Red blood cell and platelet transfusion

Published on 13/02/2015 by admin

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Last modified 13/02/2015

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Red blood cell and platelet transfusion

Brian S. Donahue, MD, PhD

Red blood cells

Collection, storage, and administration

Whole blood is collected as 450-mL aliquots to which 150 mL of an anticoagulant preservative containing citrate, phosphate, and dextrose is added. Red blood cells (RBCs) are then isolated by centrifugation and preserved with 100 mL of a solution consisting of adenine, dextrose, saline, and mannitol. Adenine and dextrose are substrates, respectively, for adenosine triphosphate formation and glycolysis. Adding a phosphate buffer prolongs the viability of the unit to 42 days; the U.S. Food and Drug Administration defines a viable unit as one from which 70% of transfused RBCs are present in the recipient’s circulation after 24 h.

During RBC storage, progressive intracellular acidosis, extracellular hyperkalemia, and decreased concentration of intracellular 2,3-diphosphoglycerate (2,3-DPG) levels are observed. Intracellular K⁺ levels rise in RBCs shortly after the RBCs are transfused, but intracellular 2,3-DPG levels remain below normal for at least 24 h.

Rare RBC phenotypes are frozen and are stored in glycerol to prevent lysis, better preserving RBC 2,3-DPG levels. Upon thawing, the RBCs are washed in saline to remove the glycerol, which also decreases the leukocyte count and the incidence of febrile reactions. Disadvantages include cost and a short (24-h) expiration time after thawing.

In the past, RBCs were infused through 40-μm to 60-μm line filters to remove microaggregates of RBCs, fibrin, and platelets because these components were thought to cause TRALI (transfusion-related acute lung injury). Filters are not routinely used now because we have a better understanding of the cause of TRALI and because of the use of leukocyte-reduced RBC products, which have fewer microaggregates.

Autologous blood transfusion and directed transfusion

Autologous donation before a scheduled surgical procedure and transfusion to the patient during surgery has been shown to decrease allogeneic exposure in routine cardiac and orthopedic surgery, but predonation does not always eliminate the need for allogeneic blood. Predonation of autologous blood is not necessarily less expensive than collection and transfusion of allogeneic blood, nor does it completely eliminate the risks of transfusion reactions.

It is controversial as to whether autotransfusion at the site of care, also known as cell salvage, reduces allogeneic transfusions or reduces costs. Typically, allogeneic transfusion requirements are reduced, but the cost of equipment and personnel far exceeds the cost of collecting and transfusing allogeneic RBCs.

Directed donation is the process in which a patient or patient’s family selects blood that comes from an identified donor, often a relative of the patient. Interestingly, directed donation may be associated with an increased infection risk because the donor who responds to a request to donate for a specific individual is no longer a volunteer; the individual may feel coerced into donating. Directed donation does not eliminate the risk of alloimmunization or immunomodulation, because this blood is allogeneic, and blood from related donors actually increases the risk of graft-versus-host disease.

Synthetic hemoglobins

The use of hemoglobin-based O₂ carriers (HBOCs) has been hampered by difficulty in defining meaningful clinical end points, safety parameters, and risk/benefit ratios. All HBOCs rapidly bind nitric oxide, resulting in increased vascular resistance as well as interference with other functions of nitric oxide. Increased levels of inflammatory cytokines, increased platelet reactivity, and decreased organ blood flow are thought to be responsible for the pancreatitis, esophageal spasm, myocardial injury, pulmonary hypertension, and acute lung injury associated with the use of HBOCs. Reactive O₂ species, resulting from free iron release, may mediate renal and central nervous system injury. A recent meta-analysis found a statistically significant increase in death and myocardial infarction associated with the use of HBOC.

Recombinant hemoglobin-based products have the advantages of O₂-binding characteristics more similar to those of native hemoglobin but are unstable in solution, scavenge nitric oxide, and also release free iron into the bloodstream.

Red blood cell transfusion

The sole reason to transfuse RBCs is to increase the content of O₂ in the blood, thereby increasing O₂ delivery (), which is a product of hemoglobin concentration, arterial O₂ saturation, and cardiac output (CO, which itself is a product of stroke volume and heart rate). A specific hematocrit value may sustain adequate if CO is adequate but may be insufficient when cardiac output is limited or when arterial saturation is impaired by the presence of a transpulmonary shunt. Therefore, despite the widely accepted hemoglobin trigger of 7 g/dL, the decision to transfuse should take into consideration the current hemoglobin level, estimated blood loss, cardiac reserve, vital signs, the likelihood of ongoing hemorrhage, and the risk of tissue ischemia. The dynamic nature of surgical hemorrhage requires a more aggressive approach to blood replacement in the operating room, compared with sites elsewhere in the hospital. In patients with chronic anemia, increased 2,3-DPG levels make O₂ transport (see Chapter 21) more efficient; in acute anemia, cardiovascular mechanisms of compensation (e.g., increased CO, heart rate, myocardial O₂ consumption) are more important.

Indications for transfusion of red blood cells

The binding of O₂ to hemoglobin is represented by a sinusoidal relationship known as the oxyhemoglobin dissociation curve, (see Chapter 21), which facilitates efficient O₂ loading of hemoglobin in the lungs (where PO₂ is high) and unloading of hemoglobin in the tissues (where PO₂ is low). Because the vast majority of O₂

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