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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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Chapter 41 fluid electrolyte and acid base balance l.jpg

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 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


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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 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


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    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


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    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


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    Fluid Output Regulation

    • Organs of water loss

      • Kidneys

      • Lungs

      • Skin

      • GI tract


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    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


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    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


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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 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


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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

    Lungs

    Regulate by altering H+ ions

    Metabolic acidosis

    Metabolic alkalosis

    Kidneys

    Regulate by altering HCO3 and H+ ions

    H+

    H+

    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


    Hyponatremia low sodium l.jpg

    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 Trousseau’s

    Carpal spasm

    Positive Chvostek’s

    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

    Chvostek’s/Trousseau’s

    Difficulty breathing


    Hypermagnesemia l.jpg

    Hypermagnesemia

    Causes

    Renal failure

    Excessive intake

    Signs/symptoms

    Low BP

    Muscle weakness

    Absent reflexes

    Bradycardia


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    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


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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 Cont’d.

    • Environmental factors affecting fluid/electrolyte alterations

    • Diet

    • Lifestyle – smoking, ETOH

    • Medications

    • Physical Assessment

      • Daily weights

      • I&O

      • 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


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