ch 11 iggy F&E

Question 1

how much of our total weight is water

Answer 1

Water (fluid) makes up about 55% to 60% of total weight for younger adults and 50% to 55% of total weight for older adults.
This water is divided into two main compartments (spaces)
Water delivers dissolved nutrients and electrolytes to all organs, tissues, and cells.

Question 2

(extracellular fluid [ECF])

Answer 2

the fluid outside the cells The ECF space is about one third (about 15 L) of the total body water.

Question 3

interstitial fluid

Transcellular fluid

Answer 3

The ECF includes interstitial fluid (fluid between cells, “third space”); blood, lymph, bone, and connective tissue water; and the transcellular fluids. Transcellular fluids include cerebrospinal fluid, synovial fluid, peritoneal fluid, and pleural fluid.

Question 4

(intracellular fluid [ICF]).

Answer 4

the fluid inside the cells

. ICF is about two thirds (about 25 L) of total body water.

Question 5

Solutes

Answer 5

Solutes are the particles dissolved or suspended in the water.

Question 6

Solvent

Answer 6

The solvent is the water portion of fluids.

Question 7

electrolytes

Answer 7

When solutes express an overall electrical charge, they are known as electrolytes.

Question 8

What three processes control FLUID AND ELECTROLYTE BALANCE to keep the internal environment stable even when the external environment changes

Answer 8

These processes (filtration, diffusion, and osmosis) determine whether fluids and particles move across cell membranes.

Question 9

Filtration

Answer 9

Filtration is the movement of fluid (water) through a cell or blood vessel membrane because of water pressure (hydrostatic pressure) differences on both sides of the membrane. This pressure is caused by water volume pressing against confining membranes.

Question 10

hydrostatic pressure

Answer 10

water pressure. caused by water volume against confining membranes. facilitates filtration (movement of fluid thru cell or blood vessel.

Water molecules in a confined space constantly press outward against the membranes, creating hydrostatic pressure (also known as water pressure). This is a “water-pushing” pressure, because it forces water outward from a confined space through a membrane

Question 11

what determines the hydrostatic pressure of any body fluid space

Answer 11

The amount (volume) of water in any body fluid space determines the hydrostatic pressure of that space. Blood, which is “thicker” than water (more viscous), is confined within the blood vessels. Blood has hydrostatic pressure because of its weight and volume and also from the pressure in arteries generated by the pumping action of the heart.

Question 12

comparing two fluid spaces

Answer 12

The hydrostatic pressures of two fluid spaces can be compared whenever a porous (permeable) membrane separates the two spaces. If the hydrostatic pressure is the same in both fluid spaces, there is no pressure difference between the two spaces, and the hydrostatic pressure is at equilibrium. If the hydrostatic pressure is not the same in both spaces, disequilibrium exists. This means that the two spaces have a graded difference (gradient) for hydrostatic pressure: one space has a higher hydrostatic pressure than the other. The human body constantly seeks equilibrium. When a gradient exists, water movement (filtration) occurs until the hydrostatic pressure is the same in both spaces (

Question 13

which direction does the water move

Answer 13

Water moves through the membrane (filters) from the space with higher hydrostatic pressure to the space with lower pressure. Filtration continues only as long as the hydrostatic pressure gradient exists. equilibrium exists when hydrostatic pressure is equal between spaces. water molecules are shared but there is no net movement

Question 14

Blood pressure

Answer 14

Blood pressure is an example of a hydrostatic filtering force. It moves whole blood from the heart to capillaries where filtration can occur to exchange water, nutrients, and waste products between the blood and the tissues. The hydrostatic pressure difference between the capillary blood and the interstitial fluid (fluid in the tissue spaces) determines whether water leaves the blood vessels and enters the tissue spaces.

Question 15

capillaries

Answer 15

Capillary membranes are only one cell layer thick, making a thin “wall” to hold blood in the capillaries. Large spaces (pores) in the capillary membrane help water filter freely when a hydrostatic pressure gradient is present

Question 16

Edema

Answer 16

Edema (excess tissue fluid) forms with changes in hydrostatic pressure differences between the blood and the interstitial fluid such as in right-sided heart failure.

In this condition the volume of blood in the right side of the heart increases because the right ventricle is too weak to pump blood well into lung blood vessels. As blood backs up into the venous and capillary systems, the capillary hydrostatic pressure rises until it is higher than the pressure in the interstitial space. Excess filtration from the capillaries into the interstitial tissue space then forms visible edema.

Question 17

Diffusion

Answer 17

Diffusion is the movement of particles (solute) across a permeable membrane from an area of higher particle concentration to an area of lower particle concentration (down a concentration gradient) until equilibrium is reached.

Particles in a fluid have random movement from the vibration of atoms in the nucleus. Random movement allows molecules to bump into each other in a confined fluid space. Each collision increases the speed of particle movement. The more particles (higher concentration) present in the confined fluid space, the greater the number of collisions.

As a result of the collisions, molecules in a solution spread out evenly through the available space. They move from an area of higher molecule concentrations to an area of lower concentrations until an equal concentration (amount) is present in all areas. Spaces with many particles have more collisions and faster particle movement than spaces with fewer particles.

Question 18

Concentration gradient

Answer 18

A concentration gradient exists when two fluid spaces have different concentrations of the same type of particles. Particle collisions cause them to move down the concentration gradient. Any membrane that separates two spaces is struck repeatedly by particles. When the particle strikes a pore in the membrane that is large enough for it to pass through, diffusion occurs

The chance of any single particle hitting the membrane and going through a pore is much greater on the side of the membrane with a higher solute particle concentration.

Question 19

impearmeable membrane

Answer 19

Cell membranes, unlike capillary membranes, are selective for which particles can diffuse. They permit diffusion of some particles but not others. Some particles cannot move across a cell membrane, even when a steep “downhill” gradient exists, because the membrane is impermeable (closed) to that particle. For these particles the concentration gradient is maintained across the membrane.

Question 20

differences in comcentrations on specific ions

Answer 20

usually the fluid outside the cell (the extracellular fluid [ECF]) has ten times more sodium ions than the fluid inside the cell (the intracellular fluid [ICF]). This extreme difference is caused by cell membrane impermeability to sodium and by special “sodium pumps” that move any extra sodium present inside the cell out of the cell “uphill” against its concentration gradient and back into the ECF.

Question 21

facilitated diffusion

Answer 21

For some particles diffusion cannot occur without help, even down steep concentration gradients, because of selective membrane permeability.

glucose cannot cross some cell membranes without the help of insulin. Insulin binds to insulin receptors on cell membranes, which then makes the membranes much more permeable to glucose. Then glucose can cross the cell membrane down its concentration gradient into the cell.

Diffusion across a cell membrane that requires a membrane-altering system (e.g., insulin) is called facilitated diffusion. This type of movement is still a form of diffusion because it does not require extra energy.

Question 22

Osmosis

Answer 22

Osmosis is the movement of water only through a selectively permeable (semipermeable) membrane. For osmosis to occur, a membrane must separate two fluid spaces, and one space must have particles that cannot move through the membrane. (The membrane is impermeable to this particle.) A concentration gradient of this particle must also exist. Because the membrane is impermeable to these particles, they cannot cross the membrane, but water molecules can.

For the fluid spaces to have equal concentrations of the particle, the water molecules move down their concentration gradient from the side with the higher concentration of water molecules (and a lower concentration of particles along with a greater hydrostatic pressure) to the side with the lower concentration of water molecules (and a higher concentration of particles along with a lower hydrostatic pressure). This movement continues until both spaces contain the same proportions of particles to water. Dilute fluid is less concentrated and has fewer particles and more water molecules than more concentrated fluid. Thus water moves by osmosis down its hydrostatic pressure gradient from the dilute fluid to the more concentrated fluid until a concentration equilibrium occurs

At this point the concentrations of particles in the fluid spaces on both sides of the membrane are equal, even though the total amounts of particles and volumes of water are different. The concentration equilibrium occurs by the movement of water molecules rather than the movement of solute particles.

Question 23

particle concentration

Answer 23

Particle concentration in body fluid is the major factor that determines whether and how fast osmosis and diffusion occur

This concentration is expressed in milliequivalents per liter (mEq/L), millimoles per liter (mmol/L), and milliosmoles per liter (mOsm/L)

Question 24

osmolarity

Answer 24

Osmolarity is the number of milliosmoles in a liter of solution;

Because 1 L of water weighs 1 kg, in human physiology osmolarity and osmolality are considered the same, although osmolarity is the actual concentration measured most often. The normal osmolarity value for plasma and other body fluids ranges from 270 to about 300 mOsm/L. The body functions best when the osmolarity of all body fluid spaces is close to 300 mOsm/L.

Question 25

osmolality

Answer 25

; osmolality is the number of milliosmoles in a kilogram of solution. Because 1 L of water weighs 1 kg, in human physiology osmolarity and osmolality are considered the same, although osmolarity is the actual concentration measured most often.

Question 26

isosmotic or isotonic (also called normotonic)

Answer 26

The body functions best when the osmolarity of all body fluid spaces is close to 300 mOsm/L. When all fluids have this particle concentration, the fluids are isosmotic or isotonic (also called normotonic) to each other.

Question 27

hyperosmotic, or hypertonic,

Answer 27

Fluids with osmolarities greater than 300 mOsm/L are hyperosmotic, or hypertonic, compared with isosmotic fluids. These fluids have a greater osmotic pressure than do isosmotic fluids and tend to pull water from the isosmotic fluid space into the hyperosmotic fluid space until an osmotic balance occurs. If a hyperosmotic (hypertonic) IV solution (e.g., 3% or 5% saline) were infused into a patient with normal extracellular fluid (ECF) osmolarity, the infusing fluid would make the adult’s blood hyperosmotic. To balance this situation, the interstitial fluid would be pulled into the circulation in an attempt to dilute the blood osmolarity back to normal. In addition, fluid would also be drawn from the intracellular fluid (ICF) compartment. As a result, the interstitial and ICF volumes would shrink, and the plasma volume would expand.

Question 28

hypo-osmotic, or hypotonic,

Answer 28

Fluids with osmolarities of less than 270 mOsm/L are hypo-osmotic, or hypotonic, compared with isosmotic fluids. Hypo-osmolar fluids have a lower osmotic pressure than isosmotic fluids, and water is pulled from the hypo-osmotic fluid space into the isosmotic fluid spaces of the interstitial and ICF fluids. As a result, the interstitial and ICF fluid volumes would expand, and the plasma volume would shrink. An example of a hypotonic IV fluid is 0.45% saline.

Question 29

What immediate response does the nurse expect as a result of infusing 1 L of an isotonic intravenous solution into a client over a 3-hour time period if urine output remains at 100 mL per hour?

Answer 29

A. Extracellular fluid (ECF) osmolarity increases; body weight increases.

B. Extracellular fluid (ECF) osmolarity decreases; body weight decreases.

C. Extracellular fluid (ECF) osmolarity is unchanged; body weight increases.

D. Extracellular fluid (ECF) osmolarity is unchanged; body weight decreases.

Question 30

CLinical application

Answer 30

Osmosis and filtration act together at the capillary membrane to maintain both extracellular fluid (ECF) and intracellular fluid (ICF) volumes within their normal ranges. The thirst mechanism is an example of how osmosis helps maintain homeostasis. The feeling of thirst is caused by the activation of cells in the brain that respond to changes in ECF osmolarity. These cells, so very sensitive to changes in ECF osmolarity, are called osmoreceptors. When an adult loses body water but most of the particles remain, such as through excessive sweating, ECF volume is decreased, and its osmolarity is increased (is hypertonic). The cells in the thirst center shrink as water moves from the cells into the hypertonic ECF. The shrinking of these cells triggers an adult’s awareness of thirst and increases the urge to drink. Drinking replaces the amount of water lost through sweating and dilutes the ECF osmolarity, restoring it to normal.

Question 31

Fluid balance

Answer 31

Fluid balance is closely linked to and affected by electrolyte concentrations.

Question 32

Sodium (Na+)

Answer 32

136-145 mEq/L
136-145 mmol/L

Elevated: Hypernatremia; dehydration; kidney disease; hypercortisolism

Low: Hyponatremia; fluid overload; liver disease; adrenal insufficiency

Question 33

magnesium(Mg2+)

Answer 33

: 1.3 to 2.1 mg/dL(PP)
Book-1.8-2.6 mEq/L
Elevated: Hypermagnesemia; kidney disease; hypothyroidism; adrenal insufficiency

Low: Hypomagnesemia; malnutrition; alcoholism; ketoacidosis

Question 34

Potassium (K+)

Answer 34

3.5-5.0 mEq/L 3.5-5.0 mmol/L
Elevated: Hyperkalemia; dehydration; kidney disease; acidosis; adrenal insufficiency; crush injuries

Low: Hypokalemia; fluid overload; diuretic therapy; alkalosis; insulin administration; hyperaldosteronism

Question 35

Calcium (Ca2+)

Answer 35

9.0-10.5 mg/dL 2.25-2.75 mmol/L
Elevated: Hypercalcemia; hyperthyroidism; hyperparathyroidism

Low: Hypocalcemia; vitamin D deficiency; hypothyroidism; hypoparathyroidism; kidney disease; excessive intake of phosphorus-containing foods and drinks

Question 36

Chloride (Cl−)

Phosphorus

Answer 36

98-106 mEq/L 98-106 mmol/L
Elevated: Hyperchloremia; metabolic acidosis; respiratory alkalosis; hypercortisolism

Low: Hypochloremia; fluid overload; excessive vomiting or diarrhea; adrenal insufficiency; diuretic therapy

phosphorus
Normal level: 3.0-4.5 mg/dL
Found in bones
Activates vitamins and enzymes; assists in cell growth and metabolism
Plasma levels of calcium and phosphorus exist in a balanced reciprocal relationship
Hypophosphatemia
Hyperphosphatemia

Question 37

Normal Plasma Electrolyte Values for People Older Than 60 Years

Answer 37

Calcium (Ca2+)
60-90-9.0-10.5 mg/dL
over 90-8.2-9.6 mg/dL

Chloride (Cl−)
60-90-98-106 mEq/L
over 90-98-111 mEq/L

Magnesium (Mg2+) 60-90-1.8-2.6 mEq/L over 90-1.8-2.6 mEq/L

PP- 1.3 to 2.1 mg/dL(PP)

Potassium (K+)
60-90-3.5-5.0 mEq/L
over 90-3.5-5.0 mEq/L

Sodium (Na+)
60-90-136-145 mEq/L
over 90-132-146 mEq/L

Question 38

what affects the distribution of body fluids

Answer 38

Age, gender, and amount of fat affect the amount and distribution of body fluids
An older adult has less total body water than a younger adult. Chart 11-2 shows age-related changes in fluid balance. An obese adult has less total water than a lean adult of the same weight because fat cells contain almost no water.

Question 39

Age related changes on fluid balance

Answer 39

Skin
Loss of elasticity

Decreased turgor

Decreased oil production

Skin becomes an unreliable indicator of fluid status, especially the back of the hand

Dry, easily damaged skin

Kidney
Decreased glomerular filtration

Decreased concentrating capacity

Poor excretion of waste products

Increased water loss,
increasing the risk for dehydration

Muscular
Decreased muscle mass
Decreased total body water

Greater risk for dehydration

Neurologic
Diminished thirst reflex
Decreased fluid intake, increasing the risk for dehydration

Endocrine
Adrenal atrophy
Poor regulation of sodium and potassium, increasing the risk for hyponatremia and hyperkalemia

Question 40

gender differences on fluid balance

Answer 40

Women of any age have less total body water and a higher risk for dehydration than men of similar sizes and ages. This difference is because men tend to have more muscle mass than women and because women have more body fat. (Muscle cells contain mostly water, and fat cells have little water.)

Question 41

Intake and output

Answer 41

Body fluids are constantly filtered and replaced as fluid balance is maintained through intake and output. The total amount of water in each fluid space is stable, but water in all spaces is exchanged continually while maintaining constant fluid volume.

Question 42

fluid intake

Answer 42

Fluid intake is regulated through the thirst drive. Fluid enters the body as liquids and solid foods, which contain up to 85% water (Table 11-2). A rising blood osmolarity or a decreasing blood volume triggers the sensation of thirst (Arai et al., 2013). An adult takes in about 2300 mL of fluid daily from food and liquids.

Question 43

Routes of Fluid Ingestion and Excretion

Answer 43

intake                   output
oral fluids              urine
parenteral fluids    emesis
enemas                  feces
irrigation fluids      drainage from 
                               body cavities

Non measureable
solid foods perspiration
metabolism vaporization
through the lungs

Question 44

fluid loss-several routes

Answer 44

The kidney is the most important and the most sensitive water loss route because it is regulated and adjustable. The volume lost through urine elimination daily varies, depending on the amount of fluid taken in and the body’s need to conserve fluids.
Other normal water loss occurs through the skin, the lungs, and the intestinal tract.

Question 45

obligatory urine output

Answer 45

The minimum amount of urine per day needed to excrete toxic waste products is 400 to 600 mL. This minimum 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 buildup of nitrogen.

Question 46

kidneys

Answer 46

The ability of the kidneys to make either concentrated or very dilute urine helps maintain fluid balance. The kidney works with various hormones to maintain fluid balance when extracellular fluid (ECF) concentrations, volumes, or pressures change.

Question 47

Insensible water loss

Answer 47

Water losses also can result from salivation, drainage from fistulas and drains, and GI suction. This loss is called insensible water loss because no mechanisms control it. In a healthy adult insensible water loss is about 500 to 1000 mL/day. This loss increases greatly during thyroid crisis, trauma, burns, states of extreme stress, and fever.

Question 48

patients at risk for insensible water loss

Answer 48

Patients at risk for excess insensible water loss include those being mechanically ventilated, those with rapid respirations, and those undergoing continuous GI suctioning. If not balanced by intake, insensible loss can lead to severe dehydration and electrolyte imbalances.

Question 49

water loss thru stool

Answer 49

Water loss through stool increases greatly with severe diarrhea or excessive fistula drainage. If not balanced by intake, insensible loss can lead to severe dehydration and electrolyte imbalances.

Question 50

Hormonal Regulation of Fluid Balance

Answer 50

Three hormones help control FLUID AND ELECTROLYTE BALANCE. These are aldosterone, antidiuretic hormone (ADH), and natriuretic peptide (NP).

Question 51

Aldosterone

Answer 51

Aldosterone is secreted by the adrenal cortex whenever sodium levels in the extracellular fluid (ECF) are low. Aldosterone prevents both water and sodium loss. When aldosterone is secreted, it acts on the kidney nephrons, triggering them to reabsorb sodium and water from the urine back into the blood. This action increases blood osmolarity and blood volume. Aldosterone also promotes kidney potassium excretion.

Question 52

antidiuretic hormone

Answer 52

Antidiuretic hormone (ADH), or vasopressin, is released from the posterior pituitary gland in response to changes in blood osmolarity. The hypothalamus contains the osmoreceptors that are sensitive to changes in blood osmolarity. Increased blood osmolarity, especially an increase in the level of plasma sodium, results in a slight shrinkage of these cells and triggers ADH release from the posterior pituitary gland. Because the action of ADH retains just water, it only indirectly regulates electrolyte retention or excretion.

ADH acts on kidney nephrons, making them more permeable to water. As a result, more water is reabsorbed by these tubules and returned to the blood, decreasing blood osmolarity by making it more dilute. When blood osmolarity decreases with low plasma sodium levels, the osmoreceptors swell slightly and inhibit ADH release. Less water is then reabsorbed, and more is excreted in the urine, bringing extracellular fluid (ECF) osmolarity up to normal.

Question 53

Natriuretic peptides (NPs)

Answer 53

Natriuretic peptides (NPs) are hormones secreted by special cells that line the atria of the heart (atrial natriuretic peptide [ANP]) and the ventricles of the heart. (The peptide secreted by the heart ventricular cells is known as brain natriuretic peptide [BNP].) These peptides are secreted in response to increased blood volume and blood pressure, which stretch the heart tissue. NP binds to receptors in the nephrons, creating effects that are opposite of aldosterone. Kidney reabsorption of sodium is inhibited at the same time that urine output is increased. The outcome is decreased circulating blood volume and decreased blood osmolarity.

Question 54

Significance of Fluid Balance

The Renin-Angiotensin II Pathway

Answer 54

most important body fluids to keep in balance for optimal function are the blood volume (plasma volume) and the fluid inside the cells (intracellular fluid).
Maintaining blood volume at a sufficient level for blood pressure to remain high enough to ensure adequate PERFUSION is critical for life.
A major regulator of fluid balance is the renin-angiotensin II pathway, also known as the renin-angiotensin system (RAS).

low blood volume and low blood pressure can rapidly lead to death, the body has many compensatory mechanisms that guard against low plasma volume.
These involve specific responses to change how water and sodium are handled to maintain blood pressure.

the kidney is a major regulator of water and sodium balance to maintain blood pressure and perfusion to all tissues and organs, the kidneys monitor blood pressure, blood volume, blood oxygen levels, and blood osmolarity (related to sodium concentration).
When kidneys sense that any one of these parameters is getting low, they secrete a substance called renin that sets into motion a group of hormonal and blood vessel responses to ensure that blood pressure is raised back up to normal.

Question 55

triggering event for renin secretion

Answer 55

triggering event for renin secretion is any change in the blood indicating that PERFUSION is at risk. Low blood pressure is a triggering event- it reduces perfusion to tissues and organs.
Anything that reduces blood volume (e.g., dehydration, hemorrhage) below a critical level always lowers blood pressure.
Low blood oxygen levels also are triggering events because with too little oxygen in the blood it cannot supply the needed oxygen and the tissues and organs could die.
A low blood sodium level also is a triggering event because sodium and water are closely linked. Where sodium goes, water follows.
So anything that causes the blood to have too little sodium prevents water from staying in the blood. The result is low blood volume with low blood pressure and poor tissue perfusion.

Question 56

process of renin angiotensin II pathway

Answer 56

Once the kidneys sense that PERFUSION is at risk, special cells in the kidney tubule begin to secrete renin into the blood. Renin then activates angiotensinogen. Activated angiotensinogen is angiotensin I, which is activated by the enzyme angiotensin-converting enzyme or ACE to its most active form, angiotensin II

Question 57

angiotensin II

Answer 57

Angiotensin II starts several actions to increase blood volume and blood pressure. First it constricts arteries and veins throughout the body which increases peripheral resistance and reduces the size of the vascular bed, which raises blood pressure as a compensatory mechanism without adding more blood volume.
Angiotensin II constricts the size of the arterioles that feed the kidney nephrons which results in a lower glomerular filtration rate and a huge reduction of urine output. Decreasing urine output prevents further water loss so more is retained in the blood to help raise blood pressure.
Angiotensin II also causes the adrenal glands to secrete the hormone aldosterone.
Aldosterone is nicknamed the “water-and-sodium-saving hormone” because it causes the kidneys to reabsorb water and sodium, preventing them from being excreted into the urine.
This response allows more water and sodium to be returned to the blood, increasing blood pressure, blood volume, and PERFUSION.

Question 58

CLinical application

Answer 58

The renin-angiotensin II pathway is stimulated whenever the patient is in shock.
This is why urine output is used as an indicator of PERFUSION adequacy after surgery or any time the patient has undergone an invasive procedure and is at risk for hemorrhage.
Patients who have hypertension are often asked to limit their intake of sodium. The reason for this is that a high sodium intake raises the blood level of sodium, causing more water to be retained in the blood volume and raising blood pressure.

Question 59

diuretic drugs for hypertension

Answer 59

Drug therapy for hypertension management may include diuretic drugs that increase the excretion of sodium so less is present in the blood, resulting in a lower blood volume.

Question 60

ACE inhibitors

Answer 60

often used to manage blood pressure is the “ACE inhibitors” (ACEIs). These drugs disrupt the renin-angiotensin II pathway by reducing the amount of angiotensin-converting enzyme (ACE) made so less angiotensin II is present. With less angiotensin II, there is less vasoconstriction and reduced peripheral resistance, less aldosterone production, and greater excretion of water and sodium in the urine. All of these responses lead to decreased blood volume and blood pressure.

Question 61

angiotensin receptor blockers (ARBs)

Answer 61

These drugs disrupt the renin-angiotensin II pathway by blocking the receptors that bind with angiotensin II so the tissues cannot respond to it and blood pressure is lowered

Question 62

direct renin inhibitors.

Answer 62

The most recent class of drugs to manage hypertension by changing the renin-angiotensin II pathway is the direct renin inhibitors. These drugs act early in the pathway and prevent the enzyme renin from changing angiotensinogen into angiotensin I. These drugs may be combined with an ARB to block the pathway in more than one place, leading to greater reduction in blood pressure

Question 63

Disturbances of Fluid and Electrolyte Balance
Fluid and Electrolyte Balance Concept Exemplar Dehydration
Pathophysiology

Answer 63

In dehydration fluid intake or retention is less than what is needed to meet the body’s fluid needs, resulting in a deficit of fluid volume, especially plasma volume. It is a condition 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 intake of fluid or too great a loss of fluid. It also can occur without an actual loss of total body water such as when water shifts from the plasma into the interstitial space. This condition is called relative dehydration.

Question 64

relative dehydration

Answer 64

can occur without an actual loss of total body water such as when water shifts from the plasma into the interstitial space. This condition is called relative dehydration.

Question 65

Considerations for Older Adults

Answer 65

Older adults are at high risk for dehydration because they have less total body water than younger adults. In addition, many older adults have decreased thirst sensation and may have difficulty with walking or other motor skills needed for obtaining fluids. They also may take drugs such as diuretics, antihypertensives, and laxatives that increase fluid excretion. Assess the FLUID AND ELECTROLYTE BALANCE status of all older adults in any setting.

Question 66

Isotonic dehydration

Answer 66

Dehydration may occur with just water (fluid) loss or with water and electrolyte loss (isotonic dehydration).

Isotonic dehydration is the most common type of fluid loss problem. Fluid is lost only from the extracellular fluid (ECF) space, including both the plasma and the interstitial spaces. There is no shift of fluids between spaces, so the intracellular fluid (ICF) volume remains normal (Fig. 11-7).

Circulating blood volume is decreased (hypovolemia) and leads to reduced perfusion.

The body’s defenses compensate during dehydration to maintain PERFUSION to vital organs in spite of hypovolemia. The main defense is increasing vasoconstriction and peripheral resistance to maintain blood pressure and circulation.