Transfusion of blood and blood products exposes patients to risks despite all precautions taken. Clinical judgment is required to determine that the expected benefits of the transfusion outweigh these risks . Adverse effects , generally referred to as transfusion reactions , occur with approximately 3% of units of blood transfused and vary greatly in severity . Most transfusion reactions are mild . Death due to transfusion is rare . Estimates of the frequency of blood transfusion-related deaths range from one in 30,000 to one in 500,000 transfusions. The majority of deaths are due to severe intravascular hemolysis following the administration of ABO-mismatched blood.

Careful pre-transfusion testing will prevent some , but not all , transfusion reactions . Each blood donation is tested for several transmissible diseases and red cell antibodies after collection . Cross match or other pre-transfusion serological testing is performed to detect antibodies in the recipient's serum that may shorten the survival of donor red cells.

Such tests however will not detect antibodies to white cells, platelets or other blood constituents.

Components of blood can cause transfusion reactions by immunological or non-immunogical mechanisms . Reactions that occur during or within 24 hours of the infusion of blood products are called immediate transfusion reactions. Those that occur some time after the transfusion are called delayed transfusion reactions. (see Table 4)



 Acute Hemolytic Transfusion Reactions:
An acute hemolytic transfusion reaction is rare ; it is usually due to the transfusion of ABO-incompatible blood following the improper identification of the recipient , either when the cross match specimen is taken or when the donor blood is transfused . Signs of acute intravascular hemolysis include fever , hypotension, hemoglobinuria and bleeding . A patient under anesthesia receiving incompatible blood may have unexplained bleeding with out other signs of a transfusion reaction.

An acute , immune-mediated transfusion reaction involves activation of the complement cascade and may cause:

     · intravascular hemolysis with hemoglobinemia and hemoglobinuria

      ·  release of vasoactive complement components resulting in hypotension and shock

      ·  thrombin and platelet activation resulting in disseminated intravascular coagulation (DIC)

The renal failure that occurs in some patients with an acute hemolytic transfusion reaction is caused by glomerular deposition of immune complexes , DIC , and reduced renal blood flow due to hypotension rather than by free hemoglobin .The rapid intravascular destruction of transfused red cells is a medical emergency due to the risk of renal failure and/or acute disseminated intravascular coagulation. THE INFUSION OF THE BLOOD COMPONENT MUST BE DISCONTINUED AND THE INTRAVENOUS LINE MUST BE KEPT OPEN WITH SALINE TO FACILITATE APPROPRIATE MANAGEMENT.

Treatment of intravascular  hemolysis is determined by the specific signs and symptoms.Hypotension should be treated with fluid replacement . Vasoactive drugs are usually not necessary. Urinary flow should be induced and maintained by fluid replacement and diuretics . If renal failure is severe , dialysis may be required . If renal failure is severe , dialysis may be required . If the patient has signs and symptoms of a hemostatic disorder , laboratory tests can determine whether platelets and/or appropriate coagulation factors should be administered.

Heparin is usually not indicated because there is no further activation of the coagulation cascade once the transfusion of the incompatible red cells is stopped .


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