Indications for transfusion: RBCs, platelets, plasma, and cryoprecipitate

Background

Blood transfusion practices should ultimately be driven by evidence-based decisions that integrate clinical observations, laboratory data, and a sound understanding of how patients can realistically benefit from blood products. In addition to acting as stewards of the local blood supply, the blood bank and transfusion medicine service are necessarily involved in ensuring that these concepts are understood and, consequently, that blood transfusions are appropriately conducted.

Content

The focus of this chapter is adult transfusion medicine, as pediatric transfusion medicine is beyond the scope of this material. Following a brief clinical practice foreword regarding informed consent, this chapter introduces the four commonly encountered blood component products in modern transfusion medicine: packed red blood cells, platelets, plasma, and cryoprecipitated antihemophilic factor. Highlights of evidence-based practices supported by current scientific medical literature at the time of writing are discussed, including clinical and laboratory parameter-related indications for transfusion, appropriate dosing, and expected responses. When applicable, special transfusion considerations for specific clinical situations are also described. In addition, there is a brief discussion of the clinical and logistical aspects of massive transfusion. The chapter concludes with a review of infrequently encountered blood products such as granulocytes and whole blood.

Introduction

Blood transfusion is one of the most common medical interventions in modern health care. While the practice at its inception was crudely conceived of and fraught with misguided assumptions, allogeneic blood transfusion (transfusing blood from one source, i.e., donor, to another, i.e., recipient) has since been recognized as having tremendous potential for reducing morbidity and mortality, especially in certain chronically and critically ill patient populations. Furthermore, transfusion practices have evolved considerably since then and continue to be refined with advances in medical and scientific evidence-based research. Although risk is certainly involved and several adverse effects of transfusions have been well described, understanding the contexts whereby transfusions may be beneficial has an integral place in the practice of medicine. This chapter will mainly focus on key aspects of red blood cell, platelet, plasma, and cryoprecipitate transfusion. It is important to note that this discussion will be limited to adults, as pediatric transfusion medicine is a complex, nuanced topic beyond the scope of this material.

Consent for blood products

As with all medical interventions or invasive procedures, transfusion requires prior informed consent from the recipient. Documentation of consent (paper or electronic forms) demonstrates that the prospective recipient has been informed of the relevant benefits and risks, as well as given the opportunity to have any questions addressed. Engagement and mutual understanding are critical for proper medical care while maintaining a patient’s rights and autonomy. Blood transfusions should never be forced upon an individual who may otherwise refuse such treatment.

If an individual is deemed to be incompetent and therefore unable to properly make informed health care decisions, a surrogate decision-making individual or party may be authorized to consent on the recipient’s behalf. Similarly, parents may have medical decision-making authority for their underage minor children. For critically ill patients who are unable to provide consent (i.e., unconscious trauma patients), hospitals may have emergency provisions that permit physician-prescribed transfusions. In any case, specific local laws and regulations may take precedence and dictate the terms and boundaries of medical decision-making, which includes transfusions. For ambiguous situations involving potential morbidity and mortality, prompt consultation with a hospital ethics board or local authorities is recommended.

Red blood cells

Packed red blood cells (pRBCs) were historically believed to provide a panacea-like spectrum of health benefits, including reinforced wound healing and nutritional supplementation. However, current evidence suggests that the sole purpose of pRBC transfusion should be to increase a patient’s oxygen-carrying capacity and consequently improve tissue oxygenation. The need to improve oxygenation may be encountered in a wide variety of clinical situations such as hypoproliferative marrow disorders, acute or chronic hemolysis (i.e., sickle cell disease [SCD]), and active blood loss due to bleeding. Decisions of whether to transfuse pRBCs may be complex and must account for multiple concurrent factors. Considerations may include a patient’s overall clinical status, the specific diagnosis leading to the oxygenation deficit, medical and surgical comorbidities, physiologic compensatory mechanisms that may prevent the need for transfusion, the availability of alternative therapies, and relevant laboratory values. Of the laboratory values used to guide pRBC transfusion, the hemoglobin (Hb) measurement component of routine complete blood counts (CBC) is typically the most relevant and informative.

Normal reference ranges for Hb are approximately 12 to 16 g/dL for females and 13.5 to 18 g/dL for males. In the absence of exacerbating factors, a certain degree of anemia, as evidenced by a lower Hb measurement, is physiologically tolerable and may be adequately compensated for through increased cardiac output and altered tissue metabolism. Prior studies in healthy volunteers demonstrated tolerance of short-term hemodilution-induced anemia down to 5.1 g/dL. The critical Hb levels tend to be higher for most patient populations that may require pRBC transfusion, although evidence-based thresholds for these values were not established until relatively recently. The Transfusion Requirements in Critical Care (TRICC) trial was the seminal investigation for modern evidence-based pRBC transfusion practices, demonstrating that restrictive thresholds to maintain Hb > 7 g/dL were not inferior to historically higher liberal thresholds to maintain Hb > 10 g/dL, and that restrictive thresholds were associated with improved survival in specific patient groups. Subsequent randomized control trials posed similar questions for various medical and surgical disciplines, including obstetrics, gastroenterology, cardiac surgery, and orthopedic surgery. With relatively few exceptions, these studies concluded that there was no apparent clinical benefit to a liberal transfusion strategy. Therefore the consensus of evidence at the time of this writing favors restrictive pRBC transfusion strategies in most situations with Hb thresholds of >7 to 8 g/dL, which is recommended by several published clinical practice guidelines. It should be noted, however, that there is insufficient high-quality evidence at this time for some critical situations where more liberal transfusion may be warranted, including acute coronary syndromes and acute brain injury. Furthermore, as Hb measurements may be of limited utility in actively bleeding patients, they should not be the sole determinant of transfusion decisions in such cases.

A single unit of pRBCs increases an adult patient’s post-transfusion Hb by approximately 1 g/dL and the hematocrit by approximately 3%, although the actual response may depend on certain factors such as blood volume. Patients with smaller or larger total blood volumes may experience a greater or lesser response, respectively, for the same amount transfused. Similarly, there may be suboptimal responses in patients with effectively larger-than-expected circulating volumes due to splenomegaly or treatment with continuous extracorporeal circuits (i.e., continuous venovenous hemodialysis (CVVHD) or extracorporeal membrane oxygenation [ECMO]). Finally, lesser responses would be expected in patients actively losing RBC mass, as observed with active bleeding and continuous destruction due to immunologic or mechanical etiologies. Therefore while the expectation of 1 g/dL per pRBC unit may be a reasonable starting point, patients may require fewer or more transfusions than initially predicted. Furthermore, with the exceptions of active bleeding and hemodynamic instability, pRBCs should be prescribed and transfused one unit at a time, and the decision to transfuse further should be supported by post-transfusion clinical and laboratory data.