Chapter 42: Fluid, Electrolyte, and Acid-Base Balance
Scientific Knowledge Base
• Location & Movement of Water & Electrolytes
 60% of the body weight of an adult man is water
o Proportion decreases w/ age only 50% for
older man
 Women usually have less water content than men
 Obese people have less water in their bodies than
lean people because fat contains less water
than muscle
 Fluid – water that contains dissolved or
suspended substances such as glucose, mineral
salts, & proteins
• Fluid Distribution
 Extracellular fluid (ECF) – outside the cell (1/3rd
of total body water in adults)
o Intravascular fluid – liquid part of blood
(plasma)
o Interstitial fluid – located between the
cells & outside the blood vessels
o Transcellular fluid – cerebrospinal,
pleural, peritoneal, & synovial fluids
secreted by epithelial cells
 Intracellular fluid (ICF) – inside the cells (2/3rd of
total body water in adults)
 Body Fluid Compartments
• Composition of Body Fluids
 Electrolytes – mineral salt compounds that
separate into ions when it dissolves in water
 Ions – charged particles
 Cations – positively charged ions
o Na+
o K+
o Ca+2
o Mg+2
 Anions – negatively charged ions
o Cl –
o HCO3–
 Laboratory Normal Values for Adults
o Osmolality – measure of the number of
particles per kg of water; some particles
pass easier through cell membranes than
others
o Isotonic – fluid w/ same tonicity as normal
blood
o Hypotonic – solution is more dilute than
the blood
o Hypertonic – solution is more concentrated
than normal blood
 Effects of isotonic, hypotonic, & hypertonic
solutions
• Movement of Water & Electrolytes
 Active Transport – requires energy in the form of
adenosine triphosphate (ATP) to move electrolytes
across cell membranes against the
concentration gradient
o From areas of lower concentration to areas
of higher concentration
 Diffusion – passive movement of electrolytes or
other particles down a concentration gradient
o From areas of higher concentration to areas
of lower concentration
 Osmosis – process by which water moves
through a membrane that separates fluids w/
different particle concentrations
o Osmotic pressure – an inward-pulling
force caused by particles in the fluid
 Osmosis through a semi-permeable membrane
 Filtration – the net effect of 4 forces, 2 that tend
to move fluid out of capillaries & small venules & 2
that tend to move fluid back into them
o Hydrostatic pressure – the force of the
fluid pressing outward against a surface
o Colloid osmotic pressure / oncotic
pressure – an inward-pulling force caused
by blood proteins that helps move fluid from
the interstitial area back into capillaries
 Capillary filtration moves fluid between vascular &
interstitial compartments
• Fluid Balance:
 Fluid Intake – occurs orally through drinking &
eating foods which contain water; food metabolism
creates additional water
 Fluid Output – normally via:
o Skin
o Lungs
o Gastrointestinal (GI) tract
o Kidney
 Abnormal Output
 Vomiting
 Wound Drainage
 Hemorrhage
 Influenced by
o Antidiuretic hormone (ADH)
o Renin-angiotensin-aldosterone system
(RAAS)
o Atrial natriuretic peptides (ANPs)
 Healthy Adult Average Fluid Intake & Output
 Fluid Distribution – movement of fluid among its
various compartments
o Fluid distribution between the extracellular
& intracellular compartments occurs by
osmosis
o Fluid distribution between the vascular &
interstitial parts of the ECF occurs by
filtration
• Thirst:
 Major hormones that influence renal fluid excretion
 An important regulator of fluid intake when plasma
osmolality increases
 Thirst-control mechanism is located w/in the
hypothalamus in the brain
 Stimuli affecting thirst mechanism
o A – Antidiuretic hormone (ADH) –
regulates the osmolality of the body fluids
by influencing how much water is excreted
in urine
o B – Aldosterone
 Renin-Angiotensin-Aldosterone
System (RAAS) – regulates ECF
volume by influencing how much
sodium and water are excreted in
urine
o C – Atrial natriuretic peptide (ANP) –
regulates ECV by influencing how much
sodium and water are excreted in urine
• Fluid Imbalances:
 If disease processes, medications, or other factors
disrupt fluid intake or output, imbalances
sometimes occur
o Volume imbalances – disturbances of the
amount of fluid in the extracellular
compartment
o Osmolality imbalances – disturbances of
the concentration of body fluid
 These imbalances can occur
separately or in combination
 Fluid volume & osmolality imbalances
• ECF Volume Imbalances:
 ECV deficit – there is insufficient isotonic fluid in
the extracellular compartment
o Hypovolemia – decreased vascular
volume
 ECV excess – there is too much isotonic fluid in
the extracellular compartment
• Osmolality Imbalances:
 Hypernatremia – hypertonic condition (water
deficit) caused by:
o Loss of relatively more water than salt
Or
o Gain of relatively more salt than water
o When the interstitial fluid becomes
hypertonic, water leaves cells by osmosis,
& they shrivel
o Clinical dehydration – Hypernatremia +
ECV deficit
 Hyponatremia – hypotonic condition (water
excess or water intoxication) which arises from:
o Gain of relative more water than salt
Or
o Loss of relative more salt than water
o Excessively dilute condition of interstitial
fluid causes water to enter cells by
osmosis, causing the cells to swell
• Electrolyte Balance:
 Processes involved in electrolyte homeostasis:
o Electrolyte intake & absorption
o Electrolyte distribution
 Plasma concentrations of K+, Ca2+,
Mg+, & phosphate (Pi) are very low
compared w/ their concentrations in
cells & bone
 Concentration differences are
necessary for normal muscle &
nerve function
o Electrolyte output
 Urine, feces, & sweat
 Vomiting, drainage, & fistulas
 Electrolyte Intake and Absorption, Distribution, and
Output
• Electrolyte Imbalances
• Potassium (K+) Imbalances
 Hypokalemia – abnormally low potassium
concentration in the blood
 Hyperkalemia – abnormally high potassium ion
concentration in the blood
• Calcium (Ca2+) Imbalances
 Hypocalcemia – abnormally low calcium
concentration in the blood
 Hypercalcemia – abnormally high calcium
concentration in the blood
• Magnesium (Mg2+) Imbalances
 Hypomagnesemia – abnormally low magnesium
concentration in the blood
 Hypermagnesemia – abnormally high
magnesium concentration in the blood
• Acid-Base Balance:
 Processes involved in Acid-base homeostasis:
o Acid production
o Acid buffering
o Acid excretion
 Normal acid-base balance is maintained w/ acid
excretion equal to acid production
o Acids release hydrogen (H+) ions; bases
(alkaline substances) take up H ions
 The more H+ ions that are present;
the more acidic is the solution
 pH scale: 1 (very acid) – 14 (very
base)
 7.0 pH is netrual
 Normal arterial blood is 7.35 pH –
7.45 pH
 Maintaining pH w/in this
normal range is important for
optimal cell function
 Arterial Blood Gas Measures
 Acid Production

 Acid Buffering
o Buffers – pairs of chemicals that work
together to maintain normal pH of body
fluids



 Acid Excretion
o 2 acid-excretion systems:
 Lungs (carbonic acid)
 Kidneys (metabolic acid)
o Excretion of carbonic acid
 When you exhale, you excrete
carbonic acid in the form of CO2 &
water
 If the PaCO2 (level of CO2 in the
blood) rises, the chemoreceptors
trigger faster & deeper respirations
to excrete the excess
 If the PaCO2 falls, the
chemoreceptors trigger slower &
shallower respirations so more of the
CO2 produced by cells remains in the
blood & makes up the deficit
o Excretion of metabolic acids
Kidneys excrete all acids except
carbonic acid; they secrete H+ into
the renal tubular fluid, putting HCO3–
back into the blood at the same time
If there are too many H+ ions in the
blood, renal cells move more H+ ions
into the renal tubules for excretion,
retaining more HCO3– in the process
If there are too few H+ ions in the
blood, renal cells secrete fewer H+
ions
If the kidneys need to excrete a lot of
H+, renal tubular cells secrete
ammonia, which combines with the
H+ ions in the tubules to make NH4+,
ammonium ions
 People who have oliguric
kidney disease often are
unable to excrete metabolic
acids normally; & these acids
accumulate, making the blood
too acidic
o If the kidneys are
unable to correct this
problem, respiratory
rate & depth increase,
causing compensatory
excretion of carbonic
acid
• Acid-Base Imbalances:
 Acidosis – condition that tends to make the blood
relatively too acidic
 Alkalosis – condition that tends to make the blood
relatively too basic (alkaline)
 Respiratory acidosis
o Arises from alveolar hypoventilation
o Lungs are unable to excrete enough CO2
o Excess of carbonic acid in the blood,
decreases pH
 Respiratory alkalosis
o Arises from alveolar hyperventilation
o Lungs excrete too much carbonic acid (CO2
& water)
o Deficit of carbonic acid in the blood,
increases pH
 Metabolic acidosis
o Occurs from increase of metabolic acid or
decrease of base (bicarbonate)
o Kidneys are unable to excrete enough
metabolic acids, which accumulate in the
blood, or bicarbonate is removed from the
body directly as w/ diarrhea
o Anion gap - reflection of unmeasured
anions in plasma
 Sum of plasma concentrations of the
anions Cl – & HCO3– minus plasma
concentration of the cation Na+
 Metabolic alkalosis
 Occurs from direct increase of base (HCO3–) or
decrease of metabolic acid
 Increases blood HCO3– by releasing it from its
buffering function
Nursing Knowledge Base
• Use the scientific knowledge base in clinical decisionmaking to provide safe, optimal fluid therapy
• Apply knowledge of risk factors for fluid imbalances &
physiology of normal aging when assessing older adults,
knowing that this age group is at high risk for fluid
imbalances
• Ask questions to elicit risk factors for fluid, electrolyte, &
acid-base imbalances
Perform clinical assessments for signs & symptoms of
these imbalances
• Critical Thinking
• Successful critical thinking requires a synthesis of
knowledge, experience, information gathered from
patients, critical thinking attitudes, & intellectual &
professional standards
• In the case of fluid, electrolyte & acid-base balance, you
integrate knowledge of physiology, pathophysiology, &
pharmacology & previous experiences & information
gathered from patients
• Nursing Process: Assessment
• Through the patient’s eyes
• Nursing History
 Age: very young & old at risk
 Environment: excessively hot?
 Dietary intake: fluids, salt, foods rich in potassium,
calcium, & magnesium
 Lifestyle: alcohol intake history
 Medications: include over-the-counter (OTC) &
herbal, in addition to prescription medications
 24 – hour I & O: compare intake versus output
 Intake includes all liquids eaten, drunk, or received
through IV
 Output = urine, diarrhea, vomitus, gastric suction,
wound drainage
• Laboratory studies
• Measuring Urine Output
 Containers for measuring urine output
• Medical history
 Recent surgery (physiological stress)
 Gastrointestinal output
 Acute illness or trauma
o Respiratory disorders
o Burns
o Trauma
 Chronic illness
o Cancer
o Heart failure
o Oliguric renal disease
• Physical Assessment
• Daily weights
 Indicator of fluid status
 Use same conditions
• Fluid intake & output (I & O)
• Nursing Diagnosis
• Planning
 Central venous access device (CVAD)
• Goals & outcomes
 Establish an individual patient plan of care for
each nursing diagnosis
• Setting priorities
 The patient’s clinical condition determines which of
the nursing diagnoses takes the greatest priority
• Teamwork & collaboration
• Implementation
• Health promotion:
 Fluid replacement education
 Teach patients w/ chronic conditions about risk
factors & signs & symptoms of imbalances
• Acute care
 Enteral replacement of fluids
 Restriction of fluids
 Parenteral replacement of fluids & electrolytes
o TPN
o Crystalloids (electrolytes)
o Colloids (blood & blood components)
• Intravenous Therapy
• IV therapy: crystalloids
• Types of solutions
 Isotonic
 Hypotonic
 Hypertonic
• Caution: Too rapid or excessive infusion of any IV fluid
has the potential to cause serious problems
• Vascular access devices
• Equipment
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Vascular access devices (VADs)
Tourniquets
Clean gloves
Dressing
IV fluid containers
 Various types of tubing
 Electronic infusion devices (EIDs), also called
infusion pumps
• Initiating the intravenous line
• Regulating the infusion flow
• Initiating IV Therapy
• Maintaining the system
 Keeping system sterile & intact
 Potential sites for contamination of VAD
 Over-the-needle catheter for venipuncture
 Common IV sites
• Changing intravenous fluid containers, tubing, &
dressings
 Assisting patient w/ self-care activities
• Complications
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Fluid overload
Infiltration
Extravasation
Phlebitis
 Local infection
 Bleeding at the infusion site
o OTC drugs
o Herbal preparations
• Discontinuing peripheral IV access
• Evaluation
• Blood Transfusion
• Through the patient’s eyes
 Blood component therapy = IV administration of
whole blood or blood component
 Blood groups & types (A+/A–, B+/B–, AB+/AB–,
O+/O–)
 Autologous transfusion – is the collection &
reinfusion of a patient's own blood
 Transfusing blood
 Transfusion reactions & other adverse affects
• Interventions
• Interventions for electrolyte imbalances
 Support prescribed medical therapies
 Aim to reverse the existing acid-base imbalance
 Provide for patient safety
• Interventions for acid-base imbalances
 Arterial blood gases
• Implementation
• Restorative Care
 Home IV therapy
 Nutrition support
 Medication Safety
o Medications
 Review w/ patients how well their major concerns
regarding fluid, electrolyte, or acid-base situations
were alleviated or addressed
• Patient outcomes
 Evaluate the effectiveness of interventions using
the goals & outcomes established for the patient’s
nursing diagnoses