Packed Red Blood Cells

Packed red blood cells (PRBCs) are prepared from whole blood by centrifugation followed by the removal of 80 to 90 percent of the plasma. A preservative solution, such as Adsol (dextrose, adenine, and mannitol), is added, resulting in a storage time of up to 42 days. PRBCs are stored at 4°C. Each unit of PRBCs transfused should raise the hemoglobin by 1 g/dL or the hematocrit by 3 percent. The advantages to the use of PRBCs compared with whole blood include reduced risk of volume overload; decreased infusion of citrate, ammonia, and organic acids; and the decreased risk of alloimmunization because the patient is exposed to fewer antigens. PRBCs provide rapid restoration of oxygen-carrying capacity in patients with acute or chronic blood loss.

It is impossible to set specific criteria for the transfusion of PRBCs, although general guidelines can be used and adapted to each clinical setting. The decision to transfuse must be individualized for each patient. The impact of blood loss is variable among patients, depending on the underlying cause, the rate of blood loss, the patient's underlying health status, the cardiopulmonary reserve, and the activity level of the patient. There are three common settings where the transfusion of PRBCs should be considered:

1. Acute hemorrhage. Acute hemorrhage, as seen in patients with trauma, bleeding from the gastrointestional (GI) tract, or from a ruptured aortic aneurysm, often requires emergency transfusion of PRBCs. In otherwise healthy patients, the loss of up to about 1500 mL of blood (about 25 to 30 percent of the blood volume in a 70-kg person) can be replaced entirely with crystalloid solutions. Blood losses greater than this usually require the transfusion of PRBCs to replace oxygen-carrying capacity and crystalloid solution to replace volume.

2. Surgical blood loss. Otherwise healthy surgical patients usually do not require preoperative transfusion of PRBCs unless the hemoglobin is less than 7 g/dL or large amounts of blood loss are expected. Intraoperative blood loss of 1500 to 2000 mL can often be replaced with just crystalloid if the patient initially had a normal hemogram. Most patients will require transfusion of PRBCs and crystalloid when blood loss exceeds 2 L.

3. Chronic anemia. Patients with chronic stable anemia probably only require transfusion of PRBCs if the hemoglobin falls to less than 7 g/dL or if they are symptomatic or have underlying cardiopulmonary disease.

Some general guidelines for patients in the emergency department (ED) whose blood should be typed and crossmatched for potential transfusion include those with (1) evidence of shock from whatever cause, since early on it may not be clear what the etiology is; (2) known blood loss of more than 1000 mL; (3) ongoing gross bleeding; (4) those with a hemoglobin less than 10 g/dL or hematocrit less than 30 percent; or (5) patients who are potentially going for surgery where blood may be lost (laparotomy after trauma or for ectopic pregnancy).

Other patients who may need blood products but do not meet these criteria should have blood sent to the blood bank for typing and antibody screening. Many institutions have criteria for the number of units to be crossmatched in a particular clinical setting. Many clinicians believe that it is not worth the risks of transfusion to transfuse just one unit of PRBCs; i.e., do not transfuse until the patient requires 2 or more units to be transfused.

In addition to PRBCs, red blood cells are available as leukocyte-poor, frozen, or washed, when required for certain patients. Leukocyte-poor RBCs have 70 to 85 percent of the leukocytes removed by centrifugation, filters, or ultraviolet irradiation. This preparation is indicated for patients who are transplant recipients or transplant candidates (bone marrow or solid organ) in order to prevent immunization against leukocytes and in patients who have a history of previous febrile nonhemolytic transfusion reactions. Frozen RBCs are prepared by adding a cryoprotective agent and then storing the cells for as long as several years at below freezing temperatures. The freezing process destroys the other blood constituents except for a small number of immunocompetent lymphocytes. Prior to transfusion, the cells are thawed and washed with a solution that removes 99.9 percent of the plasma and cellular debris. This process is expensive but can provide a supply of rare blood types, provides metabolically superior RBCs, and results in reduced antigen exposure for transplant candidates. Washed RBCs are prepared from whole blood or PRBCs. Isotonic saline is used to wash the RBCs, resulting in the removal of plasma proteins, some leukocytes, and some platelets. Washed RBCs must be infused within 24 h because of the risk of bacterial contamination during processing. Washed RBCs are used for patients who have hypersensitive reactions to plasma (usually IgA-deficient patients), neonatal transfusions, and in patients with paroxysmal nocturnal hemoglobinuria in order to avoid the precipitation of hemolytic episodes.

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