DELAYED HEMOLYTIC REACTION This reaction occurs 7 to 10 days after transfusion as a result of an antigen-antibody reaction that develops after the transfusion. Laboratory studies reflect a slowly falling hemoglobin, and a previously negative Coombs test becomes positive. The patient is generally asymptomatic. Further blood bank workup is needed to detect the causative antibody.
HYPERVOLEMIA The transfusion of PRBCs or plasma results in the rapid expansion of intravascular volume. Such expansion may not be well tolerated by patients with limited cardiovascular reserve, particularly infants and elderly patients. Patients may complain of headaches and shortness of breath; on examination, they will have signs of congestive heart failure. Treatment consists of slowing the rate of infusion and diuresis of the patient. As a general guide, infusions in adults are at a rate of 2 to 4 mL/kg/h. This can be slowed to 1 mL/kg/h in patients at risk of fluid overload.
HYPOTHERMIA Hypothermia may develop in patients who receive rapid infusion of large quantities of refrigerated blood. This is generally only a problem if three or more units are given rapidly. PRBCs are stored at 4°C, platelets at 20° to 24°C, and FFP at -18°C. Rapid infusers/warmers may be used but should not raise the temperature to more than 40°C, or hemolysis can occur. The easiest method for warming blood is to infuse it along with warmed (39° to 43°C) normal saline, which will warm and dilute the blood.
NONCARDIOGENIC PULMONARY EDEMA Noncardiogenic pulmonary edema occurs in approximately 1 in 5000 transfusions. Believed to be due to incompatibility of passively transferred leukocyte antibodies, the problem usually develops within 4 h of the transfusion. Clinically, the patient has respiratory distress, fever, chills, and tachycardia, and a chest radiograph shows diffuse patchy infiltrates without cardiomegaly. There is no evidence of fluid overload or congestive heart failure. In the majority of cases, the pulmonary infiltrates resolve over a few days and only supportive care is needed. This reaction can, however, be fatal in patients who are already critically ill.
ELECTROLYTE IMBALANCE Citrate is a component of the preservative solution used in blood storage; it functions as an anticoagulant by chelating calcium. Significant hypocalcemia rarely occurs as a result of transfusion-related citrate exposure because patients with normal hepatic function readily metabolize citrate to bicarbonate. Even with massive transfusion, calcium replacement is rarely needed.
Hypokalemia can be a problem when large amounts of blood are transfused. When the citrate is metabolized to bicarbonate, the blood becomes alkalotic and potassium is driven to the intracellular compartment.
Hyperkalemia rarely is a problem after blood transfusions even though the potassium content increases in stored blood. This may be a problem for patients with renal failure or neonates.
GRAFT-VERSUS-HOST DISEASE This unfortunate reaction, which is fatal in more than 90 percent of cases, can occur after the transfusion of nonirradiated cellular blood components into an immunocompromised host. Graft-versus-host disease occurs when immunologically competent lymphocytes are passively transferred to an immunoincompetent host who is unable to destroy the donor lymphocytes. The donor lymphocytes engraft, recognize the host as foreign, then attack the host tissues. Bone marrow aplasia commonly results.
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