Chapter 41: Fluid, Electrolyte,
and Acid-Base Balance
Bonnie M. Wivell, MS, RN, CNS
Distribution of Body Fluids
 Intracellular = inside the cell; 42% of
body weight
 Extracellular = outside the cell, 17% of
body weight
 Interstitial = contains lymph; fluid between
cells and outside blood vessels
 Intravascular = blood plasma found inside
blood vessels
 Transcellular = fluid that is separated by
cellular barrier,
Body Fluid Compartments
Functions of Body Fluid
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Major component of blood plasma
Solvent for nutrients and waste products
Necessary for hydrolysis of nutrients
Essential for metabolism
Lubricant in joints and GI tract
Cools the body through perspiration
Provides some mineral elements
Composition of Body Fluids
 Body fluids contain Electrolytes
 Anions – negative charge
Cl, HCO3, SO4
 Cations – positive charge
Na, K, Ca
 Electrolytes are measured in mEq
 Minerals are ingested as compounds and
are constituents of all body tissues and
fluids
 Minerals act as catalysts
Electrolytes in Body Fluids
 Normal Values
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Sodium (Na+)
35 – 145 mEq/L
Potassium (K+)
3.5 – 5.0 mEq/L
Ionized Calcium (Ca++) 4.5 – 5.5 mg/dL
Calcium (Ca++)
8.5 – 10.5 mg/dL
Bicarbonate (HCO3)
24 – 30 mEq/L
Chloride (Cl--)
95 – 105 mEq/L
Magnesium (Mg++)
1.5 – 2.5 mEq/L
Phosphate (PO4---)
2.8 – 4.5 mg/dL
Movement of Body Fluids
 Osmosis = movement across a semipermeable membrane from area of
lesser concentration to are of higher
concentration; high solute concentration
has a high osmotic pressure and draws
water toward itself
 Osmotic pressure = drawing power of
water (Osmolality)
 Osmolarity = concentration of solution
Movement of Body Fluids
Colloid or Oncotic pressure =
keeps fluid in the
intravascular compartment
by pulling water from the
interstitial space back into
the capillaries
Solutions
 Isotonic Solution
 The same concentration as blood plasma;
expand fluid volume without causing fluid
shift
 Hypotonic Solution
 Lower concentration than blood plasma;
moves fluid into the cells causing them to
enlarge
 Hypertonic solution
 Higher concentration than blood plasma; pulls
fluid from cells causing them to shrink
Movement of Body Fluids
Cont’d.
 Diffusion = Molecules move from higher
concentration to lower
 Concentration gradient
 Filtration = water and diffusible substances
move together across a membrane; moving
from higher pressure to lower pressure
 Edema results from accumulation of excess
fluid in the interstitial space
 Hydrostatic pressure causes the movement of
fluids from an area of higher pressure to area
of lower pressure
Active Transport
 Requires metabolic activity and uses
energy to move substances across cell
membranes
 Enables larger substances to move into cells
 Molecules can also move to an area of
higher concentration (Uphill)
 Sodium-Potassium Pump
 Potassium pumped in – higher concentration
in ICF
 Sodium pumped out – higher concentration in
ECF
Regulation of Body Fluids
 Homeostasis is maintained through
 Fluid intake
 Hormonal regulation
 Fluid output regulation
Fluid Intake
 Thirst control center located in the
hypothalamus
 Osmoreceptors monitor the serum osmotic
pressure
 When osmolarity increases (blood becomes
more concentrated), the hypothalamus is
stimulated resulting in thirst sensation
 Salt increases serum osmolarity
 Hypovolemia occurs when excess fluid is
lost
Fluid Intake
 Average adult intake
 2200 – 2700 mL per day
 Oral intake accounts for 1100 – 1400 mL
per day
 Solid foods about 800 – 1000 mL per day
 Oxidative metabolism – 300 mL per day
 Those unable to respond to the thirst
mechanism are at risk for dehydration
 Infants, patients with neuro or psych
problems, and older adults
Hormonal Regulation
 ADH (Antidiuretic hormone)
 Stored in the posterior pituitary and released
in response to serum osmolarity
 Pain, stress, circulating blood volume effect
the release of ADH
 Increase in ADH = Decrease in urine output
= Body saves water
 Makes renal tubules and ducts more
permeable to water
Hormonal Regulation Cont’d.
 Renin-angiotensin-aldosterone
mechanism
 Changes in renal perfusion initiates this
mechanism
 Renin responds to decrease in renal
perfusion secondary to decrease in
extracellular volume
 Renin acts to produce angiotensin I which
converts to angiotensin II which causes
vasoconstriction, increasing renal perfusion
 Angiotensin II stimulates the release of
aldosterone when sodium concentration is
low
Hormonal Regulation Cont’d.
 Aldosterone
 Released in response to increased plasma
potassium levels or as part of the reninangiotensin-aldosterone mechanism to
counteract hypovolemia
 Acts on the distal portion of the renal tubules
to increase the reabsorption of sodium and the
secretion and excretion of potassium and
hydrogen
 Water is retained because sodium is retained
 Volume regulator resulting in restoration of
blood volume
Hormonal Regulation Cont’d.
 Atrial Natriuretic Peptide (ANP)
 ANP is a hormone secreted from atrial
cells of the heart in response to atrial
stretching and an increase in circulating
blood volume
 ANP acts like a diuretic that causes
sodium loss and inhibits the thirst
mechanism
 Monitored in CHF
Fluid Output Regulation
 Organs of water loss
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Kidneys
Lungs
Skin
GI tract
Fluid Output Regulation Cont’d.
 Kidneys are major regulatory organ of fluid
balance
 Receive about 180 liters of plasma to filter daily
 1200 – 1500 mL of urine produced daily
 Urine volume changes related to variation in the
amount and type of fluid ingested
 Skin
 Insensible Water Loss
 Continuous and occurs through the skin and lungs
 Can significantly increase with fever or burns
 Sensible Water Loss occurs through excess perspiration
 Can be sensible or insensible via diffusion or perspiration
 500 – 600 mL of insensible and sensible fluid lost
through skin each day
Fluid Output Regulation Cont’d.
 Lungs
 Expire approx 500 mL of water daily
 Insensible water loss increases in response
to changes in resp rate and depth and
oxygen administration
 GI Tract
 3 – 6 liters of isotonic fluid moves into the
GI tract and then returns to the ECF
 200 mL of fluid is lost in the feces each day
 Diarrhea can increase this loss significantly
Regulation of Electrolytes
 Major Cations in body fluids
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Sodium (Na+)
Potassium (K+)
Calcium (Ca++)
Magnesium (Mg++)
Sodium Regulation
 Most abundant cation in the extracellular
fluid
 Major contributor to maintaining water
balance
 Nerve transmission
 Regulation of acid-base balance
 Contributes to cellular chemical reactions
 Sodium is taken in via food and balance
is maintained through aldosterone
Potassium Regulation
 Major electrolyte and principle cation in
the extracellular fluid
 Regulates metabolic activities
 Required for glycogen deposits in the liver
and skeletal muscle
 Required for transmission of nerve impulses,
normal cardiac conduction and normal
smooth and skeletal muscle contraction
 Regulated by dietary intake and renal
excretion
Calcium Regulation
 Stored in the bone, plasma and body
cells
 99% of calcium is in the bones and teeth
 1% is in ECF
 50% of calcium in the ECF is bound to protein
(albumin)
 40% is free ionized calcium
 Is necessary for
 Bone and teeth formation
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Blood clotting
Hormone secretion
Cell membrane integrity
Cardiac conduction
Transmission of nerve impulses
Magnesium Regulation
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Essential for enzyme activities
Neurochemical activities
Cardiac and skeletal muscle excitability
Regulation
 Dietary
 Renal mechanisms
 Parathyroid hormone action
 50 – 60% of magnesium contained in
bones
 1% in ECF
 Minimal amount in cell
Anions
 Chloride (Cl-)
 Major anion in ECF
 Follows sodium
 Bicarbonate (HCO3-)
 Is the major chemical base buffer
 Is found in ECF and ICF
 Regulated by kidneys
Anions Cont’d.
 Phosphate (PO4---)
Buffer ion found in ICF
Assists in acid-base regulation
Helps to develop and maintain bones and teeth
Calcium and phosphate are inversely
proportional
 Promotes normal neuromuscular action and
participates in carbohydrate metabolism
 Absorbed through GI tract
 Regulated by diet, renal excretion, intestinal
absorption and PTH
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Regulation of Acid-Base Balance
 Lungs and kidneys are our buffering
systems
 A buffer is a substance that can absorb
or release H+ to correct an acid-base
imbalance
 Arterial pH is an indirect measure of
hydrogen ion concentration
 Greater concentration of H+, more
acidic, lower pH
Regulation of Acid-Base Balance
 Lower concentration of H+, more
alkaline, higher pH
 The pH is also a reflection of the balance
between CO2 (regulated by lungs) and
bicarb (regulated by kidneys)
 Normal H+ level is necessary to
 Maintain cell membrane integrity
 Maintain speed of cellular enzymatic actions
Chemical Regulation
 Carbonic acid-bicarbonate buffer system is the
first to react to change in the pH of ECF
 H+ and CO2 concentrations are directly related
 ECF becomes more acidic, the pH decreases,
producing acidosis
 ECF receives more base substances, the pH
rises, producing alkalosis
 Lungs primarily control excretion of CO2
resulting from metabolism
 Kidneys control excretion of hydrogen and
bicarb
Biological Regulation
1. Buffer actions that
occur
1. Exchange of K+ and H+
2. Carbon dioxide goes
into RBCcarbonic acid
(HCO3-)
1. HCO3 ready to
exchange with Cl3. Chloride shift within
RBC
H+
H+
K+
K+
K+
H+
H+
H+
Acidosis vs Alkalosis
 Acidosis
 Acids have high H+ ions in solution
 Alkalosis
 Bases have low H+ ion concentration
 Acidity or Alkalinity of a solution
measured by pH
Physiological Regulators
 Lungs
 Regulate by altering
H+ ions
 Metabolic acidosis
 Metabolic alkalosis
H+
H+
H+
 Kidneys
 Regulate by altering
HCO3 and H+ ions
H+
HCO3
HCO3
HCO3
HCO3
Causes of Electrolyte Imbalances
 Excessive sweating
 Fluid loss leading to
dehydration
 Excessive vomiting
 Diuretics like Lasix (K+
depletion)
 Massive blood loss
 Dehydration may go
unnoticed in hot, dry climates
 Renal failure
Sodium
 Most abundant
in extracellular
space
 Moves among
three fluid
compartments
 Found in most
body secretions
Na
Na
Na
Na
Na
Hyponatremia – Low Sodium
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Seizures
Personality changes
Nausea/vomiting
Tachycardia
Convulsion
Normal Na (135145)
Hypernatremia
 Excessive Na in ECF
 Loss of water
 Diarrhea
 Insensible water loss
 Water deprivation
 Gain of Sodium
 Diabetes insipidus
 Heat stroke
Hypokalemia – Low Potassium
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Severe leg cramps
Flaccid muscles
Fatigue
Irregular pulse
Chest discomfort
EKG changes
 T wave flattens
 Normal Potassium3.5-5
Hyperkalemia
 CNS
 Nausea and
vomiting
 Peripheral Nervous
System
 Tremors, twitching
 Heart
 Bradycardia,
peaked T wave
Hypocalcemia – Low Calcium
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Tingling of fingers
Tetany
Muscle cramps
Positive Trousseau’s
 Carpal spasm
 Positive Chvostek’s
 Contraction of facial
muscle when facial
nerve tapped
Hypercalcemia
 Causes
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Prolonged immobility
Osteoporosis
Thiazide diuretics
Acidosis
 Signs/symptoms
 N/V, weakness
 Hypoactive reflexes
 Cardiac arrest
Hypomagnesemia
 Causes
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Malnutrition
Alcoholism
Polyuria
Pre-ecclampsia
 Signs/symptoms
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Muscle tremor
Hyperactive deep reflexes
Chvostek’s/Trousseau’s
Difficulty breathing
Hypermagnesemia
 Causes
 Renal failure
 Excessive intake
 Signs/symptoms
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Low BP
Muscle weakness
Absent reflexes
Bradycardia
Respiratory
acidosis
Respiratory
alkalosis
pH ↓
PaCO2 ↑
HCO3 ↓
pH ↑
PaCO2 ↓
HCO3 ↑
Metabolic acidosis pH ↓
PaCO2
HCO3 ↓
Metabolic
alkalosis
pH ↑
PaCO2
HCO3 ↑
Cheat Sheet
Increase pH – alkalosis
Decrease pH – acidosis
Respiratory – CO2
Metabolic (kidneys)– HCO3
CO2 has an inverse relationship with pH
When pH goes down, CO2 goes up
HCO3 follows pH. If pH goes up so does HCO3
CO2 increases, pH decreases – resp. acidosis
CO2 decreases, pH increases – resp. alkalosis
HCO3 increases, pH increases – metabolic
alkalosis
 HCO3 decreases, pH decreases – metabolic
acidosis
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Question
 An older client comes to the emergency
department experiencing chest pain and
shortness of breath. An arterial blood gas
is ordered. Which of the following ABG
results indicates respiratory acidosis?
1. pH - 7.54, PaCO2 – 28, HCO3 – 22
2. pH – 7.32, PaCO2 – 46, HCO3 – 24
3. pH – 7.31, PaCO2 – 35, HCO3 – 20
4. pH – 7.5, PaCO2 – 37, HCO3 - 28
Review
 Acid/Base Imbalance Tutorial
 How do we assess for acid-base balance?
Assessment
 Nursing history
 Age
 Prior Medical History
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Acute illness
Surgery
Burns increase fluid loss
Resp. disorder predisposes to resp. acidosis
Head Injury can alter ADH secretion
Chronic illness
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Cancer
CVD
Renal disorders
GI disturbances
Assessment Cont’d.
 Environmental factors affecting
fluid/electrolyte alterations
 Diet
 Lifestyle – smoking, ETOH
 Medications
 Physical Assessment
 Daily weights
 I&O
 Vital signs
 Laboratory Studies
Nursing Diagnosis
Decreased cardiac output
Acute confusion
Deficient fluid volume
Excess fluid volume
Impaired gas exchange
Risk for injury
Deficient knowledge regarding disease
management
 Impaired oral mucous membrane
 Impaired skin integrity
 Ineffective tissue perfusion
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Planning
 Determine goals and outcomes
 Set priorities
 Collaborative care
 MD
 Dietician
 Pharmacy
Implementation
 Health promotion
 Education
 Acute care
 Enteral replacement of fluids
 Restriction of fluids
 Parenteral replacement of fluids and
electrolytes
 TPN
 IV fluids and electrolyte therapy (crystalloids)
 Blood and blood components (colloids)
 Blood groups and types
 Autologous transfusion
 Transfusion reactions
 ABGs
Restorative Care
 Home IV therapy
 Nutritional support
 Medication safety
 Pt. education
Evaluation
 Have goals been met?
 Have changes in assessment
occurred?
 Progress determines need to continue
or revise plan of care