Chapter 14
Fluids and
Electrolytes
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Regulatory Mechanisms
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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

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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
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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.
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Assessment of Fluid and Electrolyte
Balance cont’d

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
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Assessment of Fluid and Electrolyte
Balance cont’d

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
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Assessment of Fluid and Electrolyte
Balance cont’d

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
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Assessment of Fluid and Electrolyte
Balance cont’d

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.
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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
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Diagnostic Tests
and Procedures cont’d

Urine creatinine clearance tests



Urine sodium


Detect glomerular damage in the kidney
A 24-hour specimen is required
Sodium intake and fluid volume status
Urine potassium

A measure of renal tubular function
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Diagnostic Tests
and Procedures cont’d

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
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Diagnostic Tests
and Procedures cont’d

Serum albumin


A plasma protein that helps maintain blood volume
by creating colloid osmotic pressure
Serum electrolytes

Sodium, potassium, chloride, and calcium
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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
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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
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Electrolyte Imbalances
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Acid-Base Disturbances
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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
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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
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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
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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
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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
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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
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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
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Metabolic Alkalosis cont’d

Medical treatment

Depends on the underlying cause and severity of
the condition
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Metabolic Alkalosis cont’d

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
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Metabolic Alkalosis cont’d

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
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