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

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Chapter 41 Fluid, Electrolyte, and Acid-Base
Balance

• Bonnie M. Wivell, MS, RN, CNS

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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,

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Body Fluid Compartments
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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

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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

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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

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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

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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

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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

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Movement of Body Fluids Contd.

• 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

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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

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Regulation of Body Fluids

• Homeostasis is maintained through
• Fluid intake
• Hormonal regulation
• Fluid output regulation

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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

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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

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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

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Hormonal Regulation Contd.

• 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

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Hormonal Regulation Contd.

• 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

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Hormonal Regulation Contd.

• 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

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Fluid Output Regulation

• Organs of water loss
• Kidneys
• Lungs
• Skin
• GI tract

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Fluid Output Regulation Contd.

• 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

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Fluid Output Regulation Contd.

• 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

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Regulation of Electrolytes

• Major Cations in body fluids
• Sodium (Na)
• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg)

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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

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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

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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

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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

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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

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Anions Contd.

• 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

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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

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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

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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

H
H
K
K
K
H
H
H
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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

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Physiological Regulators
H
H

• Lungs
• Regulate by altering H ions
• Metabolic acidosis
• Metabolic alkalosis
• Kidneys
• Regulate by altering HCO3 and H ions

H
H
HCO3
HCO3
HCO3
HCO3
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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

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Sodium

• Most abundant in extracellular space
• Moves among three fluid compartments
• Found in most body secretions

Na
Na
Na
Na
Na
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Hyponatremia Low Sodium

• Seizures
• Personality changes
• Nausea/vomiting
• Tachycardia
• Convulsion
• Normal Na (135-145)

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Hypernatremia

• Excessive Na in ECF
• Loss of water
• Diarrhea
• Insensible water loss
• Water deprivation
• Gain of Sodium
• Diabetes insipidus
• Heat stroke

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Hypokalemia Low Potassium

• Severe leg cramps
• Flaccid muscles
• Fatigue
• Irregular pulse
• Chest discomfort
• EKG changes
• T wave flattens
• Normal Potassium-3.5-5

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Hyperkalemia

• CNS
• Nausea and vomiting
• Peripheral Nervous System
• Tremors, twitching
• Heart
• Bradycardia, peaked T wave

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Hypocalcemia Low Calcium

• Tingling of fingers
• Tetany
• Muscle cramps
• Positive Trousseaus
• Carpal spasm
• Positive Chvosteks
• Contraction of facial muscle when facial nerve
  tapped

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Hypercalcemia

• Causes
• Prolonged immobility
• Osteoporosis
• Thiazide diuretics
• Acidosis
• Signs/symptoms
• N/V, weakness
• Hypoactive reflexes
• Cardiac arrest

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Hypomagnesemia

• Causes
• Malnutrition
• Alcoholism
• Polyuria
• Pre-ecclampsia
• Signs/symptoms
• Muscle tremor
• Hyperactive deep reflexes
• Chvosteks/Trousseaus
• Difficulty breathing

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Hypermagnesemia

• Causes
• Renal failure
• Excessive intake
• Signs/symptoms
• Low BP
• Muscle weakness
• Absent reflexes
• Bradycardia

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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

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Review

• Acid/Base Imbalance Tutorial
• How do we assess for acid-base balance?

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Assessment

• 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

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Assessment Contd.

• Environmental factors affecting fluid/electrolyte
  alterations
• Diet
• Lifestyle smoking, ETOH
• Medications
• Physical Assessment
• Daily weights
• IO
• Vital signs
• Laboratory Studies

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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

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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

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Restorative Care

• Home IV therapy
• Nutritional support
• Medication safety
• Pt. education

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Evaluation

• Have goals been met?
• Have changes in assessment occurred?
• Progress determines need to continue or revise
  plan of care