The infusion of large amounts of blood or of blood products directly into the bloodstream to remedy severe blood loss or to correct chronic anaemia. In an exchange blood transfusion, nearly all of the patient’s blood is replaced with donor blood.
How it is done
Before a transfusion, a sample of the patient’s blood is taken to identify his or her blood group, this is then matched with suitable donor blood. The donor blood is transfused into an arm vein through a plastic cannula (a tube with a smooth tip). Usually, each unit of blood is given over one to four hours; in emergencies 500mls may be given within a couple of minutes. The blood pressure, pulse of the patient and body temperature are monitored during the procedure.
If mismatched blood is accidentally introduced into the circulation, antibodies in the recipient’s blood can cause the donor cells to burst, leading to kidney failure or shock. Less extreme reactions can produce chills, fever or a rash. Reactions can also occur as the result of an allergy to a particular component of the transfused blood. There is the risk of infection although all blood used for transfusions is supposed to be carefully screened for a number of infectious agents, including hepatitis B, C and HIV.
In severely anaemic patients or the elderly, a blood transfusion can overload the circulation, which can lead to heart failure. In patients with chronic anaemia who need constant transfusions over the course of many years, excess iron can accumulate in the body (a condition called haemosiderosis) and damage organs such as the pancreas, liver and heart. Treatment with the drug desferrioxamine to remove excess iron may be needed in this case.