Blood Basics > The Blood Supply
Being your own blood donor -- autologous transfusion -- may reduce your exposure to others' blood and help conserve community blood supplies for those who cannot utilize this option. Autologous transfusion is most often considered in elective surgeries, but some techniques can be applied even in emergency situations.
There are several different ways that a patient's own blood can be used to help support the need for red blood cells.
Collecting one or more units of blood before surgery may allow the patient's bone marrow to make more cells while the collected units are stored in the refrigerator (for up to 42 days). For this approach to be helpful to the patient, he or she should be in sufficiently good health to be able to withstand the blood loss that occurs with the collection. Iron therapy is often prescribed, and, in some cases, an injectable hormone (erythropoietin) may be administered to "push" the marrow to make red cells at a faster rate.
While this approach may be helpful to some patients and even though patients may be accepted despite conditions that would disqualify them from routine donation, collection of blood preoperatively is not for all patients. Since the risk of transmitting viruses is currently so low, care must be taken that patients do not face greater risk from autologous donation than from being exposed to someone else's blood. Furthermore, the procedure should be undertaken only when there is a reasonable likelihood of a transfusion actually being needed; otherwise, the time, effort, and expense will be for naught. Most insurance carriers will pay for the costs of collecting and processing blood, but only if it actually is transfused.
This technique is similar to the one described above, but the collection takes place immediately before the start of surgery. The anesthesiologist collects several units of blood (usually after induction of anesthesia) and replaces the volume with an intravenous salt and/or protein solution. (In comparison, the smaller volume lost during preoperative blood collection is made up through routine oral intake and normal liver function.) Blood loss in surgery thus occurs at a lower hematocrit -- each drop of blood lost has fewer red cells in it -- therefore, the amount of red cells lost during the entire procedure may be reduced. Furthermore, the patient's own blood is immediately available for transfusion when needed.
Although this approach is intuitively attractive, mathematical models and actual experience have indicated that it actually reduces exposure to donor blood only if practiced aggressively, that is, only if a substantial volume of blood is withdrawn and the patient's hematocrit is allowed to fall to (or can be withstood to be at) a low level. This technique is being investigated for combination with oxygen-carrying red cell substitutes ("artificial blood") that may allow the patient to tolerate a lower hematocrit during surgery. As with preoperative collection, it can make a substantial impact only when there is significant blood loss in the procedure.
Perioperative Red Cell Recovery
Blood that is lost into the surgical wound is usually suctioned into a canister. Rather than discarding this blood, it can be anticoagulated (to prevent clotting while outside the body) and returned to the patient. The most common way of doing this today includes an instrument that washes the red cells free of plasma (which may contain activated clotting factors) and platelets (which may also be activated and could cause clotting problems if re-infused). The washed red cells, suspended in a salt solution, can be concentrated and then returned to the patient directly.
Instruments developed initially for this purpose were usually applied only in cases where there was a sufficiently large volume of blood loss to justify their application. More recently, smaller, more portable instruments have been developed that can be used (albeit at a lower processing rate) both in the operating room and post-operatively (if continued loss of blood is anticipated in the wound).
This technique is applied most frequently in cardiac, vascular, and orthopedic surgeries. It can be used in cancer surgery if the wound is not contaminated with cancer cells. It can even be used after trauma provided that the wound is not contaminated with bacteria (such as from bowel contents).
There are several different approaches that may allow a patient to utilize his or her own blood. The most appropriate choice for transfusion support will depend on the patient's condition, the surgery, and the expected blood loss. Such factors should be discussed with the surgeon as early as possible.
-- James P. AuBuchon, M.D.
Dartmouth-Hitchcock Medical Center
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