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- Define anemia.
- Describe the anatomy and physiology of the blood and red blood cell as it relates to anemia.
- Discuss the pathophysiology of anemia.
- Describe the characteristic signs and symptoms of anemia.
- Discuss the management of anemia.
- Discuss the epidemiology, pathophysiology, signs and symptoms, and management of sickle cell crisis.
Anemia is the most common blood disorder worldwide, affecting an estimated one-third of the population. The most common causes of anemia worldwide include iron and folate deficiencies, thalassemia and hemoglobinopathies (genetic disorders affecting hemoglobin). In the U.S., the most common causes are iron deficiency, thalassemia and anemia of chronic disease, such as liver and kidney disease.1 This article will explore the anatomy and physiology of the blood, pathophysiology of anemia, clinical manifestations of the disease and prehospital management of complications associated with the disease. In addition, we will explore one of the more common etiologies of anemia—sickle cell disease—that EMS encounters in the prehospital environment.
Anatomy and Physiology
Anemia exists when there is a decrease in the number of red blood cells (RBCs) or a decrease in the normal quantity of hemoglobin (Hb) in the blood. Any condition that reduces the oxygen-binding ability of Hb will also result in anemia. Anemia will lead to hypoxia secondary to the blood’s reduced ability to transport oxygen. To better understand the pathophysiology of anemia and the body’s response to the disease, it is necessary to understand the RBC and normal homeostatic mechanisms of the blood.
Blood is the fluid component of the cardiovascular system, which also consists of a pump (heart) and a container (blood vessels). Blood is actually considered a connective tissue with many functions, including stabilization of body temperature, clotting to prevent fluid loss at injury sites, defense against pathogens and toxins and maintenance of proper ion concentration (i.e., K+ and Ca++) and pH of the interstitial fluids. In addition, blood is responsible for transporting oxygen, nutrients and hormones to the peripheral tissues and carrying away the waste products of metabolism for excretion from the body.
Blood is made up of a fluid portion (plasma) and formed elements (cells, cell fragments and proteins) suspended in the plasma. The formed elements consist of red blood cells (RBCs), white blood cells (WBCs) and platelets. Platelets are an important part of the clotting process, and WBCs, or leukocytes, play a role in the body’s immune system. RBCs, or erythrocytes, are the most abundant cells in the blood and play an essential role in the transport of oxygen in the blood.
The plasma and formed elements together constitute whole blood, which can be separated, or fractionated, in a laboratory. A sample of whole blood normally consists of about 46%–63% plasma and 37%–54% formed elements. Platelets and WBCs each constitute about 0.1% of the total amount of formed elements, and RBCs account for about 99.9% of the total.2 Hematocrit is the percentage of total blood volume contributed by the formed elements. As 99.9% of the formed elements are RBCs, the hematocrit is commonly thought of as the percentage of RBCs in the blood. Normal hematocrit in an adult male is about 46%; the average hematocrit in adult females is about 42%. This difference is due to the fact that male sex hormones (androgens) stimulate production of RBCs, while female sex hormones (estrogens) do not.