Anemia is defined as a qualitative or quantitative deficiency of hemoglobin (Hb) or red blood cells (RBCs) in circulation resulting in a reduced oxygen-carrying capacity for blood to organs and tissues (Table 94-1).
TABLE 94-1Causes of Anemia ||Download (.pdf) TABLE 94-1 Causes of Anemia
Bleeding: acute or chronic
Decreased production of RBC
Increased destruction of RBC
Abnormality of RBC (genetic or inherited defect in metabolism or structure of RBC)
Anemia as a result of a reduction in RBC production is categorized as either microcytic, macrocytic, or normocytic. Chronic diseases, such as chronic kidney disease, cancer, ulcerative colitis, and rheumatoid arthritis, or disorders of bone marrow, such as lymphoma, leukemia, myelodysplasia, multiple myeloma, and aplastic anemic are often etiologies. Increased destruction of RBCs before the end of the normal lifespan occurs with hemolytic anemias, immune deficiencies, and other diseases. Genetic or inherited defects in RBC metabolism or hemoglobin structure cause anemias such as thalassemia, sickle cell anemia, and hereditary methemoglobinemia.
Perioperatively, management of anemia requires optimization of oxygen delivery to tissues according to physiological principles:
Delivery of oxygen to tissues (DO2) is dependent upon the following factors:
Oxygen consumption (VO2), a measure of adequacy of tissue oxygenation, is determined by the product of cardiac output (CO) and arteriovenous O2 content difference (CaO2 – CvO2):
O2 extraction = 250/1000 mL O2 = 25%.
PERIOPERATIVE EVALUATION AND PLANNING
Evaluation for anemia begins with a thorough history, physical examination, and laboratories. A history suggestive of poor tissue perfusion often includes easy fatigability, breathlessness, dyspnea, palpitations, or angina. Signs of high cardiac output include tachycardia, wide pulse pressure, and systolic ejection murmur. Laboratory tests, such as complete blood count (CBC), reticulocyte count, peripheral smear, and blood typing, may be indicated, along with cardiovascular evaluation via functional imaging for ischemia. No standardized minimum hematocrit reliably predicts outcome, but a hematocrit value along with estimation of compensatory mechanisms and physical status can aid in optimizing oxygen delivery to tissues.
Although hemoglobin and hematocrit measurements are low on CBC in all anemias, the reticulocyte count varies according to the cause of the anemia. A reticulocyte count above normal suggests early release of immature RBCs into circulation, replacing losses from rapid destruction, as in hemolytic anemias, bleeding, erythroblastosis fetalis, and kidney disease with increased erythropoietin production. Conversely, a low reticulocyte count with anemia suggests decreased production, or release of RBCs, as may be found in bone marrow failure from drug toxicity, tumor, or infection; folate, iron, or vitamin B12 deficiency; lead poisoning, inflammation, or kidney disease ...