chapter 14

Elsevier items and derived items © 2012 by Saunders, an imprint of Elsevier Inc. 1

Chapter 14

Fluids and Electrolytes


Homeostasis

Maintaining relatively constant conditions as in fluid compartments

To maintain internal balance, body must be able to regulate fluids

All organs and structures of the body involved in homeostasis


Homeostasis cont’d

Intracellular fluid Fluid within a cell Most of the body’s fluids found within the cell

Extracellular fluid Fluid outside the cell Intravascular fluid

• In blood vessels in the form of plasma or serum Interstitial fluid

• In fluid surrounding cells, including lymph


Water

Largest portion of body weight Percentage affected by age, sex, body fat

Percentage of body water decreases with age Females have a lower percentage of body water

than males throughout adult years because women have more fat than men and fat cells contain less water than other cells

Obese have a lower percentage of body water because of the increased number of fat cells


Solutes

Electrolyte Substance that develops an electrical charge when

dissolved in water Examples: sodium, potassium, calcium, chloride,

bicarbonate, and magnesium Maintain balance between positive and negative

charges For every positively charged cation, there is a

negatively charged anion Cations and anions combine to balance one another


Solutes cont’d

Sodium (Na) Most abundant electrolyte; primary electrolyte in

extracellular fluid Major role in regulating body fluid volumes,

muscular activity, nerve impulse conduction, and acid-base balance


Solutes cont’d

Potassium (K) Found mainly in the intracellular fluid; the major

intracellular cation Important in maintaining fluid osmolarity and volume

within the cell Essential for normal membrane excitability—

a critical factor in transmitting nerve impulses Needed for protein synthesis, for the synthesis and

breakdown of glycogen, and to maintain plasma acid-base balance


Solutes cont’d

Chloride (Cl) An extracellular anion that is usually bound with

other ions, especially sodium or potassium Functions are to regulate osmotic pressure

between fluid compartments and assist in regulating acid-base balance


Solutes cont’d

Calcium (Ca) Usually combined with phosphorus to form the

mineral salts of the bones and teeth • Of total body calcium, 99% concentrated in the bones and

teeth; 1% is in the extracellular fluid Ingested through the diet and absorbed through the

intestine Promotes transmission of nerve impulses; helps

regulate muscle contraction and relaxation


Solutes cont’d

Magnesium (Mg2+) A cation found in bone (50% to 60%), intracellular

fluid (39% to 49%), and extracellular fluid (1%) Plays a role in the metabolism of carbohydrates and

proteins, the storage and use of intracellular energy, and neural transmission

Important in heart, nerve, and muscle function


Solutes cont’d

Nonelectrolytes Other substances dissolved in the body fluids

• Urea, protein, glucose, creatinine, and bilirubin • These solutes do not carry an electrical charge


Transport of Water and Electrolytes

Membranes Selectively permeable membranes

• Separate fluid compartments and control movement of water and certain solutes

• Maintain unique composition of each compartment of the body while allowing transport of nutrients and wastes to and from cells

• Some solutes cross membranes more easily than others


Transport Processes

Diffusion The random movement of particles in all directions is for a substance to move from an area of higher

natural tendency concentration to an area of lower concentration

Facilitated diffusion • A carrier protein transports the molecules through

membranes toward an area of lower concentration


Transport Processes cont’d

Active transport Carrier proteins transport substances from an area

of lower concentration to an area of equal or greater concentration

Requires expenditure of energy Many solutes, such as sodium, potassium, glucose,

and hydrogen, are actively transported across cell membranes


Transport Processes cont’d

Filtration Transfer of water and solutes through a membrane

from an area of high pressure to an area of low pressure • Hydraulic pressure

A combination of pressures from the force of gravity on the fluid and the pumping action of the heart

Needed to move fluid out of capillaries into tissues and filter plasma through the kidneys


Transport Processes cont’d Osmosis

Movement across a membrane from a less concentrated to a more concentrated solution

Involves movement of water only; sometimes force of movement across membrane carries solutes along

If a fluid compartment has less water and more sodium, water from another compartment moves to the more concentrated compartment by osmosis to create a better fluid balance


Osmolality

Concentration of solution determined by number of dissolved particles per kg water

Controls water movement and distribution by regulating the concentration of fluid in each body fluid compartment

The osmolality of intracellular fluid and extracellular fluid tends to equalize because of the constant shifting of water


Regulatory Mechanisms


Kidneys Main regulators of fluid balance Control extracellular fluid by adjusting the

concentration of specific electrolytes, osmolality of body fluids, the volume of extracellular fluid, blood volume, and pH

The nephron is the functioning unit of the kidney Glomerulus is the filtering portion of the nephron, and

the tubule is responsible for secretion and reabsorption Nephrons conduct work of the kidney through filtration,

reabsorption, and secretion


Kidneys cont’d

Filtration Blood plasma entering the kidney via the renal

artery is delivered to the glomerulus About 20% of plasma filtered into glomerular

capsule Most remaining plasma leaves kidney through the

renal vein Filtrate then moves through the tubules, where it is

transformed into urine by tubular reabsorption and secretion


Kidneys cont’d

Tubular reabsorption A process by which most of the glomerular filtrate is

returned to the circulation Water and selected solutes move from the tubules

into the capillaries Waste products remain in tubules for excretion,

whereas most water and sodium is reabsorbed into the bloodstream

Adjusts volume and composition of the filtrate; prevents excessive fluid loss through kidneys


Kidneys cont’d

Tubular secretion The last phase in the work of the kidneys The filtrate is transformed into urine Various substances—drugs, hydrogen ions,

potassium ions, creatinine, and histamine—pass from the blood into the tubules

Process eliminates some excess substances to maintain fluid and electrolyte balance, as well as metabolic waste products


Hormones

Renin Hormone secreted when blood volume or blood

pressure falls Causes the release of aldosterone with subsequent

sodium and water retention Aldosterone

Acts on kidney tubules to increase reabsorption of sodium and decrease reabsorption of potassium

Because the retention of sodium causes water retention, aldosterone acts as a volume regulator


Hormones cont’d

Antidiuretic hormone (ADH) Causes capillaries to reabsorb more water, so urine

is more concentrated and less volume is excreted Atrial natriuretic factor (ANF)

Hormone released by the atria in response to stretching of the atria by increased blood volume

Stimulates excretion of sodium and water by the kidneys, decreased synthesis of renin, decreased release of aldosterone, and vasodilation

Reduces blood volume and lowers blood pressure


Thirst

Regulates fluid intake Increased plasma osmolality stimulates

osmoreceptors in the hypothalamus to trigger the sensation of thirst

More sodium and less water in the body make a person thirsty

Additional fluids consumed; kidneys conserve water until osmolality returns to normal


Fluid Gains and Losses

In healthy adult, 24-hour fluid intake and output approximately equal

Fluids gained by drinking and eating and lost through the kidneys, skin, lungs, and gastrointestinal tract

The usual adult urine volume is between 1 and 2 L/day, or 1 ml/kg of body weight per hour

In kidneys, water loss varies largely with the amount of solute excreted and with the level of antidiuretic hormone


Fluid Gains and Losses cont’d

Losses through the skin occur by sweating Water loss through the lungs by evaporation at

300 to 400 ml/day In the gastrointestinal tract, the usual loss of

fluid is about 100 to 200 ml/day


Age-Related Changes Affecting Fluid Balance

Aging kidney slower to adjust to changes in acid-base, fluid, and electrolyte balances

Older adult often has a reduced sense of thirst and therefore may be in a state of chronic dehydration

Total body water declines with age; greatest loss from the intracellular fluid compartment


Age-Related Changes Affecting Fluid Balance cont’d

Older person has limited reserves to maintain fluid balance when abnormal losses occur

Antihypertensives, diuretics, and antacids can also contribute to imbalances

Unless contraindicated, fluid requirements for older adults, based on ideal body weight, are

30 ml/kg for ages 55 to 65 and 25 ml/kg for 65 years and older


Assessment of Fluid and Electrolyte Balance

Health history Determines if patient has conditions that contribute

to fluid or electrolyte imbalances• Vomiting, diarrhea, kidney diseases, diabetes, salicylate

poisoning, burns, congestive heart failure, cerebral injuries, ulcerative colitis, and hormonal imbalances; the intake of drugs, such as diuretics and cathartics; and medical interventions, such as gastric suctioning

Complaints of fatigue, palpitations, dizziness, edema, muscle weakness or cramps, dyspnea, and confusion may be associated with fluid imbalances


Assessment of Fluid and Electrolyte Balance cont’d

Vital signs Pulse, respiration, temperature, and blood pressure

can indicate changes in fluid and electrolyte balance.

Temperature variations can be associated with fluid volume excess or deficit.

Pulse rate and quality may change in response to blood volume alterations; electrolyte changes can affect heart rate and rhythm. Blood pressure is directly related to blood volume. Respirations are minimally affected by electrolyte changes.



Intake and output Accurate records are essential to determine whether

the patient’s intake is equal to output All fluids entering or leaving the body should be

noted A changing urine output may reflect attempts by the

kidneys to maintain or restore balance, or it may reflect a problem that causes fluid disturbances

Urine characteristics also give clues to fluid balance • Clear, pale urine in a healthy person suggests the

excretion of excess water, whereas darker, concentrated urine indicates the kidneys are retaining water



Skin Characteristics

• Moisture, turgor, and temperature reflect fluid balance. Dry, flushed skin—dehydration. Pale, cool, clammy skin—severe fluid volume deficit that occurs with shock. Moist, edematous tissue seen with excess fluid volume

Facial characteristics• Severely dehydrated patient has a pinched, drawn facial

expression. Soft eyeballs and sunken eyes indicate severely deficient fluid volume. Puffy eyelids and fuller cheeks suggest excess fluid volume



Skin turgor Measured by pinching the skin over the sternum,

the inner aspects of the thighs, or the forehead In patients who are dehydrated, skin flattens more

slowly after the pinch is released Edema

Reflects water and sodium retention, which can result from excessive reabsorption or inadequate secretion of sodium, as may occur with kidney failure

Pitting depression remains in the tissue after pressure is applied with a fingertip



Mucous membranes Tongue turgor

• In well person, tongue has one longitudinal furrow. Fluid volume deficit causes additional longitudinal furrows, and the tongue is smaller. Sodium excess causes the tongue to appear red and swollen.

Moisture of the oral cavity• A dry mouth may be the result of deficient fluid volume or

mouth breathing. Veins

• Appearance of the jugular veins in the neck and the veins in the hands can suggest either a fluid volume deficit or excess.


Diagnostic Tests and Procedures

Urine studies Urine pH

• Determines if kidneys are responding appropriately to metabolic acid-base imbalances

Urine specific gravity• A measure of urine concentration• A good indicator of fluid balance

Osmolality • Measures the number of dissolved particles in a solution • Provides more precise measurement of kidneys’ ability to

concentrate urine


Diagnostic Tests and Procedures cont’d

Urine creatinine clearance tests Detect glomerular damage in the kidney A 24-hour specimen is required

Urine sodium Sodium intake and fluid volume status

Urine potassium A measure of renal tubular function



Blood studies Serum hematocrit

• Percentage of blood volume composed of red blood cells Serum creatinine

• A metabolic waste product • Indicator of renal function

Blood urea nitrogen (BUN) • A measure of renal function



Serum albumin A plasma protein that helps maintain blood volume

by creating colloid osmotic pressure Serum electrolytes

Sodium, potassium, chloride, and calcium


Fluid Imbalances

Deficient fluid volume Less water than normal in the body Isotonic extracellular fluid deficit

• Hypovolemia Hypertonic extracellular fluid deficit

• Dehydration Decreased intake, abnormal fluid losses,

or both Examples: loss of water from excessive

bleeding, severe vomiting/diarrhea, severe burns


Fluid Imbalances cont’d

Excess fluid volume An increase in body water

• Extracellular fluid excess Isotonic fluid excess

• Intracellular water excess Hypotonic fluid excess

From renal or cardiac failure with retention of fluid, increased production of antidiuretic hormone or aldosterone, overload with isotonic IV fluids, or administration of dextrose 5% in water (D5W) after surgery or trauma


Electrolyte Imbalances


Hyponatremia

Lower than normal sodium in the blood serum Can be actual deficiency of sodium or increase

in body water that dilutes the sodium excessively

Assessment Symptoms: headache, muscle weakness, fatigue,

apathy, confusion, abdominal cramps, and orthostatic hypotension

Take blood pressures with the patient lying or sitting and then standing to determine if a significant drop


Hyponatremia cont’d

Medical treatment The usual treatment is restriction of fluids while the

kidneys excrete excess water Diuretic: furosemide (Lasix) Sodium replacement therapy

Nursing care Administer prescribed medications and IV fluids Measure fluid intake and output and assess mental

status


Hypernatremia

Higher than normal concentration of sodium in the blood Very serious imbalance; can lead to death if not

corrected Occurs when excessive loss of water or excessive

retention of sodium Signs and symptoms

• Thirst, flushed skin, dry mucous membranes, low urine output, restlessness, increased heart rate, convulsions, and postural hypotension


Hypernatremia cont’d

Medical treatment Oral or IV replacement of water to restore balance A low-sodium diet often prescribed

Nursing care Encourage patients with hypernatremia to drink

water Closely monitor the infusion of IV fluids Teach patient to track daily intake and output and to

recognize the signs and symptoms of fluid retention or depletion


Hypokalemia

Low serum potassium May result in gastrointestinal, renal, cardiovascular,

and neurologic disturbances Can cause abnormal, potentially fatal, heart rhythm Signs and symptoms

• Anorexia, abdominal distention, vomiting, diarrhea, muscle cramps, weakness, dysrhythmias (abnormal cardiac rhythms), postural hypotension, dyspnea, shallow respirations, confusion, depression, polyuria (excessive urination), and nocturia


Hypokalemia cont’d

Medical treatment Potassium replacement by the IV or oral route

Nursing care Monitoring at-risk patients for decreased bowel

sounds, a weak and irregular pulse, decreased reflexes, and decreased muscle tone

Cardiac monitors may be used to detect dysrhythmias

Administer oral or IV potassium Urine output should be no less than 30 ml/hr


Hyperkalemia

High serum potassium Patients at risk: decreased renal function, in

metabolic acidosis, taking potassium supplements A serious imbalance because of the potential for life-

threatening dysrhythmias Signs and symptoms

• Explosive diarrhea and vomiting; muscle cramps and weakness, paresthesia, irritability, anxiety, abdominal cramps, and decreased urine output


Hyperkalemia cont’d Medical treatment

Correct the underlying cause Restrict potassium intake Polystyrene sulfonate (Kayexalate) Intravenous calcium gluconate

Nursing care Patients with low urine output or those taking

potassium-sparing diuretics must be monitored carefully for signs and symptoms

Carefully monitor flow rate of IV fluids, which should not exceed 10 mEq/hr through peripheral veins

Screen the results of laboratory studies


Chloride Imbalance

Usually bound to other electrolytes; therefore, chloride imbalances accompany other electrolyte imbalances Hyperchloremia

• Usually associated with metabolic acidosis Hypochloremia

• Usually occurs when sodium is lost because chloride most frequently bound with sodium


Calcium Imbalance

Regulated by the parathyroid glands Hypocalcemia results from diarrhea, inadequate dietary

intake of calcium or vitamin D, and multiple blood transfusions (banked blood contains citrates that bind to calcium), in addition to some diseases, including hypoparathyroidism

Hypercalcemia results from a high calcium or vitamin D intake, hyperparathyroidism, and immobility that causes stores of calcium in the bones to enter the bloodstream


Magnesium Imbalance

Hypomagnesemia: decreased gastrointestinal absorption or excessive gastrointestinal loss, usually from vomiting and diarrhea, or increased urinary loss

Hypermagnesemia occurs most often with excessive use of magnesium-containing medications or intravenous solutions in patients with renal failure or preeclampsia of pregnancy


Acid-Base Disturbances


Respiratory Acidosis

Respiratory system fails to eliminate the appropriate amount of carbon dioxide to maintain the normal acid-base balance

Caused by pneumonia, drug overdose, head injury, chest wall injury, obesity, asphyxiation, drowning, or acute respiratory failure

Medical treatment Improve ventilation, which restores partial pressure

of carbon dioxide in arterial blood (Paco2) to normal


Respiratory Acidosis cont’d

Nursing care Assess Paco2 levels in the arterial blood Observe for signs of respiratory distress:

restlessness, anxiety, confusion, tachycardia Intervention

Encourage fluid intake Position patients with head elevated 30 degrees


Respiratory Alkalosis

Low Paco2 with a resultant rise in pH Most common cause of respiratory alkalosis is

hyperventilation Medical treatment

• Major goal of therapy: treat underlying cause of condition; sedation may be ordered for the anxious patient


Respiratory Alkalosis cont’d

Nursing care Intervention

• In addition to giving sedatives as ordered, reassure the patient to relieve anxiety

• Encourage patient to breathe slowly, which will retain carbon dioxide in the body


Metabolic Acidosis

Body retains too many hydrogen ions or loses too many bicarbonate ions; with too much acid and too little base, blood pH falls

Causes are starvation, dehydration, diarrhea, shock, renal failure, and diabetic ketoacidosis

Signs and symptoms: changing levels of consciousness, headache, vomiting and diarrhea, anorexia, muscle weakness, cardiac dysrhythmias

Medical treatment: treat the underlying disorder


Metabolic Acidosis cont’d

Nursing care Assessment of the patient in metabolic acidosis

should focus on vital signs, mental status, and neurologic status

Emergency measures to restore acid-base balance. Administer drugs and intravenous fluids as prescribed. Reassure and orient confused patients


Metabolic Alkalosis Increase in bicarbonate levels or a loss of hydrogen

ions Loss of hydrogen ions may be from prolonged

nasogastric suctioning, excessive vomiting, diuretics, and electrolyte disturbances

Signs and symptoms: headache; irritability; lethargy; changes in level of consciousness; confusion; changes in heart rate; slow, shallow respirations with periods of apnea; nausea and vomiting; hyperactive reflexes; and numbness of the extremities


Metabolic Alkalosis cont’d

Medical treatment Depends on the underlying cause and severity of

the condition



Nursing care Assessment

• Take vital signs and daily weight; monitor heart rate, respirations, and fluid gains and losses

• Keep accurate intake and output records, including the amount of fluid removed by suction

• Assess motor function and sensation in the extremities; monitor laboratory values, especially pH and serum bicarbonate levels



Intervention To prevent metabolic alkalosis, use isotonic saline

solutions rather than water for irrigating nasogastric tubes because the use of water for irrigation can result in a loss of electrolytes

Provide reassurance and comfort measures to promote safety and well-being

chapter 14

Documents

body cells

derived items

body fluids

body fluid volumes

body fluid compartment

electrolyteselsevier

lymphelsevier items

homeostasiselsevier