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  1. 1. Fluid, Electrolyte, and Acid–Base Balance LEARNING OUTCOMES After completing this chapter, you will be able to: 1. Discuss the function, distribution, movement, and regu- lation of fluids and electrolytes in the body. 2. Describe the regulation of acid–base balance in the body, including the roles of the lungs, the kidneys and buffers. 3. Identify factors affecting normal body fluid, electrolyte, and acid–base balance. 4. Discuss the risk factors for and the causes and effects of fluid, electrolyte, and acid–base imbalances. 5. Collect assessment data related to the client’s fluid, electrolyte, and acid–base balances. 6. Identify examples of nursing diagnoses, outcomes, and interventions for clients with altered fluid, electrolyte, or acid–base balance. 7. Teach clients measures to maintain fluid and electrolyte balance. 8. Implement measures to correct imbalances of fluids and electrolytes or acids and bases such as enteral or parenteral replacements and blood transfusions. 9. Evaluate the effect of nursing and collaborative inter- ventions on the client’s fluid, electrolyte, or acid–base balance. CHAPTER 52 koz74686_ch52.qxd 11/8/06 2:06 PM Page 1423
  2. 2. hematocrit, 1449 hemolytic transfusion reaction, 1473 homeostasis, 1424 hydrostatic pressure, 1427 hypercalcemia, 1441 hyperchloremia, 1442 hyperkalemia, 1438 hypermagnesemia, 1442 hypernatremia, 1438 hyperphosphatemia, 1442 hypertonic, 1427 hypervolemia, 1435 hypocalcemia, 1441 hypochloremia, 1442 hypokalemia, 1438 hypomagnesemia, 1442 hyponatremia, 1438 hypophosphatemia, 1442 hypotonic, 1427 hypovolemia, 1435 insensible fluid loss, 1428 interstitial fluid, 1425 intracellular fluid (ICF), 1424 intravascular fluid, 1424 ions, 1425 isotonic, 1427 metabolic acidosis, 1442 metabolic alkalosis, 1442 milliequivalent, 1425 obligatory losses, 1429 oncotic pressure, 1427 osmolality, 1427 osmosis, 1426 osmotic pressure, 1427 overhydration, 1437 peripherally inserted central venous catheter (PICC), 1456 pH, 1432 pitting edema, 1436 plasma, 1424 renin-angiotensin-aldosterone system, 1429 respiratory acidosis, 1442 respiratory alkalosis, 1442 selectively permeable, 1426 solutes, 1426 solvent, 1426 specific gravity, 1449 third space syndrome, 1435 transcellular fluid, 1425 volume expanders, 1456 acid, 1432 acidosis, 1433 active transport, 1428 agglutinins, 1472 agglutinogens, 1472 alkalosis, 1433 anions, 1425 antibodies, 1472 antigens, 1472 arterial blood gases (ABGs), 1449 bases, 1432 buffers, 1433 cations, 1425 central venous catheters, 1456 colloid osmotic pressure, 1427 colloids, 1426 compensation, 1442 crystalloids, 1426 dehydration, 1437 diffusion, 1427 drip factor, 1465 electrolytes, 1425 extracellular fluid (ECF), 1424 filtration, 1427 filtration pressure, 1427 fluid volume deficit (FVD), 1435 fluid volume excess (FVE), 1435 KEY TERMS In good health, a delicate balance of fluids, electrolytes, and acids and bases is maintained in the body. This balance, or phys- iologic homeostasis, depends on multiple physiologic processes that regulate fluid intake and output and the move- ment of water and the substances dissolved in it between the body compartments. Almost every illness has the potential to threaten this bal- ance. Even in daily living, excessive temperatures or vigorous activity can disturb the balance if adequate water and salt intake is not maintained. Therapeutic measures, such as the use of di- uretics or nasogastric suction, can also disturb the body’s home- ostasis unless water and electrolytes are replaced. BODY FLUIDS AND ELECTROLYTES The proportion of the human body composed of fluid is surpris- ingly large. Approximately 60% of the average healthy adult’s weight is water, the primary body fluid. In good health this vol- ume remains relatively constant and the person’s weight varies by less than 0.2 kg (0.5 lb) in 24 hours, regardless of the amount of fluid ingested. Water is vital to health and normal cellular function, serving as ■ A medium for metabolic reactions within cells. ■ A transporter for nutrients, waste products, and other substances. ■ A lubricant. ■ An insulator and shock absorber. ■ One means of regulating and maintaining body temperature. Age, sex, and body fat affect total body water. Infants have the highest proportion of water, accounting for 70% to 80% of their body weight. The proportion of body water decreases with aging. In people older than 60 years of age, it represents only about 50% of the total body weight. Women also have a lower percentage of body water than men. Women and the elderly have reduced body water due to decreased muscle mass and a greater percentage of fat tissue. Fat tissue is essentially free of water, whereas lean tissue contains a significant amount of wa- ter. Water makes up a greater percentage of a lean person’s body weight than an obese person’s. Distribution of Body Fluids The body’s fluid is divided into two major compartments, intra- cellular and extracellular. Intracellular fluid (ICF) is found within the cells of the body. It constitutes approximately two-thirds of the total body fluid in adults. Extracellular fluid (ECF) is found outside the cells and accounts for about one-third of total body fluid. It is subdivided into compartments. The two main com- partments of ECF are intravascular and interstitial. Intravascular fluid, or plasma, accounts for approximately 20% of the ECF 1424 koz74686_ch52.qxd 11/8/06 2:06 PM Page 1424
  3. 3. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1425 and is found within the vascular system. Interstitial fluid, ac- counting for approximately 75% of the ECF, surrounds the cells. The other compartments of ECF are the lymph and trans- cellular fluids. Examples of transcellular fluid include cere- brospinal, pericardial, pancreatic, pleural, intraocular, biliary, peritoneal, and synovial fluids (Figure 52-1 ■). Intracellular fluid is vital to normal cell functioning. It con- tains solutes such as oxygen, electrolytes, and glucose, and it provides a medium in which metabolic processes of the cell take place. Although extracellular fluid is in the smaller of the two compartments, it is the transport system that carries nutrients to and waste products from the cells. For example, plasma car- ries oxygen from the lungs and glucose from the gastrointesti- nal tract to the capillaries of the vascular system. From there, the oxygen and glucose move across the capillary membranes into the interstitial spaces and then across the cellular mem- branes into the cells. The opposite route is taken for waste products, such as carbon dioxide going from the cells to the lungs and metabolic acid wastes going eventually to the kid- neys. Interstitial fluid transports wastes from the cells by way of the lymph system as well as directly into the blood plasma through capillaries. Composition of Body Fluids Extracellular and intracellular fluids contain oxygen from the lungs, dissolved nutrients from the gastrointestinal tract, excre- tory products of metabolism such as carbon dioxide, and charged particles called ions. Total body fluid 40 liters Cell fluid 25 liters Plasma 3 liters Interstitial and transcellular fluid 12 liters Extracellular fluid 15 liters Figure 52-1 ■ Total body fluid represents 40 L in an adult male weighing 70 kg (154 lb). Many salts dissociate in water, that is, break up into electri- cally charged ions. The salt sodium chloride breaks up into one ion of sodium (Naϩ ) and one ion of chloride (ClϪ ). These charged particles are called electrolytes because they are capa- ble of conducting electricity. The number of ions that carry a positive charge, called cations, and ions that carry a negative charge, called anions, should be equal. Examples of cations are sodium (Naϩ ), potassium (Kϩ ), calcium (Ca2ϩ ), and magnesium (Mg2ϩ ). Examples of anions include chloride (ClϪ ), bicarbonate HCO3 Ϫ , phosphate HPO4 2Ϫ , and sulfate SO4 2Ϫ . Electrolytes generally are measured in milliequivalents per liter of water (mEq/L) or milligrams per 100 milliliters (mg/100 mL). The term milliequivalent refers to the chemical combining power of the ion, or the capacity of cations to com- bine with anions to form molecules. This combining activity is measured in relation to the combining activity of the hydrogen ion (Hϩ ). Thus, 1 mEq of any anion equals 1 mEq of any cation. For example, sodium and chloride ions are equivalent, since they combine equally: 1 mEq of Naϩ equals 1 mEq of ClϪ . However, these cations and anions are not equal in weight: 1 mg of Naϩ does not equal 1 mg of ClϪ ; rather, 3 mg of Naϩ equals 2 mg of ClϪ . Clinically, the milliequivalent system is most often used. However, nurses need to be aware that different systems of measurement may be found when interpreting laboratory re- sults. For example, calcium levels frequently are reported in milligrams per deciliter (1 dL ϭ 100 mL) instead of milliequiv- alents per liter. It also is important to remember that laboratory tests are usually performed using blood plasma, an extracellular fluid. These results may reflect what is happening in the ECF, but it generally is not possible to directly measure electrolyte concentrations within the cell. The composition of fluids varies from one body compart- ment to another. In extracellular fluid, the principal elec- trolytes are sodium, chloride, and bicarbonate. Other electrolytes such as potassium, calcium, and magnesium are also present but in much smaller quantities. Plasma and inter- stitial fluid, the two primary components of ECF, contain es- sentially the same electrolytes and solutes, with the exception of protein. Plasma is a protein-rich fluid, containing large amounts of albumin, but interstitial fluid contains little or no protein. The composition of intracellular fluid differs significantly from that of ECF. Potassium and magnesium are the primary cations present in ICF, with phosphate and sulfate the major an- ions. As in ECF, other electrolytes are present within the cell, but in much smaller concentrations (Figure 52-2 ■). Maintaining a balance of fluid volumes and electrolyte com- positions in the fluid compartments of the body is essential to health. Normal and unusual fluid and electrolyte losses must be replaced if homeostasis is to be maintained. Other body fluids such as gastric and intestinal secretions also contain electrolytes. This is of particular concern when these fluids are lost from the body (for example, in severe vom- iting or diarrhea or when gastric suction removes the gastric se- cretions). Fluid and electrolyte imbalances can result from excessive losses through these routes. koz74686_ch52.qxd 11/8/06 2:06 PM Page 1425
  4. 4. 1426 UNIT X / Promoting Physiologic Health Na+ Na+ Na+ K+ K+ K+ Mg2+ Ca2+ Plasma Interstitial fluid Intracellular fluid 0 50 100 150 200 CATIONS HCO3 – HCO3 – HCO3 – HPO4 2– HPO4 2– HPO4 2– SO4 2– SO4 2– Cl– Cl– Cl– Plasma Interstitial fluid Intracellular fluid 0 50 100 150 200 ANIONS Org. acid Proteins Proteins MilliequivalentsperLiter(mEq/L) Figure 52-2 ■ Electrolyte composition (cations and anions) of body fluid compartments. Martini, Fredric H.; Halyard, Rebecca A., Fundamentals of Anatomy and Physiology Interactive, (Media Edition), 4th ed., © 1998. Reproduced with permission of Pearson Education, Inc., Upper Saddle River, New Jersey. Higher concentration Lower concentration Semipermeable membrane Dissolved substances Water molecules H20 H20 H20 Figure 52-3 ■ Osmosis: Water molecules move from the less concentrated area to the more concentrated area in an attempt to equalize the concentration of solutions on two sides of a membrane. Movement of Body Fluids and Electrolytes The body fluid compartments are separated from one another by cell membranes and the capillary membrane. While these mem- branes are completely permeable to water, they are considered to be selectively permeable to solutes as substances move across them with varying degrees of ease. Small particles such as ions, oxygen, and carbon dioxide easily move across these mem- branes, but larger molecules like glucose and proteins have more difficulty moving between fluid compartments. The methods by which electrolytes and other solutes move are osmosis, diffusion, filtration, and active transport. Osmosis Osmosis is the movement of water across cell membranes, from the less concentrated solution to the more concentrated solution (Figure 52-3 ■). In other words, water moves toward the higher concentration of solute in an attempt to equalize the concentrations. Solutes are substances dissolved in a liquid. For example, when sugar is added to coffee, the sugar is the solute. Solutes may be crystalloids (salts that dissolve readily into true solu- tions) or colloids (substances such as large protein molecules that do not readily dissolve into true solutions). A solvent is the component of a solution that can dissolve a solute. In the previ- ous example, coffee is the solvent for the sugar. In the body, water is the solvent; the solutes include elec- trolytes, oxygen and carbon dioxide, glucose, urea, amino acids, and proteins. Osmosis occurs when the concentration of solutes on one side of a selectively permeable membrane, such as the capillary membrane, is higher than on the other side. For exam- ple, a marathon runner loses a significant amount of water through perspiration, increasing the concentration of solutes in the plasma because of water loss. This higher solute concentra- tion draws water from the interstitial space and cells into the vascular compartment to equalize the concentration of solutes koz74686_ch52.qxd 11/21/06 1:08 PM Page 1426
  5. 5. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1427 in all fluid compartments. Osmosis is an important mechanism for maintaining homeostasis and fluid balance. The concentration of solutes in body fluids is usually ex- pressed as the osmolality. Osmolality is determined by the total solute concentration within a fluid compartment and is mea- sured as parts of solute per kilogram of water. Osmolality is reported as milliosmols per kilogram (mOsm/ kg). Sodium is by far the greatest determinant of serum osmolality, with glucose and urea also contributing. Potassium, glucose, and urea are the primary contributors to the osmolality of intracellular fluid. The term tonicity may be used to refer to the osmolality of a solution. Solutions may be termed isotonic, hypertonic, or hypo- tonic.An isotonic solution has the same osmolality as body fluids. Normal saline, 0.9% sodium chloride, is an isotonic solution. Hyp- ertonic solutions have a higher osmolality than body fluids; 3% sodium chloride is a hypertonic solution. Hypotonic solutions such as one-half normal saline (0.45% sodium chloride), by contrast, have a lower osmolality than body fluids. Osmotic pressure is the power of a solution to draw water across a semipermeable membrane. When two solutions of dif- ferent solute concentrations are separated by a semipermeable membrane, the solution of higher solute concentration exerts a higher osmotic pressure, drawing water across the membrane to equalize the concentrations of the solutions. For example, infus- ing a hypertonic intravenous solution such as 3% sodium chlo- ride will draw fluid out of red blood cells (RBCs), causing them to shrink. On the other hand, a hypotonic solution administered intravenously will cause the RBCs to swell as water is drawn into the cells by their higher osmotic pressure. In the body, plasma proteins exert an osmotic draw called colloid osmotic pressure or oncotic pressure, pulling water from the interstitial space into the vascular compartment. This is an important mechanism in maintaining vascular volume. Diffusion Diffusion is the continual intermingling of molecules in liquids, gases, or solids brought about by the random movement of the molecules. For example, two gases become mixed by the con- stant motion of their molecules. The process of diffusion occurs even when two substances are separated by a thin membrane. In the body, diffusion of water, electrolytes, and other substances occurs through the “split pores” of capillary membranes. The rate of diffusion of substances varies according to (a) the size of the molecules, (b) the concentration of the solution, and (c) the temperature of the solution. Larger molecules move less Higher concentration Lower concentration Dissolved substance Semipermeable membrane Figure 52-4 ■ Diffusion: The movement of molecules through a semipermeable membrane from an area of higher concentration to an area of lower concentration. quickly than smaller ones because they require more energy to move about. With diffusion, the molecules move from a solu- tion of higher concentration to a solution of lower concentration (Figure 52-4 ■). Increases in temperature increase the rate of motion of molecules and therefore the rate of diffusion. Filtration Filtration is a process whereby fluid and solutes move together across a membrane from one compartment to another. The movement is from an area of higher pressure to one of lower pressure. An example of filtration is the movement of fluid and nutrients from the capillaries of the arterioles to the interstitial fluid around the cells. The pressure in the compartment that re- sults in the movement of the fluid and substances dissolved in fluid out of the compartment is called filtration pressure. Hydrostatic pressure is the pressure exerted by a fluid within a closed system on the walls of a container in which it is contained. The hydrostatic pressure of blood is the force exerted by blood against the vascular walls (e.g., the artery walls). The principle involved in hydrostatic pressure is that fluids move from the area of greater pressure to the area of lesser pressure. Using the ex- ample of the blood vessels, the plasma proteins in the blood ex- ert a colloid osmotic or oncotic pressure (see the earlier section “Osmosis”) that opposes the hydrostatic pressure and holds the fluid in the vascular compartment to maintain the vascular vol- ume. When the hydrostatic pressure is greater than the osmotic pressure, the fluid filters out of the blood vessels. The filtration pressure in this example is the difference between the hydrostatic pressure and the osmotic pressure (Figure 52-5 ■). Arterial side of capillary bed Interstitial space Venous side of capillary bed Direction of filtration fluid and solutes Direction of filtration fluid and solutes Capillary bed Hydrostatic pressure (arterial blood pressure) Hydrostatic pressure (venous blood pressure) Colloid osmotic pressure (constant throughout capillary bed) Figure 52-5 ■ Schematic of filtration pressure changes within a capillary bed. On the arterial side, arterial blood pressure exceeds colloid osmotic pressure, so that water and dissolved substances move out of the capillary into the interstitial space. On the venous side, venous blood pressure is less than colloid osmotic pressure, so that water and dissolved substances move into the capillary. MediaLinkMembraneTransportAnimation koz74686_ch52.qxd 11/8/06 2:06 PM Page 1427
  6. 6. 1428 UNIT X / Promoting Physiologic Health Intracellular fluid Extracellular fluid Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+Na+ Na+ Na+ Na+ K+ Na+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ Cell membrane ATP ATP ATP ATP Figure 52-6 ■ An example of active transport. Energy (ATP) is used to move sodium molecules and potassium molecules across a semipermeable membrane against sodium’s and potassium’s concentration gradients (i.e., from areas of lesser concentration to areas of greater concentration). Active Transport Substances can move across cell membranes from a less con- centrated solution to a more concentrated one by active trans- port (Figure 52-6 ■). This process differs from diffusion and osmosis in that metabolic energy is expended. In active trans- port, a substance combines with a carrier on the outside surface of the cell membrane, and they move to the inside surface of the cell membrane. Once inside, they separate, and the substance is released to the inside of the cell.Aspecific carrier is required for each substance, enzymes are required for active transport, and energy is expended. This process is of particular importance in maintaining the differences in sodium and potassium ion concentrations of ECF and ICF. Under normal conditions, sodium concentra- tions are higher in the extracellular fluid, and potassium con- centrations are higher inside the cells. To maintain these proportions, the active transport mechanism (the sodium- potassium pump) is activated, moving sodium from the cells and potassium into the cells. Regulating Body Fluids In a healthy person, the volumes and chemical composition of the fluid compartments stay within narrow safe limits. Nor- mally fluid intake and fluid loss are balanced. Illness can upset this balance so that the body has too little or too much fluid. Fluid Intake During periods of moderate activity at moderate temperature, the average adult drinks about 1,500 mL per day but needs 2,500 mL per day, an additional 1,000 mL. This added volume is acquired from foods and from the oxidation of these foods during metabolic processes. Interestingly, the water content of food is relatively large, contributing about 750 mL per day. The water content of fresh vegetables is approximately 90%, of fresh fruits about 85%, and of lean meats around 60%. Water as a by-product of food metabolism accounts for most of the remaining fluid volume required. This quantity is approx- imately 200 mL per day for the average adult. See Table 52–1. The thirst mechanism is the primary regulator of fluid intake. The thirst center is located in the hypothalamus of the brain. A number of stimuli trigger this center, including the osmotic pressure of body fluids, vascular volume, and angiotensin (a hormone released in response to decreased blood flow to the kidneys). For example, a long-distance runner loses significant amounts of water through perspiration and rapid breathing dur- ing a race, increasing the concentration of solutes and the os- motic pressure of body fluids. This increased osmotic pressure stimulates the thirst center, causing the runner to experience the sensation of thirst and the desire to drink to replace lost fluids. Thirst is normally relieved immediately after drinking a small amount of fluid, even before it is absorbed from the gas- trointestinal tract. However, this relief is only temporary, and the thirst returns in about 15 minutes. The thirst is again tem- porarily relieved after the ingested fluid distends the upper gas- trointestinal tract. These mechanisms protect the individual from drinking too much, because it takes from 30 minutes to 1 hour for the fluid to be absorbed and distributed throughout the body. See Figure 52-7 ■. Fluid Output Fluid losses from the body counterbalance the adult’s 2,500-mL average daily intake of fluid, as shown in Table 52–2. There are four routes of fluid output: 1. Urine 2. Insensible loss through the skin as perspiration and through the lungs as water vapor in the expired air 3. Noticeable loss through the skin 4. Loss through the intestines in feces URINE. Urine formed by the kidneys and excreted from the uri- nary bladder is the major avenue of fluid output. Normal urine output for an adult is 1,400 to 1,500 mL per 24 hours, or at least 0.5 mL per kilogram per hour. In healthy people, urine output may vary noticeably from day to day. Urine volume automati- cally increases as fluid intake increases. If fluid loss through per- spiration is large, however, urine volume decreases to maintain fluid balance in the body. INSENSIBLE LOSSES. Insensible fluid loss occurs through the skin and lungs. It is called insensible because it is usually not no- ticeable and cannot be measured. Insensible fluid loss through TABLE 52–1 Average Daily Fluid Intake for an Adult SOURCE AMOUNT (ML) Oral fluids 1,200 to 1,500 Water in foods 1,000 Water as by-product of 200 food metabolism Total 2,400 to 2,700 MediaLinkFiltrationPressureAnimation koz74686_ch52.qxd 11/8/06 2:06 PM Page 1428
  7. 7. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1429 the skin occurs in two ways. Water is lost through diffusion and through perspiration (which is noticeable but not measurable). Water losses through diffusion are not noticeable but normally account for 300 to 400 mL per day. This loss can be significantly increased if the protective layer of the skin is lost as with burns or large abrasions. Perspiration varies depending on factors such as environmental temperature and metabolic activity. Fever and exercise increase metabolic activity and heat production, thereby increasing fluid losses through the skin. Another type of insensible loss is the water in exhaled air. In an adult, this is normally 300 to 400 mL per day. When respira- tory rate accelerates, for example, due to exercise or an elevated body temperature, this loss can increase. FECES. The chyme that passes from the small intestine into the large intestine contains water and electrolytes. The volume of chyme entering the large intestine in an adult is normally about 1,500 mL per day. Of this amount, all but about 100 mL is reab- sorbed in the proximal half of the large intestine. Certain fluid losses are required to maintain normal body function. These are known as obligatory losses. Approximately 500 mL of fluid must be excreted through the kidneys of an adult each day to eliminate metabolic waste products from the body. Water lost through respirations, through the skin, and in feces also are obligatory losses, necessary for temperature reg- ulation and elimination of waste products. The total of all these losses is approximately 1,300 mL per day. Maintaining Homeostasis The volume and composition of body fluids is regulated through several homeostatic mechanisms.Anumber of body systems con- tribute to this regulation, including the kidneys, the endocrine sys- tem, the cardiovascular system, the lungs, and the gastrointestinal system. Hormones such as antidiuretic hormone (ADH; also known as arginine vasopressin or AVP), the renin-angiotensin- aldosterone system, and atrial natriuretic factor are involved, as are mechanisms to monitor and maintain vascular volume. KIDNEYS. The kidneys are the primary regulator of body fluids and electrolyte balance. They regulate the volume and osmolal- ity of extracellular fluids by regulating water and electrolyte ex- cretion. The kidneys adjust the reabsorption of water from plasma filtrate and ultimately the amount excreted as urine. Al- though 135 to 180 L of plasma per day is normally filtered in an adult, only about 1.5 L of urine is excreted. Electrolyte balance is maintained by selective retention and excretion by the kid- neys. The kidneys also play a significant role in acid–base regu- lation, excreting hydrogen ion (Hϩ ) and retaining bicarbonate. ANTIDIURETIC HORMONE. Antidiuretic hormone, which regu- lates water excretion from the kidney, is synthesized in the ante- rior portion of the hypothalamus and acts on the collecting ducts of the nephrons. When serum osmolality rises,ADH is produced, causing the collecting ducts to become more permeable to water. This increased permeability allows more water to be reabsorbed into the blood. As more water is reabsorbed, urine output falls and serum osmolality decreases because the water dilutes body fluids. Conversely, if serum osmolality decreases, ADH is sup- pressed, the collecting ducts become less permeable to water, and urine output increases. Excess water is excreted, and serum osmolality returns to normal. Other factors also affect the pro- duction and release of ADH, including blood volume, tempera- ture, pain, stress, and some drugs such as opiates, barbiturates, and nicotine. See Figure 52-8 ■. RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM. Specialized receptors in the juxtaglomerular cells of the kidney nephrons re- spond to changes in renal perfusion. This initiates the renin- angiotensin-aldosterone system. If blood flow or pressure to the kidney decreases, renin is released. Renin causes the conversion of angiotensinogen to angiotensin I, which is then converted to angiotensin II by angiotensin-converting enzyme.Angiotensin II Increased volume of extracellular fluid and and Decreased volume of extracellular fluid Decreased osmolality of extracellular fluid Stimulates osmoreceptors in hypothalamic thirst center Decreased saliva secretion Water absorbed from gastrointestinal tract Dry mouth Increased osmolality of extracellular fluid Sensation of thirst: person seeks a drink Figure 52-7 ■ Factors stimulating water intake through the thirst mechanism. From Lemone, Priscilla; Burke, Karen M., Medical Surgical Nursing: Critical Thinking in Client Care, 3rd ed © 2004. Reproduced with permission of Pearson Education, Inc., Upper Saddle River, New Jersey. TABLE 52–2 Average Daily Fluid Output for an Adult ROUTE AMOUNT (ML) Urine 1,400 to 1,500 Insensible losses Lungs 350 to 400 Skin 350 to 400 Sweat 100 Feces 100 to 200 Total 2,300 to 2,600 MediaLinkFluidBalanceAnimation koz74686_ch52.qxd 11/13/06 4:49 PM Page 1429
  8. 8. 1430 UNIT X / Promoting Physiologic Health acts directly on the nephrons to promote sodium and water reten- tion. In addition, it stimulates the release of aldosterone from the adrenal cortex. Aldosterone also promotes sodium retention in the distal nephron. The net effect of the renin-angiotensin- aldosterone system is to restore blood volume (and renal perfu- sion) through sodium and water retention. ATRIAL NATRIURETIC FACTOR. Atrial natriuretic factor (ANF) is released from cells in the atrium of the heart in response to ex- cess blood volume and stretching of the atrial walls. Acting on the nephrons, ANF promotes sodium wasting and acts as a po- tent diuretic, thus reducing vascular volume. ANF also inhibits thirst, reducing fluid intake. Regulating Electrolytes Electrolytes, charged ions capable of conducting electricity, are present in all body fluids and fluid compartments. Just as main- taining the fluid balance is vital to normal body function, so is maintaining electrolyte balance. Although the concentration of specific electrolytes differs between fluid compartments, a bal- ance of cations (positively charged ions) and anions (negatively charged ions) always exists. Electrolytes are important for ■ Maintaining fluid balance. ■ Contributing to acid–base regulation. ■ Facilitating enzyme reactions. ■ Transmitting neuromuscular reactions. Most electrolytes enter the body through dietary intake and are excreted in the urine. Some electrolytes, such as sodium and chloride, are not stored by the body and must be consumed daily to maintain normal levels. Potassium and calcium, on the other hand, are stored in the cells and bone, respectively. When serum levels drop, ions can shift out of the storage “pool” into the blood to maintain adequate serum levels for normal function- ing. The regulatory mechanisms and functions of the major electrolytes are summarized in Table 52–3. Urine output ↓ Serum/blood osmolality ↓ as the water dilutes body fluids Osmoreceptors in hypothalamus stimulate posterior pituitary to secrete ADH ADH increases distal tubule permeability ↑ Reabsorption of H2O into blood ↑ blood osmolality Urine output ↑ Serum osmolality returns to normal ADH is suppressed ADH causes distal tubules to become less permeable to water ↓ Reabsorption of H2O into blood ↓ blood osmolality Figure 52-8 ■ Antidiuretic hormone (ADH) regulates water excretion from the kidneys. koz74686_ch52.qxd 11/8/06 2:06 PM Page 1430
  9. 9. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1431 Sodium (Naϩ ) Sodium is the most abundant cation in extracellular fluid and a major contributor to serum osmolality. Normal serum sodium levels are 135 to 145 mEq/L. Sodium functions largely in con- trolling and regulating water balance. When sodium is reab- sorbed from the kidney tubules, chloride and water are reabsorbed with it, thus maintaining ECF volume. Sodium is found in many foods, such as bacon, ham, processed cheese, and table salt. Potassium (Kϩ ) Potassium is the major cation in intracellular fluids, with only a small amount found in plasma and interstitial fluid. ICF lev- els of potassium are usually 125 to 140 mEq/L while normal serum potassium levels are 3.5 to 5.0 mEq/L. The ratio of in- tracellular to extracellular potassium must be maintained for neuromuscular response to stimuli. Potassium is a vital elec- trolyte for skeletal, cardiac, and smooth muscle activity. It is involved in maintaining acid–base balance as well, and it con- tributes to intracellular enzyme reactions. Potassium must be ingested daily because the body can’t conserve it. Many fruits and vegetables, meat, fish, and other foods contain potassium (see Box 52–1). Calcium (Ca2ϩ ) The vast majority, 99%, of calcium in the body is in the skele- tal system, with a relatively small amount in extracellular fluid. Although this calcium outside the bones and teeth amounts to only about 1% of the total calcium in the body, it is vital in reg- ulating muscle contraction and relaxation, neuromuscular func- tion, and cardiac function. ECF calcium is regulated by a complex interaction of parathyroid hormone, calcitonin, and calcitriol, a metabolite of vitamin D. When calcium levels in the TABLE 52–3 Regulation and Functions of Electrolytes ELECTROLYTE REGULATION FUNCTION Sodium (Naϩ ) Potassium (Kϩ ) Calcium (Ca2ϩ ) Magnesium (Mg2ϩ ) Chloride (ClϪ ) Phosphate (PO4 Ϫ ) Bicarbonate (HCO3 Ϫ ) ■ Regulating ECF volume and distribution ■ Maintaining blood volume ■ Transmitting nerve impulses and contracting muscles ■ Maintaining ICF osmolality ■ Transmitting nerve and other electrical impulses ■ Regulating cardiac impulse transmission and muscle contraction ■ Skeletal and smooth muscle function ■ Regulating acid–base balance ■ Forming bones and teeth ■ Transmitting nerve impulses ■ Regulating muscle contractions ■ Maintaining cardiac pacemaker (automaticity) ■ Blood clotting ■ Activating enzymes such as pancreatic lipase and phospholipase ■ Intracellular metabolism ■ Operating sodium-potassium pump ■ Relaxing muscle contractions ■ Transmitting nerve impulses ■ Regulating cardiac function ■ HCl production ■ Regulating ECF balance and vascular volume ■ Regulating acid–base balance ■ Buffer in oxygen–carbon dioxide exchange in RBCs ■ Forming bones and teeth ■ Metabolizing carbohydrate, protein, and fat ■ Cellular metabolism; producing ATP and DNA ■ Muscle, nerve, and RBC function ■ Regulating acid–base balance ■ Regulating calcium levels ■ Major body buffer involved in acid–base regulation ■ Renal reabsorption or excretion ■ Aldosterone increases Naϩ reabsorption in collecting duct of nephrons ■ Renal excretion and conservation ■ Aldosterone increases Kϩ excretion ■ Movement into and out of cells ■ Insulin helps move Kϩ into cells; tissue damage and acidosis shift Kϩ out of cells into ECF ■ Redistribution between bones and ECF ■ Parathyroid hormone and calcitriol increase serum Ca2ϩ levels; calcitonin decreases serum levels ■ Conservation and excretion by kidneys ■ Intestinal absorption increased by vitamin D and parathyroid hormone ■ Excreted and reabsorbed along with sodium in the kidneys ■ Aldosterone increases chloride reabsorption with sodium ■ Excretion and reabsorption by the kidneys ■ Parathyroid hormone decreases serum levels by increasing renal excretion ■ Reciprocal relationship with calcium: increasing serum calcium levels decrease phosphate levels; decreasing serum calcium increases phosphate ■ Excretion and reabsorption by the kidneys ■ Regeneration by kidneys BOX 52–1 Potassium-Rich Foods VEGETABLES Avocado Raw carrot Baked potato Raw tomato Spinach MEATS AND FISH Beef Cod Pork Veal FRUITS Dried fruits (e.g., raisins and dates) Banana Apricot Cantaloupe Orange BEVERAGES Milk Orange juice Apricot nectar koz74686_ch52.qxd 11/8/06 2:06 PM Page 1431
  10. 10. 1432 UNIT X / Promoting Physiologic Health ECF fall, parathyroid hormone and calcitriol cause calcium to be released from bones into ECF and increase the absorption of calcium in the intestines, thus raising serum calcium levels. Conversely, calcitonin stimulates the deposition of calcium in bone, reducing the concentration of calcium ions in the blood. With aging, the intestines absorb calcium less effectively and more calcium is excreted via the kidneys. Calcium shifts out of the bone to replace these ECF losses, increasing the risk of os- teoporosis and fractures of the wrists, vertebrae, and hips. Lack of weight-bearing exercise (which helps keep calcium in the bones) and a vitamin D deficiency because of inadequate expo- sure to sunlight contribute to this risk. Milk and milk products are the richest sources of calcium, with other foods such as dark green leafy vegetables and canned salmon containing smaller amounts. Many clients benefit from calcium supplements. Serum calcium levels are often reported in two ways, based upon the way it is circulating in the plasma. Approximately 50% of serum calcium circulates in a free, ionized, or unbound form. The other 50% circulates in the plasma bound to either plasma proteins or other nonprotein ions. The normal total serum cal- cium levels, which range from 8.5 to 10.5 mg/dL, represent both bound and unbound calcium.The normal ionized serum calcium, which ranges from 4.0 to 5.0 mg/dL, represents calcium circulat- ing in the plasma in free, or unbound, form (Hayes, 2004). Magnesium (Mg2ϩ ) Magnesium is primarily found in the skeleton and in intracellu- lar fluid. It is the second most abundant intracellular cation with normal serum levels of 1.5 to 2.5 mEq/L. It is important for in- tracellular metabolism, being particularly involved in the pro- duction and use ofATP. Magnesium also is necessary for protein and DNA synthesis within the cells. Only about 1% of the body’s magnesium is in ECF; here it is involved in regulating neuromuscular and cardiac function. Maintaining and ensuring adequate magnesium levels is an important part of care of clients with cardiac disorders. Cereal grains, nuts, dried fruit, legumes, and green leafy vegetables are good sources of mag- nesium in the diet, as are dairy products, meat, and fish. Chloride (ClϪ ) Chloride is the major anion of ECF, and normal serum levels are 95 to 108 mEq/L. Chloride functions with sodium to regulate serum osmolality and blood volume. The concentration of chlo- ride in ECF is regulated secondarily to sodium; when sodium is reabsorbed in the kidney, chloride usually follows. Chloride is a major component of gastric juice as hydrochloric acid (HCl) and is involved in regulating acid–base balance. It also acts as a buffer in the exchange of oxygen and carbon dioxide in RBCs. Chloride is found in the same foods as sodium. Phosphate PO4 Ϫ Phosphate is the major anion of intracellular fluids. It also is found in ECF, bone, skeletal muscle, and nerve tissue. Normal serum levels of phospate in adults range from 2.5 to 4.5 mg/dL. Children have much higher phosphate levels than adults, with that of a newborn nearly twice that of an adult. Higher levels of growth hormone and a faster rate of skeletal growth probably account for this difference. Phosphate is involved in many chemical actions of the cell; it is essential for functioning of muscles, nerves, and red blood cells. It is also involved in the metabolism of protein, fat, and carbohydrate. Phosphate is ab- sorbed from the intestine and is found in many foods such as meat, fish, poultry, milk products, and legumes. Bicarbonate HCO3 Ϫ Bicarbonate is present in both intracellular and extracellular flu- ids. Its primary function is regulating acid–base balance as an essential component of the carbonic acid–bicarbonate buffering system. Extracellular bicarbonate levels are regulated by the kidneys: Bicarbonate is excreted when too much is present; if more is needed, the kidneys both regenerate and reabsorb bicar- bonate ions. Unlike other electrolytes that must be consumed in the diet, adequate amounts of bicarbonate are produced through metabolic processes to meet the body’s needs. ACID–BASE BALANCE An important part of regulating the chemical balance or home- ostasis of body fluids is regulating their acidity or alkalinity. An acid is a substance that releases hydrogen ions (Hϩ ) in solution. Strong acids such as hydrochloric acid release all or nearly all their hydrogen ions; weak acids like carbonic acid release some hydrogen ions. Bases or alkalis have a low hydrogen ion con- centration and can accept hydrogen ions in solution. The rela- tive acidity or alkalinity of a solution is measured as pH. The pH reflects the hydrogen ion concentration of the solution: The higher the hydrogen ion concentration (and the more acidic the solution), the lower the pH. Water has a pH of 7 and is neutral; that is, it is neither acidic in nature nor is it alkaline. Solutions with a pH lower than 7 are acidic; those with a pH higher than 7 are alkaline. The pH scale is logarithmic: A solution with a pH of 5 is 10 times more acidic than one with a pH of 6. Regulation of Acid–Base Balance Body fluids are maintained within a narrow range that is slightly alkaline. The normal pH of arterial blood is between 7.35 and 7.45 (Figure 52-9 ■).Acids are continually produced during me- Death Acidosis Normal Alkalosis Death 6.8 7.35 7.45 7.8 1 7 14 Alkaline solution (low H+ ) Neutral pH scale pH Acidic solution (high H+ ) Figure 52-9 ■ Body fluids are normally slightly alkaline, between a pH of 7.35 and 7.45. koz74686_ch52.qxd 11/8/06 2:06 PM Page 1432
  11. 11. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1433 tabolism. Several body systems, including buffers, the respira- tory system, and the renal system, are actively involved in main- taining the narrow pH range necessary for optimal function. Buffers help maintain acid–base balance by neutralizing excess acids or bases. The lungs and the kidneys help maintain a nor- mal pH by either excreting or retaining acids and bases. Buffers Buffers prevent excessive changes in pH by removing or releas- ing hydrogen ions. If excess hydrogen ion is present in body flu- ids, buffers bind with the hydrogen ion, minimizing the change in pH. When body fluids become too alkaline, buffers can re- lease hydrogen ion, again minimizing the change in pH. The ac- tion of a buffer is immediate, but limited in its capacity to maintain or restore normal acid–base balance. The major buffer system in extracellular fluids is the bicarbon- ate (HCO3 Ϫ ) and carbonic acid (H2CO3) system. When a strong acid such as hydrochloric acid (HCl) is added, it combines with bi- carbonate and the pH drops only slightly. A strong base such as sodium hydroxide combines with carbonic acid, the weak acid of the buffer pair, and the pH remains within the narrow range of nor- mal. The amounts of bicarbonate and carbonic acid in the body vary; however, as long as a ratio of 20 parts of bicarbonate to 1 part of carbonic acid is maintained, the pH remains within its normal range of 7.35 to 7.45 (Figure 52-10 ■). Adding a strong acid to ECF can change this ratio as bicarbonate is depleted in neutraliz- ing the acid. When this happens, the pH drops, and the client has a condition called acidosis. The ratio can also be upset by adding a strong base to ECF, depleting carbonic acid as it combines with the base. In this case the pH rises and the client has alkalosis. In addition to the bicarbonate–carbonic acid buffer system, plasma proteins, hemoglobin, and phosphates also function as buffers in body fluids. Respiratory Regulation The lungs help regulate acid–base balance by eliminating or re- taining carbon dioxide (CO2), a potential acid. Combined with water, carbon dioxide forms carbonic acid (CO2 ϩ H2O → H2CO3). This chemical reaction is reversible; carbonic acid breaks down into carbon dioxide and water. Working together with the bicarbonate–carbonic acid buffer system, the lungs reg- ulate acid–base balance and pH by altering the rate and depth of respirations. The response of the respiratory system to changes in pH is rapid, occurring within minutes. Carbon dioxide is a powerful stimulator of the respiratory center. When blood levels of carbonic acid and carbon dioxide rise, the respiratory center is stimulated and the rate and depth of respirations increase. Carbon dioxide is exhaled, and car- bonic acid levels fall. By contrast, when bicarbonate levels are excessive, the rate and depth of respirations are reduced. This causes carbon dioxide to be retained, carbonic acid levels to rise, and the excess bicarbonate to be neutralized. Carbon dioxide levels in the blood are measured as the PCO2, or partial pressure of the dissolved gas in the blood. PCO2 refers to the pressure of carbon dioxide in venous blood. PaCO2 refers to the pressure of carbon dioxide in arterial blood. The normal PaCO2 is 35 to 45 mm Hg. Renal Regulation Although buffers and the respiratory system can compensate for changes in pH, the kidneys are the ultimate long-term regulator of acid–base balance. They are slower to respond to changes, re- quiring hours to days to correct imbalances, but their response is more permanent and selective than that of the other systems (Yucha, 2004). The kidneys maintain acid–base balance by selectively ex- creting or conserving bicarbonate and hydrogen ions. When ex- cess hydrogen ion is present and the pH falls (acidosis), the kidneys reabsorb and regenerate bicarbonate and excrete hydro- gen ion. In the case of alkalosis and a high pH, excess bicarbon- ate is excreted and hydrogen ion is retained. The normal serum bicarbonate level is 22 to 26 mEq/L. The relationship of the respiratory and renal regulation of acid–base balance is further explained in Box 52–2. 1 part carbonic acid or 1.2 mEq/L 20 parts bicarbonate or 24 mEq/L 6.8 7.35 7.45 7.8 NormalAcidosisDeath DeathAlkalosis Figure 52-10 ■ Carbonic acid–bicarbonate ratio and pH. BOX 52–2 Physiological Regulation of Acid–Base Balance Lungs Kidneys CO2 ϩ H2O ↔ H2CO3 ↔ H ϩ HCO3 Carbon dioxide Hydrogen ϩ Carbonic acid ϩ water bicarbonate The lungs and kidneys are the two major systems that are working on a continuous basis to help regulate the acid–base balance in the body. In the biochemical reactions above, the processes are all reversible and go back and forth as the body’s needs change. The lungs can work very quickly and do their part by either retaining or getting rid of carbon diox- ide by changing the rate and depth of respirations. The kidneys work much more slowly; they may take hours to days to regulate the bal- ance by either excreting or conserving hydrogen and bicarbonate ions. Under normal conditions, the two systems work together to maintain homeostasis. MediaLinkAcid-BaseBalanceAnimation koz74686_ch52.qxd 11/8/06 2:06 PM Page 1433
  12. 12. 1434 UNIT X / Promoting Physiologic Health FACTORS AFFECTING BODY FLUID, ELECTROLYTES, AND ACID–BASE BALANCE The ability of the body to adjust fluids, electrolytes, and acid–base balance is influenced by age, gender and body size, environmental temperature, and lifestyle. Age Infants and growing children have much greater fluid turnover than adults because their higher metabolic rate increases fluid loss. Infants lose more fluid through the kidneys because imma- ture kidneys are less able to conserve water than adult kidneys. In addition, infants’ respirations are more rapid and the body surface area is proportionately greater than that of adults, in- creasing insensible fluid losses. The more rapid turnover of fluid plus the losses produced by disease can create critical fluid imbalances in children much more rapidly than in adults. In elderly people, the normal aging process may affect fluid balance. The thirst response often is blunted. Antidiuretic hor- mone levels remain normal or may even be elevated, but the nephrons become less able to conserve water in response to ADH. Increased levels of atrial natriuretic factor seen in older adults may also contribute to this impaired ability to conserve water. These normal changes of aging increase the risk of dehy- dration. When combined with the increased likelihood of heart diseases, impaired renal function, and multiple drug regimens, the older adult’s risk for fluid and electrolyte imbalance is sig- nificant. Additionally, it is important to consider that the older adult has thinner, more fragile skin and veins, which can make an intravenous insertion more difficult. Gender and Body Size Total body water also is affected by gender and body size. Be- cause fat cells contain little or no water, and lean tissue has a high water content, people with a higher percentage of body fat have less body fluid. Women have proportionately more body fat and less body water than men. Water accounts for approxi- mately 60% of an adult man’s weight, but only 52% for an adult woman. In an obese individual this may be even less, with wa- ter responsible for only 30% to 40% of the person’s weight. Environmental Temperature People with an illness and those participating in strenuous ac- tivity are at risk for fluid and electrolyte imbalances when the environmental temperature is high. Fluid losses through sweat- ing are increased in hot environments as the body attempts to dissipate heat. These losses are even greater in people who have not been acclimatized to the environment. Both salt and water are lost through sweating. When only water is replaced, salt depletion is a risk. The person who is salt depleted may experience fatigue, weakness, headache, and gas- trointestinal symptoms such as anorexia and nausea. The risk of adverse effects is even greater if lost water is not replaced. Body temperature rises, and the person is at risk for heat exhaustion or heatstroke. Heatstroke may occur in older adults or ill people during prolonged periods of heat; it can also affect athletes and LIFESPAN CONSIDERATIONS Fluid and Electrolyte Imbalance INFANTS AND CHILDREN Infants are at high risk for fluid and electrolyte imbalance because ■ Their immature kidneys cannot concentrate urine. ■ They have a rapid respiratory rate and proportionately larger body surface area than adults, leading to greater insensate loss through the skin and respirations. ■ They cannot express thirst, nor actively seek fluids. Vomiting and/or diarrhea in infants and young children can lead quickly to electrolyte imbalance. Oral rehydration therapy (ORT) (e.g., electrolyte solutions such as Pedialyte) should be used to restore fluid and electrolyte balance in mild to moderate dehydration (American Medical Association et al., 2004). Prompt treatment with ORT can pre- vent the need for intravenous therapy and hospitalization (Spandor- fer, Alessandrini, Joffe, Localio, & Shaw, 2005). Even if the child is nauseated and vomiting, small sips of ORT can be helpful. ELDERS Certain changes related to aging place the elder at risk for serious problems with fluid and electrolyte imbalance, if homeostatic mecha- nisms are compromised. Some of the changes are ■ A decrease in thirst sensation. ■ A decrease in ability of the kidneys to concentrate urine. ■ A decrease in intracellular fluid and in total body water. ■ A decrease in response to body hormones that help regulate fluid and electrolytes. Other factors that may influence fluid and electrolyte balance in elders are ■ Increased use of diuretics for hypertension and heart disease. ■ Decreased intake of food and water, especially in elders with de- mentia or who are dependent on others to feed them and offer them fluids. ■ Preparations for certain diagnostic tests that have the client NPO for long periods of time or cause diarrhea from laxative preps. ■ Clients with impaired renal function, such as elders with diabetes. ■ Those having certain diagnostic procedures. (Dyes used for some procedures, such as arteriograms and cardiac catheterizations, may cause further renal problems. Always see that the client is well hydrated before, during, and after the procedure to help in diluting and excreting the dye. If the client is NPO for the procedure, the nurse should check with the primary care provider to see if IV flu- ids are needed.) ■ Any condition that may tax the normal compensatory mecha- nisms, such as a fever, influenza, surgery, or heat exposure. All of these conditions increase elders’ risk for fluid and electrolyte imbalance. The change can happen quickly and become serious in a short time. Astute observations and quick actions by the nurse can help prevent serious consequences. A change in mental status may be the first symptom of impairment and must be further evaluated to determine the cause. koz74686_ch52.qxd 11/8/06 2:06 PM Page 1434
  13. 13. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1435 laborers when their heat production exceeds the body’s ability to dissipate heat. Consuming adequate amounts of cool liquids, particularly dur- ing strenuous activity, reduces the risk of adverse effects from heat. Balanced electrolyte solutions and carbohydrate-electrolyte solutions such as sports drinks are recommended because they replace both water and electrolytes lost through sweat. Lifestyle Other factors such as diet, exercise, and stress affect fluid, elec- trolyte, and acid–base balance. The intake of fluids and electrolytes is affected by the diet. People with anorexia nervosa or bulimia are at risk for severe fluid and electrolyte imbalances because of inadequate intake or purging regimens (e.g., induced vomiting, use of diuretics and laxatives). Seriously malnourished people have decreased serum albumin levels, and may develop edema because the os- motic draw of fluid into the vascular compartment is reduced. When calorie intake is not adequate to meet the body’s needs, fat stores are broken down and fatty acids are released, increas- ing the risk of acidosis. Regular weight-bearing physical exercise such as walking, running, or bicycling has a beneficial effect on calcium balance. The rate of bone loss that occurs in postmenopausal women and older men is slowed with regular exercise, reducing the risk of osteoporosis. Stress can increase cellular metabolism, blood glucose con- centration, and catecholamine levels. In addition, stress can in- crease production of ADH, which in turn decreases urine production. The overall response of the body to stress is to in- crease the blood volume. Other lifestyle factors can also affect fluid, electrolyte, and acid–base balance. Heavy alcohol consumption affects elec- trolyte balance, increasing the risk of low calcium, magnesium, and phosphate levels. The risk of acidosis associated with breakdown of fat tissue also is greater in the person who drinks large amounts of alcohol. DISTURBANCES IN FLUID VOLUME, ELECTROLYTE, AND ACID–BASE BALANCES A number of factors such as illness, trauma, surgery, and med- ications can affect the body’s ability to maintain fluid, elec- trolyte, and acid–base balance. The kidneys play a major role in maintaining fluid, electrolyte, and acid–base balance, and renal disease is a significant cause of imbalance. Clients who are con- fused or unable to communicate their needs are at risk for inad- equate fluid intake. Vomiting, diarrhea, or nasogastric suction can cause significant fluid losses. Tissue trauma, such as burns, causes fluid and electrolytes to be lost from damaged cells. De- creased blood flow to the kidneys due to impaired cardiac func- tion stimulates the renin-angiotensin-aldosterone system, causing sodium and water retention. Medications such as di- uretics or corticosteroids can result in abnormal losses of elec- trolytes and fluid loss or retention. Diseases such as diabetes mellitus or chronic obstructive lung disease may affect acid–base balance. Diabetic ketoacidosis, cancer, and head in- jury may also lead to electrolyte imbalances. Fluid Imbalances Fluid imbalances are of two basic types: isotonic and osmolar. Isotonic imbalances occur when water and electrolytes are lost or gained in equal proportions, so that the osmolality of body fluids remains constant. Osmolar imbalances involve the loss or gain of only water, so that the osmolality of the serum is al- tered. Thus four categories of fluid imbalances may occur: (a) an isotonic loss of water and electrolytes, (b) an isotonic gain of water and electrolytes, (c) a hyperosmolar loss of only water, and (d) a hypo-osmolar gain of only water. These are re- ferred to, respectively, as fluid volume deficit, fluid volume excess, dehydration (hyperosmolar imbalance), and overhy- dration (hypo-osmolar imbalance). Fluid Volume Deficit Isotonic fluid volume deficit (FVD) occurs when the body loses both water and electrolytes from the ECF in similar proportions. Thus, the decreased volume of fluid remains isotonic. In FVD, fluid is initially lost from the intravascular compartment, so it often is called hypovolemia. FVD generally occurs as a result of (a) abnormal losses through the skin, gastrointestinal tract, or kidney; (b) de- creased intake of fluid; (c) bleeding; or (d) movement of fluid into a third space. See the section on third space syndrome that follows. For the risk factors and clinical signs related to fluid volume deficit, see Table 52–4. THIRD SPACE SYNDROME. In third space syndrome, fluid shifts from the vascular space into an area where it is not readily accessible as extracellular fluid. This fluid remains in the body but is essentially unavailable for use, causing an isotonic fluid volume deficit. Fluid may be sequestered in the bowel, in the in- terstitial space as edema, in inflamed tissue, or in potential spaces such as the peritoneal or pleural cavities. The client with third space syndrome has an isotonic fluid deficit but may not manifest apparent fluid loss or weight loss. Careful nursing assessment is vital to effectively identify and in- tervene for clients experiencing third-spacing. Because the fluid shifts back into the vascular compartment after time, assessment for manifestations of fluid volume excess or hypervolemia is also vital. Fluid Volume Excess Fluid volume excess (FVE) occurs when the body retains both water and sodium in similar proportions to normal ECF. This is commonly referred to as hypervolemia (increased blood vol- ume). FVE is always secondary to an increase in the total body sodium content, which leads to an increase in total body water. Because both water and sodium are retained, the serum sodium concentration remains essentially normal and the excess vol- ume of fluid is isotonic. Specific causes of FVE include (a) ex- cessive intake of sodium chloride; (b) administering sodium-containing infusions too rapidly, particularly to clients MediaLinkDeterminingBodyFluidProblemsApplication koz74686_ch52.qxd 11/8/06 2:06 PM Page 1435
  14. 14. 1436 UNIT X / Promoting Physiologic Health with impaired regulatory mechanisms; and (c) disease processes that alter regulatory mechanisms, such as heart fail- ure, renal failure, cirrhosis of the liver, and Cushing’s syndrome. The risk factors and clinical manifestations for FVE are sum- marized in Table 52–5. EDEMA. In fluid volume excess, both intravascular and intersti- tial spaces have an increased water and sodium content. Excess interstitial fluid is known as edema. Edema typically is most ap- parent in areas where the tissue pressure is low, such as around the eyes, and in dependent tissues (known as dependent edema), where hydrostatic capillary pressure is high. Edema can be caused by several different mechanisms. The three main mechanisms are increased capillary hydrostatic pres- sure, decreased plasma oncotic pressure, and increased capil- lary permeability. It may be due to FVE that increases capillary hydrostatic pressures, pushing fluid into the interstitial tissues. This type of edema is often seen in dependent tissues such as the feet, ankles, and sacrum because of the effects of gravity. Low levels of plasma proteins from malnutrition or liver or kidney diseases can reduce the plasma oncotic pressure so that fluid is not drawn into the capillaries from interstitial tissues, causing edema. With tissue trauma and some disorders such as allergic reactions, capillaries become more permeable, allowing fluid to escape into interstitial tissues. Obstructed lymph flow impairs the movement of fluid from interstitial tissues back into the vas- cular compartment, resulting in edema. Pitting edema is edema that leaves a small depression or pit after finger pressure is applied to the swollen area. The pit is caused by movement of fluid to adjacent tissue, away from the point of pressure (Figure 52-11 ■). Within 10 to 30 seconds the pit normally disappears. TABLE 52–4 Isotonic Fluid Volume Deficit RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS Loss of water and electrolytes from ■ Vomiting ■ Diarrhea ■ Excessive sweating ■ Polyuria ■ Fever ■ Nasogastric suction ■ Abnormal drainage or wound losses Insufficient intake due to ■ Anorexia ■ Nausea ■ Inability to access fluids ■ Impaired swallowing ■ Confusion, depression Complaints of weakness and thirst Weight loss ■ 2% loss ϭ mild FVD ■ 5% loss ϭ moderate ■ 8% loss ϭ severe Fluid intake less than output Decreased tissue turgor Dry mucous membranes, sunken eyeballs, decreased tearing Subnormal temperature Weak, rapid pulse Decreased blood pressure Postural (orthostatic) hypotension (significant drop in BP when moving from lying to sitting or standing position) Flat neck veins; decreased capillary refill Decreased central venous pressure Decreased urine volume (<30 mL/h) Increased specific gravity of urine (>1.030) Increased hematocrit Increased blood urea nitrogen (BUN) Assess for clinical manifestations of FVD. Monitor weight and vital signs, including temperature. Assess tissue turgor. Monitor fluid intake and output. Monitor laboratory findings. Administer oral and intravenous fluids as indicated. Provide frequent mouth care. Implement measures to prevent skin breakdown. Provide for safety, e.g., provide assistance for a client rising from bed. TABLE 52–5 Isotonic Fluid Volume Excess RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS Weight gain ■ 2% gain ϭ mild FVE ■ 5% gain ϭ moderate ■ 8% gain ϭ severe Fluid intake greater than output Full, bounding pulse; tachycardia Increased blood pressure and central venous pressure Distended neck and peripheral veins; slow vein emptying Moist crackles (rales) in lungs; dyspnea, shortness of breath Mental confusion Excess intake of sodium-containing intravenous fluids Excess ingestion of sodium in diet or medications (e.g., sodium bicarbonate antacids such as Alka-Seltzer or hypertonic enema solutions such as Fleet’s) Impaired fluid balance regulation related to ■ Heart failure ■ Renal failure ■ Cirrhosis of the liver Assess for clinical manifestations of FVE. Monitor weight and vital signs. Assess for edema. Assess breath sounds. Monitor fluid intake and output. Monitor laboratory findings. Place in Fowler’s position. Administer diuretics as ordered. Restrict fluid intake as indicated. Restrict dietary sodium as ordered. Implement measures to prevent skin breakdown. koz74686_ch52.qxd 11/8/06 2:06 PM Page 1436
  15. 15. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1437 Dehydration Dehydration, or hyperosmolar imbalance, occurs when water is lost from the body leaving the client with excess sodium. Be- cause water is lost while electrolytes, particularly sodium, are retained, the serum osmolality and serum sodium levels in- crease. Water is drawn into the vascular compartment from the interstitial space and cells, resulting in cellular dehydration. Older adults are at particular risk for dehydration because of de- creased thirst sensation. This type of water deficit also can af- fect clients who are hyperventilating or have prolonged fever or are in diabetic ketoacidosis and those receiving enteral feedings with insufficient water intake. Overhydration Overhydration, also known as hypo-osmolar imbalance or water excess, occurs when water is gained in excess of electrolytes, re- sulting in low serum osmolality and low serum sodium levels. Water is drawn into the cells, causing them to swell. In the brain this can lead to cerebral edema and impaired neurologic func- tion. Water intoxication often occurs when both fluid and elec- trolytes are lost, for example, through excessive sweating, but only water is replaced. It can also result from the syndrome of inappropriate antidiuretic hormone (SIADH), a disorder that can occur with some malignant tumors, AIDS, head injury, or ad- ministration of certain drugs such as barbiturates or anesthetics. Figure 52-11 ■ Evaluation of edema. A, Palpate for edema over the tibia as shown here and behind the medial malleolus, and over the dorsum of each foot. B, Four-point scale for grading edema. 2mm 1+ Barely detectable 4mm 2+ 2 to 4 mm 6mm 3+ 5 to 7 mm 12mm 4+ More than 7 mm BA DRUG CAPSULE Diuretic Agent furosemide (Lasix) THE CLIENT WITH FLUID VOLUME EXCESS Furosemide inhibits sodium and chloride reabsorption in the loop of Henle and the distal renal tubule. This results in significant diuresis, with renal excretion of water, sodium chloride, magnesium, hydrogen, and calcium. Furosemide is commonly used for the clinical management of edema secondary to heart failure, treatment of hypertension, and treat- ment of hepatic or renal disease. Therapeutic effects include diuresis and lowering of blood pressure. NURSING RESPONSIBILITIES ■ Assess the client’s fluid status regularly. Assessment should in- clude daily weights, close monitoring of intake and output, skin turgor, edema, lung sounds, and mucous membranes. ■ Monitor the client’s potassium levels. Furosemide is a loop diuretic which excretes potassium and may result in hypokalemia. ■ Administer in the morning to avoid increased urination during hours of sleep. ■ If the client is also taking digitalis glycosides, he or she should be assessed for anorexia, nausea, vomiting, muscle cramps, pares- thesia, and confusion. The potassium-depleting effect of furosemide places the client at increased risk for digitalis toxicity. CLIENT AND FAMILY TEACHING ■ Medication should be taken exactly as directed. If you miss a dose, take it as soon as possible; however, if a day has been missed, do not double the dose the next day. ■ Weigh on a daily basis and report weight gain or loss of more than 3 lb in 1 day to your primary care provider. ■ Contact your primary care provider immediately if you begin to experience muscle weakness, cramps, nausea, dizziness, numbness, or tingling of the extremities. ■ Some form of potassium supplementation will be needed. The primary care provider may order oral potassium supplements for you; if not, you will need to consume a diet high in potassium. ■ Make position changes slowly in order to minimize dizziness from orthostatic hypotension. Note: Prior to administering any medication, review all aspects with a current drug handbook or other reliable source. MediaLinkFurosemideDrugAnimation koz74686_ch52.qxd 11/8/06 2:07 PM Page 1437
  16. 16. 1438 UNIT X / Promoting Physiologic Health Electrolyte Imbalances The most common and most significant electrolyte imbalances involve sodium, potassium, calcium, magnesium, chloride, and phosphate. Sodium Sodium (Naϩ ), the most abundant cation in the extracellular fluid, not only moves into and out of the body but also moves in careful balance among the three fluid compartments. It is found in most body secretions, for example, saliva, gastric and intes- tinal secretions, bile, and pancreatic fluid. Therefore, continu- ous excretion of any of these fluids, such as via intestinal suction, can result in a sodium deficit. Because of its role in reg- ulating water balance, sodium imbalances usually are accompa- nied by water imbalance. Hyponatremia is a sodium deficit, or serum sodium level of less than 135 mEq/L, and is, in acute care settings, a common electrolyte imbalance. Because of sodium’s role in determining the osmolality of ECF, hyponatremia typically results in a low serum osmolality. Water is drawn out of the vascular compart- ment into interstitial tissues and the cells (Figure 52-12 ■, A), causing the clinical manifestations associated with this disorder. As sodium levels decrease, the brain and nervous system are af- fected by cellular edema. Severe hyponatremia, serum levels below 110 mEq/L, is a medical emergency and can lead to per- manent neurological damage (Astle, 2005). Hypernatremia is excess sodium in ECF, or a serum sodium of greater than 145 mEq/L. Because the osmotic pressure of ex- tracellular fluid is increased, fluid moves out of the cells into the ECF (Figure 52-12 ■, B). As a result, the cells become dehy- drated. Like hyponatremia, the primary manifestations of hy- pernatremia are neurological in nature. It is important to note that a person’s thirst mechanism pro- tects against hypernatremia. For example, when an individual becomes thirsty, the body is stimulated to drink water which helps correct the hypernatremia. Clients at risk for hyperna- tremia are those who are unable to access water (e.g., uncon- scious, unable to request fluids such as infants or elders with dementia, or ill clients with an impaired thirst mechanism). Table 52–6 lists risk factors and clinical signs for hypona- tremia and hypernatremia. Potassium Although the amount of potassium (Kϩ ) in extracellular fluid is small, it is vital to normal neuromuscular and cardiac function. Normal renal function is important for maintenance of potas- sium balance as 80% of potassium is excreted by the kidneys. Potassium must be replaced daily to maintain its balance. Nor- mally, potassium is replaced in food. See previous Box 52–1 on page 1431 for a review of foods high in potassium. Hypokalemia is a potassium deficit or a serum potassium level of less than 3.5 mEq/L. Gastrointestinal losses of potas- sium through vomiting and gastric suction are common causes of hypokalemia, as are the use of potassium-wasting diuretics, such as thiazide diuretics or loop diuretics (e.g., furosemide). Symptoms of hypokalemia are usually mild until the level drops below 3 mEq/L unless the decrease in potassium was rapid. When the decrease is gradual, the body compensates by shifting potassium from the intracellular environment into the serum. Hyperkalemia is a potassium excess or a serum potassium level greater than 5.0 mEq/L. Hyperkalemia is less common than hypokalemia and rarely occurs in clients with normal renal function. It is, however, more dangerous than hypokalemia and can lead to cardiac arrest. As with hypokalemia, symptoms are more severe and occur at lower levels when the increase in potassium is abrupt. Table 52–6 lists risk factors and clinical signs for hypokalemia and hyperkalemia. RESEARCH NOTE How Prevalent Is Chronic Dehydration in Elders? Previous research has documented that dehydration is a problem in hospitalized elders, and low fluid intake has been documented to be a problem in nursing home residents. The authors questioned whether chronic dehydration is also a problem in elders living in the community. The researchers conducted a descriptive, retrospective study of 185 eld- ers ranging from 75 to 100 years old. This group of elders visited a hos- pital emergency department during a 1-month period of time. Dehydration was defined as a ratio of blood urea nitrogen to creatine (BUN:Cr) greater than 20:1. Forty-eight percent of the group were de- hydrated on admission to the emergency department. The elders from a residential facility were most likely to be dehydrated (65%); however, 44% of the elders living in the community were dehydrated. IMPLICATIONS The results demonstrated that dehydration is a problem with both eld- ers living in the community as well as elders living in residential facili- ties. Prevention of dehydration is an important intervention for nurses working with elders. Nursing interventions need to include talking with elders and their families about the dangers of dehydration and sug- gesting strategies to prevent dehydration. Note: From “Unrecognized Chronic Dehydration in Older Adults. Examining Preva- lence Rate and Risk Factors,” by J. A. Bennett, V. Thomas, and B. Riegel, 2004, Journal of Gerontological Nursing, 30(1), pp. 22–28. Copyright © 2004 SLACK, Inc. Reprinted with permission. H2O H2O H2O Cell swells as water is pulled in from ECF Hyponatremia: Na+less than 135 mEq/L A Figure 52-12 ■ The extracellular sodium level affects cell size. A, In hyponatremia, cells swell; B, in hypernatremia, cells shrink in size. H2O Cell shrinks as water is pulled out into ECF Hypernatremia: Na+greater than 145 mEq/L B koz74686_ch52.qxd 11/8/06 2:07 PM Page 1438
  17. 17. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1439 TABLE 52–6 Electrolyte Imbalances RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS Hyponatremia Loss of sodium ■ Gastrointestinal fluid loss ■ Sweating ■ Use of diuretics Gain of water ■ Hypotonic tube feedings ■ Excessive drinking of water ■ Excess IV D5W (dextrose in water) administration Syndrome of inappropriate ADH (SIADH) ■ Head injury ■ AIDS ■ Malignant tumors Hypernatremia Loss of water ■ Insensible water loss (hyperventilation or fever) ■ Diarrhea ■ Water deprivation Gain of sodium ■ Parenteral administration of saline solutions ■ Hypertonic tube feedings without adequate water ■ Excessive use of table salt (1 tsp contains 2,300 mg of sodium) Conditions such as ■ Diabetes insipidus ■ Heat stroke Hypokalemia Loss of potassium ■ Vomiting and gastric suction ■ Diarrhea ■ Heavy perspiration ■ Use of potassium-wasting drugs (e.g., diuretics) ■ Poor intake of potassium (as with debilitated clients, alcoholics, anorexia nervosa) ■ Hyperaldosteronism Hyperkalemia Decreased potassium excretion ■ Renal failure ■ Hypoaldosteronism ■ Potassium-conserving diuretics High potassium intake Lethargy, confusion, apprehension Muscle twitching Abdominal cramps Anorexia, nausea, vomiting Headache Seizures, coma Laboratory findings: Serum sodium below 135 mEq/L Serum osmolality below 280 mOsm/kg Thirst Dry, sticky mucous membranes Tongue red, dry, swollen Weakness Severe hypernatremia: ■ Fatigue, restlessness ■ Decreasing level of consciousness ■ Disorientation ■ Convulsions Laboratory findings: Serum sodium above 145 mEq/L Serum osmolality above 300 mOsm/kg Muscle weakness, leg cramps Fatigue, lethargy Anorexia, nausea, vomiting Decreased bowel sounds, decreased bowel motility Cardiac dysrhythmias Depressed deep-tendon reflexes Weak, irregular pulses Laboratory findings: Serum potassium below 3.5 mEq/L Arterial blood gases (ABGs) may show alkalosis T wave flattening and ST segment depression on ECG Gastrointestinal hyperactivity, diarrhea Irritability, apathy, confusion Cardiac dysrhythmias or arrest Muscle weakness, areflexia (absence of reflexes) Decreased heart rate; Irregular pulse Assess clinical manifestations. Monitor fluid intake and output. Monitor laboratory data (e.g., serum sodium). Assess client closely if administering hypertonic saline solutions. Encourage food and fluid high in sodium if permitted (e.g., table salt, bacon, ham, processed cheese). Limit water intake as indicated. Monitor fluid intake and output. Monitor behavior changes (e.g., restlessness, disorientation). Monitor laboratory findings (e.g., serum sodium). Encourage fluids as ordered. Monitor diet as ordered (e.g., restrict intake of salt and foods high in sodium). Monitor heart rate and rhythm. Monitor clients receiving digitalis (e.g., digoxin) closely, because hypokalemia increases risk of digitalis toxicity. Administer oral potassium as ordered with food or fluid to prevent gastric irritation. Administer IV potassium solutions at a rate no faster than 10–20 mEq/h; never administer undiluted potassium intravenously. For clients receiving IV potassium, monitor for pain and inflammation at the injection site. Teach client about potassium-rich foods. Teach clients how to prevent excessive loss of potassium (e.g., through abuse of diuretics and laxatives). Closely monitor cardiac status and ECG. Administer diuretics and other medications such as glucose and insulin as ordered. Hold potassium supplements and Kϩ conserving diuretics. continued on page 1440 koz74686_ch52.qxd 11/8/06 2:07 PM Page 1439
  18. 18. 1440 UNIT X / Promoting Physiologic Health RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS Hyperkalemia—continued TABLE 52–6 Electrolyte Imbalances—continued ■ Excessive use of Kϩ containing salt substitutes ■ Excessive or rapid IV infusion of potassium ■ Potassium shift out of the tissue cells into the plasma (e.g., infections, burns, acidosis) Hypocalcemia Surgical removal of the parathyroid glands Conditions such as ■ Hypoparathyroidism ■ Acute pancreatitis ■ Hyperphosphatemia ■ Thyroid carcinoma Inadequate vitamin D intake ■ Malabsorption ■ Hypomagnesemia ■ Alkalosis ■ Sepsis ■ Alcohol abuse Hypercalcemia ■ Prolonged immobilization Conditions such as ■ Hyperparathyroidism ■ Malignancy of the bone ■ Paget’s disease Hypomagnesemia ■ Excessive loss from the gastrointestinal tract (e.g., from nasogastric suction, diarrhea, fistula drainage) ■ Long-term use of certain drugs (e.g., diuretics, aminoglycoside antibiotics) Conditions such as ■ Chronic alcoholism ■ Pancreatitis ■ Burns Paresthesias and numbness in extremities Laboratory findings: Serum potassium above 5.0 mEq/L Peaked T wave, widened QRS on ECG Numbness, tingling of the extremities and around the mouth Muscle tremors, cramps; if severe can progress to tetany and convulsions Cardiac dysrhythmias; decreased cardiac output Positive Trousseau’s and Chvostek’s signs (see Table 52–8) Confusion, anxiety, possible psychoses Hyperactive deep tendon reflexes Laboratory findings: Serum calcium less than 8.5 mg/dL or 4.5 mEq/L (total) Lengthened QT intervals Prolonged ST segments Lethargy, weakness Depressed deep-tendon reflexes Bone pain Anorexia, nausea, vomiting Constipation Polyuria, hypercalciuria Flank pain secondary to urinary calculi Dysrhythmias, possible heart block Laboratory findings: Serum calcium greater than 10.5 mg/dL or 5.5 mEq/L (total) Shortened QT intervals Shortened ST segments Neuromuscular irritability with tremors Increased reflexes, tremors, convulsions Positive Chvostek’s and Trousseau’s signs (see Table 52–8) Tachycardia, elevated blood pressure, dysrhythmias Disorientation and confusion Vertigo Anorexia, dysphagia Respiratory difficulties Laboratory findings: Serum magnesium below 1.5 mEq/L Prolonged PR intervals, widened QRS complexes, prolonged QT intervals, depressed ST segments, broad flattened T waves, prominent U waves Monitor serum Kϩ levels carefully; a rapid drop may occur as potassium shifts into the cells. Teach clients to avoid foods high in potassium and salt substitutes. Closely monitor respiratory and cardiovascular status. Take precautions to protect a confused client. Administer oral or parenteral calcium supplements as ordered. When administering intravenously, closely monitor cardiac status and ECG during infusion. Teach clients at high risk for osteoporosis about ■ Dietary sources rich in calcium. ■ Recommendation for 1,000–1,500 mg of calcium per day. ■ Calcium supplements. ■ Regular exercise. ■ Estrogen replacement therapy for postmenopausal women. Increase client movement and exercise. Encourage oral fluids as permitted to maintain a dilute urine. Teach clients to limit intake of food and fluid high in calcium. Encourage ingestion of fiber to prevent constipation. Protect a confused client; monitor for pathologic fractures in clients with long-term hypercalcemia. Encourage intake of acid-ash fluids (e.g., prune or cranberry juice) to counteract deposits of calcium salts in the urine. Assess clients receiving digitalis for digitalis toxicity. Hypomagnesemia increases the risk of toxicity. Take protective measures when there is a possibility of seizures. ■ Assess the client’s ability to swallow water prior to initiating oral feeding. ■ Initiate safety measures to prevent injury during seizure activity. ■ Carefully administer magnesium salts as ordered. Encourage clients to eat magnesium-rich foods if permitted (e.g., whole grains, meat, seafood, and green leafy vegetables). Refer clients to alcohol treatment programs as indicated. koz74686_ch52.qxd 11/8/06 2:07 PM Page 1440
  19. 19. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1441 RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS TABLE 52–6 Electrolyte Imbalances—continued Hypermagnesemia Abnormal retention of magnesium, as in ■ Renal failure ■ Adrenal insufficiency ■ Treatment with magnesium salts Peripheral vasodilation, flushing Nausea, vomiting Muscle weakness, paralysis Hypotension, bradycardia Depressed deep-tendon reflexes Lethargy, drowsiness Respiratory depression, coma Respiratory and cardiac arrest if hypermagnesemia is severe Laboratory findings: Serum magnesium above 2.5 mEq/L Electrocardiogram showing prolonged QT interval, prolonged PR interval, widened QRS complexes, tall T waves Monitor vital signs and level of consciousness when clients are at risk. If patellar reflexes are absent, notify the primary care provider. Advise clients who have renal disease to contact their primary care provider before taking over-the-counter drugs. CLINICAL ALERT Potassium may be given intravenously for severe hypokalemia. It must ALWAYS be diluted appropriately and NEVER be given IV push. Potassium that is to be given IV should be mixed in the pharmacy and double- checked prior to administration by two nurses. The usual concentration of IV potassium is 20 to 40 mEq/L. ■ Calcium Regulating levels of calcium (Ca2ϩ ) in the body is more com- plex than the other major electrolytes so calcium balance can be affected by many factors. Imbalances of this electrolyte are rel- atively common. Hypocalcemia is a calcium deficit, or a total serum calcium level of less than 8.5 mg/dL or an ionized calcium level of less than 4.0 mg/dL. Severe depletion of calcium can cause tetany with muscle spasms and paresthesias (numbness and tingling around the mouth and hands and feet) and can lead to convul- sions. Two signs indicate hypocalcemia: The Chvostek’s sign is contraction of the facial muscles that is produced by tapping the facial nerve in front of the ear (Figure 52-13 ■, A). Trousseau’s sign is a carpal spasm that occurs by inflating a blood pressure cuff on the upper arm to 20 mm Hg greater than the systolic pressure for 2 to 5 minutes (Figure 52-13 ■, B). Clients at great- est risk for hypocalcemia are those whose parathyroid glands have been removed. This is frequently associated with total thy- roidectomy or bilateral neck surgery for cancer. Low serum magnesium levels (hypomagnesemia) and chronic alcoholism also increase the risk of hypocalcemia. Hypercalcemia, or total serum calcium levels greater than 10.5 mg/dL, or an ionized calcium level of greater than 5.0 mg/dL, most often occurs when calcium is mobilized from the bony skeleton. This may be due to malignancy or prolonged im- mobilization. B. Positive Trousseau's SignA. Positive Chvostek's Sign Figure 52-13 ■ A, Positive Chvostek’s sign. B, Positive Trousseau’s sign. From Lemone, Priscilla; Burke, Karen M., Medical Surgical Nursing: Critical Thinking in Client Care, 3rd ed © 2004. Reproduced with permission of Pearson Education, Inc., Upper Saddle River, New Jersey. koz74686_ch52.qxd 11/13/06 4:49 PM Page 1441
  20. 20. 1442 UNIT X / Promoting Physiologic Health The risk factors and clinical manifestations related to cal- cium imbalances are found in Table 52–6. Magnesium Magnesium (Mg2ϩ ) imbalances are relatively common in hospitalized clients, although they may be unrecognized. Hypomagnesemia is a magnesium deficiency, or a total serum magnesium level of less than 1.5 mEq/L. It occurs more fre- quently than hypermagnesemia. Chronic alcoholism is the most common cause of hypomagnesemia. Magnesium deficiency also may aggravate the manifestations of alcohol withdrawal, such as delirium tremens (DTs). Hypermagnesemia is present when the serum magnesium level rises above 2.5 mEq/L. It is due to in- creased intake or decreased excretion. It is often iatrogenic, that is, a result of overzealous magnesium therapy. Table 52–6 lists risk factors and manifestations for clients with altered magesium balance. Chloride Because of the relationship between sodium ions and chloride ions (ClϪ ), imbalances of chloride commonly occur in conjunc- tion with sodium imbalances. Hypochloremia is a decreased serum chloride level, in adults a level below 95 mEq/L, and is usually related to excess losses of chloride ion through the GI tract, kidneys, or sweating. Hypochloremic clients are at risk for alkalosis and may experience muscle twitching, tremors, or tetany. Conditions that cause sodium retention also can lead to a high serum chloride level or hyperchloremia, in adults a level above 108 mEq/L. Excess replacement of sodium chloride or potassium chloride are additional risk factors for high serum chloride levels. The manifestations of hyperchloremia include acidosis, weak- ness, and lethargy, with a risk of dysrhythmias and coma. Phosphate The phosphate anion PO4 Ϫ is found in both intracellular and ex- tracellular fluid. Most of the phosphorus (Pϩ ) in the body exists as PO4 Ϫ . Phosphate is critical for cellular metabolism because it is a major component of adenosine triphosphate (ATP). Phosphate imbalances frequently are related to therapeutic in- terventions for other disorders. Glucose and insulin administra- tion and total parenteral nutrition can cause phosphate to shift into the cells from extracellular fluid compartments, leading to hypophosphatemia, defined in adults as a total serum phosphate level less than 2.5 mg/dL.Alcohol withdrawal, acid–base imbal- ances, and the use of antacids that bind with phosphate in the GI tract are other possible causes of low serum phosphate levels. Manifestations of hypophosphatemia include paresthesias, mus- cle weakness and pain, mental changes, and possible seizures. Hyperphosphatemia, defined in adults as a total serum phos- phate level greater than 4.5 mg/dL, occurs when phosphate shifts out of the cells into extracellular fluids (e.g., due to tissue trauma or chemotherapy for malignant tumors), in renal failure, or when excess phosphate is administered or ingested. Infants who are fed cow’s milk are at risk for hyperphosphatemia, as are people using phosphate-containing enemas or laxatives. Clients who have high serum phosphate levels may experience numbness and tingling around the mouth and in the fingertips, muscle spasms, and tetany. Acid–Base Imbalances Acid–base imbalances generally are classified as respiratory or metabolic by the general or underlying cause of the disorder. Car- bonic acid levels are normally regulated by the lungs through the retention or excretion of carbon dioxide, and problems of regula- tion lead to respiratory acidosis or alkalosis. Bicarbonate and hy- drogen ion levels are regulated by the kidneys, and problems of regulation lead to metabolic acidosis or alkalosis. Healthy regula- tory systems will attempt to correct acid–base imbalances, a process called compensation. Respiratory Acidosis Hypoventilation and carbon dioxide retention cause carbonic acid levels to increase and the pH to fall below 7.35, a condition known as respiratory acidosis. Serious lung diseases such as asthma and COPD are common causes of respiratory acidosis. Central nervous system depression due to anesthesia or a narcotic overdose can sufficiently slow the respiratory rate so that carbon dioxide is retained. When respiratory acidosis occurs, the kidneys retain bicarbonate to restore the normal carbonic acid to bicarbon- ate ratio. Recall, however, that the kidneys are relatively slow to respond to changes in acid–base balance, so this compensatory response may require hours to days to restore the normal pH. Respiratory Alkalosis When a person hyperventilates, more carbon dioxide than nor- mal is exhaled, carbonic acid levels fall, and the pH rises to greater than 7.45. This condition is termed respiratory alkalosis. Psychogenic or anxiety-related hyperventilation is a common cause of respiratory alkalosis. Other causes include fever and respiratory infections. In respiratory alkalosis, the kidneys will excrete bicarbonate to return the pH to within the normal range. Often, however, the cause of the hyperventilation is eliminated and the pH returns to normal before renal compensation occurs. Metabolic Acidosis When bicarbonate levels are low in relation to the amount of carbonic acid in the body, the pH falls and metabolic acidosis develops. This may develop because of renal failure and the in- ability of the kidneys to excrete hydrogen ion and produce bi- carbonate. It also may occur when too much acid is produced in the body, for example, in diabetic ketoacidosis or starvation when fat tissue is broken down for energy. Metabolic acidosis stimulates the respiratory center, and the rate and depth of res- pirations increase. Carbon dioxide is eliminated and carbonic acid levels fall, minimizing the change in pH. This respiratory compensation occurs within minutes of the pH imbalance. Metabolic Alkalosis In metabolic alkalosis, the amount of bicarbonate in the body exceeds the normal 20-to-1 ratio. Ingestion of bicarbonate of soda as an antacid is one cause of metabolic alkalosis. Another koz74686_ch52.qxd 11/8/06 2:07 PM Page 1442
  21. 21. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1443 ANATOMY & PHYSIOLOGY REVIEW Gas Exchange QUESTIONS 1. Hypoventilation can affect gas exchange. What are some causes of hypoventilation? 2. How does the shallow breathing from hypoventilation cause the PaCO2 to increase and the pH to decrease? 3. ABGs that indicate an increased PaCO2 and a decreased pH reflect which acid–base imbalance? 4. Hyperventilation can also affect gas exchange. What are some causes of hyperventilation? 5. How does hyperventilation cause a decreased PaCO2 and increased pH? 6. ABGs that indicate a decreased PaCO2 and an increased pH reflect which acid–base imbalance? cause is prolonged vomiting with loss of hydrochloric acid from the stomach. The respiratory center is depressed in metabolic al- kalosis, and respirations slow and become more shallow. Car- bon dioxide is retained and carbonic acid levels increase, helping balance the excess bicarbonate. The risk factors and manifestations for acid–base imbalances are listed in Table 52–7. NURSING MANAGEMENT Assessing Assessing clients for fluid, electrolyte, and acid–base balance and imbalances is an important nursing care function. Compo- nents of the assessment include (a) the nursing history, (b) phys- ical assessment of the client, (c) clinical measurements, and (d) review of laboratory test results. Nursing History The nursing history is particularly important for identifying clients who are at risk for fluid, electrolyte, and acid–base im- balances. The current and past medical history reveal conditions such as chronic lung disease or diabetes mellitus that can disrupt normal balances. Medications prescribed to treat acute or chronic conditions (e.g., diuretic therapy for hypertension) also may place the client at risk for altered homeostasis. Functional, developmental, and socioeconomic factors must also be consid- ered in assessing the client’s risk. Older people and very young children, clients who must depend on others to meet their needs for food and fluid intake, and people who cannot afford or do not have the means to cook food for a balanced diet (e.g., home- less people) are at greater risk for fluid and electrolyte imbal- ances. Common risk factors are listed in Box 52–3. When obtaining the nursing history, the nurse needs to not only recognize risk factors but also elicit data about the client’s Bronchiole Pulmonary vein Pulmonary artery branch Red blood cell O2 molecule CO2 molecule Blood Capillary wall Alveolar wall O2 O2 CO2 CO2 From Turley, Susan M., Medical Language, 1st ed., © 2002. Reproduced with permission of Pearson Education, Inc., Upper Saddle River, New Jersey. koz74686_ch52.qxd 11/13/06 4:49 PM Page 1443
  22. 22. 1444 UNIT X / Promoting Physiologic Health TABLE 52–7 Acid–Base Imbalances RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS Respiratory Acidosis Increased pulse and respiratory rates Headache, dizziness Confusion, decreased level of consciousness (LOC) Convulsions Warm, flushed skin Chronic: Weakness Headache Laboratory findings: Arterial blood pH less than 7.35 PaCO2 above 45 mm Hg HCO3 Ϫ normal or slightly elevated in acute; above 26 mEq/L in chronic Complaints of shortness of breath, chest tightness Light-headedness with circumoral paresthesias and numbness and tingling of the extremities Difficulty concentrating Tremulousness, blurred vision Laboratory findings (in uncompensated respiratory alkalosis): Arterial blood pH above 7.45 PaCO2 less than 35 mm Hg Kussmaul’s respirations (deep, rapid respirations) Lethargy, confusion Headache Weakness Nausea and vomiting Laboratory findings: Arterial blood pH below 7.35 Serum bicarbonate less than 22 mEq/L PaCO2 less than 38 mm Hg with respiratory compensation Decreased respiratory rate and depth Dizziness Circumoral paresthesias, numbness and tingling of the extremities Hypertonic muscles, tetany Laboratory findings: Arterial blood pH above 7.45 Serum bicarbonate greater than 26 mEq/L PaCO2 higher than 45 mm Hg with respiratory compensation Acute lung conditions that impair alveolar gas exchange (e.g., pneumonia, acute pulmonary edema, aspiration of foreign body, near-drowning) Chronic lung disease (e.g., asthma, cystic fibrosis, or emphysema) Overdose of narcotics or sedatives that depress respiratory rate and depth Brain injury that affects the respiratory center Airway obstruction Mechanical chest injury Respiratory Alkalosis Hyperventilation due to ■ Extreme anxiety ■ Elevated body temperature ■ Overventilation with a mechanical ventilator ■ Hypoxia ■ Salicylate overdose Brain stem injury Fever Increased basal metabolic rate Metabolic Acidosis Conditions that increase nonvolatile acids in the blood (e.g., renal impairment, diabetes mellitus, starvation) Conditions that decrease bicarbonate (e.g., prolonged diarrhea) Excessive infusion of chloride-containing IV fluids (e.g., NaCl) Excessive ingestion of acids such as salicylates Cardiac arrest Metabolic Alkalosis Excessive acid losses due to ■ Vomiting ■ Gastric suction Excessive use of potassium-losing diuretics Excessive adrenal corticoid hormones due to ■ Cushing’s syndrome ■ Hyperaldosteronism Excessive bicarbonate intake from ■ Antacids ■ Parenteral NaHCO3 Frequently assess respiratory status and lung sounds. Monitor airway and ventilation; insert artificial airway and prepare for mechanical ventilation as necessary. Administer pulmonary therapy measures such as inhalation therapy, percussion and postural drainage, bronchodilators, and antibiotics as ordered. Monitor fluid intake and output, vital signs, and arterial blood gases. Administer narcotic antagonists as indicated. Maintain adequate hydration (2–3 L of fluid per day). Monitor vital signs and ABGs. Assist client to breathe more slowly. Help client breathe in a paper bag or apply a rebreather mask (to inhale CO2). Monitor ABG values, intake and output, and LOC. Administer IV sodium bicarbonate carefully if ordered. Treat underlying problem as ordered. Monitor intake and output closely. Monitor vital signs, especially respirations, and LOC. Administer ordered IV fluids carefully. Treat underlying problem. koz74686_ch52.qxd 11/8/06 2:07 PM Page 1444
  23. 23. CHAPTER 52 / Fluid, Electrolyte, and Acid–Base Balance 1445 food and fluid intake, fluid output, and the presence of signs or symptoms suggestive of altered fluid and electrolyte balance. The Assessment Interview provides examples of questions to elicit information regarding fluid, electrolyte, and acid–base balance. Physical Assessment Physical assessment to evaluate a client’s fluid, electrolyte, and acid–base status focuses on the skin, the oral cavity and mucous membranes, the eyes, the cardiovascular and respira- tory systems, and neurologic and muscular status. Data from this physical assessment are used to expand and verify infor- mation obtained in the nursing history. The focused physical assessment is summarized in Table 52–8 on page 1446. Refer to Tables 52–5 through 52–8 for possible abnormal findings related to specific imbalances. Clinical Measurements Three simple clinical measurements that the nurse can initiate without a primary care provider’s order are daily weights, vital signs, and fluid intake and output. DAILY WEIGHTS. Daily weight measurements provide a rela- tively accurate assessment of a client’s fluid status. Significant changes in weight over a short time (e.g., more than 5 pounds BOX 52–3 Common Risk Factors for Fluid, Electrolyte, and Acid–Base Imbalances CHRONIC DISEASES AND CONDITIONS ■ Chronic lung disease (COPD, asthma, cystic fibrosis) ■ Heart failure ■ Kidney disease ■ Diabetes mellitus ■ Cushing’s syndrome or Addison’s disease ■ Cancer ■ Malnutrition, anorexia nervosa, bulimia ■ Ileostomy ACUTE CONDITIONS ■ Acute gastroenteritis ■ Bowel obstruction ■ Head injury or decreased level of consciousness ■ Trauma such as burns or crushing injuries ■ Surgery ■ Fever, draining wounds, fistulas MEDICATIONS ■ Diuretics ■ Corticosteroids ■ Nonsteroidal anti-inflammatory drugs TREATMENTS ■ Chemotherapy ■ IV therapy and total parenteral nutrition ■ Nasogastric suction ■ Enteral feedings ■ Mechanical ventilation OTHER FACTORS ■ Age: Very old or very young ■ Inability to access food and fluids independently ASSESSMENT INTERVIEW Fluid, Electrolyte, and Acid–Base Balance CURRENT AND PAST MEDICAL HISTORY ■ Are you currently seeing a health care provider for treatment of any chronic diseases such as kidney disease, heart disease, high blood pressure, diabetes insipidus, or thyroid or parathyroid disorders? ■ Have you recently experienced any acute conditions such as gas- troenteritis, severe trauma, head injury, or surgery? If so, describe them. MEDICATIONS AND TREATMENTS ■ Are you currently taking any medications on a regular basis such as diuretics, steroids, potassium supplements, calcium supple- ments, hormones, salt substitutes, or antacids? ■ Have you recently undergone any treatments such as dialysis, par- enteral nutrition, or tube feedings or been on a ventilator? If so, when and why? FOOD AND FLUID INTAKE ■ How much and what type of fluids do you drink each day? ■ Describe your diet for a typical day. (Pay particular attention to the client’s intake of foods high in sodium content, of protein, and of whole grains, fruits, and vegetables.) ■ Have there been any recent changes in your food or fluid intake, for example, as a result of following a weight-loss program? ■ Are you on any type of restricted diet? ■ Has your food or fluid intake recently been affected by changes in ap- petite, nausea, or other factors such as pain or difficulty breathing? FLUID OUTPUT ■ Have you noticed any recent changes in the frequency or amount of urine output? ■ Have you recently experienced any problems with vomiting, diar- rhea, or constipation? If so, when and for how long? ■ Have you noticed any other unusual fluid losses such as excessive sweating? FLUID, ELECTROLYTE, AND ACID–BASE IMBALANCES ■ Have you gained or lost weight in recent weeks? ■ Have you recently experienced any symptoms such as excessive thirst, dry skin or mucous membranes, dark or concentrated urine, or low urine output? ■ Do you have problems with swelling of your hands, feet, or ankles? Do you ever have difficulty breathing, especially when lying down or at night? How many pillows do you use to sleep? ■ Have you recently experienced any of the following symptoms: dif- ficulty concentrating or confusion; dizziness or feeling faint; mus- cle weakness, twitching, cramping, or spasm; excessive fatigue; abnormal sensations such as numbness, tingling, burning, or prick- ling; abdominal cramping or distention; heart palpitations? koz74686_ch52.qxd 11/8/06 2:07 PM Page 1445