Chapter 6 Fluid and Electrolytes

Learning Objectives

Differentiate between intracellular and extracellular fluid

Differentiate between diffusion and osmosis

Define tonicity and differentiate between isotonic, hypotonic, and hypertonic

Differentiate between DI and SIADH

Describe the causes and manifestations of sodium, potassium, calcium, phosphorus, and magnesium imbalances

Water

Water is essential to sustain life

Likewise, body fluids are vital to maintain normal body functioning

Total Body Fluid (TBW) - accounts for approx. 60% of total body weight

• 70%+ in a newborn

• 50-55% in a mature woman

Total Body Fluid can be divided into Intracellular and Extracellular

When the Body Demands More

Water requirements increase

• Fever

• Sweating

• Burns

• Tachypnea

• Polyuria

• Surgical Drains

• GI losses: vomiting or diarrhea

Water requirements increase by 100 to 150 mL/day for each C degree of body temperature elevation

Fluid Compartments

Intracellular Fluid (ICF) (2/3)

• Found inside the plasma membrane of the body’s cells

• In humans (average 70kg) or about 28 liters of fluid

Extracellular Fluid (ECF) (1/3)

• Interstitial (2/3)

  • When excessive fluid accumulates in the interstitial space, edema develops

• Intravascular (plasma) (1/3)

  • Blood and in humans is about 70-75 mL/Kg

• Transcellular

  • CSF

  • Pleural fluid

  • Synovial fluid

Tonicity and Fluid Shifts

Tonicity - the ability of the extracellular solution to cause water to move into or out of the cell via osmosis

• Isotonic: No net water movement → cells stay the same size

  • 0.9% Normal Saline (NS), Lactated Ringers, D5W (dextrose 5% in water)

• Hypotonic: Water moves into cells → cells swell (may burst)

  • 0.45% NS, 0.33%NS

• Hypertonic: Water moves out of cells → cells shrink

  • 3% NS, 5% NS, D10W, TPN

Osmolarity - the concentration of solute particles in a solution, determines how water will move between body compartments

• Osmosis - movement of water from low to high solute concentration

Normal Fluid Balance in an Adult

Hormones That Control Fluid Balance

Normal Physiology / Fluid Regulation    

Calculation of Fluid Gain or Loss

• One liter of water weighs 2.2lbs (1kg)

• Body weight change is an excellent indicator of overall fluid volume loss or gain

Controlled by thirst and water excretion

• Regulatory hormones include:

  • Antidiuretic hormone (ADH)

  • Aldosterone

  • Atrial Natriuretic Peptide (ANP)

Fluid Balance: Sources, Losses, and Regulation

Fluid Sources:

• Oral intake

• Intravenous solutions (iso-, hypo-, or hypertonic)

Fluid Losses:

• Urine

• Feces

• Insensible losses

Fluid Balance: Fluid Excess

Types of Fluid Excess:

• Third spacing

• Edema

• Anasarca

• Hypervolemia or fluid volume excess

• Water intoxication

Causes:

• Excessive sodium or water intake

• Inadequate sodium or water elimination    

Manifestations:

• Edemas: peripheral, periorbital, cerebral, and anasarca

• Dyspnea

• Tachycardia

• Hypertension

Diagnosis:

• History

• Physical Examination

• Daily Weights

• Measurements of I&Os

• Lab Results: blood chemistry, urine analysis, complete blood count

Treatment:

• Administering diuretics

• Restricting sodium and fluids

• Maintaining high Fowler’s position

Fluid Balance: Fluid Deficit

Types of Fluid Deficits:

• Dehydration

• Hypovolemia or fluid volume deficit

• Can occur independently without electrolyte defects

Causes:

• Inadequate fluid intake

• Excessive fluid or sodium losses

Leads to:

• Increased level of blood solutes

• Cell shrinkage

• Hypotension

Manifestations:

• Altered level of consciousness

• Hypotension

• Dry mucous membranes

• Decreased skin turgor

Diagnosis:

• History

• Physical Examination

• Daily Weights

• Measurements of I&Os

• Lab Results: blood chemistry, urine analysis, complete blood count

Treatment:

• Managing underlying cause

• Fluid replacement

Fluid Imbalances at a Glance

Imbalance Manifestations Comparison

Electrolytes

Cations +, Anions -

Major Influences on

• Body water regulation

• Osmolarity

• Acid Base regulation

• Enzyme reactions

• Neuromuscular activity

• ECF high in Na+, Cl-, Ca+

• ICF high in K+, bicarb

Sodium

Most abundant cation in ECF

Normal value: 135-145 mEq/L

Functions

• regulates fluid and blood volume → ‘where sodium goes, water follows’

• Maintains ECF-ICF balance via osmolarity

• Supports muscle contraction (with calcium) and nerve impulse conduction

Regulation

• Moves by active transport across cell membranes (requires energy)

• Controlled by aldosterone and ADH

• Reabsorbed/excreted by kidneys; minimal loss via sweat and feces

• Low sodium may result from excess water intake

Sodium Deficit (Hyponatremia)

Decreased Na+ levels in the blood

Serum Sodium is less than 135 mEq/L

Causes: vomiting, sweating, diarrhea, fistulas or use of diuretics, water deprivation

Clinical Manifestations:

• Headache, Confusion, Irritability, Weakness, Lethargy, or Coma

• Hypotension, tachycardia

• Anorexia, nausea, vomiting, diarrhea, and abdominal cramping

• Dry mucosa, poor skin turgor

• Muscle cramps or twitching (cells swelling), decreased deep tendon reflexes fatigue

• Reduced or absent urine output (oliguria to anuria)

Diagnosis:

• History, physical examination

• Lab results: blood chemistry, urine analysis

Treatment:

• Limit fluids

• Increase salt intake

Sodium Excess (Hypernatremia)

Increased Na+ levels in the blood

Serum Sodium is greater than 145 mEq/L

Causes: excessive water or deficient sodium

Clinical Manifestations:

• Thrist, dry swollen tongue, sticky mucous membrane, dysphagia

• Restlessness, weakness, agitation

• Disorientation, delusions

• Flushed skin, elevated temperature

• Edema, weight gain

• Decreased urine output

• Severe: hallucinations, irritability, lethargy, seizures

Treatment:

• Fluid replacement

• Diuretics

Sodium Controls Water

Potassium

Normal Range: 3.5-5 mEq/L

• Primary intracellular cation

• Mainly obtained through diet

Regulation:

• Controlled by Aldosterone

• Excreted through kidneys and gastrointestinal tract

Plays a role in:

• Electrical conduction (both heart and skeletal muscle)

• Acid-base balance

• Metabolism

Serum potassium cannot fluctuate much without causing serious issue

Hyperkalemia

Potassium >5 mEq/L

Causes:

• Deficient excretion; kidney failure

• Excessive intake

• Increased release from cells

• Addison’s Disease, some medications

Manifestations:

• Mainly Cardiac: dysrhythmias, Tall T waves on ECG

• Skeletal muscle weakness, paresthesia

• May see nausea, intermittent intestinal colic and diarrhea, abdominal pain

Diagnosis:

• History, physical examination

• Lab results: blood chemistry, 12-lead EKG, arterial blood gas

Treatment:

• Decrease intake

• Medications particularly insulin

Hypokalemia

Potassium <3.5 mEq/L

Causes:

• Excessive loss

• Deficient intake

• Increased shift into the cell

Manifestations:

• Fatigue, dizziness

• Anorexia, nausea and vomiting, abdominal distension, decreased bowel motility

• Muscle weakness and leg cramps, parenthesis

• Hypotension

• Dysrhythmias, Flat T-Wave on ECG

• Excessive thirst

Diagnosis:

• History, physical examination

• Lab results: blood chemistry, 12-lead EKG, arterial blood gas

Treatment:

• Potassium replacement

• Eliminate cause

Calcium

Normal range: 4–5 mEq/L

• Mostly found in the bone and teeth

• Has inverse relationship with phosphorus

• Has synergistic relationship with magnesium

• Main source is dietary intake (vitamin D aids absorption)

Regulation

• Regulated by vitamin K, parathyroid hormone, and calcitonin

Plays a role in:

• Blood clotting

• Hormone secretion

• Receptor functions

• Nerve transmission

• Muscular contraction

Hypercalcemia

Calcium > 5 mEq/L

Causes:

• Increased intake or release

• Deficit excretion

• Malignancies

Manifestations:

• Muscle weakness, incoordination, bizarre behaviors

• Anorexia, nausea, vomiting, diarrhea

• Confusion, impaired memory, slurred speech, lethargy to acute psychotic behavior, and come

• Polyuria and polydipsia (excessive thirst and excessive urination)

• Kidney stones

Diagnosis:

• History, physical examination

• Lab results: blood chemistry and 12-lead EKG

Treatment:

• Increasing mobility

• Administering IV fluids

• Medications

Hypocalcemia

Calcium <4 mEq/L

Causes:

• excessive losses

• deficient intake

Manifestations include:

• Dysrhythmias

• Tetany (neuromuscular)

  • Trousseau’s Sign

  • Chvostek’s Sign

• Anxiety

• Seizure

• Depression, impaired memory, confusion, delirium, laryngeal spasms

Diagnosis:

• History, physical examination

• Lab results: blood chemistry and 12-lead EKG

Treatment:

• Calcium replacement

• Decrease phosphorus

Phosphorus

Normal range: 2.5-4.5 mg/dL

• Mostly found in the bones

• Small amounts in the bloodstream

• Has inverse relationship with calcium

• Mainly obtained through diet

• Excreted through the kidneys

Plays a role in:

• Bone and tooth mineralization

• Cellular metabolism

• Acid-base balance

• Cell membrane formation

Hyperphosphatemia

Phosphorus >4.5 mg/dL

Causes:

• Deficient excretion

• Excessive intake or cellular exchange

Manifestations:

• Rarely seen alone

• Tetany

• Anorexia, nausea

• Muscle weakness, tingling of extremities

• Tachycardia

Diagnosis:

• History, physical examination

• Blood chemistry

Treatment:

• Medications

• Treating symptoms

Hypophosphatemia

Phosphorus <2.5 mg/dL

Causes:

• Excessive excretion or cellular exchange

• Deficient intake

Manifestations:

• Similar to hypercalcemia

  • Muscle weakness, incoordination, bizarre behaviors

  • Anorexia, nausea, vomiting, diarrhea

  • Confusion, impaired memory, slurred speech, lethargy to acute psychotic behavior, and come

  • Polyuria and polydipsia (excessive thirst and excessive urination)

  • Kidney stones

Diagnosis:

• History, physical examination

• Blood chemistry

Treatment:

• Increase mobility

• Administer Fluids

Magnesium

Normal range: 1.8-2.5 mEq/L

• Intracellular cation

• Mostly stored in the bone and muscle

• Mainly obtained through diet

• Excreted through the kidneys

Regulation:

• Parathyroid hormone

Plays a role in:

• Muscle and nerve function

• Cardiac rhythm

• Immune function

• Bone strength

• Blood glucose management

• Blood pressure

• Energy metabolism

Hypermagnesemia

Magnesium >2.5 mEq/L

Causes:

• Renal failure (most common)

• Excessive laxative and antacid use

Manifestations:

• Similar to hypercalcemia

  • Low blood pressure due to peripheral vasodilation

  • Nausea, vomiting

  • Weakness, decreased respirations and bradycardia

  • Facial flushing and sensations of warmth

  • Lethargy, difficult talking

  • Loss of deep tendon reflexes may lead to paralysis

  • Cardiac arrest

Diagnosis:

• History, physical examination

• Blood chemistry

Treatment:

• Diuretic

• Dialysis

• Intravenous calcium

Hypomagnesemia

Magnesium <1.8 mEq/L

Causes:

• Inadequate intake, chronic alcoholism, malnutrition

• Pregnancy

• Diarrhea

• Diuretics

• Stress

• Usually occurs in association with hypokalemia and hypocalcemia

Manifestations:

• Similar to hypocalcemia

  • Neuromuscular irritability

  • Disorientation

  • Mood changes

  • Hyperexcitability with muscle weakness, tremors

  • Athetoid movements (slow involuntary twisting and writhing)

  • Positive Trousseau and Chvostek sign

  • ECG Changes; dysrhythmias

Diagnosis:

• History, physical examination

• Blood chemistry

Treatment:

• Magnesium replacement

Chloride

Normal Range: 98-108 mEq/l

• Mineral electrolyte and major extracellular anion

• Found in gastric secretions, pancreatic juices, bile, and CSF

• Mainly obtained through dietary intake

• Excreted through the kidneys

Regulation

• Aldosterone and ADH levels

• Plays a role in acid-base balance

Hyperchloremia

Chloride >108 mEq/L

Causes:

• Increased chloride intake or exchange

• Decreased chloride excretion

Manifestations:

• Reflect the underlying cause

  • Hypervolemia

  • Hypernatremia

  • Tachypnea

  • Weakness, lethargy, diminished cognitive ability

  • Hypertension, deep rapid respirations

  • Dysrhythmias and decreased cardiac output

Diagnosis

• History, physical examination

• Lab results: blood chemistry, urine analysis, arterial blood gas

Treatment:

• Diuretics

• Bicarbonate

Hypochloremia

Chloride <98 mEq/L

Causes:

• Decreased chloride intake or exchange

• Increased chloride excretion

• GI tube drainage, severe vomiting, diarrhea

Manifestations:

• Reflect the underlying cause

  • Signs of hyponatremia, hypokalemia, and metabolic alkalosis

  • May experience hyperexcitability of muscles, tetany, deep hyperactive deep tendon reflexes, weakness, twitching, muscle cramps

• Acid base imbalances

Diagnosis:

• History, physical examinations

• Lab results: blood chemistry, urine analysis, arterial blood gase

Treatment:

• Sodium replacement (oral or intravenous)

• Ammonium chloride

• Saline irrigation of gastric tubes

Summary of Electrolytes

Memory Pearls

Sodium → water

Potassium → heart

Calcium → muscles/nerves

Magnesium → calms everything

Phosphorus → ATP energy

Chloride → Acid-base balance