's and donor's blood to exclude bacterial contamination, repeat cross-matching, a full blood count and examination of red cell morphology, and a Coombs' test. The donor blood should be returned to the blood bank and advice sought from the haematologist regarding any further investigation thought desirable. All aspects should be rigorously documented. The urinary output must be carefully monitored while an attempt is made to obtain a brisk diuresis. Severe reactions can occur from 30 mL of mismatched blood, are life threatening, and may require dialysis. Non-haemolytic reactions, often with severe associated urticaria, usually occur after administration of larger quantities of whole blood or packed cells, and may often be controlled with intravenous benadryl. Washed red cells may be given if further transfusion is required.
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