Emergency physicians encounter patients with anemia on a daily basis. Some of these patients have an acute anemia as a result of blood loss from trauma, gastrointestinal bleeding, or other acute hemorrhage. Many emergency department (ED) patients have chronic anemia that may or may not be related to the complaint that brought them to the ED.
Anemia is defined as a reduced concentration of red blood cells (RBCs). In healthy persons, normal erythropoiesis (RBC production) ensures that the number of RBCs present is adequate to meet the body's demand for oxygen and that RBC destruction equals production in order to maintain a stable RBC concentration. Anemia results when RBC production cannot keep up with RBC loss resulting from blood loss, hemolysis, or normal RBC senescence. Quantification of the RBC concentration is reflected in the RBC count per pL, hemoglobin concentration, or hematocrit (percentage of RBC mass to blood volume). Normal RBC values for adults are slightly different for males and females (Iabje...21,0:1.). Based on pathophysiologic mechanisms, there are three categories of anemia (T§bJie.21i0i-i2i).
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TABLE 210-1 Normal RBC Values for Adults
TABLE 210-2 Pathophysiologic Classification of Anemia
Regardless of the cause of anemia, the clinical manifestations are the same. The severity of symptoms and signs related to anemia depend on several factors: the rate of development of anemia, the extent of anemia that is present, and the adequacy of cardiopulmonary adaptation. The symptoms of anemia are reflective of the cardiovascular compensation that occurs in an attempt to maintain tissue oxygenation in the face of decreased oxygen-carrying capacity in the blood. These compensatory mechanisms are increased cardiac output and the centralization of blood flow to provide oxygen to the most sensitive tissues. Symptoms such as palpitations, dizziness, feeling of postural faintness, exertional intolerance, and tinnitus are reflective of increased cardiac output. Clinical signs of increased cardiac output are tachycardia, a hyperdynamic precordium, and systolic murmurs. Pallor of the conjunctivae, skin, and nail beds reflects centralization of blood flow. Tachypnea at rest and hypotension are late signs and are ominous. Decreased tissue perfusion occurs long before hypotension. Coronary artery blood flow usually is not limited until the hemoglobin is 50 percent or less of normal, although it can occur at lesser levels of anemia in patients with restriction of coronary blood flow. In an otherwise healthy patient, the symptoms and signs of anemia resulting from increased cardiac output may not occur at rest until the hemoglobin concentration is below about 7g/dL, although tissue perfusion may be impaired. The emergency physician must keep in mind that the hemodynamic response to anemia may be altered by the use of ethanol, prescription drugs, or recreational drugs.
The diagnosis of anemia is established by the finding of a decreased RBC count, hemoglobin, and hematocrit on the routine complete blood count (CBC). Other than in patients who are acutely hemorrhaging, it is often not essential that a specific cause of anemia be established in the ED. Further workup can be initiated in the ED and should be started before the transfusion of packed red blood cells (PRBCs).
The basic evaluation of a patient newly diagnosed with anemia includes the following: Hemocult (Smith-Kline Diagnostics, Inc.) examination if not already performed, review of the RBC indices provided with the CBC, reticulocyte count, and review of the peripheral blood smear ( TabJe,..210.:.3.). The mean cellular volume (MCV) is the most useful guide to the possible etiology of an anemia. The reticulocyte count reflects activity in the bone marrow and, along with the MCV, can help classify an anemia quickly and provides a differential diagnosis and further course of action (Iabje...21,0:4.).
TABLE 210-3 Initial Laboratory Evaluation of Anemia
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