Anemia is common among perioperative patients.
Hemoglobin (Hb) concentration or hematocrit (HCT) level is used to rapidly assess the severity of anemia in most clinical situations.
Treatment of anemia is based on the physiology and etiology of anemia. Restoration of normovolemia and cardiac output are necessary but insufficient aims in treating anemia.
Tachycardia and hypotension can be important clinical signs of hypovolemia and anemia, but compensatory increases in heart and cardiac output may be impeded by insufficient cardiac reserve or anesthetic-related sympathectomy.
Consideration of the magnitude of hemorrhage along with the physiologic signs and laboratory evidence for inadequate tissue oxygen delivery is mandatory before making the decision to transfuse red blood cells. The storage duration of red blood cells is not a clinical issue that should affect the decision to transfuse.
Evidence-based outcomes supporting a transfusion trigger level of Hb or HCT in all perioperative clinical settings do not exist; however, available information suggests that for most patients Hb levels as low as 7 to 8 g/dL may be as safe as higher levels in critically ill patients.
Goals of the perioperative management of patients with sickle cell disease focus on clinical measures to avoid precipitating a vaso-occlusive crisis and include avoiding hypoxia, hypothermia, and dehydration. In addition, use of standard or exchange red blood cell transfusions to reduce the HbS concentration to less than 30% to 40% can be helpful to reduce the incidence of a perioperative vaso-occlusive crisis.
Anemia is a common disorder of perioperative patients.1 The main consequence of significant anemia to the surgical patient is inadequate tissue oxygen delivery, which may lead to tissue hypoxia, biochemical imbalances, organ dysfunction, and ultimately organ damage.2 Mismanaging the anemic surgical patient can adversely affect perioperative outcomes.3 Understanding the laboratory techniques used to assess anemia as well as the physiology and appropriate treatment of it allows the anesthesiologist to optimize perioperative care.
ANEMIA DEFINED AND MEASURED
Anemia is defined as a reduction of the total red cell mass (RCM). Both hematocrit (HCT) level and hemoglobin (Hb) concentration measurements reflect the body’s RCM but do not define it. The HCT level, defined as the fractional volume of sampled blood that erythrocytes occupy, is an indirect measurement of the body’s RCM (Figure 15-1). The HCT is a simple, commonly used test to indirectly assess the severity of anemia as well as estimate whole-blood viscosity, oxygen-carrying capacity, and RCM. Hb is the predominant protein component of blood and serves as the major transporter of oxygen, carbon dioxide, and nitric oxide (NO). Hb concentration is a directly measured value that is commonly used to indirectly assess RCM.4,5
Graphic representation of a test tube containing a centrifuged sample of whole blood that illustrates its different components.