Fluid, Electrolyte, and Acid-Base Balance PDF

Unit VI Meeting Basic Physiologic Needs chapter 25 Fluid, Electrolyte, and Acid-Base Balance http://evolve.elsevier.com/Williams/fundamental Objectives Upon completing this chapter, you should be able to do the following: Theory 1. Discuss the various functions water performs in the body. 2. Lis...

Unit VI Meeting Basic Physiologic Needs chapter 25 Fluid, Electrolyte, and Acid-Base Balance http://evolve.elsevier.com/Williams/fundamental Objectives Upon completing this chapter, you should be able to do the following: Theory 1. Discuss the various functions water performs in the body. 2. List the major electrolytes and the function of each. 3. Describe three ways in which body luids are continuously being distributed among the luid compartments. 4. Identify the signs and symptoms of the common luid and electrolyte imbalances. 5. State the main signs and symptoms of acid-base imbalances. Clinical Practice 1. Assess an assigned patient for signs of luid and electrolyte imbalance. 2. From patient laboratory results, identify electrolyte values that are abnormal. 3. Implement patient education for someone with hypokalemia. 4. Develop a plan of care for a patient who has a luid and electrolyte imbalance. 5. Identify patients who might be at risk for an acid-base imbalance. Skills Skill 25.1 Measuring Intake and Output 455 Key Terms acidosis (ă-sĭ-DŌ-sĭs, p. 445) active transport (p. 440) alkalosis (ăl-kă-LŌ-sĭs, p. 446) ascites (ă-SĪ-tēz, p. 442) dehydration (dē-hī-DRĀ-shŭn, p. 438) diffusion (dĭ-FŪ-zhŭn, p. 439) edema (ĕ-DĒ-mă, p. 442) electrolytes (ĕ-LĔK-trō-līts, p. 438) extracellular (ĕks-tră-SĔL-ū-lăr, p. 438) filtration (fĭl-TRĀ-shŭn, p. 440) hydrostatic pressure (hī-drō-STĂ-tĭk PRĔ-shŭr, p. 440) hypercalcemia (hī-pĕr-kăl-SĒ-mē-ă, p. 446) hyperchloremia (hī-pĕr-klōr-Ē-mē-ă, p. 446) hyperkalemia (hī-pĕr-kă-LĒ-mē-ă, p. 446) hypermagnesemia (hī-pĕr-măg-nĕ-SĒ-mē-ă, p. 446) hypernatremia (hī-pĕr-nā-TRĒ-mē-ă, p. 445) hyperphosphatemia (hī-pĕr-fŏs-fă-TĒ-mē-ă, p. 447) hypertonic (hī-pĕr-TŎN-ĭk, p. 439) Concepts Covered in This Chapter • • • • • Acid-base balance Elimination Fluid and electrolyte balance Metabolism Perfusion 436 hyperventilation (p. 449) hypervolemia (hī-pĕr-vō-LĒ-mē-ă, p. 442) hypocalcemia (hī-pō-kăl-SĒ-mē-ă, p. 446) hypochloremia (hī-pō-klōr-Ē-mē-ă, p. 446) hypokalemia (hī-pō-kă-LĒ-mē-ă, p. 445) hypomagnesemia (hī-pō-măg-nĕ-SĒ-mē-ă, p. 446) hyponatremia (hī-pō-nā-TRĒ-mē-ă, p. 442) hypophosphatemia (hī-pō-fŏs-fă-TĒ-mē-ă, p. 446) hypotonic (hī-pō-TŎN-ĭk, p. 439) hypovolemia (hī-pō-vō-LĒ-mē-ă, p. 438) interstitial (ĭn-tĕr-STĬSH-ăl, p. 438) intracellular (ĭn-tră-SĔL-ū-lăr, p. 438) intravascular (ĭn-tră-văs-kū-lăr, p. 438) isotonic (ī-sō-TŎN-ĭk, p. 439) osmosis (ŏz-MŌ-sĭs, p. 439) tetany (TĔT-ă-nē, p. 450) transcellular (trănz-SĔ-lū-lăr, p. 438) turgor (p. 441) COMPOSITION OF BODY FLUIDS WATER The two largest constituents of the body luids are water and electrolytes. Water is present in greater proportion than electrolytes are. Water serves many functions, but the four main functions of water in the body are: (1) to act as a vehicle for the transportation of substances to and from the cells; (2) to aid heat regulation Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 by providing perspiration, which evaporates; (3) to assist in maintenance of hydrogen (H+) balance in the body; and (4) to serve as a medium for the enzymatic action of digestion. More than half of the body’s weight is water. The amount varies by age, sex, and health status. The adult male body contains about 60% water; the adult female body, because of more fat tissue, contains about 50% water. The greater the amount of fat the body contains, the less the percentage of water it has because fat contains less water than other tissue does. The infant and the older adult are affected more quickly and seriously by minor changes in their luid balance and can become rapidly dehydrated. The infant, because of its large body surface area compared with body weight, loses more luid through the skin than the adult does. The infant’s kidneys are not as eficient as the adult’s are, and less luid is reabsorbed. The older adult has an age-related decline in total body water, diminished thirst sensation, a decrease in urine concentrating ability of the kidney, and a decrease in the effectiveness of antidiuretic hormone (ADH). These factors cause dehydration to occur more quickly than in the younger adult. Dehydration may cause hypovolemia (Concept Map 25.1). If an excess of luid volume is present in the body, hypervolemia occurs. Water is critical to maintaining homeostasis because water is the medium in which most metabolic and chemical reactions in the body take place. Without suficient water, cells cannot function, and death results. Water is the avenue for transportation within the body. It carries nutrients to the cells and transports waste for excretion. Body water continuously moves in and out of the blood, through the lymph vessels, between the cells, and in and out of the cells. Table 25.1 shows sources of water and avenues of water loss. Think Critically How might NPO (nothing by mouth) status before tests or surgery affect a person’s body? REGULATION OF BODY FLUID VOLUME ADH release (Inhibited) HYPERVOLEMIA Excess fluid volume HYPOVOLEMIA Decreased fluid volume Inhibits Stimulates Aldosterone release (Inhibited) Thirst (Inhibited) 437 Thirst (Stimulated) ADH release (Stimulated) Aldosterone release (Stimulated) Contribute to Contribute to INCREASED URINATION of dilute urine DECREASED URINATION of concentrated urine NORMAL FLUID VOLUME RESTORED CONCEPT MAP 25.1 Regulation of body luid volume. ADH, Antidiuretic hormone. (Redrawn from Black, J. M., & Hawks, J. H. [2005]. Medical-Surgical Nursing: Clinical Management for Positive Outcomes [7th ed.]. Philadelphia, PA: Saunders.) (From White, B. [1994]. Maintaining luid and electrolyte balance. In V. B. Bolander [Ed.], Sorensen and Luckmann’s Basic Nursing: A Physiologic Approach [3rd ed.]. Philadelphia, PA: Saunders.) 438 UNIT VI Meeting Basic Physiologic Needs ELECTROLYTES Electrolytes are minerals or salts that are dissolved in body luid. They are measured in milliequivalents per liter (mEq/L), which is a unit of measure of the chemical activity that occurs when the electrolyte reacts with hydrogen. When in solution, they break up into particles known as ions that have a tiny electrical charge. The ions develop a positive electrical charge and then they are known as cations, or they develop a negative electrical charge and are anions. For each positively charged cation in a luid compartment, there must be a negatively charged anion so that balance is maintained. As luids move from compartment to compartment, the body works to maintain homeostasis in each compartment by balancing the anions and cations so that there is electrical neutrality. Electrolytes move within the body freely, but each has a primary location. Because disturbances in homeostasis upset the normal balance of electrolytes, the location and function of each electrolyte become important in understanding what is occurring in the body. The major source of electrolytes is from diet. Table 25.2 presents the electrolytes, their normal ranges, and their functions. Table 25.1 Sources of Water and Avenues of Loss SOURCES Oral luids 24 H 1500 mL AVENUES OF LOSS Urine 24 H 1500 mL Food 800 mL Perspiration 400 mL Metabolism 200 mL Feces 200 mL — — Expired air 400 mL Total 2500 mL — 2500 mL Table 25.2 NONELECTROLYTES The intermediate products of metabolism—amino acids (proteins), glucose, and fatty acids—are nonelectrolytes. They remain bound together when dissolved in body luid. In the healthy individual who is eating normally, the nonelectrolytes circulating in the body luid remain stable. BLOOD The body has 4 to 6 L of circulating blood volume, depending on body size and sex. Erythrocytes (red cells), leukocytes (white cells), and platelets (thrombocytes) are the blood cells that are carried in the plasma. Any condition that alters body luid volume also alters the plasma volume of the blood and can affect blood pressure and circulation. The plasma proteins and colloids contribute to plasma colloid osmotic pressure, which helps keep luid in the vascular compartment. DISTRIBUTION OF BODY FLUIDS Body luids are either intracellular (within the cell) or extracellular (outside of the cell). Extracellular luid (ECF) is of three types: intravascular, interstitial, and transcellular. Table 25.3 describes these luids. When luid shifts from the plasma in the vascular space out to the interstitial space, blood volume drops and dehydration (removal of water from a tissue) and hypovolemia (decreased volume of plasma) may occur. MOVEMENT OF FLUID AND ELECTROLYTES The amount of luid leaving the body should be balanced by water entering it. Water is taken in through the ingestion of luids and food and is produced by cell metabolism. The thirst mechanism located in the hypothalamus helps control luid balance in the body. The Major Electrolytes: Normal Range and Function ELECTROLYTE Sodium (Na+) NORMAL RANGE 135-145 mEq/L FUNCTION Major cation of the extracellular luid. Major role in regulation of water balance. Regulates extracellular luid volume through osmotic pressure. Water follows sodium concentration in the body. Essential to the transmission of nerve impulses and helps maintain neuromuscular irritability. Important in controlling contractility of the heart. Helps maintain acid-base balance. Aids in maintenance of electroneutrality. Potassium (K+) 3.5-5.0 mEq/L Major intracellular cation. Important in nerve transmission and muscle contraction. Helps maintain normal heart rhythm. Helps maintain plasma acid-base balance. Calcium (Ca2+) 8.4-10.6 mg/dL Involved in formation of bone and teeth. Necessary for blood coagulation. Essential for normal nerve and muscle activity. Magnesium (Mg2+) 1.3-2.1 mg/dL Necessary for building bones and teeth. Necessary for nerve transmission and is involved in muscle contraction. Plays an important role in many metabolic reactions, where it acts as a cofactor to cellular enzymes. Phosphate (PO43−) 2.7-4.5 mg/dL Necessary for formation of ATP. Cofactor in carbohydrate, protein, and lipid metabolism. Activates B-complex vitamins. Chloride (Cl−) 96-106 mEq/L Helps maintain acid-base balance. Important in formation of hydrochloric acid for secretion to the stomach. Aids in maintaining plasma electroneutrality. Bicarbonate (HCO3−) 22-26 mEq/L A buffer that neutralizes excess acids in the body. Helps regulate acid-base balance. ATP, Adenosine triphosphate. Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 It monitors luid volume and concentration. Hypothalamic receptors sense when luid is more concentrated and stimulate nerve impulses that are interpreted in the brain as thirst, which motivates the person to drink. Intake of suficient water lowers the concentration and the receptors are no longer stimulated. Fluid is lost in the urine and feces and through insensible (invisible) losses via exhaled air and through the skin as perspiration. The kidney is the main organ through which luid excretion is achieved. Urine output is affected by several hormones, particularly ADH, aldosterone, and atrial natriuretic peptide (ANP). ADH is secreted by the posterior pituitary. More ADH is released when the blood becomes more concentrated; circulating blood volume is decreased; or the person is experiencing pain, nausea, or stress. With increased ADH, the renal tubules reabsorb more water, and urine output decreases. Aldosterone is released by the adrenal cortex when ECF volume is low or when sodium concentration is decreased, causing reabsorption of sodium from kidney tubules. This creates an osmotic gradient by which more water is retained. The release of aldosterone is stimulated by the renin-angiotensinaldosterone system. ANP acts to protect the body from luid overload, and it is released from sites in the myocardium and the brain. Blood volume and pressure also affect the glomerular iltration rate and urine output. Water and the substances suspended or dissolved in it must move from compartment to compartment, so that they are normally distributed within the body. They must pass through the semipermeable membranes of the body’s cells to do this. The heart circulates blood throughout the body. As the blood lows Table 25.3 Body Fluid Distribution BODY FLUID Extracellular fluid DISTRIBUTION Approximately ⅓ of total body water. Transports water, nutrients, oxygen, and waste, to and from the cells. Regulated by renal, metabolic, and neurologic factors. High in sodium (Na+) content. Intravascular fluid Fluid within the blood vessels. Consists of plasma and fluid within blood cells. Contains large amounts of protein and electrolytes. Interstitial fluid Fluid in the spaces surrounding the cells. High in sodium (Na+) content. Transcellular fluid Includes aqueous humor; saliva; cerebrospinal, pleural, peritoneal, synovial, and pericardial fluids; gastrointestinal secretions; and fluid in the urinary system and lymphatics. Intracellular fluid About ⅔ of total body fluid. Fluid contained within the cell walls. Most cell walls are permeable to water. High in potassium (K+) content. 439 through the capillaries, luid and solutes can move into the interstitial spaces, where substances in every cell of the body can be exchanged. Several processes move luids, electrolytes, nutrients, and waste products back and forth across the cell membranes. Passive Transport Diffusion. Diffusion is the process by which substances freely move back and forth across the membrane until they are evenly distributed throughout the available space. Substances move from a high to a low concentration until the concentration on both sides of the membrane is equal. This is called movement down a concentration gradient. Glucose, oxygen, carbon dioxide, water, and other small ions and molecules move by diffusion. It is a process of equalization. Diffusion may occur by movement along an electrical gradient as well. The attraction between particles of opposite charge and the repellent action between particles of like charge comprise an electrical gradient. Many intracellular proteins have a negative charge that tends to attract the positively charged sodium and potassium ions from the ECF. Osmosis. Osmosis refers to the movement of a pure solvent (liquid) across a membrane. In the body, water diffuses by osmosis. When there are differences in concentration of luids in the various compartments, water (and other luids) move from the area of less solute concentration to the area of greater concentration until the solutions in the compartments are of equal concentration. The process takes place via a semipermeable membrane—a membrane that allows some substances to pass through but prevents the passage of other substances. Fluid moves between the interstitial and intracellular and the interstitial and intravascular compartments by osmosis. Cell wall membranes are semipermeable, as are the walls of blood vessels. When living cells are surrounded by a solution that has the same concentration of particles, the water concentration of the intracellular luids (ICF) and ECF will be equal. Such a solution is termed isotonic (of equal solute concentration). If cells are surrounded by a solution that has a greater concentration of solute than the cells have, the water in the cells moves to the more concentrated solution, and the cells dehydrate and shrink. The solution is hypertonic (of greater concentration) in relation to the cells. If the cells are surrounded by a solution that has less solute than the cells have, the solution is hypotonic (of less concentration) in relation to the cells. The particles within the cells exert an osmotic pressure, drawing water inward through the semipermeable membrane. The cells swell from the extra luid (overhydrate). These concepts are important to the administration of intravenous (IV) luids (see Chapter 36). Solutions are classiied as isotonic, hypertonic, or hypotonic according to their concentration of electrolytes and other solutes. Therefore, by osmosis, water 440 UNIT VI Meeting Basic Physiologic Needs Membrane A Before diffusion Semipermeable membrane B After diffusion Before osmosis After osmosis FIGURE 25.1 (A and B) Diffusion and osmosis. (From Lewis, S. L., Heitkemper, M. M., Dirksen, S. R., Bucher, L., & Camera, I. [2011]. Medical-Surgical Nursing: Assessment and Management of Clinical Problems [8th ed.]. St. Louis, MO: Mosby.) Diffusion Osmosis Greater concentration Active transport Intracellular ATP fluid Na+ Na+ ATP Na+ Greater concentration Na+ Na+ Molecules Water molecules K+ Lesser concentration A Lesser concentration C B Semipermeable cell membrane Semipermeable cell membrane K+ K+ K+ K+ K+ K+ Capillaries Hydrostatic pressure Na+ ATP Na+ Na+ ATP K+ K+ Filtration ATP K+ K+ Colloid osmotic pressure K+ ATP Extracellular fluid Semipermeable cell membrane Interstitial compartment D Semipermeable capillary membrane FIGURE 25.2 Movement of water and electrolytes by (A) diffusion; (B) osmosis; (C) active transport; and (D) iltration. (From Leahy, J. M., & Kizilary, P. E. [1998]. Foundations of Nursing Practice: A Nursing Process Approach. Philadelphia, PA: Saunders.) passes rather freely across cell membranes. The process of osmosis is essential to the life of the cells and to the balance of water and electrolytes in the body. Osmotic pressure within vessels helps to keep luid from leaking out into the interstitial spaces (Fig. 25.1). Filtration. Filtration is the movement of water and suspended substances outward through a semipermeable membrane. The pumping action of the heart creates hydrostatic pressure (pressure exerted by luid) within the capillaries. Hydrostatic pressure causes luid to press outward on the vessel. That force promotes iltration, forcing movement of water and electrolytes through the capillary wall to the interstitial luid (see Fig. 25.1B). Active Transport Active transport, contrary to diffusion, osmosis, and iltration, requires cellular energy. This force can move molecules into cells regardless of their electrical charge or the concentrations already in the cell. Active transport may move substances from an area of lower concentration to an area of higher concentration. The energy source for the process is adenosine triphosphate (ATP). ATP is produced during the complex metabolic processes in the body’s cells. Enzyme reactions metabolize carbon chains of sugars, fatty acids, and amino acids, yielding carbon dioxide, water, and high-energy phosphate bonds. Active transport can move amino acids, glucose, iron, hydrogen, sodium, potassium, and calcium through the cell membrane (Fig. 25.2). FLUID AND ELECTROLYTE IMBALANCES Healthy people maintain intake and output (I & O) balance by drinking suficient luids and eating a balanced diet each day. The healthy kidney regulates luid and electrolyte balance by regulating the volume and composition of ECF. Illness affects luid balance in many ways. The patient may be unable to ingest food or liquids, may have a problem with absorption from the intestinal tract, or may have a kidney impairment that affects excretion or reabsorption of water and electrolytes. Any disease that affects circulation (e.g., heart failure) ultimately affects the distribution and composition of Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 body luids. Burns, in which large amounts of body luid may be lost through open wounds, also present problems of luid balance. In fact, any seriously ill patient is at risk for a luid and electrolyte imbalance. Life-Span Considerations Older Adults Any patient over age 65 is at risk for confusion from fluid and electrolyte imbalance. Always look for signs of a fluid and electrolyte imbalance when an older adult becomes confused. A luid imbalance exists when the body has an excess (too much) or a deicit (too little) of water. When this occurs, there will be an accompanying imbalance in the substances dissolved in the water. When considering sodium imbalances, it is important to remember that water follows sodium in the body. The sodium concentration causes an osmotic pull, and water goes to where that concentration is highest. Box 25.1 • • • • • • • • • • • • • • • • • 441 Signs and Symptoms of Dehydration (Fluid Volume Deficit) Complaints of dizziness Confusion Cool, dry skin Dark, concentrated urine Decreased blood pressure Decreased urine production Dry, cracked lips and tongue Dry mucous membranes Elevated temperature Flat neck veins when lying down Increased pulse rate Poor skin turgor Postural hypotension Thick saliva Thirst Weak, thready pulse Weakness Focused Assessment Assessing Fluid and Electrolyte Status For patients admitted with vomiting, diarrhea, high fever, or a history of heart failure, diabetes, renal disease, head injury, thyroid disease, adrenal disease, or inflammatory bowel disease, perform a general head-to-toe assessment and assess for: • Fatigue • Weakness • Tissue turgor • Edema, dependent or generalized, and degree of pitting • Dyspnea • Confusion • Dizziness • Blood pressure change • Rapid pulse • Cool, dry skin • Sunken eyeballs • Mucous membranes for dryness • Jugular vein distention • Rapidity of hand vein emptying and refill • Changes in vital signs • Changes in daily weight • Alteration in input and output balance DEFICIENT FLUID VOLUME Those at risk for deicient luid volume are: (1) patients unable to take in suficient quantities of luid because of impaired swallowing, extreme weakness, disorientation, coma, or the unavailability of water; and (2) patients who lose excessive amounts of luid through prolonged vomiting, diarrhea, hemorrhage, diaphoresis (sweating), or excessive wound drainage. Treatments that can cause a luid deicit are diuretic therapy and gastrointestinal suction without luid replacement. Clinical Cues Keep an accurate record of the amount of drainage removed by suction so that adequate fluid can be replaced and dehydration can be avoided. FIGURE 25.3 Testing for tissue turgor and signs of dehydration. (From Seidel, H. M., Ball, J. W., & Dains, J.E., & Benedict W. G. [2003]. Mosby’s Guide to Physical Examination [5th ed.]. St. Louis, MO: Mosby.) Burns and drainage from large wounds or istulas can deplete the luid volume. Treatment of deicient luid volume involves remedying the underlying cause and replacing luids. Dehydration When a luid deicit occurs, it causes loss of water from the cells (dehydration). When there is too little water in the plasma, water is drawn out of the cells by osmosis to equalize the concentration, and the cells shrivel. Dehydration is treated by luid administration, either orally or intravenously. Signs and symptoms of dehydration are listed in Box 25.1. Tissue turgor (degree of elasticity) is checked by gently pinching up the skin over the abdomen, forearm, sternum, forehead, or thigh (Fig. 25.3). In a person with normal luid balance, the pinched skin immediately falls back to normal when released. If a luid deicit is present, the skin may remain elevated 442 UNIT VI Meeting Basic Physiologic Needs or tented for several seconds after the pinch. This test measures skin elasticity, as well, and it is not always a valid indicator of luid loss in the elderly and infants. Weight loss and dark or limited urine output can also be signs of dehydration. Dehydrated infants may show evidence of sunken eyeballs and a depressed anterior fontanel. Life-Span Considerations Clinical Pitfall Recall that plasma proteins are responsible for maintaining colloid osmotic pressure and, thus, for keeping fluid in the vascular compartment. Although we often see peripheral edema and automatically assume excess fluid volume, in a patient with severe protein deficiency, it is possible to exhibit peripheral edema in the presence of deficient fluid volume, because of decreased colloid osmotic pressure. Remember, what is in the vascular space determines fluid volume deficit versus excess! Older Adults The older adult who suffers from nausea, vomiting, or diarrhea is especially prone to dehydration. If the person has a fever, this adds to the fluid loss. Because of the fluid and accompanying electrolyte losses, the person may become confused. Offering the patient small amounts of water frequently or an electrolyte solution such as Gatorade, if it can be kept down, helps prevent additional problems. EXCESS FLUID VOLUME Healthy people do not ordinarily drink too much water. When people become ill, they may take in more water than they excrete. This can happen if they receive IV luid too quickly, are given tap water enemas, or are persuaded to drink more luids than they can eliminate. If these events happen, the patient suffers a luid volume excess. Impaired elimination, such as occurs in renal failure, is an important cause of luid volume excess. Signs of overhydration are weight gain, crackles in the lungs, slow bounding pulse, elevated blood pressure, and possibly edema. When luid volume excess occurs, hypervolemia (excessive blood volume) may also occur. Hypervolemia causes an elevation of blood pressure. Edema Edema is an excessive accumulation of interstitial (tissue) luid. It is often a sign of luid overload, but it may be due to other causes. FIGURE 25.4 Example of pitting edema. The finger depressions (arrows) do not refill quickly after pressure has been exerted. (Patton, K. T., & Thibodeau, G. A. [2014]. The Human Body in Health and Disease [6th ed.]. St. Louis, MO: Mosby.) In ambulatory patients, the excessive luid tends to accumulate in the lower extremities (Fig. 25.4). In the bedridden patient, the luid accumulates in the sacral region. These types of luid accumulations are termed dependent edema. Generalized edema occurs when excess interstitial luid is spread throughout the body. It is most visible in the hands and face, where swelling is detectable. Causes of generalized edema are: (1) kidney failure, (2) heart failure, (3) liver failure, and (4) hormonal disorders involving the overproduction of aldosterone and ADH (Fig. 25.5). Local edema may be caused by infection or injury and the resulting inlammation. Treatment involves correcting the underlying cause and assisting the body to rebalance luid content. The patient may have luid intake restricted or be given a diuretic drug, which causes the kidneys to increase the excretion of luid. Think Critically Why should you auscultate the lungs of older adult patients who are receiving IV fluids even if they have no current lung problems? ELECTROLYTE IMBALANCES A summary of the normal ranges of the major electrolytes, the causes of imbalances, the signs and symptoms of imbalances, and nursing interventions is provided in Table 25.4. Sodium Imbalances Hyponatremia. A deicit of sodium in the blood is called hyponatremia (Na+ less than 135 mEq/L). This can occur from sodium loss or an excess of water. This is the most common electrolyte imbalance patients’ experience. Sodium loss may occur from excessive vomiting or diarrhea when the luid loss is replaced with plain water. Decreased secretion of aldosterone can result in sodium loss. Heart failure, liver disease with ascites (abnormal accumulation of luid within the peritoneal cavity), and sometimes chronic renal failure, result in excessive water retention without concurrent sodium retention. The result of this is hypervolemia combined with hyponatremia. The average intake of sodium is 6 to 12 g/day. If there is a problem with water balance, the patient may be advised to restrict sodium in the diet. Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 443 FLUID OVERLOAD Increased hydrostatic pressure in arterial end of capillary Increased peripheral vascular resistance Fluid movement into tissues Increased left ventricular pressure Edema Increased left atrial pressure Pulmonary edema A DECREASED PLASMA AND ALBUMIN ALTERED LYMPHATIC FUNCTION Decreased production of plasma proteins Lymphatic obstruction decreases absorption of interstitial fluid Decreased capillary oncotic pressure Increased capillary permeability Movement of plasma protein into tissues Decreased transport of capillary filtered protein Decreased reabsorption at venous end Increased tissue oncotic pressure Increased tissue oncotic pressure, which pulls fluid toward it Edema B TISSUE INJURY Edema Edema C D FIGURE 25.5 Mechanisms of edema formation. (A) Fluid overload. (B) Decreased plasma and albumin. (C) Altered lymphatic function. (D) Tissue injury. (From Black, J. M., & Hawks, J. H. [2009]. Medical-Surgical Nursing: Clinical Management for Positive Outcomes [8th ed.]. St. Louis, MO: Saunders.) Table 25.4 SERUM VALUE Electrolyte Imbalances SIGNS AND SYMPTOMS CAUSES AND RISK FACTORS NURSING INTERVENTIONS SODIUM: NORMAL RANGE: 135-145 MEQ/L Less than Inadequate sodium intake, as in paRestrict water intake as ordered Hyponatremia. Central nervous 135 mEq/L tients on low sodium diets. Excessive for patients with heart failure, system and neuromuscular intake or retention of water (kidney kidney failure, and inadequate changes resulting from failure of failure and heart failure). Loss of bile, antidiuretic hormone producswollen cells to transmit electriwhich is rich in sodium, because of tion. Liberalize diet of patient cal impulses. Mental confuistulas, drainage, gastrointestinal on low sodium diet. Closely sion, headache, altered level of surgery, nausea and vomiting, and monitor patient receiving IV soconsciousness, anxiety, coma, suction. Loss of sodium through lutions to correct hyponatremia. anorexia, nausea, vomiting, burn wounds. Administration of IV Replace water loss with fluids muscle cramps, seizures, and fluids that do not contain electrolytes. containing sodium. decreased sensation. Greater than Hypernatremia. Dry mucous High sodium diet, inadequate water 145 mEq/L intake as in comatose, mentally membranes, loss of skin turgor, confused, or debilitated patient. intense thirst, flushed skin, Excessive sweating, diarrhea, oliguria, and possibly elevated and failure of kidneys to reabsorb temperature; weakness, letharwater from urine. Administration of gy, irritability, twitching, seizures, high-protein, hyperosmotic tube coma, and intracranial bleeding; feedings and osmotic diuretics. low-grade fever. Encourage increased fluid intake; measure I & O; give water between tube feedings; restrict sodium intake; monitor temperature. Continued 444 UNIT VI Meeting Basic Physiologic Needs Table 25.4 Electrolyte Imbalances—cont’d Less than 3.5 mEq/L Greater than 5.0 mEq/L Less than 8.4 mg/dL POTASSIUM: NORMAL RANGE: 3.5-5.0 MEQ/L Inadequate intake of potassium-rich Hypokalemia. Abdominal pain, foods. Loss of potassium in urine gaseous distention of inteswhen kidneys do not reabsorb the tines; cardiac arrhythmias, mineral. Loss of potassium from muscle weakness, decreased intestinal tract because of diarrhea reflexes, paralysis, paralytic or vomiting, drainage from fistulas, ileus, urinary retention, lethargy, or overuse of gastric suction. confusion, ECG changes, and Improper use of diuretics. increased urinary pH. Hyperkalemia. Muscle weakness, hypotension, paresthesias, paralysis, cardiac arrhythmias, ECG changes. Decrease intake of foods high in potassium. Increase fluid intake to enhance urinary excretion of potassium; provide adequate carbohydrate intake to prevent use of body proteins for energy. Carefully administer proper dose of insulin to diabetic patients. Instruct patient in proper use of salt substitutes containing potassium. CALCIUM: NORMAL RANGE: 8.4-10.6 MG/DL Inadequate dietary intake of calcium Encourage adults to conand vitamin D. Impaired absorption of sume sufficient calcium calcium from the intestinal tract, as in from cheese, broccoli, diarrhea, sprue, overuse of laxatives shrimp, and other dietary and enemas containing phosphates sources. Have 10% cal(phosphorus tends to be more readily cium gluconate solution at absorbed from the intestinal tract the bedside of the patient than calcium is, and it suppresses having a thyroidectomy in calcium retention in the body). The case of surgical damage parathyroid regulates calcium and to the parathyroid glands. phosphorus levels. Hyposecretion Give all oral medicines of parathyroid hormone can result in containing calcium ½ hour hypocalcemia. before meals to facilitate absorption. Hypocalcemia. Paresthesias, seizures, muscle spasms, tetany, hand spasm, positive Chvostek sign, positive Trousseau sign, cardiac arrhythmia, wheezing, dyspnea, difficulty swallowing, colic, and cardiac failure. Greater than 10.6 Hypercalcemia. Anorexia, mg/dL abdominal pain, constipation, polyuria, confusion, renal calculi, pathologic fractures, and cardiac arrest. Less than 1.3 mEq/L Conditions that alter kidney function or decrease kidney’s ability to excrete potassium. Intestinal obstruction that prevents elimination of potassium in the feces. Addison disease, digitalis toxicity, uncontrolled diabetes mellitus, insulin deficit, crushing injuries, and burns. Instruct patients (especially those taking diuretics) about foods high in potassium content; encourage intake. Observe closely for signs of digitalis toxicity in patients taking this drug. Teach patients to watch for signs of hypokalemia. Administer potassium chloride supplement as ordered. Monitor I & O and cardiac rhythm. Excess intake of calcium, as in the patient taking antacids indiscriminately. Excess intake of vitamin D. Conditions that cause movement of calcium out of bones and into extracellular fluid (e.g., bone tumor and multiple fractures). Tumors of the lung, stomach, and kidney and multiple myeloma. Immobility and osteoporosis. Administer diuretics as prescribed to increase urine output and calcium excretion. Monitor I & O; encourage high fluid intake (3000-4000 mL/day). MAGNESIUM: NORMAL RANGE: 1.3-2.1 MEQ/L Chronic malnutrition; chronic Diet counseling to help patients at diarrhea. Bowel resection risk increase level of magnesium with ileostomy or colostomy; (e.g., milk and cereals). Monitor chronic alcoholism; prolonged closely IV infusions of magnegastric suction; acute pancresium. Monitor I & O. atitis; biliary or intestinal fistula; osmotic diuretic therapy; diabetic ketoacidosis. Hypomagnesemia. Insomnia, hyperactive reflexes, leg and foot cramps, twitching, tremors, seizures, cardiac arrhythmias, positive Chvostek sign, positive Trousseau sign, vertigo, hypocalcemia, and hypokalemia. Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 Table 25.4 445 Electrolyte Imbalances—cont’d Greater than 2.1 mEq/L MAGNESIUM: NORMAL RANGE: 1.3-2.1 MEQ/L Overuse of antacids and cathar- Teach patients to avoid abuse of Hypermagnesemia. Hypotentics containing magnesium; laxatives and antacids; instruct sion; sweating and flushing, aspiration of seawater, as patients with renal problems to nausea and vomiting; muscle in near drowning. Chronic avoid over-the-counter drugs that weakness, paralysis, respikidney disease. contain magnesium. Encourage ratory depression; cardiac fluid intake to increase urinary dysrhythmias. excretion of magnesium if not contraindicated. Monitor I & O. Administer diuretics as ordered. PHOSPHATE: NORMAL RANGE: 2.7-4.5 MG/DL Vitamin D deficiency or hyperparathyroidism; use of aluminum-containing antacids. Less than 2.7 mg/ dL Hypophosphatemia. Confusion, seizures, numbness, weakness, and possible coma. Chronic state may cause rickets and osteomalacia. Greater than 4.5 mg/dL Hyperphosphatemia. Anorexia, nausea, and vomiting. Life-Span Considerations Renal insufficiency. Assess for vitamin D deficiency, hyperparathyroidism, or overuse of aluminum-containing antacids. Assess for restlessness, confusion, chest pain, and cyanosis. Monitor respirations. Check all electrolyte levels. Patient Education Older Adults Foods High in Sodium Older adults are more susceptible to hyponatremia than younger ones are. Those taking thiazide diuretics or selective serotonin reuptake inhibitors (SSRIs) are particularly at risk for hyponatremia. The problem is especially prevalent in long-term care residents. The patient who is experiencing a fluid volume excess or who has been advised to decrease sodium intake should avoid the foods listed below. The patient who is low in sodium may add some of these foods to the diet. • Buttermilk • Canned meats or fish • Canned soups (regular) • Canned vegetables (regular) • Casserole and pasta mixes • Cheese (all kinds) • Dried fruits • Dried soup mixes • Foods containing monosodium glutamate (MSG) • Frozen vegetables with sauces • Gravy mixes • Ham • Hot dogs • Ketchup • Lunch meats • Olives • Pickles • Prepared mustard • Preserved meats • Processed foods • Salted nuts • Salted popcorn • Salted snack foods • Softened water high in sodium • Soy sauce (regular) • Tomato or vegetable juice Hypernatremia. When the serum sodium concentration rises above 145 mEq/L, a state of hypernatremia exists. This occurs when there is an excess of sodium or a loss of body water. Excessive administration of sodium bicarbonate for the treatment of acidosis (excess of acid or depletion of alkaline substances in the blood and body tissues) is one cause. More commonly, water loss from fever, respiratory tract infection, or watery diarrhea is the cause. QSEN Considerations: Safety Long-Term Steroid Risk Patients on long-term corticosteroids that cause potassium depletion may develop hypernatremia. Observe for signs of edema in these patients. Decreased water intake may occur in immobile, confused, or dependent patients or in those who have sustained damage to the thirst center in the hypothalamus. The body tries to correct the situation by conserving water through reabsorption in the renal tubules. Hypernatremia causes an osmotic shift of luid from the cells to the interstitial spaces, causing cellular dehydration and interruption of normal cell processes. Sodium intake is restricted for the patient with hypernatremia. Potassium Imbalances Hypokalemia. When the potassium level falls below 3.5 mEq/L, hypokalemia exists. Extra potassium must 446 UNIT VI Meeting Basic Physiologic Needs be given to help correct the imbalance. Hypokalemia may be a result of malnutrition, illness causing a shift of potassium from ECF to ICF, or increased potassium loss. Hypokalemia can also be related to laxative or enema abuse, and medications such as Amphotericin B, diuretics, and antibiotics, and certain genetic disorders (Thomas, 2015). Vomiting, diarrhea, and prolonged gastrointestinal suction may deplete potassium levels (Lederer, 2014). Potassium-sparing diuretics help restore serum potassium when a diuretic is needed. The patient is encouraged to eat foods high in potassium, and IV replacement may be necessary Patient Education Foods High in Potassium The patient with hypokalemia should be encouraged to add the foods listed below to the daily diet. Patients in renal failure may need to restrict their intake of these foods. • Apricots • Avocados • Bananas • Cantaloupe • Codish • Dates • Meats • Milk • Orange juice • Oranges • Potatoes • Raisins • Salmon • Tuna Safety Alert Hypokalemia Severe hypokalemia (K+ less than 2.5 mEq/L) may cause cardiac arrest. Potassium-wasting diuretics used without potassium replacement can cause hypokalemia. Premature ventricular contractions and changes in the electrocardiogram (ECG) pattern such as ST segment depression, a prolonged Q-T interval, and U wave occurrence may be seen. Hyperkalemia. When the serum potassium level rises above 5.0 mEq/L, a state of hyperkalemia exists. Patients with renal failure, severe burns, or crush injuries and those undergoing major surgery are at risk for hyperkalemia. The mechanical disruption of cell membranes causes a shift of potassium from the ICF to the ECF. Hyperkalemia occurs in overuse of potassiumsparing diuretics, digitalis toxicity, overuse of potassium-containing salt substitutes, uncontrolled diabetes mellitus, and a variety of other illnesses. Clinical Cues Hyperkalemia can cause life-threatening cardiac arrhythmia. Tall or peaked T waves may be seen on the ECG. P waves may be small. Calcium Imbalances Hypocalcemia. When the calcium level drops below 8.4 mg/dL, hypocalcemia occurs. This can result from nutritional deiciency of calcium or vitamin D. Hypocalcemia occurs in disorders in which there is a shift of calcium into the bone. Metastatic cancer invading bone is one such cause. Removal or injury of the parathyroid glands during thyroidectomy causes parathyroid hormone deiciency and consequent hypocalcemia. Excessive infusion of bicarbonate solution, alkalosis (excess of alkaline or decrease of acid substances in the blood and body luids), blood transfusions, and hypoparathyroidism may cause hypocalcemia. Hypercalcemia. Hypercalcemia, a serum calcium level above 10.6 mg/dL, can occur during periods of lengthy immobilization when calcium is mobilized from the bone or when an excess of calcium or vitamin D is taken into the body. Most cases are related to hyperparathyroidism or malignancy in which there is metastasis with bone resorption. Such malignancies include multiple myeloma and lung or renal cancers. Magnesium Imbalances Hypomagnesemia. Hypomagnesemia, a serum level below 1.3 mEq/L, can result from numerous situations including decreased magnesium intake from starvation, malabsorption, or alcoholism; pancreatitis; and gastrointestinal losses from diarrhea, vomiting, or gastric suction. Genetic abnormalities in the renal tubules and medications can also be the cause (Fulop, 2014). Uncontrolled diabetes, hypercalcemia, and diuretic therapy can be causes of hypomagnesemia (Lewis, 2013). Recent studies suggest proton pump inhibitors may lead to hypomagnesemia in patients already receiving diuretics (Zipursky et al., 2014). Hypomagnesemia often accompanies hypokalemia. Hypermagnesemia. Hypermagnesemia, a serum level above 2.1 mEq/L, occurs rarely and usually in the presence of renal failure, although magnesiumcontaining laxatives or antacids or severe dehydration can cause it. Anion Imbalances Imbalances of chloride, phosphate, and bicarbonate accompany cation imbalances because of the principle of electroneutrality. Hypochloremia, a chloride level below 96 mEq/L, is associated with hyponatremia. It can also occur with severe vomiting and is seen as a compensatory decrease in acid-base disorders. Hyperchloremia, a chloride level above 106 mEq/L, occurs along with hypernatremia and a form of metabolic acidosis. Hypophosphatemia occurs when the level of phosphate falls below 2.7 mg/dL. It may result from use of aluminum-containing antacids that bind phosphate, from vitamin D deiciency, or from Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 hyperparathyroidism. Hyperphosphatemia, a phosphate level above 4.5 mg/dL, commonly occurs in renal failure. Think Critically Why may some older adults have a low serum calcium even though they take in suficient calcium in the diet? What type of fluid and electrolyte imbalances can occur in the patient who is undergoing diuretic therapy? Why? ACID-BASE BALANCE Acid-base balance is very important to maintaining homeostasis in the body because cell enzymes can function only within a very narrow range of pH. PH pH is a measure of the degree to which a solution is acidic or alkaline. Cell metabolism constantly produces carbon dioxide, which combines with water to form carbonic acid (H2CO3), which immediately breaks down into hydrogen ions and bicarbonate ions. The concentration of hydrogen ions (H+) determines the pH reading. The normal serum pH is 7.35 to 7.45. Death may occur at a serum pH below 6.8 or above 7.8. Because of the production of acids by the body’s metabolic systems, the body tends to become acidic if homeostasis is upset. BICARBONATE Bicarbonate is an important substance in maintaining acid-base balance. The normal range of bicarbonate (HCO3−) is 22 to 26 mEq/L. The major function of this alkaline electrolyte is the regulation of the acid-base balance in the body. Bicarbonate acts as a buffer to neutralize the excess acids in the body and maintain the bicarbonate-to-carbonic acid ratio at 20:1, which is needed for homeostasis. The kidneys selectively reabsorb or excrete bicarbonate to regulate serum levels and help maintain acid-base balance. CONTROL MECHANISMS For the serum pH to remain within the normal range of 7.35 to 7.45, the ratio of bicarbonate ion to carbonic acid must be 20:1. If one component of the ratio changes, the other must change proportionately to maintain the proper balance for serum pH to be within the normal range. There are three control mechanisms for pH. The irst is the blood buffer system, which consists of weak acids and weak bases. These buffer pairs can act quickly to stabilize the serum pH. The buffer pair that is monitored in clinical settings is the sodium bicarbonate–carbonic acid buffer system. When an acid is added to the blood, it combines with the base (bicarbonate) component of the buffer, forming a weaker acid. Because weak acids do not readily release free 447 H+, changes in serum pH are minimized. When a base is added to the blood, it combines with the acid component of the buffer to form a weaker base. The other blood buffer systems are protein buffers and phosphate buffers. They minimize pH changes but do not remove acid or base from the body. The second control mechanism for pH is the lungs. In the lungs, the hydrogen ion and the bicarbonate ion dissociation reaction can be reversed, and water and carbon dioxide (CO2) are reformed. The carbon dioxide and water are expired from the lungs, decreasing the amount of acid in the body. The lungs can either expel more carbon dioxide or conserve it to help balance the pH. The respiratory system can readjust quickly to help control serum pH. The third control mechanism for pH is the urinary system. In the kidney, enzymes promote the dissociation of carbonic acid to free hydrogen ions, which can be excreted in the urine. The bicarbonate ions are returned to the blood to restore the levels of buffer. The kidneys reduce the acid content of the serum by exchanging hydrogen for sodium with the help of aldosterone, and the kidneys can neutralize acids by combining them with ammonia and other chemicals. When there is excess alkali (base), the kidney can also excrete excess bicarbonate. This compensatory ability of the kidney takes more time to work compared with the compensatory action in the lungs. Figure 25.6 shows the interaction of these control mechanisms. Clinical Cues Usually about 3 days are needed for the kidneys to stabilize pH within normal range. Think Critically If the blood flow to the kidneys is reduced for a considerable time, what effect might it have on serum pH? ACID-BASE IMBALANCES There are four types of acid-base imbalances, as shown in Table 25.5. To determine if an acid-base imbalance exists, the pH, arterial carbon dioxide partial pressure (PaCO2), and bicarbonate ion are measured by arterial blood gas analysis performed on a sample of arterial blood. An increase in hydrogen ions results in acidosis (decrease in pH). A decrease in hydrogen ions results in alkalosis (increase in pH). Imbalances may be acute or chronic. An initial change in carbon dioxide is nearly always the result of a respiratory disorder. Disorders that show an initial change in bicarbonate ions are metabolic. The three control mechanisms continually work together to maintain acid-base balance. When an imbalance occurs, the lungs and kidneys try to compensate by working to bring the pH back toward normal limits. 448 UNIT VI Meeting Basic Physiologic Needs 1. Cells produce acids 2. CO2 + H2O 10. CO . 2 expired H2CO3 3. H+ binds CO2 Other H+ 11. Less H2CO3 to HCO3– in buffer CELLS CO2 Cell metabolism L R KIDNEYS 4. KIDNEYS H+ H2CO3 LUNGS CIRCULATING BLOOD into filtrate + HCO3– HEART CO2+ H2O L CELL 5. Blood has less H+ more HCO3– 2 H2CO3 R CO 9. LUNGS me Ce tab ll oli sm Alveolus into blood 6. BUFFER ACTION CO2 HCO3– 7. CO2 + H2O H2CO3 8. More acids in blood and less bicarbonate buffer FIGURE 25.6 Regulation of acid-base balance by chemical buffers, respiratory system, and renal system. CO2, Carbon dioxide; H+, hydrogen ion; HCO3−, bicarbonate; H2CO3, carbonic acid; H2O, water. Table 25.5 Acid-Base Imbalances IMBALANCE Respiratory acidosis ARTERIAL BLOOD GAS VALUESa pH less than 7.35; CAUSES Slow, shallow respirations/hypoventilation; respiratory congestion or obstruction; can be due to COPD, severe pneumonia, or excessive sedation; respiratory muscle weakness SIGNS AND SYMPTOMS Hypoventilation; dyspnea; anxiety; confusion Metabolic acidosis Shock; diabetic ketoacidosis; lactic acidosis; renal failure; diarrhea; starvation Kussmaul respirations; headache; confusion; malaise pH less than 7.35 HCO3; less than 22 mEq/L Respiratory alkalosis Hyperventilation caused by anxiety or pain; mechanical ventilation Hyperventilation; confusion; lightheadedness pH greater than 7.45; PaCO2 less than 35 mm Hg Metabolic alkalosis Vomiting; prolonged gastric suction; hypokalemia; medications: diuretics, antacids or bicarbonate, mineralocorticoids Hypoventilation; confusion; numbness/tingling; decreased LOC pH greater than 7.45; HCO3 greater than 26 mEq/L aNormal PaCO2 greater than 45 mm Hg blood gas values: pH: 7.35-7.45; PaO2: 80-100 mm Hg; PaCO2: 35-45 mm Hg; HCO3−: 22-26 mEq/L. Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 Periods of heavy exercise Diabetes (uncontrolled) Excess lactic acid Ketoacid buildup Kidney disease Excretion of acids 449 Diarrhea Production of HCO3 Loss of HCO3 Metabolic acidosis Signs and symptoms Headache Lethargy Confusion Weakness Kussmaul respirations Unrelieved Coma Causes Death Sign or symptom CONCEPT MAP 25.2 Causes, signs, and symptoms of metabolic acidosis. HCO3−, Bicarbonate. RESPIRATORY ACIDOSIS Carbon dioxide levels increase in a variety of disorders, including acute problems such as airway obstruction, pneumonia, asthma, or chest injuries. Increased levels are also seen in patients taking opiates, which depress the respiratory rate. Chronic respiratory acidosis is prevalent among people with chronic obstructive pulmonary disease (COPD), also called chronic airlow limitation (CAL). METABOLIC ACIDOSIS An excessive loss of bicarbonate ions or an increased production or retention of hydrogen ions leads to metabolic acidosis. The loss of bicarbonate ions with diarrhea is one cause of metabolic acidosis. Metabolic acidosis also occurs when large amounts of acid are produced within the body. This happens when more energy than usual is expended and lactic acid builds up in the body, a condition called lactic acidosis, one type of metabolic acidosis. Lactic acidosis is most commonly caused by poor tissue perfusion in states such as shock (Gunnerson, 2015). The faulty metabolism of a patient with diabetes can cause a buildup of ketoacids, resulting in another type of metabolic acidosis, diabetic ketoacidosis. The other major cause of metabolic acidosis is kidney disease, in which there is decreased excretion of acids and decreased production of bicarbonate (Concept Map 25.2). In this instance, dialysis is required to maintain the pH within life-permitting limits. Effects of Acidosis Acidosis depresses the nervous system, causing headache, lethargy, weakness, and confusion. If the acidosis is unrelieved, coma and death will ensue. Evidence that the compensatory mechanisms are at work in metabolic acidosis is deep rapid breathing (Kussmaul respirations) and secretion of urine with a low pH. Clinical Goldmine Kussmaul respiration is the body’s attempt to correct acidosis by “blowing off” carbon dioxide, which is an acid. RESPIRATORY ALKALOSIS Hyperventilation (a rapid respiratory rate) results in respiratory alkalosis. It is usually caused by anxiety, high fever, or an overdose of aspirin. Head injuries 450 UNIT VI Meeting Basic Physiologic Needs may also lead to hyperventilation. Treatment for hyperventilation is to treat the underlying disorder. The person may breathe through a rebreather mask temporarily, mixing the excessively exhaled carbon dioxide with oxygen so that carbon dioxide is inhaled. METABOLIC ALKALOSIS The most common cause of metabolic alkalosis is diuretic administration (Soifer & Kim, 2014). Vomiting and gastrointestinal suction, resulting in loss of hydrochloric acid from the stomach, as well as excessive antacid consumption, may also be causes. Clinical Cues Hypokalemia (low serum potassium) is associated with metabolic alkalosis through various mechanisms. For example, with vomiting, there is a loss of chloride and hydrogen ions, leading to alkalosis. The body attempts to compensate for the lack of hydrogen ions by releasing them from the cell in exchange for potassium ions (potassium goes in/hydrogen comes out). Thus, the serum K+ becomes lower and hypokalemia occurs. Effects of Alkalosis Irritability of the nervous system occurs when the pH balance shifts to alkalosis. The patient may display restlessness, muscle twitching, and tingling and numbness of the ingers. If alkalosis progresses, tetany occurs, and seizures and coma result. Tetany is characterized by severe muscle cramps, carpopedal spasms, laryngeal spasms, and stridor (shrill, harsh sound on inspiration). Think Critically Can you identify the type of imbalance that might result from (1) rapid respiratory rate, (2) out-of-control diabetes, (3) renal failure, and (4) consuming excess antacids for a nervous stomach? More in-depth information about acid-base imbalances will be covered in your medical-surgical nursing courses and can be found in a medical-surgical nursing textbook. APPLICATION OF THE NURSING PROCESS ASSESSMENT (DATA COLLECTION) First, assess the patient for risk of luid, electrolyte, or acid-base imbalance. Then assess for physical signs and symptoms of alterations in normal balance. Examine laboratory test results for electrolyte levels that are outside the normal range. Evaluate blood gas levels to determine whether an acid-base imbalance exists, and, if so, what type of imbalance is present. Evaluate I & O records to determine whether there is a luid imbalance. The urine volume the adult usually excretes in 24 hours is approximately 1500 mL. In stressful situations, it may decrease slightly from the effects of increased aldosterone and ADH. Urine concentration provides another clue to the luid status. Urine concentration is commonly measured by the speciic gravity. The concentration of urine is compared with the speciic gravity of distilled water, which is 1.000. Urine contains urea, electrolytes, and other substances, so its speciic gravity will exceed 1.000. Urine speciic gravity normally ranges between 1.003 and 1.030. The average range is 1.010 to 1.025. The urine speciic gravity is measured with a urinometer, a refractometer, or a dipstick that contains a reagent for speciic gravity. Speciic gravity is lower in older adults because the kidneys do not concentrate urine as well as in a younger person. Tracking daily weight is another way to assess for alterations in luid balance. Assignment Considerations Daily Weight When assigning the measurement of daily weight, remind the unlicensed assistive personnel (UAP) that the weight needs to be measured at the same time every morning, with the patient in the same clothing, on the same scale, after the patient has voided and before eating. Otherwise, accurate measurement of weight gain or loss is impossible. Ask the UAP to report to you any change of more than 1 kg (2.2 lb) immediately. Clinical Cues A weight gain or loss of 1 kg (2.2 lb) in 24 h indicates a gain or loss of 1 L of fluid. Skin turgor (elastic condition) is partially dependent on the amount of tissue luid supporting the skin. Checking skin turgor is useful when assessing luid balance (see Fig. 25.3), although it is unreliable in older adults. The sternum is one of the most reliable places to check skin turgor. Edema may be an indicator of luid volume overload. Look for puffy eyelids and swollen hands. Edema may sometimes be evidenced by a pit developing when a ingertip is pressed into the tissue over a bony prominence, such as the malleolus or tibia, and held for 5 seconds. After the inger is removed, the pit slowly disappears. A better method of assessing the course of peripheral edema is to measure the circumference of the extremity in the same location each day. Changes in vital signs are pertinent when assessing luid, electrolyte, and acid-base balance. Fever increases luid loss and predisposes the patient to luid-volume deicit. A pulse rate greater than 100 bpm may be an early sign of decreased vascular volume from luid volume deicit. A weak, thready pulse accompanies luid volume deicit, and a bounding pulse is associated with luid volume overload. Potassium and magnesium Fluid, Electrolyte, and Acid-Base Balance CHAPTER 25 deicits may cause an irregular pulse rate. Rapid breathing may cause an alkaline blood pH by expelling large amounts of carbon dioxide, or it may be the body’s way to compensate for an acidic blood pH. Moist respiratory sounds in the absence of cardiac or respiratory disease are a sign of excess luid in the lungs from luid overload. Fluid overload causes a rise in systolic blood pressure. Clinical Cues To assess for a fluid deficit, measure the blood pressure and pulse in the lying, sitting, and standing positions. If systolic blood pressure drops 20 mm Hg, or the diastolic blood pressure drops 10 mm Hg, accompanied by a pulse rate increase of 20 bpm at 1 min after the position change, deficient fluid volume is present (see Chapter 21). Severe luid volume deicit decreases blood low to the brain and results in decreased sensorium and confusion. Imbalances in sodium have direct effects on the brain volume and mental function as well. Neuromuscular irritability is assessed when imbalances in calcium and magnesium are suspected. Deep tendon relexes may be tested to monitor neuromuscular irritability. Check for Chvostek and Trousseau signs when calcium or magnesium deicit is a possibility. Chvostek sign is assessed by tapping the facial nerve about an inch in front of the earlobe. A unilateral twitching of the face is a positive response. To test for Trousseau sign, place a blood pressure cuff on the arm and inlate it above the patient’s systolic pressure for 3 minutes. A spasm of the hand indicates a positive Trousseau sign. Deep tendon relexes are tested by tapping a partially stretched muscle tendon with a percussion hammer. The extent of the relex is scored from 0 to 4+, with 0 representing no response, 2+ a normal response, and 4+ a hyperactive response. Life-Span Considerations Older Adults Checking for tenting is not an accurate way to assess dehydration in older adults because their skin loses elasticity with aging and will tent with normal hydration. It is better to check for dry mucous membranes, concentrated urine, and other signs and symptoms in these patients. NURSING DIAGNOSIS Using critical thinking, analyze the assessment database, identify problem areas, and choose nursing diagnoses. Nursing diagnoses commonly used for patients with luid, electrolyte, or acid-base imbalances are as follows: • Deicient luid volume • Exces