Packed RBCs consist of refrigerated stored blood with about three fourths of the plasma removed. Packed cells help avoid the problem of overloading the patient’s blood volume and instigating pulmonary edema. This is especially useful in patients with anemias due to destruction or poor production of RBCs, when the plasma volume does not need replacement. In fact, when anemia is due to pure RBC deficiency, plasma volume becomes greater than usual, because extracellular fluid tends to replace the missing RBC volume to maintain total blood volume. Packed cells are sometimes used when the donor RBCs type satisfactorily but antibodies are present in donor plasma. Packed cell administration also helps diminish some of the other problems of stored blood, such as elevated plasma potassium or ammonium levels. Packed RBCs retain about 20%-25% of the plasma and most of the white blood cells (WBCs) and platelets. Preserved in CPDA-1, on day 1 plasma potassium averages about 5.1 mEq/L (mmolL) and on day 35 averages about 78.5 mEq/L (mmolL), due in part to the small amount of plasma remaining with the RBC. Plasma Hb on day 1 averages about 78 mg/L and on day 35 averages about 658 mg/L (also partially due to small plasma volume).
Category: Blood Transfusions
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Blood Donation
The standard time interval between blood donations is 8 weeks. However, most healthy persons can donate one unit every 5-7 days for limited periods of time (1-2 months), assisted by oral iron supplements.
Since the use of blood transfusion has increased dramatically over the years, maintenance of adequate donor sources has been a constant problem. In Russia, cadaver blood apparently has been used to a limited extent. If collected less than 6 hours postmortem, it does not differ significantly from stored (bank) blood, except that anticoagulation is not required. A few experimental studies have been done in the United States, with favorable results.
Autotransfusion (autologous transfusion) is the collection and subsequent transfusion of the patient’s own blood. This avoids all problems of transfusion reaction or transfusion-related infection, and in addition is useful in patients whose religious beliefs preclude receiving blood from others. Depending on the circumstances, one or more units may be withdrawn at appropriate intervals (every 5-7 days) before elective surgery and either preserved as whole blood, as packed RBCs, or in long-term storage as frozen RBC, depending on the time interval between processing and transfusion. Another type of autotransfusion consists of equipment that enables operating room personnel to reclaim suctioned blood from operative sites and recycle it back into the patient as a transfusion.
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Whole Blood
Useful life. Whole blood is collected in a citrate anticoagulant-preservative solution. The original acid-citrate-dextrose (ACD) formulation was replaced by citrate-phosphate-dextrose (CPD), which has a storage limit of 21 days when refrigerated between 1°C and 6°C. Addition of adenine (CPDA-1) increased the shelf-life to 35 days. More recently, other nutrient-additive solutions (e.g., AS-1, Adsol) have extended storage capability to 42 days, at which time there is at least 70% red blood cell (RBC) viability 24 hours after transfusion. AS-1 is currently approved only for packed RBCs, not for whole blood. If preserved in CPDA-1, plasma potassium on day 1 is about 4.2 mEq/L (4.2 mmo1/L) and on day 35 is 27.3 mEq/L (27.3 mmol/L). Plasma hemoglobin (Hb) on day 1 averages about 82 mg/L and on day 35 averages about 461 mg/L. It takes about 24 hours for RBCs stored more than two thirds of maximum storage life to regain all of their normal hemoglobin function (this is also true for packed RBC units).
Platelets in whole blood. Platelets devitalize rapidly on storage in refrigerated whole blood (discussed in greater detail in Chapter 11). Platelets in fresh whole blood are about 60% effective at 24 hours and almost completely ineffective after 48 hours. Ordinary stored whole blood or packed RBCs, therefore, essentially have no functioning platelets even though the platelet count may be normal. This may produce difficulty in massive transfusions using stored whole blood or packed RBCs, although there is usually no problem when administration takes place over longer periods of time.
Transfusion indications. The traditional cutoff point for transfusion, especially when a patient is undergoing surgical procedures, is a Hb level of 10.0 gm/100 ml (100 g/L) or a hematocrit of 33%. Based in part on experience from open-heart surgery, use of this level has recently been challenged, and a Hb level of 9.0 gm/100 ml (or hematocrit of 25%-30%) is being advocated to replace the old standard. Even more recently, based in part on surgical experience with Jehovah’s Witnesses who refuse transfusion on religious grounds, it was found that transfusion could be avoided in most cases without undue risk with Hb as low as 7.0 gm/100 ml or even lower. This led to a 1988 National Institutes of Health (NIH) Consensus Conference endorsement of Hb 7.0 gm as a suggested cutoff point. This in turn led to a study commissioned and adapted into guidelines by the American Academy of Physicians in 1992 that recommended “avoid an empiric automatic transfusion threshold.” The most important trigger was to be symptoms related to the need for blood that could not be corrected by other means.
Whole blood is used for restoration of blood volume due to acute simultaneous loss of both plasma and RBCs. This is most frequently seen in acute hemorrhage, both external and internal. Stored blood is adequate for this purpose in most cases. Actually, packed RBCs are being used in many of these patients.
Transfusion speed. Under usual circumstances, the American Association of Blood Banks (AABB) recommends that one unit of whole blood or packed cells be administered in 1.5 hours. The infusion rate should be slower during the first 15 minutes (100 ml/hour), during which time the patient is observed for signs and symptoms of transfusion reaction. One unit of whole blood or packed cells raises the Hb level approximately 1 gm/100 ml and hematocrit approximately 3 percentage units. (Various factors can modify these average values.) RBCs will hemolyze when directly mixed with 5% dextrose in either water or 0.25% saline or with Ringer’s solution.
Fresh whole blood is used within 2 days and preferably 1 day after collection. Platelets are still viable, and the labile coagulation factor VIII (antihemophilic globulin) and factor V still retain nearly normal activity. Most other disadvantages of prolonged storage are obviated. Obviously, donor and administrative problems greatly limit use and availability of fresh blood. Also, there is usually not sufficient time to perform screening tests for hepatitis B and C or human immunodeficiency virus-I (HIV-I) and II. Current official policy of the AABB states that there are no valid indications for specifically ordering fresh whole blood. Specific blood components would be more effective. In a few circumstances when whole blood is useful but long-term storage is undesirable (e.g., infant exchange transfusion), blood less than 4-5 days old is acceptable.