Practice nursing care for Clients with Electrolyte and Fluid imbalances

Practice nursing care for Clients with Electrolyte and Fluid imbalances

 

 HOMEOSTASIS

The human body functions best when certain conditions are kept within a narrow range of normal. Examples of such conditions include body temperature, specific serum electrolyte values (e.g., sodium, potassium, and calcium), blood pH, and blood volume. Nothing functions very well if the body gains or loses 2 liters of blood. To keep conditions as close to normal as possible (a situation called homeostasis), the body has many regulatory mechanisms (homeostatic mechanisms) to prevent unacceptable changes. For example, if a person is in a hot environment (e.g., 110° F) and does not have good homeostatic mechanisms, his or her body temperature could go as high as 110° F, resulting in death. The homeostatic mechanisms of sweating to cool by evaporation and dilating blood vessels to dissipate body heat help to prevent body temperature from going more than 1° F above the normal 98.6° F, thereby maintaining homeostasis of body temperature.

One area extremely important for homeostasis is mainte­nance of the body’s normal fluid volume and composition. Water is the most common substance in the body. It is needed to deliver dissolved nutrients, electrolytes, and other substances to all organs, tissues, and cells. Changes in body fluid in terms of either the amount of water or the concentration of electrolytes can affect the functioning of all cells, tissues, and organs. For proper physiologic function, the volume of all body fluids and the types and amount of dissolved substances must be carefully regulated.

ANATOMY AND PHYSIOLOGY REVIEW

Physiologic Influences on Fluid and Electrolyte Balance

 

 

Many physical and biologic processes control the normal bal­ance of body fluids and electrolytes. These processes work to­gether to keep homeostatic balance so the internal environment remains stable even when the external environment un­dergoes dramatic changes.

Knowing the terminology related to solutions is necessary for understanding the processes involved in fluid and elec­trolyte balance. Body fluids are composed of water and particles either dissolved or suspended in water.

The solvent is the water portion of body fluids.

Solutes are the particles dissolved in the water. Solutes vary in type and con­centration from one body fluid compartment to another. Proper body function is dependent on keeping the correct balance of fluid and electrolytes within each body fluid compartment.

Important processes involved in fluid and electrolyte balance include filtration, diffusion, osmosis, and active transport. Capillary dynamics also affect fluid and electrolyte balance. All of these processes determine how, when, and where fluids and particles move across cell membranes.

 FILTRATION

 Definition

Filtration is the movement of fluid through a cell or blood vessel membrane because of hydrostatic pressure differences on both sides of the membrane. Basically, filtration depends on differences in water volume exerting pressure against confining walls.

All fluid has weight. The overall weight of a fluid is related to the amount of fluid present in the confined space. Water molecules in a confined space constantly press outward against the confining walls or boundaries.

Hydrostatic pressure is the force exerted by water molecules against the confining walls of a space. This pressure is caused by the weight of fluid against the walls. Hydrostatic pressure may be thought of as “water-pushing” pressure, because it is a force that moves water outward from a confined space through a membrane (Figure 11-1).

 ■ Physiologic Activity

Water is the largest component of any body fluid. The amount of water in any body fluid compartment is a main factor in determining the hydrostatic pressure of that compartment. The proportion of water present in a fluid is inversely related to the viscosity (thickness) of that fluid. Thus more water and less solute results in decreased viscosity, and less water with more solute results in increased viscosity. Blood, a viscous fluid (more viscous than water), is confined within the blood vessels. Blood has hydrostatic pressure because of its weight and volume and also because the heart is pumping blood into the arterial circulation.

The hydrostatic pressures of two fluid compartments can be compared whenever a permeable (porous) membrane sep­arates the two compartments.

If the hydrostatic pressure is the same in both fluid compartments, a state of equilibrium exists for hydrostatic pressure. If the hydrostatic pressure is not the same in both compartments, a state of disequilibrium

This means that the two compartments have a gradient, or graded difference, of hydrostatic pressure: one compartment has a higher hydrostatic pressure than the other. Because the human body constantly seeks equilibrium, a gradient across a cell membrane causes forces to rearrange the distribution of substances on both sides of the membrane until an equilibrium is reached.

Figure   •    The process of filtration. (© 1992 M. Linda Workman. All rights reserved.)

Compartment A has more water molecules and greater hydrostatic pressure than does compartment B.

Water molecules move down the hydrostatic pressure gradient from compartment A through the permeable membrane into compartment B, which has a lower hydrostatic pressure.

Enough water molecules have moved down the hydrostatic pressure gradient from compartment A into compartment В that both sides now have the same amount of water and the same amount of hydrostatic pressure. An equilibrium of hydrostatic pressure now exists between the two compartments, and no further net movement of water will occur.

In most instances, substances move or are rearranged from the greater amount of pressure or concentration to the lesser amount. Thus when a hydrostatic pressure gradient exists between two fluid compartments, fluid from the compartment with the higher hydrostatic pressure moves through (filters) the membrane into the compartment with the lower hydrostatic pressure. This filtration continues only as long as the hydrostatic pressure gradient exists. An equilibrium is reached when enough fluid leaves one compartment and enters the other compartment to make the hydrostatic pressure in both compartments equal.

When the two compartments are in equilibrium for hydrostatic pressure, a gradient no longer exists between them. Although water molecules may be exchanged evenly back and forth between two compartments in equilibrium, no net filtration of fluid occurs. In equilibrium, neither compartment gains or loses water molecules, and the hydrostatic pressure in both compartments remains the same.

 Clinical Function and Significance

Blood pressure is a hydrostatic filtering force measured in millimeters of mercury (mm Hg). It moves whole blood from the heart to tissue areas where filtration can occur. Filtration is important for the exchange of water, nutrients, and waste products when blood arrives at the tissue capillaries. One factor that determines whether or not fluid leaves the blood vessels and enters the tissue spaces (interstitial fluid) is the difference between the hydrostatic pressure of the fluid in the capillaries and that of the fluid in the interstitial tissue spaces.

The lining of the capillaries is only one cell layer thick. Therefore the “wall” that holds blood in the capillaries is thin. Large spaces (pores) between the cells in the capillary membrane help water filter freely through capillary membranes in either direction if a hydrostatic pressure gradient is present (Figure 11-3).

 

Edema (tissue swelling) can develop as a result of changes iormal hydrostatic pressure gradients, such as in clients with right-sided congestive heart failure. In this condition, the volume of blood in the right side of the heart increases greatly because the right ventricle is too weak to pump blood efficiently into the pulmonary blood vessels. As blood volume accumulates, blood backs up into the venous system, and venous hydrostatic pressure rises. The increased venous pressure causes capillary hydrostatic pressure to increase until it is higher than the hydrostatic pressure in the interstitial spaces. Excess filtration of fluid from the capillaries into the interstitial tissue spaces occurs, resulting in the formation of visible edema.

 DIFFUSION

Definition

Diffusion is the free movement of particles (solute) across a permeable membrane down a concentration gradient, that is, from an area of higher concentration to an area of lower concentration. Diffusion controls the movement of particles in solution across various body membranes.

 

 

Physiologic Activity

The diffusion of particles into and out of cells and fluid com­partments occurs via brownian motion, the kinetic energy of molecular motion. Brownian motion is the vibration of single molecules caused by electrons orbiting at the core of each molecule. Such motion produces totally random movement of molecules, which causes molecules to move and bump into each other within a confined space. These collisions cause a temporary increase in the speed of movement.

As a result of the collisions, molecules in a solution spread out evenly through whatever space is available. They move from an area of higher concentration of molecules to an area of lower concentration until equal concentrations are present in all areas. The number of collisions is related to the concen­tration of molecules in a confined space. Spaces with many molecules have more collisions and faster molecule motion than spaces with fewer molecules.

A concentration gradient exists when two areas have different concentrations of the same type of molecules. Brownian motion of the molecules causes them to move down the concentration gradient. As a result of brownian motion, any membrane that separates two areas is struck repeatedly by molecules. When the molecule strikes a pore in the membrane that is large enough for it to pass through, diffusion occurs (Figure 11-4).

 

The likelihood of any single molecule colliding with the membrane and going through a pore is much greater on the side of the membrane with a higher molecule concentration.

The speed of diffusion is directly related to the degree of concentration difference between the two sides of the membrane. The degree of concentration difference is usually referred to as the steepness of the gradient: The larger the concentration difference between the two sides, the steeper the gradient. Diffusion is more rapid when the concentration gradient is steeper (just as a ball rolls downhill more rapidly when the hill is steep than when the hill is nearly flat). The greater the difference in concentration, the more rapidly diffusion occurs from the area of higher concentration to the area of lower concentration.

Diffusion of solute particles continues through the membrane as long as a concentration gradient exists between the two sides of the membrane. When the concentration of solute is the same on both sides of the membrane, an equilibrium exists and an equal exchange (not a net movement) of solute continues.

 Clinical Function and Significance

Diffusion is important in the transport of gases and in the movement of most electrolytes, atoms, and molecules through cell membranes. Unlike capillary membranes, which permit the diffusion of most small-sized substances down a concen­tration gradient, cell membranes are selective. They permit the movement of some substances and inhibit the movement of other substances. Some molecules cannot move across a cell membrane, even when a steep “downhill” gradient exists, because the membrane is impermeable (not porous) to that molecule. Thus the concentration gradient is maintained mpermeability and special transport systems cause differences in the concentrations of specific substances from one fluid compartment to another. For example, under normal conditions the fluid outside of the cells, the extracellular fluid (ECF), contains almost ten times more sodium ions than the fluid inside the cell, the intracellular fluid (ICF). This extreme concentra­tion difference results from the relative impermeability of the cell membrane to sodium and from a special “sodium pump” that moves any extra sodium out of the cell “uphill” against its concentration gradient and back into the ECF.

In some instances diffusion cannot occur without assistance, even down steep concentration gradients, because of membrane selectivity. A clinical example is the fact that even though the concentration of glucose is much higher in the ECF than in the ICF (creating a steep gradient for glucose), glucose cannot cross most cell membranes without the help of insulin. When insulin is present in the ECF, it binds to insulin receptor sites on cell membranes, which makes the membranes much more perme­able to glucose. Glucose can then cross the cellular membrane down its concentration gradient until either an equilibrium of glucose concentration is created or insulin binding decreases.

Diffusion across a cell membrane that requires the assis­tance of a transport system or membrane-altering system (e.g., insulin) is called facilitated diffusion or facilitated transport. Because this type of transport occurs down a concentration gradient and requires no energy from the cell, it is a form of diffusion.

OSMOSIS

 Definition

 

Osmosis is the process by which only water molecules (sol­vent) move through a selectively permeable membrane. For osmosis to occur, a membrane must separate two fluid compartments, at least one of which must contain a solute that cannot move through the membrane. (The membrane is therefore impermeable to this solute.) A concentration gradient of this solute must also exist. If the membrane were permeable to this solute, then the solute would diffuse through the membrane down its concentration gradient until the concentrations of solute were equal on both sides of the membrane. Because the membrane is impermeable to the solute, these particles cannot cross the membrane, but water molecules can.

 Physiologic Activity

For the fluid compartments to have equal concentrations of solute, the water molecules must move down their concentra­tion gradient from the side with the higher concentration of water molecules (and thus a lower concentration of solute molecules) to the side with the lower concentration of water molecules (and thus a higher concentration of solute mole­cules). This movement continues until both compartments contain the same proportions of solute to solvent. The more dilute (less concentrated) fluid contains proportionately fewer solute molecules and more water molecules than the more concentrated fluid. Thus water moves by osmosis down its concentration gradient from the area of more dilute solute to the area of more concentrated solute until a new equilibrium is achieved (Figure 11-5).

 

 

At this point, the concentrations of solute in the fluid com­partments (the proportion of solute to solvent) on both sides of the membrane are equal, even though the total numbers of solute and volume of water may be different. This equilibrium is achieved by the movement of water molecules rather than the movement of solute molecules.

Factors that determine whether and how fast osmosis oc­curs include the overall concentration of particles (solute) in solution, how easily the solute dissolves in water (solubility), and the amount of membrane available for osmosis.

  CONCENTRATION OF SOLUTE

The concentration of particles in body fluids is expressed in milliequivalents per liter (mEq/L), millimoles per liter (mmol/L), and milliosmoles per liter (mOsm/L). Osmoles and milliosmoles are used to describe the total concentration of solute particles (including electrolytes) contained in a solution. The number of milliosmoles present in body fluids can be expressed as either osmolarity or osmolality.

Osmolarity is the number of milliosmoles in a liter of solution; osmolality is the number of milliosmoles in a kilogram of solution. The normal osmolarity value for plasma and other body fluids ranges from 270 to 300 mOsm/L.

The body functions best when the osmolarity of the fluids in all compartments is approximately 300 mOsm/L. Many mechanisms work to keep the solute concentration close to optimum levels. When all body fluids have this solute concentration, the osmotic pressures (water-pulling) of the various fluid compartments are essentially equal, and no net water movement occurs. In such a situation, the body fluids are said to be isosmotic to each other. Another term with essentially the same meaning is isotonic (sometimes called normotonic).

Examples of specific intravenous (IV) solutions with overall concentrations of specific substances equaling 270 to 300 mOsm/L include 0.9% sodium chloride in water and Ringer’s lactate in water. Because these solutions are isotonic (or isosmotic) to plasma, their addition to plasma does not change the osmolarity or osmotic pressure of the plasma.

Fluids with osmolarities (solute concentrations) greater than 300 mOsm/L are hyperosmotic, or hypertonic, compared with isosmotic fluids. Hyperosmotic fluids have a greater osmotic pressure than do isosmotic fluids and tend to pull water from the isosmotic fluid compartment into the hyperosmotic fluid compartment until an osmotic balance is achieved.

Fluids with osmolarities of less than 270 mOsm/L are hypo-osmotic, or hypotonic, compared with isosmotic fluids. Hypo-osmolar fluids have a lower or smaller osmotic pressure than isosmotic fluids. As a result, water tends to be pulled from the hypo-osmotic fluid compartment into the isosmotic fluid compartment until an osmotic balance is achieved.

 SOLUBILITY OF SOLUTE

Solubility refers to the degree to which a solute dissolves or dissociates completely in water. Solubility is directly related to osmotic pressure: The greater the solubility of the solutes in a fluid, the higher the osmotic pressure of that fluid.

 AMOUNT OF AVAILABLE MEMBRANE

The greater the amount of membrane available for osmosis, the faster the rate of osmosis. More membrane increases thechances that water molecules will strike the membrane at a point where penetration is possible.

 

Clinical Function and Significance

Osmosis and filtration act together in capillary fluid dynamics to regulate both extracellular and intracellular fluid volumes. The thirst mechanism is an excellent example of the importance of osmosis in maintaining homeostasis. Thirst re­sults from the activation of cells in the hypothalamus of the brain that respond to changes in extracellular fluid (ECF) osmolarity. These cells are so sensitive to changes in ECF os-molarity that they are called osmoreceptors. When a person loses body water, such as through excessive sweating during prolonged heavy exercise, ECF volume is decreased and os-molarity is increased (hypertonic conditions exist). The cells in the thirst center shrink as water moves from the cells into the hypertonic ECF. The shrinking of these cells stimulates a person’s awareness of thirst and increases the urge to drink. The person will usually drink enough fluid to replace the wa­ter lost through sweating and restore the ECF osmolarity to normal. After the ECF volume and osmolarity return to nor­mal levels, the osmoreceptors return to their normal size and no longer send stimulatory messages.

 ACTIVE TRANSPORT

Definition

A cell must use extra energy to move a substance across the cell membrane against a concentration gradient (uphill). This type of movement is called active transport because the cell must make active efforts for net movement to occur. Because of its energy demands and uphill movement, active transport is sometimes called “pumping,” and the mechanisms are known as membrane pumps.

 Physiologic Activity

Active transport systems, or pumps, are usually located in the cell membrane and act as “gatekeepers” to maintain special en­vironments inside cells. Some active transport pumps can carry more than one substance across the membrane at the same time. The sodium-potassium pump is an example of a common ac­tive transport system that simultaneously moves two substances in opposite directions against concentration gradients.

Sodium tends to diffuse slightly down its concentration gradient into the intracellular fluid (ICF) because it has such a high extracellular fluid (ECF) concentration compared with its ICF concentration. Similarly, because potassium has such a high concentration inside the cells compared with its concentration in ECF, it tends to diffuse slightly down its concentration gradient into the ECF. The action of the sodium-potassium pump moves the extra sodium out of the cell and returns the lost potassium back into the cell. The sodium-potassium pump requires the use of cellular energy.

The energy for this process usually comes from breaking a high-energy bond (~P), which occurs when a phosphate group is split off from an adenosine triphosphate (ATP) molecule. The functioning of active transport pumps depends on the presence of adequate cellular ATP.

Clinical Function and Significance

Cells use active transport to regulate cell volume and to con­trol the intracellular concentration of many substances. All cells function best when their internal environments are main­tained separately from the changes occurring in the extracel­lular fluid (ECF) environment.

A clinical example of what occurs when active transport fails is what results from tissue hypoxia (decreased oxygen supply in the body). Without adequate oxygen, ATP cannot be produced in sufficient amounts. Without ATP, the sodium-potassium pump cannot remove the extra sodium ions that have diffused from the ECF into the cell. The increased sodium concentration inside the cell increases the osmolarity and the osmotic pressure of the fluid inside the cell. Water moves into the cell in response to the increased osmotic pressure, causing the cell to swell and perhaps to lyse (break open) and die if oxygen is not provided.

CAPILLARY DYNAMICS

The circulatory system delivers nutrients and removes wastes at the tissue level. The important blood vessels for nutrient waste exchange are the thin-walled, porous capillaries. Nutrient delivery and waste removal depend on fluid movement in the capillary.

Fluid movement at the capillary level is dynamic not only because it is continuous but also because the homeostasis of plasma and interstitial fluid volumes must be maintained. Opposing processes must occur for nutrients to move into tissue spaces, for wastes to move into circulation, and for the fluid volumes of both the vascular and tissue spaces to be maintained.

During these processes, some fluid with nutrients must leave the capillary and enter the interstitial (tissue space) fluid compartment for a short period, which temporarily expands the interstitial fluid volume. The nutrients in the interstitial fluid are taken up by the cells through various membrane transport processes. Water may be exchanged between the intracellular compartment and the interstitial compartment, but under normal circumstances there is no net change in water volume. Metabolic wastes created in the cells are moved into the interstitial fluid. These waste products and any extra fluid in the interstitial space must be returned via the capillary to the systemic circulation. If there were no way to return the fluid originally lost into the interstitial compartment back to the blood, the blood volume would be depleted to the point of circulatory failure, and the interstitial fluid compartment would greatly expand.

 Capillary Forces Influencing Fluid Movement

Forces at the capillary level permit capillary fluid loss to be followed by a return of fluid to the capillary so that a near-equilibrium of fluid distribution is maintained at the capillary tissue level. These forces, known as Starling’s forces.

The near-equilibrium is based on the fact that the forces tending to move fluid out from the capillary at the arterial end are nearly equal to the forces tending to move fluid from the interstitial compartment back into the capillary at the venous end.

Blood flowing from the arterial end of the capillary to the venous end is controlled by the following:

* Hydrostatic pressure of the blood

* Dynamic ejection of the blood from the left ventricle of the heart

* Patency or openness of the capillaries

The blood entering the arterial end of the capillary has a blood pressure, or a capillary (plasma) hydrostatic pressure (PHP), of about 32 mm Hg. The capillary membrane is and permeable, and the usual tissue hydrostatic pressure is low. These factors create a natural tendency for filtration of fluid from the blood outward into the tissue spaces. The fluid portion of the blood, along with most of the smaller substances dissolved in the blood, filters through the capillary membrane into the tissue spaces. Through this process, nutrients and other essential substances can reach the cells.

If net filtration as a result of plasma hydrostatic pressure were the only force or factor involved at this level, blood volume would be progressively lost from circulation and would appear in the tissues. Fortunately, other mechanisms that favor the reabsorption of tissue fluid into the capillaries are also part of capillary dynamics. These mechanisms are plasma osmotic pressure and tissue hydrostatic pressure.

Osmosis (of water) through the capillary membrane (in either direction) occurs in response to differences in the concentrations of osmotically active substances in the capillary blood and tissue fluid. Tissue osmotic pressure (TOP) tends to draw fluid out of the capillary. Plasma osmotic pressure(POP) in the capillary tends to keep fluid in the capillary and draw fluid from the interstitial space into the capillary. Under normal conditions, osmotic pressure in capillary plasma is greater than osmotic pressure in tissue because there is a higher concentration of proteins in the blood than in the interstitial fluid.

Because the capillary membrane is highly impermeable to proteins, it does not allow blood proteins to pass freely through it into the tissue space. Therefore blood proteins remain in the capillary and add to the osmotic pressure. The specific type of osmotic pressure exerted by plasma proteins is called colloidal oncotic pressure because it is caused by the presence of proteins (colloidal substances) rather than by dissociated ions such as sodium (crystalloid substances). The average colloidal oncotic pressure in capillary blood is about 22 mm Hg.

Blood pressure (hydrostatic pressure) is greater than col­loidal oncotic pressure at the arterial end of the capillary. Capillary hydrostatic pressure favors the filtration of fluid from the the capillary into the tissue spaces, and colloidal oncotic pressure favors the reabsorption of fluid from the interstitial space into the capillary. The difference between these two capillary pressures at the arterial end of the capillary indicates that the filtering force outward is greater than the reabsorbing force inward.

Tissue Forces Influencing Fluid Movement

 

Tissue forces also influence the movement of solutions at the capillary level. These forces are tissue hydrostatic pres­sure (THP) and tissue osmotic pressure (TOP), both of which are usually relatively small forces. In some diseases, however, these forces increase greatly and change capillary dynamics.

To determine the direction of fluid movement in any one area of the capillary, the forces that move fluid out from the capillary are compared with the forces that move fluid into the capillary. Two forces at the arterial end that move fluid out from the capillary are the plasma hydrostatic pressure (PHP) (normally about 32 mm Hg) and the TOP (normally about 10 mm Hg). The pressures at the arterial end that return fluid to the capillary are the plasma colloidal oncotic pressure (normally about 22 mm Hg) and the tissue hydrostatic pressure (THP) (normally about 4 mm Hg). Because the outward filtration force is 16 mm Hg higher than the inward reabsorbing force, the overall result at the arterial end of the capillary is the outward filtration of fluid and small solute particles into the tissue spaces.

Plasma hydrostatic pressure (PHP) decreases as blood flows through the length of the capillary. As filtration pro­ceeds along the capillary, water is lost from the capillary, and the PHP gradually decreases. Therefore the pressures that cre­ate the outward filtration force (from the capillary into the in­terstitial fluid) decrease, whereas the pressures that create the inward reabsorption force (from the interstitial fluid into the capillary) remain the same. Eventually, the outward filtration pressures and the inward reabsorption pressures become equal.

 Clinical Function and Significance

Finally, at the venous end of the capillary, the inward reabsorption forces exceed the outward filtration forces. The ve­nous end of the capillary has a much lower hydrostatic pressure than does the arterial end. This decreased hydrostatic pressure has two causes:

– Because much of the water in the blood was filtered out of the capillary at the arterial end, the volume of water remaining in the blood at the venous end of the capillary is diminished.

– Because the venous portion of the capillary is farther away from the heart than the arterial end, blood pressure is lower in the venous end.

At the venous end of the capillary, the hydrostatic pres­sure is low and the interstitial fluid (tissue) hydrostatic pres­sure is high (because water has moved from the arterial end of the capillary into the interstitial space). The colloidal osmotic pressure at the venous end of the capillary exceeds that at the arterial end because water has been lost, which increases the concentration of proteins. The tissue osmotic pressure at the venous end of the capillary is lower than at the venous end.

Lymph

In most cases, not all of the fluid that leaves the capillary at the arterial end and enters the interstitial space is returned to the capillary at the venous end. A small amount remains in the tissues. If this situation is not balanced by another mechanism to return the fluid to the systemic circulation, blood volume would become depleted and the interstitial areas would constantly be edematous. Instead, this extra fluid leaking out from the capillaries is returned to the systemic circulation as lymph.

Lymph fluid is similar to blood plasma (from which it is formed) but contains far less protein. It is returned to the circulation by lymph vessels, or lymphatics. Lymphatics begin as small, thin-walled, vein-like vessels that join to form larger lymphatic vessels. Two large groups of lymphatic vessels connect the entire lymph system with the general circulatory system. The left thoracic lymph duct drains lymph from the abdomen, gastrointestinal tract, pelvis, lower extremities, left side of the thorax, left arm, and left side of the head and neck into the left subclavian vein at the point where it joins the left internal jugular vein (Figure 11-7).

 Lymph from the right arm, right side of the thorax, and right side of the head and neck drains into the right subclavian vein through three lymph ducts. Lymph nodes are situated along the lymphatic paths and filter the lymph fluid.

Lymphatics carry lymph fluid in one direction: toward the heart. Lymph flow is slower than blood flow because lymph has no pump and no direct connection between the arterial blood circulation and the lymphatic system. Lymph flow is enhanced by skeletal muscle contractions, intrathoracic pressure changes during breathing, and a peristalsis-like motion in the lymph vessels.

Hormonal Regulation of Fluid and Electrolyte Balance

The endocrine system helps to control fluid and electrolyte balance. Three hormones that help control these critical bal­ances are aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP).

 ALDOSTERONE

 

Aldosterone is a hormone secreted by the adrenal cortex. Al­dosterone secretion is stimulated by either a decreased sodium level in the extracellular fluid (ECF) or an increased sodium level in urine. The secretion and function of aldosterone, angiotensinogen, and angiotensin are outlined in Figure 11-8.

 

 

Aldosterone directly influences sodium balance by preventing sodium loss. Because sodium in body fluids exerts osmotic (water-pulling) pressure, water attempts to follow sodium in physiologically proportionate amounts (Guyton & Hall, 2000). As a result of this sodium-water relationship, aldosterone secretion also indirectly regulates water balance.

In the kidney, blood is supplied to the nephrons via the afferent arteriole. Specialized cells (juxtaglomerular cells) inside the afferent arteriole near the nephron glomeralus are sensitive to changes in serum concentrations of sodium. This area of the afferent arteriole comes into direct contact with a specialized area of the distal convoluted tubule (the macula densa). Together, the juxtaglomerular cells and the macula densa form the juxtaglomerular complex. When this com­plex senses that actual serum sodium concentrations are lower thaormal or that the total blood volume is low, the macula densa stimulates juxtaglomerular cells to secrete renin.

Renin acts on an inactive plasma protein called an-giotensinogen, converting it to angiotensin I. Angiotensin I is immediately further degraded into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE). Angiotensin II causes the constriction of many blood vessels and stimulates an increased secretion of aldosterone from the adrenal cortex.

Aldosterone acts on the distal convoluted tubules of the nephrons. When serum osmolarity is too low, aldosterone se­cretion stimulates these areas to reabsorb sodium from the urine back into the circulation (in exchange for potassium); this increases serum osmolarity. Aldosterone secretion in­creases when blood osmolarity or serum sodium levels are low, and its presence is normally required to prevent excessiverenal excretion of sodium. Aldosterone secretion also helps to prevent serum potassium levels from becoming too high. The secretion of aldosterone is inhibited when blood osmolarity or serum sodium levels are greater thaormal.

ANTIDIURETIC HORMONE

 

Antidiuretic hormone (ADH), also known as vasopressin, is produced in the brain and stored in the posterior pituitary gland. The release of ADH from the posterior pituitary gland is controlled by the hypothalamus in response to changes in blood osmolarity. The hypothalamus contains specialized cells (osmoreceptors) that are sensitive to changes in blood osmolarity. Increased blood osmolarity, especially an increase in the concentration of plasma sodium, results in a slight shrinkage of these cells and triggers the hypothalamus to stimulate the posterior pituitary to release ADH.

ADH acts directly on kidney tubules and collecting ducts, making them more permeable to water. As a result, more water is reabsorbed by these tubules and returned to the cir­culation, which in turn decreases the osmolarity of the blood by making it more dilute. When blood osmolarity decreases, especially when the plasma sodium concentration is below normal, the osmoreceptors swell slightly and inhibit the re­lease of ADH. Less water is reabsorbed and more is lost from the body in the urine. As a result, the amount of water in the extracellular fluid (ECF) decreases, bringing osmolar­ity to normal.

ATRIAL NATRIURETIC PEPTIDE

Atrial natriuretic peptide (ANP) is secreted by special cells that line the atria of the heart. It is secreted in response to increased blood volume and blood pressure. ANP binds to receptor sites in the collecting ducts of the nephrons, creating effects opposite those of aldosterone. Kidney reabsorp-tion of sodium is inhibited at the same time that glomerular filtration is increased (Briggs et al., 1996). The outcome is increased output of urine with a high sodium content, which results in decreased circulating blood volume and decreased blood osmolarity.

Body Fluids

Fluids, especially water, make up about 55% to 60% of to­tal adult body weight and can be divided into the extracel­lular fluid (ECF) and intracellular fluid (ICF). The ECF compartment accounts for approximately 15 L (40%) of total body water and includes interstitial fluid, blood plasma, lymph, bone and connective tissue water, and the fluid within special spaces (transcellular fluid), such as cere-brospinal fluid, synovial fluid, peritoneal fluid, and pleural fluid. ICF accounts for the remaining 25 L (60%) of total body water.

A person’s age, gender, and ratio of lean mass to body fat influence the amount and distribution of body fluids. An older adult has less total body water than a younger adult. Because fat cells contain practically no water, an obese person has less total body water than a lean person of the same body weight.

Body fluids allow cell nutrition and transport active mol­ecules (e.g., hormones) that are important to the regulation of normal physiologic functions. Most physiologic processes occur only in a watery environment. Body fluids are constantly renewed, purified, and replaced as fluid balance is maintained through intake and output. The total amount of water within each fluid compartment is stable, but water moves continually among all compartments. Water is not static in any compartment but is exchanged constantly while maintaining a volume equilibrium.

 

WOMEN’S HEALTH CONSIDERATIONS

A woman of any age usually has less total body water than does a man of similar size and age. This difference exists be­cause men generally have more muscle mass than women and because women have a higher percentage of body fat. Differences in muscle mass and percentage of body fat are partly a result of the influence of sex hormones. These differences in fat to lean body weight may be responsible for some of the differences seen in women’s and men’s responses to drugs.

 

 SOURCES OF FLUID INTAKE

Fluid intake is regulated through the thirst drive. Fluids enter the body primarily as liquids (Table 11-4).

Because solid foods contain up to 85% water, some fluid also enters the body as ingested solid foods. In addition, water is a by-product of cellular metabolism. This metabolic water accounts for about 300 mL of the daily water requirement. A rising plasma osmolarity or a decreasing plasma volume stimulates the sensation of thirst. Sensations such as mouth dryness or the thought that a person has not had a drink recently can trigger the thirst drive. An adult drinks an average of 1500 mL of fluid per day and obtains an additional 800 mL of fluid from ingested foods kidney is the most important and the most sensitive. Water loss via the kidney is closely regulated and is adjustable. The volume of urine excreted daily varies depending on the amount of fluid intake and the body’s need to conserve fluids.

The minimum amount of urine per day needed to dissolve and excrete toxic waste products is 400 to 600 mL. This min­imal volume is called the obligatory urine output. If the 24-hour urine output falls below the obligatory output amount, wastes are retained and can cause lethal electrolyte imbalances, acidosis, and a toxic build up of nitrogen. This urine is maximally concentrated, with a specific gravity (the weight of the liquid compared with the weight of pure water) of 1.032 or higher and an osmolarity of at least 1200 mOsm/L.

Urine can also become very dilute, with a specific gravity of 1.005 and an osmolarity of 200 mOsm/L. Dilution can re­sult from a large fluid intake and is reflected in a large volume of urine output. The ability of the kidneys to make either concentrated or very dilute urine helps to maintain fluid and electrolyte balance. With the influence of aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP), the kidney is able to respond when extracellular fluid concentra­tions, volumes, or pressures change.

Other normal water loss occurs through the skin, the lungs, and the gastrointestinal tract. Additional water losses can oc­cur via salivation, drainage from fistulas and drains, and gas­trointestinal suction.“Measured by subtracting the amount returned from the amount instilled. tMeasurement is accurate only when these substances are excreted in liquid form.

Water loss from the skin, lungs, and stool—called insensible water loss because it cannot be controlled—can be sig­nificant. In a healthy adult, insensible water loss is about 15 to 20 mL/kg/day. Insensible water loss can increase dramatically in hypermetabolic states such as thyroid crisis, trauma, burns, states of extreme stress, and fever. For every degree Celsius of increase in body temperature, insensible water loss increases by 10%. Insensible water loss also increases when atmospheric conditions are hot and dry.

Examples of clients at risk for increased insensible water loss include those undergoing mechanical ventilation and those with rapid respirations (tachypnea). Insensible water loss (not including sweat) is pure water and does not contain electrolytes. Therefore ex­cessive amounts of insensible water loss result in a more hy­pertonic extracellular fluid (ECF) with a smaller volume. If this loss is not balanced by intake, the hypertonic ECF and accompanying dehydration can lead to hypernatremia (elevated serum sodium level).

Loss by sweating is variable and can reach a maximum rate of about 2 L/hr. Although it contains electrolytes, sweat is slightly hypotonic compared to plasma. The amount of sweating is regulated by the autonomic nervous system, body temperature, and blood flow in the skin.

Water loss through stool is normally minimal. However, this loss can increase significantly with severe diarrhea or ex­cessive fistula drainage. Clients with ulcerative colitis can ex­perience a diarrheal fluid loss of several liters per day. Diar-rheal fluid contains water, potassium, sodium, bicarbonate, and chloride. Thus, with diarrhea, hypotonic fluid containing some electrolytes is lost.

Electrolytes

Electrolytes, or ions, are substances in body fluids that carry an electrical charge. Cations are positively charged ions; an-ions are negatively charged ions. Body fluids are electro-chemically neutral, which means that the number of positive ions is balanced by an equal number of negative ions. However, the distribution of ions differs in the extracellular fluid (ECF) and the intracellular fluid (ICF)

Most electrolytes have different concentrations in the ICF and ECF. This concentration difference helps maintain membrane excitability and transmit nerve impulses. The ranges of electrolyte concentration in these fluid compartments are extremely narrow. Thus even small changes in these concentrations can result in major pathologic alterations.

Electrolyte homeostasis is controlled by balancing the di­etary intake of electrolytes with the renal excretion or reab-sorption of electrolytes. For example, the concentration of plasma potassium is maintained between 3.5 and 5.0 mmol/L. In theory, the potassium in common foods could greatly increase the ECF potassium concentration and lead to major problems. Usually, however, the excretion of potassium by the kidney keeps pace with potassium intake and prevents major changes in the concentration of plasma potassium.

 SODIUM

Sodium (Na⁺) is the major cation in the extracellular fluid (ECF) and is the main factor responsible for maintaining ECF osmolarity. The activity of the sodium-potassium pump keeps the sodium concentration of the intracellular fluid (ICF) low (about 14 mmol/L) while maintaining high sodium concentrations in the plasma and other extracellular fluids. Maintaining this difference in sodium concentration is vital for the following physiologic functions:

·        Initiation of skeletal muscle contraction

·        Initiation of cardiac contractions

·        Transmission of nerve impulses

·        Maintenance of ECF osmolarity Maintenance of ECF volume

·        Maintenance of the kidney urine-concentrating system

The concentration of sodium in the ECF determines whether water is retained, excreted, or moved from one body compartment to another.

To maintain electrical balance, the concentration of sodium (a cation) within a body fluid must be matched by an equal concentration of anions (negatively charged substances). Each positive charge in the ECF must be balanced by a negative charge so the fluid does not carry either an overall positive or an overall negative charge. When this balance is present, a state of electroneutrality exists in that fluid. Changes in the concentration of plasma sodium seriously change fluid volume and the distribution of other electrolytes.

The normal concentration of plasma sodium ranges be­tween 136 and 145 mEq/L or mmol/L. Sodium enters the body through the ingestion of many foods and fluids . The average dietary intake of sodium is about 6 to 12 g/day. Sodium is also stored deep within the kidney tissues and can be released to the ECF as needed. De­spite great variations in sodium intake, the concentration of serum sodium usually remains within the normal range. Serum sodium balance is regulated by the kidney under the influences of aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP).

Low serum sodium levels inhibit the secretion of ADH and ANP and stimulate aldosterone secretion. Together these actions increase serum sodium concentration by increasing kidney re-absorption of sodium and enhancing kidney loss of water.

High serum sodium levels inhibit aldosterone secretion and directly stimulate the secretion of ADH and ANP. To­gether these hormones cause an increase in kidney excretion of sodium and kidney reabsorption of water.

 POTASSIUM

In contrast to sodium, potassium (K⁺) is the major cation of the intracellular fluid (ICF). The normal plasma concentration of potassium ranges from 3.5 to 5.0 mEq/L or mmol/L (see Table 11-5). The normal ICF concentration of potassium is about 140 mEq/L (mmol/L). Because of its high concentration inside cells, potassium has some control over intracellular osmolarity and volume. Keeping this large difference in potassium concentration between the ICF and the extracellular fluid (ECF) is critical for excitable tissues to generate action potentials and transmit impulses. Functions of potassium include the following:

·        Regulation of protein synthesis

·        Regulation of glucose use and storage

·        Maintenance of action potentials in excitable membranes

·        Because potassium levels in the plasma and interstitial fluid

Because potassium levels in the plasma and interstitial fluid are so low, any change in concentration is poorly tolerated by the body and seriously affects physiologic activities. For example, a decrease in plasma potassium of only 1 mEq/L (from 4 mEq/L to 3 mEq/L) is a 25% difference in total ECF potassium concentration. In contrast, a decrease in plasma sodium of 1 mEq/L (from 140 mEq/L to 139 mEq/L) is, overall, a much smaller change (less than 1%) in total ECF sodium concentration.

Potassium drifts out of cells down its concentration gradi­ent into the ECF. Almost all foods contain potassium. Potassium intake averages approximately 2 to 20 g/day. Despite heavy potassium intake and the drifting of potassium from cellular storage sites into the ECF, the healthy body keeps plasma potassium levels within the narrow range of normal values required for physiologic function.

The primary controller of ECF potassium concentration is the sodium-potassium pump within the membranes of all body cells. This pump removes three sodium ions from the fluid inside the cell for every two potassium ions that it returns to the cell. In this way, the levels of both serum sodium and cellular potassium remain high.

Some potassium regulation also occurs through kidney function. The kidney is the excretory route for ridding the body of ECF potassium (80% of potassium removed from the body occurs via the kidney). Unlike sodium, no hormone has been identified that directly controls kidney reabsorption of potassium; thus the kidney does not conserve potassium directly.

 CALCIUM

CALCIUM VALUES OF COMMON FOODS*

Data from Pennington, J. (1998). Bowe’s and Church’s food values of portions commonly used (17th ed.). Philadelphia: J.B. Lippincott. *U.S. Department of Agriculture recommended daily allowance for adults: 800-1200 mg.

 

Calcium (Ca²⁺) is a mineral whose presence and functions are closely related to those of phosphorus and magnesium. Calcium is a divalent cation (an ion having two positive charges) that exists in the body in two forms: bound and ionized (unbound or free).

Bound calcium is usually connected to specific serum pro­teins, especially albumin. Ionized calcium is present in the blood and other extracellular fluid (ECF) as free calcium. Free calcium is the active form and must be kept within a narrow range in the ECF. The body functions best when plasma calcium concentrations are maintained between 9.0 and 10.5 mg/dL, or between 2.25 and 2.75 mmol/L (see Table 11-5). Because the concentration of calcium in the intracellular fluid (ICF) is low, calcium has a steep gradient between ECF and ICF. Calcium functions in many ways and in many special­ized body systems, including the following:

•  Enhances the activity of enzymes or reactions

•  Increases skeletal muscle contraction

•  Increases cardiac muscle contraction

•  Regulates nerve impulse transmission

•  Assists in blood clotting

•  Provides bone strength and density

Calcium enters the body by dietary intake and absorption through the intestinal tract (Table 11-8). Absorption of dietary calcium requires the active form of vitamin D. Calcium is stored in the bones. When both plasma calcium levels and stored calcium levels are adequate, intestinal absorption of dietary calcium is inhibited and urine excretion of excess calcium increases. When more plasma calcium is needed, parathyroid hormone (PTH) is secreted and released from the parathyroid glands. PTH causes serum cal­cium levels to increase in the following ways:

•  Releasing free calcium from bone storage sites directly into the ECF (resorption)

•  Stimulating vitamin D activation, thus increasing intestinal absorption of dietary calcium

•  Inhibiting kidney excretion of calcium and stimulating kidney reabsorption of calcium

When excess calcium is present in plasma, secretion of PTH is inhibited and the secretion of thyrocalcitonin (TCT), a hor­mone secreted by the thyroid gland, is increased. TCT causes the plasma calcium level to decrease in the following ways:

•  Inhibiting bone resorption of calcium

•  Inhibiting activation of vitamin D, causing decreased gastrointestinal uptake of calcium

•  Increasing kidney excretion of calcium in the urine

 

POTASSIUM VALUES OF COMMON FOODS*

Food Source                                  Amount (mg)

Data from Pennington, J. (1998). Bowe’s and Church’s food values of portions commonly used (17th ed.). Philadelphia: J.B. Lippincott. *U.S. Department of Agriculture recommended daily allowance for adults: 1875-5625 mg.

 

PHOSPHORUS

Phosphorus (P) is present in the body in both inorganic and organic forms. Normal serum levels of phosphorus range from 3.0 to 4.5 mg/dL, or 0.97 to 1.45 mmol/L (see Table 11-5). Most phosphorus (80%) can be found in the bones. Phosphorus is the major anion in the intracellular fluid (ICF), and its concentration inside cells is much higher than in ex­tracellular fluid (ECF). Phosphorus is needed for the follow­ing cellular activities:

•  Activating B-complex vitamins

•  Forming and activating high-energy substances, including adenosine triphosphate (ATP)

•  Assisting in cell division

•  Cooperating in carbohydrate metabolism

•  Cooperating in protein metabolism

– Cooperating in lipid (fat) metabolism

Other phosphorus functions include acid-base buffering and calcium homeostasis. Phosphorus is found in a variety of foods, such as nuts, legumes, dairy products, red meat, organ meat, bran, and whole grains (Table 11-10). The average North American diet is high in phosphorus (1 to 2 g/day).

Phosphorus balance and calcium balance are intertwined. Normally, plasma concentrations of calcium and phosphorus exist in a reciprocal relationship, which means that the product of the plasma concentrations remains constant. Therefore a change in the concentration of phosphorus results in an equal and opposite change in the concentration of calcium (and vice versa).

The regulation of ECF phosphorus occurs through the activity of parathyroid hormone (PTH). Increased PTH levels cause a net loss of phosphorus. Reduced PTH levels enhance kidney reabsorption of phosphorus, resulting in increased concentrations of ECF phosphorus.

PHOSPHORUS  VALUES OF COMMON FOODS*

Food Source        Amount (mg)

Data from Pennington, J. (1998). Bowe’s and Church’s food values of portions commonly used (17th ed.). Philadelphia: J.B. Lippincott. *U.S. Department of Agriculture recommended daily allowance for adults: 800 mg.

 

MAGNESIUM

Magnesium (Mg²⁺) is another mineral that forms a cation when dissolved in water. Adults have an average of 25 g of magnesium, most of which (60%) is stored in bones and catilage. Little magnesium is present in the extracellular fluid (ECF). Serum levels of free magnesium range from 1.2 to 2.0 mg/dL, or 0.66 to 1.07 mmol/L. Much more magnesium is present in the intracellular fluid (ICF), and has more functions inside the cells than in the plasma. Magnesium is critical for the following intracellular reactions or activities:

•  Stimulating skeletal muscle contraction

•  Participating in carbohydrate metabolism

•  Activating adenosine triphosphate (ATP)

•  Activating B-complex vitamins

•  Enhancing deoxyribonucleic acid (DNA) synthesis

•  Enhancing protein synthesis

Extracellular magnesium regulates blood coagulation and skeletal muscle contractility.

Magnesium is found in many foods, such as nuts, vegetables, fish, and whole grains (Table 11-11). The daily magnesium requirement for adults is approximately 300 mg.

Although magnesium is similar to calcium in many re­spects and its presence in serum must be kept within a narrow range of normal values, little is known about its regulation. Magnesium is absorbed from the intestinal tract at the same place as calcium. The absorption of phosphorus inhibits mag­nesium absorption. Parathyroid hormone (PTH) stimulates the release of magnesium from bone in much the same way that it stimulates the release of calcium.

 

  CHLORIDE

Chloride (Cl~) is the major anion of the extracellular fluid (ECF) and works with sodium in aintaining ECF osmotic pressure. Chloride is important in the formation of hydrochloric acid in the stomach. The normal plasma concentration of chloride ranges from 90 to 110 mEq/L or mmol/L

Only a small amount of chloride is present inside the cells because negatively charged particles on the cell membrane repel chloride and prevent it from crossing the membrane. However, extracellular chloride can enter cells when exchanged for another anion that is leaving the cell. This situation, called a chloride shift, results in decreased concentra­tions of plasma chloride but no net body loss of chloride. Bicarbonate (HCO₃) is the anion most commonly exchanged for chloride. Chloride enters the body through dietary intake. Because chloride (along with sodium, potassium, and many other minerals) is a part of a salt, most diets contain enough chloride to meet the normal needs of the body.

 

Fluid and Electrolyte Changes Associated with Aging

Only 45% to 50% of the body weight of older adults is water, compared with 55% to 60% in younger adults. This decrease occurs because of a loss of muscle mass and a reduced ratio of lean body weight to total body weight. This decrease in to­tal body water places older adults at greater risk for dehydra­tion. Multiple symptoms point to fluid volume deficit in the older adult.

Skin turgor (the normal resiliency of a pinched fold of skin) is not always an accurate assessment of extracellular fluid (ECF) volume deficit (dehydration) in the older adult because the natural aging process is associated with de­creased turgor (Chart 11-1). Furthermore, the older adult may have a diminished thirst sensation and decreased kid­ney function, both of which contribute to the risk for dehy­dration and make assessment more difficult. Wheurses work with older clients, it is extremely important that they accurately record intake and output and weight, because these measurements reflect hydration status more accurately than does skin turgor.

The normal concentration of serum electrolytes also changes with the aging process. Chart 11-2 lists the normal electrolyte values for people older than 60 years of age.

 

Electrolyte balance may be more difficult to maintain in older adults. In particular, small changes in the concentrations of potassium and calcium may produce unexpectedly serious results. Although the ranges of electrolytes in plasma and in-tracellular fluid (ICF) may remaiormal, the balance is frag­ile and more easily disturbed in an older adult. Part of this fragility is related to decreased regulatory functions that occur with aging. Age-related kidney changes include decreased blood flow, decreased filtration, and decreased numbers of functional nephrons. Kidney and capillary changes associated with hypertension are more likely to be present in the older adult.

 

 

 

 

 

 

ASSESSMENT OF FLUID AND ELECTROLYTE BALANCE

History

One way of organizing history data to assess the client’s fluid and electrolyte status is to use Gordon’s Functional Health Patterns (Gordon, 2000). The patterns that most affect fluid and electrolyte status are the Nutritional-Metabolic Pattern and the Elimination Pattern (Chart 11-3).

 

The client’s nutritional history can often reveal a problem that affects fluid and electrolyte balance. The nurse obtains this information directly because the client may not understand the connection between dietary intake and the onset of fluid and electrolyte imbalances.

The guidelines for obtaining a thorough fluid and electrolyte history do not differ from those for assessing any other system; however, the information collected is more specific. For example, exact intake and output volumes are important, as are serial daily weights. The nurse may need to guide the client in accurately reporting the amount of fluid ingested and changes in urine patterns. The nurse also assesses the types of fluids and foods ingested to determine amount and osmolar-ity. Many clients do not consider solid food to contain liquid. Solid foods such as ice cream, gelatin, and ices are liquids at body temperature, and the nurse includes them when calcu­lating fluid intake.

Output fluids include losses not only through urine but also through perspiration, diarrhea, and insensible loss during fevers. The nurse asks specific questions about prescribed and over-the-counter medications and checks the dosage, the length of time taken, and the client’s compliance with the medication regimen. A client who is taking diuretics can have an imbalance of fluid, potassium, sodium, or hydrogen ions if additional conditions of water loss, such as vomiting or ex­cessive sweating, also occur.

Older adults often use laxatives, which can disturb fluid and electrolyte balance. Misuse and overuse of these drugs can lead to serious imbalances.

Other important areas of the client history include body weight changes, thirst or excessive drinking, exposure to hot environments, and the presence of other disorders, such as kidney or endocrine diseases (e.g., Cushing’s disease, Addi-son’s disease, diabetes mellitus, and diabetes insipidus). The nurse makes a general assessment of the client’s level of consciousness and mental status, because changes in mental status may support findings of imbalance. In such cases, the nurse may need to check the accuracy of historical data with family members.

Physical Assessment

Hydration is the normal state of fluid balance. A normally hydrated adult is alert and has moist eyes and mucous membranes, a urine output nearly the same as the amount of fluid ingested (with a urine specific gravity of approximately 1.015), and good skin turgor.

The nurse assesses skin turgor by pinching a fold of skin. This pinched fold should return immediately to its original shape after release. Decreased turgor, a sign of dehydration, is present when the fold remains in a pinched shape after being released and rebounds slowly (tenting). (Figure 11-11).

 

The nurse can best assess skin turgor in body areas that contain little fat tissue, such as over the sternum, on the forehead, or on the back of the hand. An older person may have poor skin turgor because of the loss of tissue elasticity related to the aging process; thus a true state of hydration may be more difficult to assess in an older adult than in a younger adult. The best areas for assessing turgor in the older adult are over the sternum and on the forehead.

Skin hydration assessment also includes an examination for dryness. The mucous membranes and the conjunctiva are normally moist. An assessment of fluid balance always in­cludes an examination of the eyes, nose, and oral mucous membranes. A dry, sticky, “cottony” mouth; the absence of tearing; weight loss; and decreased urine output all indicate an actual fluid volume deficit.

A major criterion used in assessing fluid and electrolyte status is accurate measurement of fluid intake and output. Ac­curate assessment of actual fluid intake and output is the nurse’s responsibility, and volumetric measuring devices must be used.

Behavioral and neurologic assessments are included in fluid assessment because changes in fluid balance can result in an alteration of neurologic function. In hypertonic states, neuronal cell shrinkage may induce serious nervous system excitability and hyperactivity, and convulsions may occur. Another variable to assess is the degree of thirst, but this may be difficult to gauge in a confused older client.

The nurse approximates insensible water loss (e.g., sweat) in every client. Special situations also require an as­sessment of fluid loss from other routes, including the fol­lowing:

•  Fluid losses from wounds

•  Gastric or intestinal drainage

•  Blood loss from hemorrhage

•  Drainage of body secretions, such as bile and pancreatic
juices, through fistulas

Electrolytes control the activity of excitable membranes, and electrolyte imbalances are associated with altered function of these membranes. Electrolyte assessment includes a complete neuromuscular assessment of muscle tone and strength, movement, coordination, and tremors. Assessment of other systems, including the cardiac system (heart rate, the strength of contractions, and the presence of dysrhythmias) and gastrointestinal system (peristalsis), may indicate changes of excitable membrane function.

Part of the nurse’s assessment focuses on changes from previous findings (including mental status, physical examination data, and laboratory data). Fluid and electrolyte imbalances can occur quickly; therefore the nurse must be familiar with the client’s baseline assessment data to detect any changes.

Psychosocial Assessment

Psychosocial assessment related to fluid and electrolyte status includes both psychologic and cultural factors that might influence balance. Depressed clients may refuse fluids or forget to drink adequate fluids. Clients with bulimia or anorexia nervosa (eating disorders) may use laxatives to excess or may induce vomiting, resulting in fluid and electrolyte imbalances. The nurse also assesses social practices. For example, excessive alcohol or drug use may lead to fluid or electrolyte imbalance.

Diagnostic Assessment

Laboratory results are important in identifying specific fluid and electrolyte imbalances or disorders that alter fluid and electrolyte status. Other laboratory values that are helpful in assessing fluid and electrolyte status include blood urea nitrogen level (BUN), glucose concentration, creatinine level, pH, bicarbonate level, osmolarity, hemoglobin, and hematocrit.

The urine test results may be helpful in assessing fluid status. If a laboratory report is not available, the nurse can perform various tests using a dipstick to help determine fluid and electrolyte status, including detecting substances that should not be present in the urine, such as glucose, acetone, protein, and blood. Urine measurements such as pH and specific gravity also can be determined in this way.

 

Normal body functioning requires a proper balance of all body fluids. Many health problems can disrupt fluid intake or output, placing all clients at risk for some degree of fluid imbalance. Although most imbalances of fluid are accompanied by electrolyte imbalances, this chapter focuses only on client problems associated with fluid imbalances.

DEHYDRATION

 OVERVIEW

In dehydration, the body’s fluid intake is not sufficient to meet the body’s fluid needs, resulting in a fluid volume deficit.

Three basic types of dehydration are possible (Figure 12-1):

• Isotonic dehydration, in which water and dissolved electrolytes are lost in equal proportions

      Hypertonic dehydration, in which water loss is greater than electrolyte loss

– Hypotonic dehydration, in which electrolyte loss is greater than water loss

Dehydration is a clinical state rather than a disease and can be caused by many factors. Dehydration may be an actual de­crease in total body water caused by either too little an intake of fluid or too great a loss of fluid. Dehydration also can occur without an actual decrease in total body water, such as when water shifts from the plasma into the interstitial space. This condition is called relative dehydration.

 

  Pathophysiology

 ISOTONIC DEHYDRATION

Isotonic dehydration is the most common type of fluid vol­ume deficit. Problems caused by isotonic dehydration result from loss of plasma volume. Isotonic dehydration involves loss of isotonic fluids from the extracellular fluid (ECF) compartment, including both the plasma and the interstitial space. Because isotonic fluid is lost, plasma osmolarity remains normal. This type of dehydration does not cause a shift of fluids between compartments, so the intracellular fluid (ICF) volume remains normal. Isotonic dehydration decreases circulating blood volume (hypovolemia) and leads to inadequate tissue perfusion. Compensatory mechanisms attempt to maintain adequate tissue perfusion to vital organs in spite of decreased vascular volume

Isotonic dehydration has many causes. These include inadequate intake of fluids and solutes, fluid shifts be­tween compartments, and excessive losses of isotonic body fluids.

 HYPERTONIC DEHYDRATION

Hypertonic dehydration is the second most common type of fluid volume deficit. The problems caused by hypertonic dehydration result from changes in the concentrations of specific electrolytes.

Hypertonic dehydration occurs when water loss from the extracellular fluid (ECF) is greater than electrolyte loss. This water loss increases the osmolarity of the remaining plasma, making it hypertonic or hyperosmolar compared with normal ECF. The hyperosmolar plasma has an in­creased osmotic pressure that causes fluid to move from the intracellular fluid (ICF) into the plasma and interstitial fluid spaces. The fluid shift leads to cellular dehydration and shrinkage. The fluid shift also causes the plasma volume to increase to normal or greater thaormal levels.

Thus the compensatory mechanisms and signs and symptoms of hy-povolemic shock are not present. However, excitable membrane activity and cardiac contractility are affected by altered plasma levels of potassium and calcium. Compensatory mechanisms for hypertonic dehydration occur in response to the increased ECF osmolarity (Figure 12-3).

 

Hypertonic dehydration is caused by the loss of any body fluid that is hypotonic (low osmolarity, or decreased concen­tration of solute particles compared with isotonic body fluid) or occurs when water loss is greater than electrolyte loss. Common causes of hypertonic dehydration are conditions such as excessive perspiration, hyperventilation, ketoacido­sis, prolonged fevers, diarrhea, early-stage renal failure, dia­betes insipidus, and ketoacidosis in the diuretic phase

 

TABLE 12-1      COMMON CAUSES OF DEHYDRATION

ISOTONIC DEHYDRATION

Hemorrhage

Vomiting

Diarrhea

Profuse salivation

Fistulas

Abscesses

lleostomy

Cecostomy

Frequent enemas

Profuse diaphoresis

Burns

Severe wounds

Long-term NPO (nothing by mouth)

Diuretic therapy

Gastrointestinal suction

HYPERTONIC DEHYDRATION

Hyperventilation

Watery diarrhea

Renal failure

Ketoacidosis

Diabetes insipidus

Excessive fluid replacement (hypertonic)

Excessive sodium bicarbonate administration

Tube feedings

Dysphagia

Impaired thirst

Unconsciousness

Fever

Impaired motor function

Systemic infection

HYPOTONIC DEHYDRATION

Chronic illness

Excessive fluid replacement (hypotonic)

Renal failure

Chronic or severe malnutrition

 

HYPOTONIC DEHYDRATION

Hypotonic dehydration is the least common type of fluid vol­ume deficit. The problems caused by hypotonic dehydration result from fluid shifts between compartments, causing a de­crease in plasma volume.

Hypotonic dehydration involves excessive loss of sodium and potassium from the ECF. This loss leads to decreased os­molarity of the remaining ECF, making it hypotonic compared with normal ECF. The decreased ECF osmolarity lowers the osmotic pressure of plasma and interstitial fluids to below that of the fluid inside the cells, the ICE As a result of this difference in osmotic pressure, water moves from the plasma and interstitial spaces into the cells, creating a plasma volume deficit and causing the cells to swell.

Cell swelling causes widespread problems and symptoms. Because brain cells are more sensitive to swelling than the cells of other tissues, neurologic problems usually occur with hypotonic dehydration. Hypotonic fluid also dilutes the normal electrolyte concentrations and causes sodium and potassium imbalances.

Hypotonic dehydration is usually associated with chronic illness. Chronic renal failure, in which the kidneys waste sodium, leads to hypotonic dehydration. Chronic malnutrition and taking in excessive amounts of hypotonic fluids also cause hypotonic dehydration.

   Incidence/Prevalence

The actual incidence of dehydration is not known; however every ill client is at risk. Older clients are at high risk because they have less total body water than younger adults. Conditions contributing to inadequate fluid intake in the older adult include decreased thirst sensation and difficulty with ambula-tion or other motor skills necessary for ingesting fluids.

Nurs ing home residents older than 85 years of age who are semidependent with eating and are less dependent on others for function appear to be at greatest risk for dehydration

Evidence – based practice for Nursing

This prospective, descriptive clinical study examined the wa­ter intake of 99 nursing home residents for two 24-hour peri­ods. The study represents an expansion and replication of a previous study conducted by the same investigator. The con­venience sample included subjects over 70 years of age who were not on fluid restriction and were not receiving tube feed­ings. Fluid intake was monitored by direct observation and measurement.

Water intake among the 99 subjects ranged from 597 mL to 2988 mL/day with a mean of 1968 mL/day. Only 8 (8%) sub­jects met or exceeded the standard required minimum water intake per day of 1600 mL/m². Subjects with lower water in­take were older, were semidependent with eating, and scored higher on the Norton At-Risk for Pressure Sore Scale. These subjects also had fewer ingestion sessions per day than those who had higher water intake. Often these subjects consumed fluids only during meals or with medications.

Critique. The study was well designed and executed. The conclusions derived were supported by the data obtained. Inclusion of weight, cardiovascular, and integumentary indi­cators of hydration status could have added depth to the study.

Implications for Nursing. Nursing home residents have long been assumed to be at risk for inadequate fluid intake as a result of age-related diminished thirst sensation, immobility, and dependence on others for assistance with nutritional intake, including fluids. This study indicates that nurses and as-sistive nursing personnel may be purposefully providing increased ingestion sessions for clients who are more dependent with eating. Those who are independent or semidependent may be assumed to be able to ingest adequate fluid without assistance or cues. The results of this study indicate that nurses need to provide increased fluid ingestion opportunities for all residents, regardless of mobility or feeding status.

COLLABORATIVE MANAGEMENT

 Assessment

 HISTORY

The nurse collects data on risk factors and factors causing dehydration

AGE.

Age is an important consideration because dehydration in the older adult can develop quickly in response to relatively small fluid losses. In addition, older people are more likely to have chronic illnesses or to be taking medications, such as diuretics, that can lead to fluid and electrolyte imbalances.

HEIGHT AND WEIGHT.

Measuring height and weight is important for calculating approximate fluid needs. If this information is not known or if the client is confused, the nurse obtains these measurements directly. Because 1 L of water weighs about 2.2 pounds (1 kg), changes in daily weights are good indicators of fluid losses or excesses. A weight change of 1 pound corresponds to a fluid volume change of about 500 mL.

OTHER CHANGES.

The nurse asks the client about changes in the tightness of clothing, rings, and shoes. A sudden decrease in tightness may indicate dehydration; an increase may reflect edema. Other related findings include the sensation of palpitations or lightheadedness on moving from a lying or a sitting position to a standing position (caused by orthostatic, or postural, hypotension).

The nurse asks about any abnormal or excessive fluid losses, such as perspiration, diarrhea, bleeding, vomiting, urination, salivation, and wound drainage. Other important information to collect includes chronic illnesses, recent acute illnesses, recent surgery, and medications.

The nurse asks specific questions about urine output, including the frequency and amount of voidings. The nurse also asks about the client’s usual fluid intake and the intake during the previous 24 hours. It is just as important to determine the types of fluids ingested as it is to determine the amount of fluids ingested, because fluids vary widely in osmolarity. The nurse also asks whether the client has recently engaged in strenuous physical activity and, if so, whether the activity took place in hot or dry environmental conditions.

RISK FACTORS FOR DEHYDRATION

ILLNESSES

•  Vomiting

•  Diarrhea

•  Burns

•  Large, draining wounds

•  Liver dysfunction

•  Diabetes mellitus

•  Diabetes insipidus

•  Renal disease

•  Hemorrhage

•  Major venous obstruction

•  Prolonged febrile state

OTHER SITUATIONS

• Extremes of age:

older adults, infants

• Unconsciousness

• Motor limitations

THERAPIES

• Surgery

• Diuretics

• Nothing by mouth

• Excessive hypertonic enemas

• Nasogastric suction

PHYSICAL ASSESSMENT/CLINICAL MANIFESTATIONS

The clinical manifestations of dehydration depend on which fluid compartments lose fluid, although all body systems are affected to some degree (Chart 12-1).

The most obvious and life-threatening clinical manifestations are seen when dehydration causes a decrease in the plasma volume.

 

CARDIOVASCULAR MANIFESTATIONS.

Cardiovascular changes are the most reliable indicators of changes in plasma volume. The heart rate increases with plasma vol­ume deficits in an attempt to maintain circulation with less blood. Peripheral pulses are weaker, difficult to find, and easily blocked with light pressure. If interstitial edema accompanies the dehydration, the peripheral pulses may not be palpable. The blood pressure also decreases, as does the pulse pressure, with a greater decrease in the systolic blood pressure. Hypotension is more severe with the client in the standing position than with the client in the sitting or lying posi­tion. Because the blood pressure with the client standing may be much lower than in other positions, blood pressure is measured first with the client lying down, then sitting, and finally standing.

Another indicator of hydration status is the degree of neck and hand vein filling. Normally, hand veins fill and become engorged when the hands are lower than the level of the heart. As the hands are raised above the level of the heart, the veins flatten or collapse (Figure 12-4).

Neck veins are normally distended when a client is in the supine position. These veins flatten when the client moves to a sitting position. When dehydration involves a plasma volume deficit, neck and hand veins are flat, even when the neck and hands are not raised above the level of the heart. These cardiovascular changes are not seen in hypertonic dehydration.

RESPIRATORY MANIFESTATIONS.

 The respiratory rate increases directly with the degree of fluid loss from plasma volume. The decreased blood volume is perceived by the body as decreased oxygen levels (hypoxia), and increased respiration is an attempt to maintain oxygen delivery.

 

INTEGUMENTARY MANIFESTATIONS.

Changes in skin may be useful indicators of hydration. The nurse assesses for changes in the skin and mucous membranes that may indicate dehydration, including skin color, mois­ture, skin turgor, and edema. In older clients this informa­tion is less reliable because of poor skin turgor resulting from the loss of elastic tissue and the loss of tissue fluids with aging.

The nurse assesses skin turgor by noting the following:

•  How easily the skin over the back of the hand and arm can be gently pinched between the thumb and the forefinger to form a “tent”

•  How soon the pinched skin resumes its normal position after release

•  Whether depressions (pits) remain in the skin after a finger is pressed firmly but gently (over the shin, over the sternum, and over the sacrum)

•  How deep the depression is (in millimeters)

•  How long the depression remains

In generalized dehydration, skin turgor is poor, with the tenting remaining for minutes after pinching the skin, and no skin depressions occur with gentle pressure. The skin appears dry and scaly. The nurse assesses skin turgor in an older adult by pinching the skin over the sternum, the forehead, or the abdomen because these areas more reliably indicate hydration (see Figure 11-11). As a person ages, the skin loses elasticity and tents on extremities even when the person is well hydrated.

In dehydration, oral mucous membranes are not moist. They may be covered with a thick, sticky, pastelike coating and may have cracks and fissures. The surface of the tongue may have deep furrows.

 

NEUROLOGIC MANIFESTATIONS.

 Dehydration may cause changes in body temperature and mental status as the brain is less perfused. The client with dehydration typically has a low-grade fever. One cause of the fever is the constriction of blood vessels that occurs as a compensation for hypovolemia. The blood vessel constriction makes heat dissipation more difficult.

Fever can also cause dehydration. A client with a tem­perature greater than 102° F (39° C) for longer than 6 hours is especially at risk. Older adults, who normally have a body temperature range of 96° to 98° F (35.4° to 36.6° C), are at greater risk for dehydration during epi­sodes of fever. Mental status changes are also common with dehydration. Chart 12-2 outlines how to assess men­tal status quickly.

RENAL MANIFESTATIONS.

The volume and the composition of urine output indicate the hydration status of the renal system. The nurse monitors urine output, comparing total output with total fluid intake and daily weights. Accurate intake and output measurement is a major nursing responsibility. Urine output below 500 mL/day for any client without renal disease is cause for concern. A client with fluid imbalance is weighed each day at the same time and on the same scale. When possible, the client wears the same amount and type of clothing for each weigh-in. Metabolic weight loss (even in starvation) usually accounts for only about V₂ pound of weight loss per day. Any weight loss in excess of this amount is considered fluid loss.

PSYCHOSOCIAL ASSESSMENT

The nurse observes the client for behavioral changes that accompany dehydration. Initially, a dehydrated client may have a flat affect and may seem unconcerned about his or her stateof health and possible treatment regimens. As dehydration worsens, psychosocial activities reflect abnormal functioning of the central nervous system. The client may become anxious, restless, lethargic, and confused. These behavioral changes are more obvious in hypertonic and hypotonic dehydration be­cause of intracellular fluid (ICF) shifts in brain cells, resulting in shrinkage or swelling of the cells. If the conditions causing the dehydration continue, circulation to cerebral tissues be­comes so impaired that delirium and coma can occur.

 LABORATORY ASSESSMENT

No single laboratory test result confirms or rales out dehydra­tion. Instead, a diagnosis of dehydration is based on laboratory findings along with presenting signs and symptoms. Laboratory findings depend on the type of dehydration present. Isotonic and hypotonic dehydration states with accompanying plasma volume deficits show hemoconcentration (elevated levels of hemoglobin, hematocrit, serum osmolarity, glucose, protein, blood urea nitrogen, and various electrolytes) because only the water is lost and other substances remain. Hemocon­centration is not present when dehydration is caused by hemor­rhage, because loss of all blood and plasma products occurs.

Specific urine laboratory values can help to confirm dehy­dration if the client does not have renal dysfunction. Usually the urine of the client with dehydration is concentrated, with a specific gravity greater than 1.030. Volume is decreased, and osmolarity is greatly increased. Usually the color is dark am­ber and a strong odor is evident.

 Analysis

COMMON NURSING DIAGNOSES AND COLLABORATIVE PROBLEMS

The following are priority nursing diagnoses for clients with dehydration:

1.    Deficient Fluid Volume related to excessive fluid loss or inadequate fluid intake

2.    Decreased Cardiac Output related to decreased plasma volume

3.    Impaired Oral Mucous Membrane related to inadequate oral secretions

The primary collaborative problem is Potential for Dys-rhythmias.

ADDITIONAL NURSING DIAGNOSES AND COLLABORATIVE PROBLEMS

In addition to the commoursing diagnoses and collabora­tive problems, clients with dehydration may have one or more of the following:

•  Constipation related to decreased body fluids

•  Risk for Injury (fall) related to orthostatic (postural) hypotension

•  Deficient Knowledge related to medication regimen and preventive measures

•  Risk for Impaired Skin Integrity related to deficiencies of interstitial fluid and inadequate tissue perfusion

•  Ineffective Airway Clearance related to thick, tenacious secretions

•  Potential for Hypovolemic Shock

•  Potential for Electrolyte Imbalances

Planning and Implementation

DEFICIENT FLUID VOLUME

PLANNING: EXPECTED OUTCOMES. 

The client with dehydration is expected to have body fluid levels restored to normal.

INTERVENTIONS. Management of dehydration aims to prevent further fluid losses and increase fluid compartment volumes to normal ranges.

FLUID MANAGEMENT. Diet therapy, oral rehydration therapy, and drug therapy are the methods of choice to manage fluid volume deficit.

DIET THERAPY. Mild to moderate dehydration is corrected with oral fluid replacement if the client is alert enough to swallow and can tolerate oral fluids. The nurse or assistive nursing personnel encourages and measures fluid intake. The specific type of fluid needed for replacement varies with the type of dehydration.

The client’s compliance in drinking oral replacement fluids can be enhanced by using fluids he or she enjoys and by carefully timing the intake schedule. Dividing the total amount of fluids needed by nursing shifts helps to meet fluid needs more evenly with less danger of overhydration. The conscious client is offered small volumes of fluids every hour to increase intake.

ORAL REHYDRATION THERAPY. Oral rehydration ther­apy (ORT) is the most cost-effective way to replace fluids for the client with dehydration. Specifically formulated solutions containing glucose and electrolytes cause water to be absorbed even when the client is vomiting or has diarrhea. Fluid losses from diarrhea are usually 2 to 3 L/day and should be re­placed liter for liter, especially in older clients. A typical order might be “Resol 1 L every 8 hours.” Table 12-3 lists commercially available ORT solutions.

DRUG THERAPY. Drug therapy for dehydration is di­rected at restoring fluid balance and controlling the causes of dehydration. Whenever possible, fluids are replaced by the oral route. When dehydration is severe or life threatening, intravenous (IV) fluid replacement may be necessary. Calculation of how much fluid to replace is based on the client’s weight loss and clinical manifestations. The rate of fluid replacement depends on the degree of dehydration and the presence of pre-existing cardiac, pulmonary, or renal problems.

The type of fluid ordered by the health care provider varies with the type of dehydration and the client’s cardiovascular status. The desired outcomes of therapy are appropriate fluid replacement and normal volumes in all body fluid compart­ments. Usually the client receives IV infusions of water with whatever solutes (especially electrolytes) are determined nec­essary on the basis of laboratory values. Generally, isotonic dehydration is treated with isotonic fluid solutions, hypertonic dehydration is treated with hypotonic fluid solutions, and hypotonic dehydration is treated with hy­pertonic fluid solutions.

Drug therapy includes the use of medications to correct the cause of the dehydration. Antidiarrheal medications are ordered when excessive diarrhea causes dehydration. Antimicrobial therapy may be used in clients with bacterial diarrhea. Antiemet-ics to control vomiting may be necessary when excessive vomiting produces dehydration. Antipyretics to reduce body temperature are helpful when fever contributes to dehydration.

DECREASED CARDIAC OUTPUT

PLANNING: EXPECTED OUTCOMES. The client with dehydration is expected to have cardiac output restored to normal levels and to maintain adequate oxygenation to vital organs.

INTERVENTIONS. Interventions of drug and oxygen therapy aim to increase circulating fluid volume, support compensatory mechanisms, and prevent complications.

DRUG THERAPY. Drug therapy to increase body fluid volume and prevent excessive fluid loss is the same as that for the client with fluid volume deficit. Drugs to increase venous return or improve cardiac contractility are used only when a cardiac problem also is present.

OXYGEN THERAPY. Oxygen is usually delivered by mask or nasal cannula to the client with dehydration. The nurse administers water-nebulized oxygen at the rate oramount specified by the health care provider’s order.

 FLUID MONITORING. Monitoring vital signs and level of consciousness is important when caring for clients with dehy­dration (see Chart 12-4). The nurse or assistive nursing per­sonnel monitors the pulse, blood pressure, pulse pressure, central venous pressure, respiratory rate, skin and mucous membrane color, and urine output at least every hour until the fluid imbalance is resolved.

IMPAIRED ORAL MUCOUS MEMBRANE

PLANNING: EXPECTED OUTCOMES. The client with dehydration is expected to have less discomfort and re­main free of complications.

INTERVENTIONS

ORAL HEALTH RESTORATION. Interventions include drug therapy, fluid replacement, and good oral hygiene, as well as the early diagnosis and prevention of complications (see Chart 12-4).

DRUG THERAPY. Drug therapy to increase fluid volume and prevent fluid loss is the same as that discussed earlier for deficient fluid volume (p. 165). Saliva substitutes, such as Salivart, can reduce the sensation of mouth dryness. To prevent aspiration, the nurse does not use such agents in an unconscious client.

ORAL HYGIENE. Nursing actions to promote oral hygiene can increase the client’s comfort. The lips are kept clean and moist. The thick, sticky coating on the tongue and mouth during dehydration can be reduced with frequent mouth care. Mouth care includes gentle toothbrushing several times a day and rinsing hourly. The nurse teaches the client to avoid mouthwashes and swabs that contain alcohol or glycerin be­cause these products dry the oral mucosa further and may cause more discomfort by stinging or burning open areas of the mucosa. Rinsing the mouth with dilute solutions of hy­drogen peroxide two or three times per day is a good form of oral hygiene; however, when used more frequently, this treat­ment increases oral dryness. Tap water and normal salinerinses can be used safely as often as the client wishes.

PREVENTION OF COMPLICATIONS. A dry mouth can lead to the development of sores and fissures in the mucosa, providing a portal of entry for many pathogens. The thick, sticky coating also is an excellent breeding ground for microorganisms. A major complication of mouth dryness is a wide variety of oral infections. Chart 12-4 summarizes nurs­ing interventions for mouth care.

 POTENTIAL FOR DYSRHYTHMIAS

PLANNING: EXPECTED OUTCOMES. The client with dehydration is expected to maintain his or her normal cardiac rhythm.

INTERVENTIONS. Interventions are aimed at correcting the dehydration and recognizing dysrhythmias so that appropriate drug therapy can be initiated.

DRUG THERAPY. Drug therapy to increase body fluid volume and prevent excessive fluid loss is the same as that discussed earlier for deficient fluid volume (p.165).

Elevated potassium or calcium levels can cause life-threat­ening dysrhythmias. Drug therapy to reduce these electrolytes may be ordered. If potassium levels are elevated, a combina­tion of 20 units of regular insulin in 100 mL of 20% dextrose may be administered to promote movement of potassium from the blood into the intracellular fluid (ICF). Drugs such as etidronate (Didronel) and plicamycin (Mithracin) may be ad­ministered to reduce an elevated serum calcium level.

MONITORING. The nurse monitors the client for signs and symptoms of cardiac dysrhythmias every 15 minutes un­til he or she is fully rehydrated. The rate, rhythm, and quality of the apical pulse are assessed and compared with the client’s baseline measurements. The nurse further assesses for fatigue, chest discomfort or pain, and shortness of breath. Hand grasps and deep tendon reflexes are assessed, and changes from baseline are noted.

Clients at risk for dysrhythmias are monitored using elec-trocardiography (ECG). The pattern may show tall T waves or a shortened ST segment. Any change from the client’s base­line ECG is reported to the physician immediately.

 Community-Based Care

No extensive home care preparations are necessary for clients with mild dehydration or for those with dehydration of sudden onset. The imbalance is corrected before discharge from the facility and, with minimal precautions, is unlikely to recur. Clients who are most likely to be discharged before the imbalance is completely corrected and who are susceptible to recurrent episodes are those with chronic pathologic condi­tions, such as renal insufficiency, diabetes, malignancy, adre­nal insufficiency, and many endocrine disorders. These clients often require long-term diet and drug therapy.

The nurse performs a focused assessment  and a mental status check at every home visit to a client at risk for dehydration. Medications, signs and symptoms of dehydration, and health care resources are reviewed with the client and family.

Education is important in the prevention and early detection of dehydration. The nurse teaches the client at risk for dehydration about diet, drug regimens, and the signs and symptoms of dehydration, explaining the meaning of changes found on assessment.

The nurse stresses the importance of recording accurate daily weights in assessing hydration status. Clients are in­structed to weigh themselves on the same scale daily, close to the same time each day, and with approximately the same amount of clothing on each time. Keeping a chart comparing the recorded weights from one day to the next can help the client recognize early-stage dehydration.

Clients are instructed to take medications as prescribed and not increase the use of diuretics. The nurse explains that if a diuretic is not taken one day, the next day’s dose should not be doubled. Clients are taught how and where to assess skin turgor. The nurse teaches them how to measure their own peripheral pulse and obtains a return demonstration.

The nurse instructs the family to keep fluids for the client in places that he or she can access. Container modifications, such as opening zip-top cans and covering them with foil, can be made to ensure that the client can easily open container lids. “Sipper” containers not only provide easy access but also are unbreakable and reduce spillage.

OVERHYDRATION

Overhydration, also called fluid overload, is an excess of body fluid. It is not an actual disease but rather a clinical sign of a physiologic problem in which fluid intake or retention is greater than the body’s fluid needs. Overhydration may be either an actual excess of total body fluid or a relative fluid excess in one or more fluid compartments. The three basic types of fluid volume excess are isotonic overhydration, hypotonic overhydration, and hypertonic overhydration.

Most problems caused by overhydration are related to fluid volume excess in the vascular space or to dilution of specific electrolytes and blood components. Clinical manifestations vary with the type and degree of overhydration. The conditions leading to overhydration (fluid overload) are related to excessive intake or inadequate excretion of fluid.

 Isotonic Overhydration

Isotonic overhydration is also called hypervolemia because the problems result from excessive fluid in the extracellular fluid (ECF) compartment. In isotonic overhydration, isotonic fluids are ingested or retained, so that osmolarity remains normal. Only the ECF compartment is expanded, and fluid does not shift between the extracellular and intracellular compartments. The problems caused by severe isotonic overhydration are circulatory overload and development of edema. When isotonic overhydration is severe, or when it occurs in a person with poor cardiac function, overhydration can lead to congestive heart failure and pulmonary edema.

 Hypotonic Overhydration

In hypotonic overhydration (water intoxication), the excess fluid is hypotonic to normal body fluids. Thus the osmolarity of the ECF decreases, and hydrostatic pressure increases. Fluid moves into the intracellular space because of the decreased vascular osmotic pressure, and all body fluid compartments expand (see Figure12-5). Because the excessive fluid is hypotonic, electrolyte imbalances caused by dilution accompany hypotonic overhydration.

 Hypertonic Overhydration

Hypertonic overhydration is rare and is caused by an exces­sive sodium intake. The hyperosmolarity of the plasma and interstitial compartments draws fluid from the intracellular fluid (ICF) compartment. Thus the ECF volume expands, and the ICF volume contracts (see Figure 12-5).

COLLABORATIVE MANAGEMENT

 Assessment

Clinical manifestations of overhydration vary with the spe­cific type, the fluid compartments involved, and the degree of overhydration. Clients with isotonic overhydration or hyper­tonic overhydration have signs and symptoms of circulatory overload and pitting edema (Figure 12-7). 

Clients with hypotonic overhydration have problems with cellular swelling and electrolyte dilution.

Chart 12-6 summarizes the common clinical manifestations of overhydration.