CHAPTER 41. Hematologic and Oncologic Emergencies
Daun A. Smith
The hematologic system (blood components and the organs that form them) plays a vital role in maintaining homeostasis of the whole body, affecting multiple cellular activities, including oxygen transport and delivery, hemostasis, and immune response. In turn, oncologic conditions and their treatments may have detrimental effects on the hematologic system. Patients with hematologic and oncologic disorders may present for emergency department (ED) care for an acute onset of a new condition, a sudden exacerbation of an existing disease, or with a therapy-related complication of their underlying disease. This chapter provides an overview of blood physiology, discusses general assessment of individuals with hematologic and oncologic emergencies, and describes specific hematologic and oncologic emergencies, including anemia, sickle cell disease (SCD), leukemia, thrombocytopenia, hemophilia, disseminated intravascular coagulation (DIC), fever and neutropenia, tumor lysis syndrome (TLS), syndrome of inappropriate antidiuretic hormone secretion (SIADH), superior vena cava syndrome, and spinal cord compression.
ANATOMY AND PHYSIOLOGY
Blood is a suspension of erythrocytes, leukocytes, platelets, and other particulate material in an aqueous colloid solution. This suspension provides a medium for exchange between fixed cells in the body and the external environment. Nutrients such as oxygen and glucose are carried to each cell, whereas cellular wastes such as carbon dioxide and nitrogen are removed. Other essential functions include regulation of pH, temperature, and cellular water; prevention of fluid loss through coagulation; and protection against toxins and foreign microbes.
Plasma
Plasma is a clear, yellow fluid containing blood cells, electrolytes, gases, amino acids, glucose, fats, and nonprotein nitrogens such as urea, creatine, and uric acid. 11 These and other substances may be dissolved in the plasma or may bind with various plasma proteins for transport. Albumin, the primary plasma protein, maintains blood volume by providing colloid osmotic pressure, regulates pH and electrolyte balance, and transports substances, including many drugs. Other major plasma proteins include globulins and fibrinogen.
Erythrocytes
Adults have approximately 5 million erythrocytes or red blood cells (RBCs) per microliter of blood. The number of RBCs is slightly higher in men. Natives living at altitudes greater than 14,000 feet may have as many as 7 million/μL. The primary role of RBCs is transport of oxygen and carbon dioxide. Erythrocytes have no nucleus and cannot reproduce. Their average life span is only 120 days, so new cells must be constantly produced. 5 The normal rate of hematopoiesis, or RBC production, is 2 million RBCs per second. Production occurs in the bone marrow but is regulated by the kidneys. When oxygen levels drop, the kidneys release erythropoietin, which stimulates RBC production by the bone marrow. Reticulocytes are erythrocyte precursors that mature within 24 to 48 hours of release into the circulation. Increased reticulocytes indicate increased bone marrow activity.
Erythrocytes are soft, pliable cells that change shape easily, thereby increasing the cell’s oxygen-carrying capability by increasing surface area. The outer stroma of the cell contains antigens A, B, and Rh factor, whereas the inner stroma contains hemoglobin, the primary vehicle for oxygen transport. Hemoglobin molecules are so small they would leak across the blood vessel’s endothelial membrane if left floating free in plasma. There are 300 different types of genetically determined hemoglobin (Hb). With the exception of normal fetal hemoglobin (Hb F), normal adult hemoglobin (Hb A), and sickle cell hemoglobin (Hb S), hemoglobins are identified by sequential letters of the alphabet. Abnormal hemoglobin molecules are produced in response to molecular abnormalities within blood. Tests such as hemoglobin electrophoresis are used to differentiate normal and abnormal hemoglobin. The most common hemoglobins are described in Table 41-1.
| Type | Significance |
|---|---|
| Hb A | Normal adult hemoglobin |
| Hb A 1c | Glycosylated hemoglobin |
| Hb A 2 | b-Thalassemia, makes up 2% of hemoglobin in normal adults |
| Hb F | Fetal hemoglobin, thalassemia after 6 months |
| Hb C | Hemolytic anemia |
| Hb S | Sickle cell anemia |
| Hb M | Methemoglobinemia |
Red cell indices provide information about the size and weight of average red cells and are used to differentiate acute and chronic anemias. Mean corpuscular volume, mean corpuscular hemoglobin content, and mean corpuscular hemoglobin concentration values provide information on how well red cells function. Table 41-2 includes normal values for these indices as well as the other components of a complete blood count (CBC).
| Component | Normal Values | Comments |
|---|---|---|
| White blood cell count | 5000 to 10,000/mm 3 | |
| Red blood cell count | Male: 4.6 to 6.2 million/mm 3 Female: 4.2 to 5.4 million/mm 3 | |
| Hemoglobin level | Male: 14 to 18 g/dL Female: 12 to 16 g/dL | A conjugated protein responsible for oxygen and carbon dioxide transport in the blood |
| Hematocrit | Male: 40% to 54% Female: 37% to 47% | Proportion of blood that consists of packed red blood cells; expressed as a percentage by volume |
| Mean corpuscular volume | 82 to 92 μm 3 | Average volume of red blood cells in a sample |
| Mean corpuscular hemoglobin content | 27 to 37 mcg | Average hemoglobin content of red blood cells in a sample |
| Mean corpuscular hemoglobin concentration | 32% to 36% | Average hemoglobin content in 100 mL of blood |
| Platelets | 150,000 to 400,000/μL | Platelets aid in hemostasis and maintenance of vascular integrity |
Erythrocyte sedimentation rate (ESR) measures the time required for erythrocytes in a whole blood specimen to settle to the bottom of a vertical tube. ESR is a product of red cell volume, surface area, density, aggregation, and surface charge. 2 Increased ESR occurs with widespread inflammation, red cell aggregation, pregnancy, and some malignancies, whereas polycythemia, SCD, and decreased plasma proteins are associated with decreased ESR.
Leukocytes
The body’s primary defense against infection are leukocytes, or white blood cells (WBCs). Six types of leukocytes normally occur in the blood: neutrophils, eosinophils, basophils, monocytes, lymphocytes, and, occasionally, plasma cells (Table 41-3). The WBC count quantifies the total number of leukocytes in the circulation, whereas the differential count quantifies the percentage of each type. This count is based on 100 WBCs; therefore a differential count should always total 100%. The normal ratio of RBCs to WBCs is 700:1.
| WBCs, White blood cells. | |||
| Name | Percent of Total WBCs | Function | Circulatory Life Span |
|---|---|---|---|
| Neutrophils | 62.0 | Attack and destroy bacteria and viruses through phagocytosis | 4-8 hr |
| Eosinophils | 2.3 | Attach to surface of parasites, then release substances that kill the organism; detoxify inflammatory substances that occur in allergic reactions | 4-8 hr |
| Basophils | 0.4 | Prevent coagulation and speed fat removal from blood after a fatty meal | 4-8 hr |
| Monocytes | 5.3 | Consume bacteria, viruses, necrotic tissue, and other foreign material | 10-20 hr |
| Lymphocytes | 30.0 | Provide immunity against acquired infections; basis for antibody formation | 2-3 hr |
| Plasma cells | — | Produce γ-globulin antibodies in response to specific antigens | Varies with need for antibodies |
Neutrophils
Neutrophils are the primary defense against bacterial infection. Bone marrow contains a reserve approximately 10 times greater than daily neutrophil production. About one half of all mature neutrophils adhere to vessel walls and are not measured by the traditional WBC count. The bone marrow reserve and the number of neutrophils on vessel walls allow for sudden increases in the circulating WBC count in response to stress or infection. After being released into the circulation, neutrophils live 4 to 8 hours. Immature neutrophils are called bands (also called stabs); mature neutrophils are called polymorphonuclear neutrophil leukocytes (PMNs or segs). An increased number of bands indicates acute infection.
Eosinophils
Eosinophils accumulate at the site of allergic reactions. Increases also occur during asthma attacks, drug reactions, and parasitic infections. Eosinophils decrease in response to stressors such as trauma, shock, or burns. Cell half-life is approximately 41⁄2 to 5 hours after release into the circulation.
Basophils
Basophils contain histamine, heparin, bradykinin, serotonin, and lysosomal enzymes. During allergic reactions, basophils rupture and release these substances into surrounding tissue. This accounts for many of the typical manifestations of an allergic reaction. The number of basophils also increases in chronic inflammation and during times of stress.
Monocytes
Monocytes remain in the circulation less than 20 hours before moving into surrounding tissue to become macrophages. A macrophage acts as a “garbage collector,” consuming bacteria and other debris in areas such as the spleen, lungs, and lymph nodes. Macrophages can live for months or even years. Monocytes are the body’s second line of defense and are usually associated with chronic infection.
Lymphocytes
Lymphocytes play a major role in immunity against acquired infections. Their life span may be weeks, months, or years, depending on the body’s needs. Two types of lymphocytes provide essential protection against bacteria and viruses: B-cell lymphocytes become antibodies and are responsible for humoral immunity; T-cell lymphocytes are responsible for cell-mediated immunity. At least three major types of T-cell lymphocytes have been identified: helper T cells, cytotoxic T cells, and suppressor T cells (Table 41-4). Lymphocyte increases are associated with viral infection.
| AIDS, Acquired immunodeficiency syndrome. | |
| Name | Function |
|---|---|
| Helper T cells | Regulate immune functions by forming lymphokines or protein mediators such as interleukin and interferon; inactivated or destroyed by AIDS virus |
| Cytotoxic T cells | Also called killer T cells; capable of direct attack on microorganisms and on the body’s own cells; role in destroying cancer cells and heart transplant cells |
| Suppressor T cells | Protect from attack by the person’s own immune system; suppress helper and cytotoxic T-cell functions |
Plasma Cells
Plasma cells produce γ-globulin (gamma globulin) antibodies in response to a specific antigen. Production continues until plasma cells die from exhaustion days or even weeks later.
Platelets
Platelets, or thrombocytes, provide hemostasis at the site of injury. These granular, disk-shaped fragments form when a parent cell breaks into thousands of cell fragments. The parent cell has no nucleus, so it cannot divide. Platelet life span is 9 to 12 days. Approximately one third of the body’s platelets are stored in the spleen as a reserve. Clotting factors V, VIII, and IX are found on the platelet’s surface. Platelets provide hemostasis by clumping at the site of injury to form a platelet plug and seal bleeding capillaries. Substances such as ethanol and salicylates interfere with platelet aggregation by impairing their ability to clump. Decreased platelet aggregation leads to increased bleeding.
Hemostasis
Hemostasis refers to processes that prevent blood loss after vascular damage (i.e., vascular spasm, platelet aggregation, coagulation, and fibrinolysis). When vessel injury occurs, the initial response is reflex vasoconstriction. Arterioles contract, decreasing blood flow by decreasing vessel size and pressing endothelial surfaces together. Next, serotonin and histamine release cause immediate vasoconstriction and decrease blood flow to the injured area. Vasoconstriction is followed by platelet aggregation at the injury site. This temporary measure prevents bleeding by sealing capillaries.
Platelet aggregation is followed by clot formation, which requires activation of the coagulation cascade. The coagulation cascade is a complex network of 12 different clotting factors (Table 41-5). A defect of any clotting factor or an injury that overwhelms the entire system can cause failure of the coagulation cascade and lead to life- or limb-threatening hemorrhage. The cascade may be activated by intrinsic factors, such as damage to a vessel wall, or extrinsic factors, such as damage to surrounding tissue. Regardless of the method of activation, the end result of the coagulation cascade is formation of a clot—a protein mesh made of fibrin strands.
| Factor | Synonyms | Description/Function |
|---|---|---|
| I | Fibrinogen | Fibrin precursor |
| II | Prothrombin | Thrombin precursor |
| III | Tissue thromboplastin | Activates prothrombin |
| IV | Calcium | Essential for prothrombin activation and fibrin formation |
| V | Labile factor, proaccelerin | Accelerates conversion of prothrombin to thrombin |
| VII | Prothrombin conversion accelerator | Accelerates conversion of prothrombin to thrombin |
| VIII | Antihemophilic factor A (AHF) | Associated with factors IX, XI, and XII; essential for thromboplastin formation |
| IX | Christmas factor, antihemophilic factor B | Associated with factors VIII, XI, and XII; essential for thromboplastin formation |
| X | Thrombokinase factor, Stuart-Prower factor | Triggers prothrombin conversion; requires vitamin K |
| XI | Plasma thromboplastin antecedent, antihemophilic factor C | Formation of thromboplastin in association with factors VIII, IX, and XII |
| XII | Contact factor, Hageman factor | Activates factor XI in thromboplastin formation |
| XIII | Fibrin-stabilizing factor | Strengthens fibrin clot |
The final step in hemostasis is clot resolution via the fibrinolytic system. Clot resolution maintains blood in a fluid state by removing clots that are no longer needed. Without this system, circulation to affected areas may be permanently lost because of obstructed blood vessels.
PATIENT ASSESSMENT
The type and severity of hematologic or oncologic emergency depend on the individual’s situation. Assessment is often complicated by vague complaints (e.g., fatigue, headache, fever, syncope, dyspnea on exertion). Therefore it is important to observe the patient for clues to hematologic/oncologic problems, such as pale, jaundiced, or cyanotic skin. Ecchymosis, purpura, petechia, and ulcerations may be present. Evaluate skin for temperature, diaphoresis, warmth, coolness, texture, and turgor. Observe for joint deformity, edema, redness, limitation of movement, and difficulty or inability to ambulate. Obtain vital signs, noting pulse pressure; orthostatic blood pressure and pulse rate may be measured.
It is important to note new onset of fever, weakness, cough, rash, dyspnea, and increased or unusual bruising. Does the patient complain of spontaneous bleeding, such as epistaxis or menorrhagia? Are bleeding gums, hematemesis, melena, dark urine, or hemoptysis present? These symptoms suggest a hematologic/oncologic problem and indicate the need for more detailed evaluation.
Identify existing hematologic/oncologic diseases and family history of such disorders. Obtain medication history, including use of prescription and over-the-counter medications. It is also important to query the patient about herbals that may affect clotting. For example, evening primrose, garlic, and skull cap increase clotting time, whereas ginseng, cinnamon, and parsley decrease clotting time. Document allergies, exposure to toxic substances, and dietary history.
Complete Blood Cell Count
The CBC is used to determine the patient’s hematologic status. Historically a CBC has been reported in two parts: the cell count and the differential count. The cell count is done by machine, with the differential count done manually. Electronic particle counters have made this process almost obsolete, providing an automated cell count and differential count; however, if the automated differential count reported is abnormal, a manual count is then done.
The cell count of the CBC provides normal values for leukocytes, erythrocytes, hemoglobin, and hematocrit (see Table 41-2). Normal CBC values vary with age and sex of the patient. The differential count provides information on red cell morphology and the percentage distribution of leukocytes.
SPECIFIC HEMATOLOGIC EMERGENCIES
Anemia
Anemia is a reduction in the total number of RBCs or a deficiency in the cells’ ability to transport oxygen. Anemia may be acute or chronic. Severity depends on the patient’s ability to compensate for RBC loss and provide essential oxygen to the cells. Oxygenation depends on blood flow and on hemoglobin’s oxygen-carrying capacity and affinity for oxygen. A defect in any of these factors affects cellular oxygen.
Acute Anemia
Acute anemia is usually the result of blood loss. Causes include trauma, gastrointestinal hemorrhage, vaginal bleeding, and uterine rupture. Response to blood loss depends on the patient’s age, physical condition, and rapidity of blood loss. Signs and symptoms include cool, clammy skin; tachycardia; decreased blood pressure; narrowing pulse pressure; tachypnea; postural hypotension; and decreased urinary output. Thirst and complaints of “feeling cold” are early clues to acute blood loss. A decreased level of consciousness may also occur.
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