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blood-brain barrier disruption

Treating a patient with drugs that permit chemotherapy to reach cancers of thecentral nervous system. The brain and spinal cord are selectively protected from exposure to many substances by a network of cells that anatomically and physiologically block the diffusion of harmful chemicals into neurons.

blood cell casts

SEE: under cast.

blood component therapy

Transfusion of one or more of the components of whole blood. The blood components may have been taken from the patient previously (autologous transfusion) or donated by someone else (homologous transfusion). Except in the case of acute hemorrhage, the transfusion of whole blood is rarely needed. Use of a component rather than whole blood permits several patients to benefit from a single blood donation. Blood components used in clinical medicine include packed red blood cells (RBCs); leukocyte-poor RBCs; frozen glycerolized RBCs; thawed deglycerolized RBCs; washed RBCs; whole blood; heparinized whole blood; granulocytes; platelets; and plasma and plasma fractions. The latter include antihemophilic factor (Factor VIII), prothrombin complex (Factors VII, IX, and X), gamma globulin, and albumin.

PATIENT CARE: Irradiation of blood by gamma rays (gamma irradiation) incapacitates donor lymphocytes in whole blood, RBCs, platelets, or granulocytes. These lymphocytes are blocked from proliferating in response to foreign antigens, esp. those in the bone marrow, of immunocompromised recipients, causing transfusion-associated graft-versus-host disease. In patients who are not immunocompromised, the donor white blood cells (WBCs) are destroyed. Irradiated blood is given to patients who are donating or receiving bone marrow transplants or who have hematological or lymphatic cancers. In addition, blood used for intrauterine or neonatal exchange transfusions and blood donated by a biological relative also is irradiated.

Washing blood (RBCs, platelets) in 0.9% sodium chloride removes most, but not all, of the antibodies that could trigger an adverse reaction, esp. in patients with a history of hypersensitivity reactions to blood transfusions, even when given antihistamine prophylaxis. Washed RBCs must be given within 24 hours because the risk of bacterial contamination is increased when the saline is injected into the bag of RBCs.

Use of leukocyte-poor blood reduces the risk of unwanted responses to WBCs (leukocytes), antibodies, and cytokines by the recipient. WBCs can be eliminated by using special filters in the intravenous line or through aphoresis. The process is used for patients with a history of allergic reactions to blood products or those expected to require multiple transfusions. It also prevents transmission of cytomegalovirus (CMV) to immunocompromised patients.

Screening blood for CMV and RBC antigens helps to identify CMV-negative blood, which is needed for high-risk patients. More than half of persons over 35 have been infected with CMV. However, this screened blood is beneficial for premature infants; infants under age 4 weeks; recipients of intrauterine transfusion regardless of the mother's CMV status; any patient who ...

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