f and e imbalance

Fluid,Electrolyte,andAcidBaseBalanceLEARNING OUTCOMESAfter 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 acidbase balance in thebody, including the roles of the lungs, the kidneys andbuffers.

3. Identify factors affecting normal body fluid, electrolyte,and acidbase balance.

4. Discuss the risk factors for and the causes and effects offluid, electrolyte, and acidbase imbalances.

5. Collect assessment data related to the clients fluid,electrolyte, and acidbase balances.

6. Identify examples of nursing diagnoses, outcomes, andinterventions for clients with altered fluid, electrolyte, oracidbase balance.

7. Teach clients measures to maintain fluid and electrolytebalance.

8. Implement measures to correct imbalances of fluidsand electrolytes or acids and bases such as enteral orparenteral replacements and blood transfusions.

9. Evaluate the effect of nursing and collaborative inter-ventions on the clients fluid, electrolyte, or acidbasebalance.

CHAPTER

52

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hematocrit, 1449hemolytic transfusion reaction,

1473homeostasis, 1424hydrostatic pressure, 1427hypercalcemia, 1441hyperchloremia, 1442hyperkalemia, 1438hypermagnesemia, 1442hypernatremia, 1438hyperphosphatemia, 1442hypertonic, 1427hypervolemia, 1435hypocalcemia, 1441hypochloremia, 1442hypokalemia, 1438hypomagnesemia, 1442hyponatremia, 1438hypophosphatemia, 1442hypotonic, 1427hypovolemia, 1435insensible fluid loss, 1428interstitial fluid, 1425intracellular fluid (ICF), 1424intravascular fluid, 1424ions, 1425

isotonic, 1427metabolic acidosis, 1442metabolic alkalosis, 1442milliequivalent, 1425obligatory losses, 1429oncotic pressure, 1427osmolality, 1427osmosis, 1426osmotic pressure, 1427overhydration, 1437peripherally inserted central

venous catheter (PICC), 1456pH, 1432pitting edema, 1436plasma, 1424renin-angiotensin-aldosterone

system, 1429respiratory acidosis, 1442respiratory alkalosis, 1442selectively permeable, 1426solutes, 1426solvent, 1426specific gravity, 1449third space syndrome, 1435transcellular fluid, 1425volume expanders, 1456

acid, 1432acidosis, 1433active transport, 1428agglutinins, 1472agglutinogens, 1472alkalosis, 1433anions, 1425antibodies, 1472antigens, 1472arterial blood gases (ABGs), 1449bases, 1432buffers, 1433cations, 1425central venous catheters, 1456colloid osmotic pressure, 1427colloids, 1426compensation, 1442crystalloids, 1426dehydration, 1437diffusion, 1427drip factor, 1465electrolytes, 1425extracellular fluid (ECF), 1424filtration, 1427filtration pressure, 1427fluid volume deficit (FVD), 1435fluid volume excess (FVE), 1435

KEY TERMS

In good health, a delicate balance of fluids, electrolytes, andacids and bases is maintained in the body. This balance, or phys-iologic homeostasis, depends on multiple physiologicprocesses that regulate fluid intake and output and the move-ment of water and the substances dissolved in it between thebody compartments.

Almost every illness has the potential to threaten this bal-ance. Even in daily living, excessive temperatures or vigorousactivity can disturb the balance if adequate water and salt intakeis not maintained. Therapeutic measures, such as the use of di-uretics or nasogastric suction, can also disturb the bodys home-ostasis unless water and electrolytes are replaced.

BODY FLUIDS AND ELECTROLYTESThe proportion of the human body composed of fluid is surpris-ingly large. Approximately 60% of the average healthy adultsweight is water, the primary body fluid. In good health this vol-ume remains relatively constant and the persons weight variesby less than 0.2 kg (0.5 lb) in 24 hours, regardless of the amountof 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 havethe highest proportion of water, accounting for 70% to 80% oftheir body weight. The proportion of body water decreases withaging. In people older than 60 years of age, it represents onlyabout 50% of the total body weight. Women also have a lowerpercentage of body water than men. Women and the elderlyhave reduced body water due to decreased muscle mass and agreater percentage of fat tissue. Fat tissue is essentially free ofwater, whereas lean tissue contains a significant amount of wa-ter. Water makes up a greater percentage of a lean persons bodyweight than an obese persons.

Distribution of Body FluidsThe bodys fluid is divided into two major compartments, intra-cellular and extracellular. Intracellular fluid (ICF) is found withinthe cells of the body. It constitutes approximately two-thirds ofthe total body fluid in adults. Extracellular fluid (ECF) is foundoutside the cells and accounts for about one-third of total bodyfluid. It is subdivided into compartments. The two main com-partments of ECF are intravascular and interstitial. Intravascularfluid, or plasma, accounts for approximately 20% of the ECF

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CHAPTER 52 / Fluid, Electrolyte, and AcidBase Balance 1425

and is found within the vascular system. Interstitial fluid, ac-counting for approximately 75% of the ECF, surrounds thecells. 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 itprovides a medium in which metabolic processes of the celltake place.

Although extracellular fluid is in the smaller of the twocompartments, it is the transport system that carries nutrientsto 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 membranesinto the interstitial spaces and then across the cellular mem-branes into the cells. The opposite route is taken for wasteproducts, such as carbon dioxide going from the cells to thelungs and metabolic acid wastes going eventually to the kid-neys. Interstitial fluid transports wastes from the cells by wayof the lymph system as well as directly into the blood plasmathrough capillaries.

Composition of Body FluidsExtracellular and intracellular fluids contain oxygen from thelungs, dissolved nutrients from the gastrointestinal tract, excre-tory products of metabolism such as carbon dioxide, andcharged particles called ions.

Total body fluid40 liters

Cell fluid25 liters

Plasma3 liters

Interstitial andtranscellular fluid

12 liters

Extracellularfluid

15 liters

Figure 52-1 ! Total body fluid represents 40 L in an adult maleweighing 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 oneion of sodium (Na!) and one ion of chloride (Cl"). Thesecharged particles are called electrolytes because they are capa-ble of conducting electricity. The number of ions that carry apositive charge, called cations, and ions that carry a negativecharge, called anions, should be equal. Examples of cations aresodium (Na!), potassium (K!), calcium (Ca2!), and magnesium(Mg2!). Examples of anions include chloride (Cl"), bicarbonateHCO3", phosphate HPO42", and sulfate SO42".

Electrolytes generally are measured in milliequivalents perliter of water (mEq/L) or milligrams per 100 milliliters(mg/100 mL). The term milliequivalent refers to the chemicalcombining power of the ion, or the capacity of cations to com-bine with anions to form molecules. This combining activity ismeasured in relation to the combining activity of the hydrogenion (H!). Thus, 1 mEq of any anion equals 1 mEq of anycation. For example, sodium and chloride ions are equivalent,since they combine equally: 1 mEq of Na! equals 1 mEq ofCl". However, these cations and anions are not equal inweight: 1 mg of Na! does not equal 1 mg of Cl"; rather, 3 mgof Na! equals 2 mg of Cl" .

Clinically, the milliequivalent system is most often used.However, nurses need to be aware that different systems ofmeasurement may be found when interpreting laboratory re-sults. For example, calcium levels frequently are reported inmilligrams per deciliter (1 dL# 100 mL) instead of milliequiv-alents per liter. It also is important to remember that laboratorytests are usually performed using blood plasma, an extracellularfluid. These results may reflect what is happening in the ECF,but it generally is not possible to directly measure electrolyteconcentrations 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. Otherelectrolytes such as potassium, calcium, and magnesium arealso 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 exceptionof protein. Plasma is a protein-rich fluid, containing largeamounts of albumin, but interstitial fluid contains little or noprotein.

The composition of intracellular fluid differs significantlyfrom that of ECF. Potassium and magnesium are the primarycations 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 tohealth. Normal and unusual fluid and electrolyte losses must bereplaced if homeostasis is to be maintained.

Other body fluids such as gastric and intestinal secretionsalso contain electrolytes. This is of particular concern whenthese 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 fromexcessive losses through these routes.

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Na+Na+

Na+

K+

K+K+

Mg2+Ca2+

Plasma Interstitialfluid

Intracellularfluid

0

50

100

150

200CATIONS

HCO3HCO3

HCO3

HPO42

HPO42

HPO42SO42

SO42

Cl

Cl

Cl

Plasma Interstitialfluid

Intracellularfluid

0

50

100

150

200ANIONS

Org. acid

Proteins

Proteins

Mill

iequ

ival

ents

per

Lite

r (mE

q/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 PearsonEducation, Inc., Upper Saddle River, New Jersey.

Higher concentration Lower concentration

Semipermeablemembrane

Dissolvedsubstances

Watermolecules

H20

H20

H20

Figure 52-3 ! Osmosis: Water molecules move from the lessconcentrated area to the more concentrated area in an attempt toequalize the concentration of solutions on two sides of a membrane.

Movement of Body Fluids and ElectrolytesThe body fluid compartments are separated from one another bycell membranes and the capillary membrane. While these mem-branes are completely permeable to water, they are consideredto be selectively permeable to solutes as substances move acrossthem 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 havemore difficulty moving between fluid compartments.

The methods by which electrolytes and other solutes moveare osmosis, diffusion, filtration, and active transport.

OsmosisOsmosis is the movement of water across cell membranes,from the less concentrated solution to the more concentratedsolution (Figure 52-3 !). In other words, water moves towardthe higher concentration of solute in an attempt to equalizethe concentrations.

Solutes are substances dissolved in a liquid. For example,when sugar is added to coffee, the sugar is the solute. Solutesmay be crystalloids (salts that dissolve readily into true solu-tions) or colloids (substances such as large protein moleculesthat do not readily dissolve into true solutions). A solvent is thecomponent 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 soluteson one side of a selectively permeable membrane, such as thecapillary membrane, is higher than on the other side. For exam-ple, a marathon runner loses a significant amount of waterthrough perspiration, increasing the concentration of solutes inthe plasma because of water loss. This higher solute concentra-tion draws water from the interstitial space and cells into thevascular compartment to equalize the concentration of solutes

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in all fluid compartments. Osmosis is an important mechanismfor maintaining homeostasis and fluid balance.

The concentration of solutes in body fluids is usually ex-pressed as the osmolality. Osmolality is determined by the totalsolute 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, andurea are the primary contributors to the osmolality of intracellularfluid. The term tonicity may be used to refer to the osmolality of asolution. 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 suchas 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 wateracross a semipermeable membrane. When two solutions of dif-ferent solute concentrations are separated by a semipermeablemembrane, the solution of higher solute concentration exerts ahigher osmotic pressure, drawing water across the membrane toequalize 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 themto shrink. On the other hand, a hypotonic solution administeredintravenously will cause the RBCs to swell as water is drawninto the cells by their higher osmotic pressure. In the body,plasma proteins exert an osmotic draw called colloid osmoticpressure or oncotic pressure, pulling water from the interstitialspace into the vascular compartment. This is an importantmechanism in maintaining vascular volume.

DiffusionDiffusion is the continual intermingling of molecules in liquids,gases, or solids brought about by the random movement of themolecules. For example, two gases become mixed by the con-stant motion of their molecules. The process of diffusion occurseven when two substances are separated by a thin membrane. Inthe body, diffusion of water, electrolytes, and other substancesoccurs through the split pores of capillary membranes.

The rate of diffusion of substances varies according to (a) thesize of the molecules, (b) the concentration of the solution, and(c) the temperature of the solution. Larger molecules move less

Higher concentration Lower concentration

Dissolvedsubstance Semipermeable

membrane

Figure 52-4 ! Diffusion: The movement of molecules through asemipermeable membrane from an area of higher concentration to anarea of lower concentration.

quickly than smaller ones because they require more energy tomove 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 ofmotion of molecules and therefore the rate of diffusion.

FiltrationFiltration is a process whereby fluid and solutes move togetheracross a membrane from one compartment to another. Themovement is from an area of higher pressure to one of lowerpressure. An example of filtration is the movement of fluid andnutrients from the capillaries of the arterioles to the interstitialfluid around the cells. The pressure in the compartment that re-sults in the movement of the fluid and substances dissolved influid out of the compartment is called filtration pressure.Hydrostatic pressure is the pressure exerted by a fluid within aclosed system on the walls of a container in which it is contained.The hydrostatic pressure of blood is the force exerted by bloodagainst the vascular walls (e.g., the artery walls). The principleinvolved in hydrostatic pressure is that fluids move from the areaof 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 sectionOsmosis) that opposes the hydrostatic pressure and holds thefluid in the vascular compartment to maintain the vascular vol-ume. When the hydrostatic pressure is greater than the osmoticpressure, the fluid filters out of the blood vessels. The filtrationpressure in this example is the difference between the hydrostaticpressure and the osmotic pressure (Figure 52-5 !).

Arterial side of capillary bed

Interstitialspace

Venous side of capillary bed

Direction of filtrationfluid and solutes

Direction of filtrationfluid 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 pressurechanges within a capillary bed. On the arterial side,arterial blood pressure exceeds colloid osmoticpressure, so that water and dissolved substancesmove out of the capillary into the interstitial space. Onthe venous side, venous blood pressure is less thancolloid osmotic pressure, so that water and dissolvedsubstances move into the capillary.

MediaLink

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brane Transport Animation

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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 tomove sodium molecules and potassium molecules across asemipermeable membrane against sodiums and potassiumsconcentration gradients (i.e., from areas of lesser concentration toareas of greater concentration).

Active TransportSubstances 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 andosmosis in that metabolic energy is expended. In active trans-port, a substance combines with a carrier on the outside surfaceof the cell membrane, and they move to the inside surface of thecell membrane. Once inside, they separate, and the substance isreleased to the inside of the cell. A specific carrier is required foreach substance, enzymes are required for active transport, andenergy is expended.

This process is of particular importance in maintaining thedifferences in sodium and potassium ion concentrations ofECF 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 theseproportions, the active transport mechanism (the sodium-potassium pump) is activated, moving sodium from the cellsand potassium into the cells.

Regulating Body FluidsIn a healthy person, the volumes and chemical composition ofthe fluid compartments stay within narrow safe limits. Nor-mally fluid intake and fluid loss are balanced. Illness can upsetthis balance so that the body has too little or too much fluid.

Fluid IntakeDuring periods of moderate activity at moderate temperature, theaverage adult drinks about 1,500 mL per day but needs 2,500 mLper day, an additional 1,000 mL. This added volume is acquiredfrom foods and from the oxidation of these foods during metabolicprocesses. Interestingly, the water content of food is relativelylarge, contributing about 750 mL per day. The water content offresh 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 mostof the remaining fluid volume required. This quantity is approx-imately 200 mL per day for the average adult. See Table 521.

The thirst mechanism is the primary regulator of fluid intake.The thirst center is located in the hypothalamus of the brain. Anumber of stimuli trigger this center, including the osmoticpressure of body fluids, vascular volume, and angiotensin (ahormone released in response to decreased blood flow to thekidneys). For example, a long-distance runner loses significantamounts 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 pressurestimulates the thirst center, causing the runner to experience thesensation of thirst and the desire to drink to replace lost fluids.

Thirst is normally relieved immediately after drinking asmall amount of fluid, even before it is absorbed from the gas-trointestinal tract. However, this relief is only temporary, andthe 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 individualfrom drinking too much, because it takes from 30 minutes to 1hour for the fluid to be absorbed and distributed throughout thebody. See Figure 52-7 !.

Fluid OutputFluid losses from the body counterbalance the adults 2,500-mLaverage daily intake of fluid, as shown in Table 522. There arefour routes of fluid output:

1. Urine2. Insensible loss through the skin as perspiration and through

the lungs as water vapor in the expired air3. Noticeable loss through the skin4. 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 urineoutput for an adult is 1,400 to 1,500 mL per 24 hours, or at least0.5 mL per kilogram per hour. In healthy people, urine outputmay 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 maintainfluid balance in the body.

INSENSIBLE LOSSES. Insensible fluid loss occurs through theskin and lungs. It is called insensible because it is usually not no-ticeable and cannot be measured. Insensible fluid loss through

TABLE 521 Average Daily Fluid Intake for an AdultSOURCE AMOUNT (ML)Oral fluids 1,200 to 1,500Water in foods 1,000Water as by-product of 200food metabolismTotal 2,400 to 2,700

Med

iaLi

nk

Filtr

atio

n Pr

essu

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the skin occurs in two ways. Water is lost through diffusion andthrough perspiration (which is noticeable but not measurable).Water losses through diffusion are not noticeable but normallyaccount for 300 to 400 mL per day. This loss can be significantlyincreased if the protective layer of the skin is lost as with burnsor large abrasions. Perspiration varies depending on factors suchas environmental temperature and metabolic activity. Fever andexercise increase metabolic activity and heat production, therebyincreasing fluid losses through the skin.

Another type of insensible loss is the water in exhaled air. Inan adult, this is normally 300 to 400 mL per day. When respira-tory rate accelerates, for example, due to exercise or an elevatedbody temperature, this loss can increase.

FECES. The chyme that passes from the small intestine into thelarge intestine contains water and electrolytes. The volume ofchyme entering the large intestine in an adult is normally about1,500 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 bodyfunction. These are known as obligatory losses. Approximately500 mL of fluid must be excreted through the kidneys of anadult each day to eliminate metabolic waste products from thebody. Water lost through respirations, through the skin, and infeces also are obligatory losses, necessary for temperature reg-ulation and elimination of waste products. The total of all theselosses is approximately 1,300 mL per day.

Maintaining HomeostasisThe volume and composition of body fluids is regulated throughseveral 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 gastrointestinalsystem. Hormones such as antidiuretic hormone (ADH; alsoknown as arginine vasopressin or AVP), the renin-angiotensin-aldosterone system, and atrial natriuretic factor are involved, asare mechanisms to monitor and maintain vascular volume.

KIDNEYS. The kidneys are the primary regulator of body fluidsand 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 fromplasma filtrate and ultimately the amount excreted as urine. Al-though 135 to 180 L of plasma per day is normally filtered in anadult, only about 1.5 L of urine is excreted. Electrolyte balanceis maintained by selective retention and excretion by the kid-neys. The kidneys also play a significant role in acidbase regu-lation, excreting hydrogen ion (H!) 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 ductsof 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 reabsorbedinto the blood. As more water is reabsorbed, urine output fallsand serum osmolality decreases because the water dilutes bodyfluids. 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 serumosmolality 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. Specializedreceptors 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 thekidney decreases, renin is released. Renin causes the conversionof angiotensinogen to angiotensin I, which is then converted toangiotensin II by angiotensin-converting enzyme. Angiotensin II

Increased volumeof extracellular fluid

and

and

Decreased volumeof extracellular fluid

Decreased osmolalityof extracellular fluid

Stimulates osmoreceptorsin hypothalamic

thirst center

Decreased saliva secretion

Water absorbed fromgastrointestinal tract

Dry mouth

Increased osmolalityof extracellular fluid

Sensation of thirst:person seeks a drink

Figure 52-7 ! Factors stimulating water intake through the thirstmechanism.From Lemone, Priscilla; Burke, Karen M., Medical Surgical Nursing: Critical Thinking inClient Care, 3rd ed 2004. Reproduced with permission of Pearson Education, Inc.,Upper Saddle River, New Jersey.

TABLE 522 Average Daily Fluid Output for an AdultROUTE AMOUNT (ML)Urine 1,400 to 1,500Insensible losses

Lungs 350 to 400Skin 350 to 400

Sweat 100Feces 100 to 200

Total 2,300 to 2,600

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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 retentionin 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 onthe nephrons, ANF promotes sodium wasting and acts as a po-tent diuretic, thus reducing vascular volume. ANF also inhibitsthirst, reducing fluid intake.

Regulating ElectrolytesElectrolytes, charged ions capable of conducting electricity, arepresent 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 ofspecific electrolytes differs between fluid compartments, a bal-ance of cations (positively charged ions) and anions (negativelycharged ions) always exists. Electrolytes are important for

! Maintaining fluid balance.! Contributing to acidbase regulation.! Facilitating enzyme reactions.! Transmitting neuromuscular reactions.

Most electrolytes enter the body through dietary intake andare excreted in the urine. Some electrolytes, such as sodium andchloride, are not stored by the body and must be consumed dailyto maintain normal levels. Potassium and calcium, on the otherhand, are stored in the cells and bone, respectively. When serumlevels drop, ions can shift out of the storage pool into theblood to maintain adequate serum levels for normal function-ing. The regulatory mechanisms and functions of the majorelectrolytes are summarized in Table 523.

Urine output Serum/blood osmolality as the water dilutes body fluids

Osmoreceptors inhypothalamus

stimulate posteriorpituitary to secrete ADH

ADH increasesdistal tubulepermeability

Reabsorptionof H2O

into blood

blood osmolality

Urine output Serum osmolality returns to normal

ADH is suppressed

ADH causes distaltubules to becomeless permeableto water

Reabsorptionof H2O

into blood

blood osmolality

Figure 52-8 ! Antidiuretic hormone (ADH) regulates water excretion from the kidneys.

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Sodium (Na!)Sodium is the most abundant cation in extracellular fluid and amajor contributor to serum osmolality. Normal serum sodiumlevels 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 arereabsorbed with it, thus maintaining ECF volume. Sodium isfound in many foods, such as bacon, ham, processed cheese,and table salt.

Potassium (K!)Potassium is the major cation in intracellular fluids, with onlya small amount found in plasma and interstitial fluid. ICF lev-els of potassium are usually 125 to 140 mEq/L while normalserum potassium levels are 3.5 to 5.0 mEq/L. The ratio of in-tracellular to extracellular potassium must be maintained forneuromuscular response to stimuli. Potassium is a vital elec-trolyte for skeletal, cardiac, and smooth muscle activity. It isinvolved in maintaining acidbase balance as well, and it con-tributes to intracellular enzyme reactions. Potassium must beingested daily because the body cant conserve it. Many fruitsand vegetables, meat, fish, and other foods contain potassium(see Box 521).

Calcium (Ca2!)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 toonly 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 acomplex interaction of parathyroid hormone, calcitonin, andcalcitriol, a metabolite of vitamin D. When calcium levels in the

TABLE 523 Regulation and Functions of ElectrolytesELECTROLYTE REGULATION FUNCTIONSodium (Na!)

Potassium (K!)

Calcium (Ca2!)

Magnesium (Mg2!)

Chloride (Cl")

Phosphate (PO4")

Bicarbonate (HCO3")

! 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 acidbase 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 acidbase balance! Buffer in oxygencarbon 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 acidbase balance! Regulating calcium levels! Major body buffer involved in acidbase regulation

! Renal reabsorption or excretion! Aldosterone increases Na! reabsorption in collecting

duct of nephrons! Renal excretion and conservation! Aldosterone increases K! excretion! Movement into and out of cells! Insulin helps move K! into cells; tissue damage and

acidosis shift K! out of cells into ECF

! Redistribution between bones and ECF! Parathyroid hormone and calcitriol increase serum

Ca2! 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 thekidneys

! Aldosterone increases chloride reabsorption withsodium

! 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; decreasingserum calcium increases phosphate

! Excretion and reabsorption by the kidneys! Regeneration by kidneys

BOX 521 Potassium-Rich Foods

VEGETABLESAvocadoRaw carrotBaked potatoRaw tomatoSpinach

MEATS AND FISHBeefCodPorkVeal

FRUITSDried fruits (e.g., raisins and dates)BananaApricotCantaloupeOrange

BEVERAGESMilkOrange juiceApricot nectar

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ECF fall, parathyroid hormone and calcitriol cause calcium tobe released from bones into ECF and increase the absorption ofcalcium in the intestines, thus raising serum calcium levels.Conversely, calcitonin stimulates the deposition of calcium inbone, reducing the concentration of calcium ions in the blood.

With aging, the intestines absorb calcium less effectively andmore calcium is excreted via the kidneys. Calcium shifts out ofthe bone to replace these ECF losses, increasing the risk of os-teoporosis and fractures of the wrists, vertebrae, and hips. Lackof weight-bearing exercise (which helps keep calcium in thebones) 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 cannedsalmon containing smaller amounts. Many clients benefit fromcalcium supplements.

Serum calcium levels are often reported in two ways, basedupon 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 plasmaproteins or other nonprotein ions. The normal total serum cal-cium levels, which range from 8.5 to 10.5 mg/dL, represent bothbound 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 (Mg2!)Magnesium is primarily found in the skeleton and in intracellu-lar fluid. It is the second most abundant intracellular cation withnormal 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 of ATP. Magnesium also is necessary for proteinand DNA synthesis within the cells. Only about 1% of thebodys magnesium is in ECF; here it is involved in regulatingneuromuscular and cardiac function. Maintaining and ensuringadequate magnesium levels is an important part of care ofclients 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 (Cl")Chloride is the major anion of ECF, and normal serum levels are95 to 108 mEq/L. Chloride functions with sodium to regulateserum osmolality and blood volume. The concentration of chlo-ride in ECF is regulated secondarily to sodium; when sodium isreabsorbed in the kidney, chloride usually follows. Chloride is amajor component of gastric juice as hydrochloric acid (HCl)and is involved in regulating acidbase balance. It also acts as abuffer in the exchange of oxygen and carbon dioxide in RBCs.Chloride is found in the same foods as sodium.

Phosphate PO4"

Phosphate is the major anion of intracellular fluids. It also isfound in ECF, bone, skeletal muscle, and nerve tissue. Normalserum 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 ofgrowth hormone and a faster rate of skeletal growth probablyaccount for this difference. Phosphate is involved in manychemical actions of the cell; it is essential for functioning ofmuscles, nerves, and red blood cells. It is also involved in themetabolism of protein, fat, and carbohydrate. Phosphate is ab-sorbed from the intestine and is found in many foods such asmeat, fish, poultry, milk products, and legumes.

Bicarbonate HCO3"

Bicarbonate is present in both intracellular and extracellular flu-ids. Its primary function is regulating acidbase balance as anessential component of the carbonic acidbicarbonate bufferingsystem. Extracellular bicarbonate levels are regulated by thekidneys: Bicarbonate is excreted when too much is present; ifmore is needed, the kidneys both regenerate and reabsorb bicar-bonate ions. Unlike other electrolytes that must be consumed inthe diet, adequate amounts of bicarbonate are produced throughmetabolic processes to meet the bodys needs.

ACIDBASE BALANCEAn important part of regulating the chemical balance or home-ostasis of body fluids is regulating their acidity or alkalinity. Anacid is a substance that releases hydrogen ions (H!) in solution.Strong acids such as hydrochloric acid release all or nearly alltheir hydrogen ions; weak acids like carbonic acid release somehydrogen 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 pHreflects the hydrogen ion concentration of the solution: Thehigher the hydrogen ion concentration (and the more acidic thesolution), 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. Solutionswith a pH lower than 7 are acidic; those with a pH higher than7 are alkaline. The pH scale is logarithmic: A solution with a pHof 5 is 10 times more acidic than one with a pH of 6.

Regulation of AcidBase BalanceBody fluids are maintained within a narrow range that is slightlyalkaline. The normal pH of arterial blood is between 7.35 and7.45 (Figure 52-9 !). Acids are continually produced during me-

Death Acidosis Normal Alkalosis Death

6.8 7.35 7.45 7.8

1 7 14Alkalinesolution(low H+)

Neutral

pH scale

pH

Acidicsolution

(high H+)

Figure 52-9 ! Body fluids are normally slightly alkaline, between a pHof 7.35 and 7.45.

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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 acidbase balance by neutralizing excessacids or bases. The lungs and the kidneys help maintain a nor-mal pH by either excreting or retaining acids and bases.

BuffersBuffers 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 changein 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 tomaintain or restore normal acidbase balance.

The major buffer system in extracellular fluids is the bicarbon-ate (HCO3") and carbonic acid (H2CO3) system. When a strongacid such as hydrochloric acid (HCl) is added, it combines with bi-carbonate and the pH drops only slightly. A strong base such assodium hydroxide combines with carbonic acid, the weak acid ofthe buffer pair, and the pH remains within the narrow range of nor-mal. The amounts of bicarbonate and carbonic acid in the bodyvary; however, as long as a ratio of 20 parts of bicarbonate to 1 partof carbonic acid is maintained, the pH remains within its normalrange of 7.35 to 7.45 (Figure 52-10 !). Adding a strong acid toECF can change this ratio as bicarbonate is depleted in neutraliz-ing the acid. When this happens, the pH drops, and the client hasa condition called acidosis. The ratio can also be upset by addinga strong base to ECF, depleting carbonic acid as it combines withthe base. In this case the pH rises and the client has alkalosis.

In addition to the bicarbonatecarbonic acid buffer system,plasma proteins, hemoglobin, and phosphates also function asbuffers in body fluids.

Respiratory RegulationThe lungs help regulate acidbase balance by eliminating or re-taining carbon dioxide (CO2), a potential acid. Combined withwater, carbon dioxide forms carbonic acid (CO2 ! H2O "H2CO3). This chemical reaction is reversible; carbonic acid

breaks down into carbon dioxide and water. Working togetherwith the bicarbonatecarbonic acid buffer system, the lungs reg-ulate acidbase balance and pH by altering the rate and depth ofrespirations. The response of the respiratory system to changesin pH is rapid, occurring within minutes.

Carbon dioxide is a powerful stimulator of the respiratorycenter. When blood levels of carbonic acid and carbon dioxiderise, the respiratory center is stimulated and the rate and depthof respirations increase. Carbon dioxide is exhaled, and car-bonic acid levels fall. By contrast, when bicarbonate levels areexcessive, the rate and depth of respirations are reduced. Thiscauses carbon dioxide to be retained, carbonic acid levels torise, and the excess bicarbonate to be neutralized.

Carbon dioxide levels in the blood are measured as thePCO2, 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 RegulationAlthough buffers and the respiratory system can compensate forchanges in pH, the kidneys are the ultimate long-term regulatorof acidbase balance. They are slower to respond to changes, re-quiring hours to days to correct imbalances, but their responseis more permanent and selective than that of the other systems(Yucha, 2004).

The kidneys maintain acidbase balance by selectively ex-creting or conserving bicarbonate and hydrogen ions. When ex-cess hydrogen ion is present and the pH falls (acidosis), thekidneys 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 serumbicarbonate level is 22 to 26 mEq/L.

The relationship of the respiratory and renal regulation ofacidbase balance is further explained in Box 522.

1 partcarbonicacid or

1.2 mEq/L

20 partsbicarbonate

or24 mEq/L

6.8 7.35 7.45 7.8

NormalAcidosisDeath DeathAlkalosis

Figure 52-10 ! Carbonic acidbicarbonate ratio and pH.

BOX 522 Physiological Regulation of AcidBase Balance

Lungs KidneysCO2 ! H2O H2CO3 H ! HCO3

Carbon dioxide Hydrogen! Carbonic acid !

water bicarbonate

The lungs and kidneys are the two major systems that are working ona continuous basis to help regulate the acidbase balance in the body.In the biochemical reactions above, the processes are all reversible andgo back and forth as the bodys needs change. The lungs can work veryquickly and do their part by either retaining or getting rid of carbon diox-ide by changing the rate and depth of respirations. The kidneys workmuch 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 maintainhomeostasis.

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FACTORS AFFECTING BODY FLUID,ELECTROLYTES, AND ACIDBASE BALANCEThe ability of the body to adjust fluids, electrolytes, andacidbase balance is influenced by age, gender and body size,environmental temperature, and lifestyle.

AgeInfants and growing children have much greater fluid turnoverthan adults because their higher metabolic rate increases fluidloss. 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 bodysurface area is proportionately greater than that of adults, in-creasing insensible fluid losses. The more rapid turnover offluid plus the losses produced by disease can create critical fluidimbalances in children much more rapidly than in adults.

In elderly people, the normal aging process may affect fluidbalance. The thirst response often is blunted. Antidiuretic hor-mone levels remain normal or may even be elevated, but thenephrons become less able to conserve water in response toADH. Increased levels of atrial natriuretic factor seen in olderadults may also contribute to this impaired ability to conservewater. These normal changes of aging increase the risk of dehy-dration. When combined with the increased likelihood of heartdiseases, impaired renal function, and multiple drug regimens,the older adults 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 makean intravenous insertion more difficult.

Gender and Body SizeTotal body water also is affected by gender and body size. Be-cause fat cells contain little or no water, and lean tissue has ahigh water content, people with a higher percentage of body fathave less body fluid. Women have proportionately more bodyfat and less body water than men. Water accounts for approxi-mately 60% of an adult mans weight, but only 52% for an adultwoman. In an obese individual this may be even less, with wa-ter responsible for only 30% to 40% of the persons weight.

Environmental TemperaturePeople with an illness and those participating in strenuous ac-tivity are at risk for fluid and electrolyte imbalances when theenvironmental temperature is high. Fluid losses through sweat-ing are increased in hot environments as the body attempts todissipate heat. These losses are even greater in people who havenot been acclimatized to the environment.

Both salt and water are lost through sweating. When onlywater is replaced, salt depletion is a risk. The person who is saltdepleted may experience fatigue, weakness, headache, and gas-trointestinal symptoms such as anorexia and nausea. The risk ofadverse effects is even greater if lost water is not replaced. Bodytemperature rises, and the person is at risk for heat exhaustionor heatstroke. Heatstroke may occur in older adults or ill peopleduring prolonged periods of heat; it can also affect athletes and

LIFESPAN CONSIDERATIONS Fluid and Electrolyte Imbalance

INFANTS AND CHILDRENInfants 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 throughthe skin and respirations.

! They cannot express thirst, nor actively seek fluids.

Vomiting and/or diarrhea in infants and young children can leadquickly to electrolyte imbalance. Oral rehydration therapy (ORT) (e.g.,electrolyte solutions such as Pedialyte) should be used to restore fluidand electrolyte balance in mild to moderate dehydration (AmericanMedical 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 isnauseated and vomiting, small sips of ORT can be helpful.

ELDERSCertain changes related to aging place the elder at risk for seriousproblems 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 inelders 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 offerthem fluids.

! Preparations for certain diagnostic tests that have the client NPOfor 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 wellhydrated before, during, and after the procedure to help in dilutingand excreting the dye. If the client is NPO for the procedure, thenurse 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 electrolyteimbalance. The change can happen quickly and become serious in ashort time. Astute observations and quick actions by the nurse canhelp prevent serious consequences. A change in mental status maybe the first symptom of impairment and must be further evaluated todetermine the cause.

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laborers when their heat production exceeds the bodys abilityto dissipate heat.

Consuming adequate amounts of cool liquids, particularly dur-ing strenuous activity, reduces the risk of adverse effects fromheat. Balanced electrolyte solutions and carbohydrate-electrolytesolutions such as sports drinks are recommended because theyreplace both water and electrolytes lost through sweat.

LifestyleOther factors such as diet, exercise, and stress affect fluid, elec-trolyte, and acidbase balance.

The intake of fluids and electrolytes is affected by the diet.People with anorexia nervosa or bulimia are at risk for severefluid and electrolyte imbalances because of inadequate intake orpurging regimens (e.g., induced vomiting, use of diuretics andlaxatives). Seriously malnourished people have decreasedserum 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 bodys 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 andolder men is slowed with regular exercise, reducing the risk ofosteoporosis.

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 urineproduction. The overall response of the body to stress is to in-crease the blood volume.

Other lifestyle factors can also affect fluid, electrolyte, andacidbase balance. Heavy alcohol consumption affects elec-trolyte balance, increasing the risk of low calcium, magnesium,and phosphate levels. The risk of acidosis associated withbreakdown of fat tissue also is greater in the person who drinkslarge amounts of alcohol.

DISTURBANCES IN FLUID VOLUME, ELECTROLYTE, AND ACIDBASE BALANCESA number of factors such as illness, trauma, surgery, and med-ications can affect the bodys ability to maintain fluid, elec-trolyte, and acidbase balance. The kidneys play a major role inmaintaining fluid, electrolyte, and acidbase balance, and renaldisease 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 suctioncan 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 diabetesmellitus or chronic obstructive lung disease may affect

acidbase balance. Diabetic ketoacidosis, cancer, and head in-jury may also lead to electrolyte imbalances.

Fluid ImbalancesFluid imbalances are of two basic types: isotonic and osmolar.Isotonic imbalances occur when water and electrolytes are lostor gained in equal proportions, so that the osmolality of bodyfluids remains constant. Osmolar imbalances involve the lossor 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 isotonicgain of water and electrolytes, (c) a hyperosmolar loss of onlywater, and (d) a hypo-osmolar gain of only water. These are re-ferred to, respectively, as fluid volume deficit, fluid volumeexcess, dehydration (hyperosmolar imbalance), and overhy-dration (hypo-osmolar imbalance).

Fluid Volume DeficitIsotonic fluid volume deficit (FVD) occurs when the body losesboth 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 itoften is called hypovolemia.

FVD generally occurs as a result of (a) abnormal lossesthrough the skin, gastrointestinal tract, or kidney; (b) de-creased intake of fluid; (c) bleeding; or (d) movement of fluidinto a third space. See the section on third space syndromethat follows.

For the risk factors and clinical signs related to fluid volumedeficit, see Table 524.

THIRD SPACE SYNDROME. In third space syndrome, fluidshifts from the vascular space into an area where it is not readilyaccessible as extracellular fluid. This fluid remains in the bodybut is essentially unavailable for use, causing an isotonic fluidvolume deficit. Fluid may be sequestered in the bowel, in the in-terstitial space as edema, in inflamed tissue, or in potentialspaces such as the peritoneal or pleural cavities.

The client with third space syndrome has an isotonic fluiddeficit 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 fluidshifts back into the vascular compartment after time, assessmentfor manifestations of fluid volume excess or hypervolemia isalso vital.

Fluid Volume ExcessFluid volume excess (FVE) occurs when the body retains bothwater and sodium in similar proportions to normal ECF. This iscommonly referred to as hypervolemia (increased blood vol-ume). FVE is always secondary to an increase in the total bodysodium content, which leads to an increase in total body water.Because both water and sodium are retained, the serum sodiumconcentration 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) administeringsodium-containing infusions too rapidly, particularly to clients

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with impaired regulatory mechanisms; and (c) diseaseprocesses that alter regulatory mechanisms, such as heart fail-ure, renal failure, cirrhosis of the liver, and Cushings syndrome.

The risk factors and clinical manifestations for FVE are sum-marized in Table 525.

EDEMA. In fluid volume excess, both intravascular and intersti-tial spaces have an increased water and sodium content. Excessinterstitial fluid is known as edema. Edema typically is most ap-parent in areas where the tissue pressure is low, such as aroundthe eyes, and in dependent tissues (known as dependent edema),where hydrostatic capillary pressure is high.

Edema can be caused by several different mechanisms. Thethree 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 thefeet, ankles, and sacrum because of the effects of gravity. Lowlevels of plasma proteins from malnutrition or liver or kidneydiseases can reduce the plasma oncotic pressure so that fluid isnot drawn into the capillaries from interstitial tissues, causingedema. With tissue trauma and some disorders such as allergicreactions, capillaries become more permeable, allowing fluid toescape into interstitial tissues. Obstructed lymph flow impairsthe 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 pitafter finger pressure is applied to the swollen area. The pit iscaused by movement of fluid to adjacent tissue, away from thepoint of pressure (Figure 52-11 !). Within 10 to 30 seconds thepit normally disappears.

TABLE 524 Isotonic Fluid Volume DeficitRISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONSLoss of water and electrolytes from! Vomiting! Diarrhea! Excessive sweating! Polyuria! Fever! Nasogastric suction! Abnormal drainage or wound lossesInsufficient intake due to! Anorexia! Nausea! Inability to access fluids! Impaired swallowing! Confusion, depression

Complaints of weakness and thirst Weight loss! 2% loss # mild FVD! 5% loss # moderate! 8% loss # severeFluid intake less than outputDecreased tissue turgorDry mucous membranes, sunken eyeballs,decreased tearingSubnormal temperatureWeak, rapid pulseDecreased blood pressurePostural (orthostatic) hypotension (significantdrop in BP when moving from lying to sittingor standing position)Flat neck veins; decreased capillary refillDecreased central venous pressureDecreased urine volume (1.030)Increased hematocritIncreased blood urea nitrogen (BUN)

Assess for clinical manifestations of FVD.Monitor weight and vital signs, includingtemperature.Assess tissue turgor.Monitor fluid intake and output.Monitor laboratory findings.Administer oral and intravenous fluids asindicated.Provide frequent mouth care.Implement measures to prevent skinbreakdown.Provide for safety, e.g., provide assistance fora client rising from bed.

TABLE 525 Isotonic Fluid Volume ExcessRISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS

Weight gain! 2% gain # mild FVE! 5% gain # moderate! 8% gain # severeFluid intake greater than outputFull, bounding pulse; tachycardiaIncreased blood pressure and central venouspressureDistended neck and peripheral veins; slowvein emptyingMoist crackles (rales) in lungs; dyspnea,shortness of breathMental confusion

Excess intake of sodium-containingintravenous fluidsExcess ingestion of sodium in diet ormedications (e.g., sodium bicarbonateantacids such as Alka-Seltzer or hypertonicenema solutions such as Fleets)Impaired fluid balance regulation relatedto! 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 Fowlers position.Administer diuretics as ordered.Restrict fluid intake as indicated.Restrict dietary sodium as ordered.Implement measures to prevent skinbreakdown.

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DehydrationDehydration, or hyperosmolar imbalance, occurs when water islost from the body leaving the client with excess sodium. Be-cause water is lost while electrolytes, particularly sodium, areretained, the serum osmolality and serum sodium levels in-crease. Water is drawn into the vascular compartment from theinterstitial 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 orare in diabetic ketoacidosis and those receiving enteral feedingswith insufficient water intake.

OverhydrationOverhydration, also known as hypo-osmolar imbalance or waterexcess, 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 brainthis 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, butonly water is replaced. It can also result from the syndrome ofinappropriate antidiuretic hormone (SIADH), a disorder that canoccur 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 ofeach foot. B, Four-point scale for grading edema.

2mm

1+ Barely detectable

4mm

2+ 2 to 4 mm

6mm

3+ 5 to 7 mm

12mm4+ More than 7 mm

BA

DRUG CAPSULE Diuretic Agent furosemide (Lasix)

THE CLIENT WITH FLUID VOLUME EXCESSFurosemide 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 clients fluid status regularly. Assessment should in-

clude daily weights, close monitoring of intake and output, skinturgor, edema, lung sounds, and mucous membranes.

! Monitor the clients potassium levels. Furosemide is a loop diuretic which excretes potassium and may result in hypokalemia.

! Administer in the morning to avoid increased urination duringhours of sleep.

! If the client is also taking digitalis glycosides, he or she should beassessed for anorexia, nausea, vomiting, muscle cramps, pares-thesia, and confusion. The potassium-depleting effect offurosemide 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 beenmissed, do not double the dose the next day.

! Weigh on a daily basis and report weight gain or loss of morethan 3 lb in 1 day to your primary care provider.

! Contact your primary care provider immediately if you begin toexperience muscle weakness, cramps, nausea, dizziness,numbness, or tingling of the extremities.

! Some form of potassium supplementation will be needed. Theprimary care provider may order oral potassium supplements foryou; if not, you will need to consume a diet high in potassium.

! Make position changes slowly in order to minimize dizzinessfrom orthostatic hypotension.

Note: Prior to administering any medication, review all aspects with a current drug handbook or other reliable source.

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Electrolyte ImbalancesThe most common and most significant electrolyte imbalancesinvolve sodium, potassium, calcium, magnesium, chloride, andphosphate.

SodiumSodium (Na!), the most abundant cation in the extracellularfluid, not only moves into and out of the body but also moves incareful balance among the three fluid compartments. It is foundin 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 intestinalsuction, 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 ofless than 135 mEq/L, and is, in acute care settings, a commonelectrolyte imbalance. Because of sodiums role in determiningthe osmolality of ECF, hyponatremia typically results in a lowserum 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 levelsbelow 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 sodiumof greater than 145 mEq/L. Because the osmotic pressure of ex-tracellular fluid is increased, fluid moves out of the cells into theECF (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 persons thirst mechanism pro-tects against hypernatremia. For example, when an individualbecomes thirsty, the body is stimulated to drink water whichhelps 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 withdementia, or ill clients with an impaired thirst mechanism).

Table 526 lists risk factors and clinical signs for hypona-tremia and hypernatremia.

PotassiumAlthough the amount of potassium (K!) in extracellular fluid issmall, 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 521 onpage 1431 for a review of foods high in potassium.

Hypokalemia is a potassium deficit or a serum potassiumlevel of less than 3.5 mEq/L. Gastrointestinal losses of potas-sium through vomiting and gastric suction are common causesof 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 dropsbelow 3 mEq/L unless the decrease in potassium was rapid.When the decrease is gradual, the body compensates by shiftingpotassium from the intracellular environment into the serum.

Hyperkalemia is a potassium excess or a serum potassiumlevel greater than 5.0 mEq/L. Hyperkalemia is less commonthan hypokalemia and rarely occurs in clients with normal renalfunction. It is, however, more dangerous than hypokalemia andcan lead to cardiac arrest. As with hypokalemia, symptoms aremore severe and occur at lower levels when the increase inpotassium is abrupt. Table 526 lists risk factors and clinicalsigns for hypokalemia and hyperkalemia.

RESEARCH NOTE How Prevalent Is Chronic Dehydration in Elders?

Previous research has documented that dehydration is a problem inhospitalized elders, and low fluid intake has been documented to be aproblem in nursing home residents. The authors questioned whetherchronic 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 froma residential facility were most likely to be dehydrated (65%); however,44% of the elders living in the community were dehydrated.

IMPLICATIONSThe 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 nursesworking with elders. Nursing interventions need to include talking withelders 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. 2228. Copyright 2004 SLACK,Inc. Reprinted with permission.

H2O

H2O

H2O

Cell swells as wateris pulled in from ECF

Hyponatremia:Na+less than 135 mEq/L

A

Figure 52-12 ! The extracellular sodium level affects cell size. A, Inhyponatremia, cells swell; B, in hypernatremia, cells shrink in size.

H2O

Cell shrinks as wateris pulled out into ECF

Hypernatremia:Na+greater than 145 mEq/L

B

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TABLE 526 Electrolyte ImbalancesRISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONSHyponatremiaLoss 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)

administrationSyndrome of inappropriate ADH(SIADH)! Head injury! AIDS! Malignant tumors

HypernatremiaLoss of water! Insensible water loss (hyperventilation

or fever)! Diarrhea! Water deprivationGain 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

HypokalemiaLoss 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, anorexianervosa)

! Hyperaldosteronism

HyperkalemiaDecreased potassium excretion! Renal failure! Hypoaldosteronism! Potassium-conserving diureticsHigh potassium intake

Lethargy, confusion, apprehensionMuscle twitchingAbdominal crampsAnorexia, nausea, vomitingHeadacheSeizures, comaLaboratory findings:Serum sodium below 135 mEq/LSerum osmolality below 280 mOsm/kg

ThirstDry, sticky mucous membranesTongue red, dry, swollenWeakness

Severe hypernatremia:! Fatigue, restlessness! Decreasing level of consciousness! Disorientation! ConvulsionsLaboratory findings:Serum sodium above 145 mEq/LSerum osmolality above 300 mOsm/kg

Muscle weakness, leg crampsFatigue, lethargyAnorexia, nausea, vomitingDecreased bowel sounds, decreased bowelmotilityCardiac dysrhythmiasDepressed deep-tendon reflexesWeak, irregular pulsesLaboratory findings:Serum potassium below 3.5 mEq/LArterial blood gases (ABGs) may show alkalosis T wave flattening and ST segment depressionon ECG

Gastrointestinal hyperactivity, diarrheaIrritability, apathy, confusionCardiac dysrhythmias or arrestMuscle weakness, areflexia (absence ofreflexes)Decreased heart rate;Irregular pulse

Assess clinical manifestations.Monitor fluid intake and output.Monitor laboratory data (e.g., serum sodium).Assess client closely if administeringhypertonic saline solutions.Encourage food and fluid high in sodium ifpermitted (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., serumsodium).Encourage fluids as ordered.Monitor diet as ordered (e.g., restrict intake ofsalt and foods high in sodium).

Monitor heart rate and rhythm.Monitor clients receiving digitalis (e.g., digoxin)closely, because hypokalemia increases risk ofdigitalis toxicity.Administer oral potassium as ordered withfood or fluid to prevent gastric irritation.Administer IV potassium solutions at a rate nofaster than 1020 mEq/h; never administerundiluted potassium intravenously. For clientsreceiving IV potassium, monitor for pain andinflammation at the injection site.Teach client about potassium-rich foods.Teach clients how to prevent excessive loss ofpotassium (e.g., through abuse of diureticsand laxatives).

Closely monitor cardiac status and ECG.Administer diuretics and other medicationssuch as glucose and insulin as ordered.Hold potassium supplements and K!

conserving diuretics.

continued on page 1440

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RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONSHyperkalemiacontinued

TABLE 526 Electrolyte Imbalancescontinued

! Excessive use of K! containing saltsubstitutes

! Excessive or rapid IV infusion ofpotassium

! Potassium shift out of the tissue cellsinto the plasma (e.g., infections, burns,acidosis)

HypocalcemiaSurgical removal of the parathyroidglandsConditions such as ! Hypoparathyroidism! Acute pancreatitis! Hyperphosphatemia! Thyroid carcinoma

Inadequate vitamin D intake! Malabsorption! Hypomagnesemia! Alkalosis! Sepsis! Alcohol abuse

Hypercalcemia! Prolonged immobilizationConditions such as! Hyperparathyroidism! Malignancy of the bone! Pagets 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 extremitiesLaboratory findings:Serum potassium above 5.0 mEq/LPeaked T wave, widened QRS on ECG

Numbness, tingling of the extremities andaround the mouthMuscle tremors, cramps; if severe can progressto tetany and convulsionsCardiac dysrhythmias; decreased cardiac outputPositive Trousseaus and Chvosteks signs (seeTable 528)Confusion, anxiety, possible psychosesHyperactive deep tendon reflexesLaboratory findings:Serum calcium less than 8.5 mg/dL or 4.5 mEq/L (total)Lengthened QT intervalsProlonged ST segments

Lethargy, weaknessDepressed deep-tendon reflexesBone painAnorexia, nausea, vomitingConstipationPolyuria, hypercalciuriaFlank pain secondary to urinary calculiDysrhythmias, possible heart blockLaboratory findings:Serum calcium greater than 10.5 mg/dL or 5.5 mEq/L (total)Shortened QT intervalsShortened ST segments

Neuromuscular irritability with tremorsIncreased reflexes, tremors, convulsionsPositive Chvosteks and Trousseaus signs (seeTable 528)

Tachycardia, elevated blood pressure,dysrhythmiasDisorientation and confusionVertigoAnorexia, dysphagiaRespiratory difficultiesLaboratory findings:Serum magnesium below 1.5 mEq/LProlonged PR intervals, widened QRScomplexes, prolonged QT intervals, depressedST segments, broad flattened T waves,prominent U waves

Monitor serum K! levels carefully; a rapid dropmay occur as potassium shifts into the cells.Teach clients to avoid foods high in potassiumand salt substitutes.

Closely monitor respiratory and cardiovascularstatus.Take precautions to protect a confused client.Administer oral or parenteral calciumsupplements as ordered. When administeringintravenously, closely monitor cardiac statusand ECG during infusion.Teach clients at high risk for osteoporosis about! Dietary sources rich in calcium.! Recommendation for 1,0001,500 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 maintaina dilute urine.Teach clients to limit intake of food and fluidhigh in calcium.Encourage ingestion of fiber to preventconstipation.Protect a confused client; monitor forpathologic fractures in clients with long-termhypercalcemia.Encourage intake of acid-ash fluids (e.g.,prune or cranberry juice) to counteractdeposits of calcium salts in the urine.

Assess clients receiving digitalis for digitalistoxicity.Hypomagnesemia increases the risk of toxicity.

Take protective measures when there is apossibility of seizures.! Assess the clients 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-richfoods if permitted (e.g., whole grains, meat,seafood, and green leafy vegetables).Refer clients to alcohol treatment programs asindicated.

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RISK FACTORS CLINICAL MANIFESTATIONS NURSING INTERVENTIONS

TABLE 526 Electrolyte Imbalancescontinued

HypermagnesemiaAbnormal retention of magnesium, as in! Renal failure! Adrenal insufficiency

! Treatment with magnesium salts

Peripheral vasodilation, flushingNausea, vomitingMuscle weakness, paralysisHypotension, bradycardiaDepressed deep-tendon reflexesLethargy, drowsinessRespiratory depression, comaRespiratory and cardiac arrest ifhypermagnesemia is severeLaboratory findings:Serum magnesium above 2.5 mEq/LElectrocardiogram showing prolonged QTinterval, prolonged PR interval, widened QRScomplexes, tall T waves

Monitor vital signs and level of consciousnesswhen clients are at risk.If patellar reflexes are absent, notify theprimary care provider.Advise clients who have renal disease tocontact their primary care provider beforetaking over-the-counter drugs.

CLINICAL ALERTPotassium may be given intravenously for severe hypokalemia. It mustALWAYS be diluted appropriately and NEVER be given IV push. Potassiumthat is to be given IV should be mixed in the pharmacy and double-checked prior to administration by two nurses. The usual concentration ofIV potassium is 20 to 40 mEq/L. !

CalciumRegulating levels of calcium (Ca2!) in the body is more com-plex than the other major electrolytes so calcium balance can beaffected by many factors. Imbalances of this electrolyte are rel-atively common.

Hypocalcemia is a calcium deficit, or a total serum calciumlevel of less than 8.5 mg/dL or an ionized calcium level of lessthan 4.0 mg/dL. Severe depletion of calcium can cause tetanywith 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 Chvosteks sign iscontraction of the facial muscles that is produced by tapping thefacial nerve in front of the ear (Figure 52-13 !, A). Trousseaussign is a carpal spasm that occurs by inflating a blood pressurecuff on the upper arm to 20 mm Hg greater than the systolicpressure for 2 to 5 minutes (Figure 52-13 !, B). Clients at great-est risk for hypocalcemia are those whose parathyroid glandshave been removed. This is frequently associated with total thy-roidectomy or bilateral neck surgery for cancer. Low serummagnesium levels (hypomagnesemia) and chronic alcoholismalso increase the risk of hypocalcemia.

Hypercalcemia, or total serum calcium levels greater than10.5 mg/dL, or an ionized calcium level of greater than 5.0mg/dL, most often occurs when calcium is mobilized from thebony skeleton. This may be due to malignancy or prolonged im-mobilization.

B. Positive Trousseau's SignA. Positive Chvostek's SignFigure 52-13 ! A, Positive Chvosteks sign. B, Positive Trousseaus 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., UpperSaddle River, New Jersey.

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The risk factors and clinical manifestations related to cal-cium imbalances are found in Table 526.

MagnesiumMagnesium (Mg2!) imbalances are relatively common in hospitalized clients, although they may be unrecognized. Hypomagnesemia is a magnesium deficiency, or a total serummagnesium level of less than 1.5 mEq/L. It occurs more fre-quently than hypermagnesemia. Chronic alcoholism is the mostcommon cause of hypomagnesemia. Magnesium deficiency alsomay aggravate the manifestations of alcohol withdrawal, such asdelirium tremens (DTs). Hypermagnesemia is present when theserum magnesium level rises above 2.5 mEq/L. It is due to in-creased intake or decreased excretion. It is often iatrogenic, thatis, a result of overzealous magnesium therapy.

Table 526 lists risk factors and manifestations for clientswith altered magesium balance.

ChlorideBecause of the relationship between sodium ions and chlorideions (Cl"), imbalances of chloride commonly occur in conjunc-tion with sodium imbalances. Hypochloremia is a decreasedserum chloride level, in adults a level below 95 mEq/L, and isusually related to excess losses of chloride ion through the GItract, kidneys, or sweating. Hypochloremic clients are at riskfor alkalosis and may experience muscle twitching, tremors, ortetany.

Conditions that cause sodium retention also can lead to a highserum chloride level or hyperchloremia, in adults a level above108 mEq/L. Excess replacement of sodium chloride or potassiumchloride 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.

PhosphateThe phosphate anion PO4" is found in both intracellular and ex-tracellular fluid. Most of the phosphorus (P!) in the body existsas PO4". Phosphate is critical for cellular metabolism because itis 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 shiftinto the cells from extracellular fluid compartments, leading tohypophosphatemia, defined in adults as a total serum phosphatelevel less than 2.5 mg/dL. Alcohol withdrawal, acidbase imbal-ances, and the use of antacids that bind with phosphate in the GItract 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 shiftsout of the cells into extracellular fluids (e.g., due to tissue traumaor chemotherapy for malignant tumors), in renal failure, or whenexcess phosphate is administered or ingested. Infants who are fedcows milk are at risk for hyperphosphatemia, as are people usingphosphate-containing enemas or laxatives. Clients who have high

serum phosphate levels may experience numbness and tinglingaround the mouth and in the fingertips, muscle spasms, and tetany.

AcidBase ImbalancesAcidbase imbalances generally are classified as respiratory ormetabolic by the general or underlying cause of the disorder. Car-bonic acid levels are normally regulated by the lungs through theretention 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 ofregulation lead to metabolic acidosis or alkalosis. Healthy regula-tory systems will attempt to correct acidbase imbalances, aprocess called compensation.

Respiratory AcidosisHypoventilation and carbon dioxide retention cause carbonic acidlevels to increase and the pH to fall below 7.35, a conditionknown as respiratory acidosis. Serious lung diseases such asasthma and COPD are common causes of respiratory acidosis.Central nervous system depression due to anesthesia or a narcoticoverdose can sufficiently slow the respiratory rate so that carbondioxide is retained. When respiratory acidosis occurs, the kidneysretain bicarbonate to restore the normal carbonic acid to bicarbon-ate ratio. Recall, however, that the kidneys are relatively slow torespond to changes in acidbase balance, so this compensatoryresponse may require hours to days to restore the normal pH.

Respiratory Alka