chapter 41 fluid electrolyte and acid base balance l.
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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

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Chapter 41: Fluid, Electrolyte, and Acid-Base Balance

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distribution of body fluids
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,
functions of body fluid
Functions of Body Fluid
  • 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
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
Electrolytes in Body Fluids
  • Normal Values
    • 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
Movement of Body Fluids
  • Osmosis = movement across a semi-permeable 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 fluids8
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
  • 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
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
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
Regulation of Body Fluids
  • Homeostasis is maintained through
    • Fluid intake
    • Hormonal regulation
    • Fluid output regulation
fluid intake
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 intake18
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
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
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 d21
Hormonal Regulation Cont’d.
  • Aldosterone
    • Released in response to increased plasma potassium levels or as part of the renin-angiotensin-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 d22
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
Fluid Output Regulation
  • Organs of water loss
    • Kidneys
    • Lungs
    • Skin
    • GI tract
fluid output regulation cont d
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 d25
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
Regulation of Electrolytes
  • Major Cations in body fluids
    • Sodium (Na+)
    • Potassium (K+)
    • Calcium (Ca++)
    • Magnesium (Mg++)
sodium regulation
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
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
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
      • Blood clotting
      • Hormone secretion
      • Cell membrane integrity
      • Cardiac conduction
      • Transmission of nerve impulses
      • Muscle contraction
magnesium regulation
Magnesium Regulation
  • 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
  • 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
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
regulation of acid base balance
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 balance34
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
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
Biological Regulation

Buffer actions that occur

Exchange of K+ and H+

Carbon dioxide goes into RBCcarbonic acid (HCO3-)

HCO3 ready to exchange with Cl-

Chloride shift within RBC









acidosis vs alkalosis
Acidosis vs Alkalosis


Acids have high H+ ions in solution


Bases have low H+ ion concentration

Acidity or Alkalinity of a solution measured by pH

physiological regulators
Physiological Regulators


Regulate by altering H+ ions

Metabolic acidosis

Metabolic alkalosis


Regulate by altering HCO3 and H+ ions









causes of electrolyte imbalances
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


Most abundant in extracellular space

Moves among three fluid compartments

Found in most body secretions






hyponatremia low sodium
Hyponatremia – Low Sodium


Personality changes




Normal Na (135-145)


Excessive Na in ECF

Loss of water


Insensible water loss

Water deprivation

Gain of Sodium

Diabetes insipidus

Heat stroke

hypokalemia low potassium
Hypokalemia – Low Potassium

Severe leg cramps

Flaccid muscles


Irregular pulse

Chest discomfort

EKG changes

T wave flattens

Normal Potassium-3.5-5



Nausea and vomiting

Peripheral Nervous System

Tremors, twitching


Bradycardia, peaked T wave

hypocalcemia low calcium
Hypocalcemia – Low Calcium

Tingling of fingers


Muscle cramps

Positive Trousseau’s

Carpal spasm

Positive Chvostek’s

Contraction of facial muscle when facial nerve tapped



Prolonged immobility


Thiazide diuretics



N/V, weakness

Hypoactive reflexes

Cardiac arrest








Muscle tremor

Hyperactive deep reflexes


Difficulty breathing



Renal failure

Excessive intake


Low BP

Muscle weakness

Absent reflexes


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

Cheat Sheet
  • 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


Acid/Base Imbalance Tutorial

How do we assess for acid-base balance?

  • Nursing history
    • Age
  • Prior Medical History
    • Acute illness
    • Surgery
    • Burns increase fluid loss
    • Resp. disorder predisposes to resp. acidosis
    • Head Injury can alter ADH secretion
    • Chronic illness
      • Cancer
      • CVD
      • Renal disorders
      • GI disturbances
assessment cont d
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
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
  • Determine goals and outcomes
  • Set priorities
  • Collaborative care
    • MD
    • Dietician
    • Pharmacy
  • 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
Restorative Care
  • Home IV therapy
  • Nutritional support
  • Medication safety
    • Pt. education
  • Have goals been met?
  • Have changes in assessment occurred?
  • Progress determines need to continue or revise plan of care