Fluid and Electrolytes Overview

Fluid and Electrolytes

• Objectives:

  • Identify body fluid compartments
  • Describe mechanisms regulating fluid and electrolyte balance
  • Identify factors affecting fluid and electrolyte balances
  • Explain routes by which water and electrolytes enter and leave the body
  • Describe types of electrolytes in the body
  • Distinguish between electrolyte balance and imbalance

• Introduction:

  • Body functions depend on proper fluid and electrolyte distribution between intracellular and extracellular compartments
  • Fluid and electrolyte balance is regulated by renal, hormonal, and metabolic mechanisms
  • Imbalances can occur due to other disorders or as therapy complications
  • The main goal is replacement of fluid and electrolyte losses and prior deficits, along with adequate nutrition.

Fluids

• Importance:

  • Crucial for body functions
  • Maintains blood volume
  • Aids digestion
  • Transports materials to and from body cells
  • Acts as a medium for cellular metabolism
  • Excretes waste
  • Regulates body temperature

• Composition:

  • Water is the largest component, forming 50-70% of an adult's body weight and 75-80% of an infant's
  • By age two, the fluid percentage is similar to an adult (60%)
  • Elderly percentages of total body water (TBW) drop to 45-60%

Body Fluid Compartments

• Intracellular fluid (ICF):

  • Found within cells
  • Accounts for approximately 40-50% of total body weight
  • Potassium (K) is the major electrolyte, crucial for cellular chemical functions

• Extracellular fluid (ECF):

  • Found outside cells
  • Made up of two compartments:
    • Interstitial fluid: found in spaces between cells (15% of total body weight in adults)
    • Intravascular fluid: found in blood and lymph vessels (about 5% of total body weight in adults)
    • Sodium (Na) is the major electrolyte in ECF

Distribution and Concentration of Electrolytes in Body Fluid

• Regulated by:
  • Osmosis
  • Diffusion
  • Active transport
  • Filtration
  • Pinocytosis (liquid absorption by cells like macrophages)

Osmosis

• Process by which water moves through a semi-permeable membrane from a lower concentration of solution to a higher concentration
• Continues until equilibrium is reached on both sides of the membrane
• Water moves towards areas with more concentrated electrolytes

Common Sources of Fluid and Electrolyte Imbalance

• Vomiting/Gastric suction:

  • Reduction in acidic gastric juices leads to loss of vital electrolytes (hydrogen, chloride, potassium, and sodium)
  • Results in decreased total body fluid and potential metabolic alkalosis due to increased base bicarbonate

• Diarrhea:

  • Significant fluid loss in 24 hours (up to 17,000mL)
  • Intestinal suction also leads to substantial daily fluid loss (over 3,000mL).

• Other causes:

  • Prolonged laxative or enema use
  • Gastrointestinal fistulas or drainage tubes
  • Gastrointestinal obstructions

• Wound exudates:

  • Fluid loss from wounds leads to protein and sodium losses and possibly affects extracellular fluid volume.

• Excessive perspiration:

  • Significant water, sodium, and chloride loss
  • Prolonged loss without replenishment causes decreased fluid volume and reduced electrolyte proportions.
  • Can cause sodium excess if water intake is insufficient

• Insensible loss:

  • Water loss through lungs and skin (about 600-1000mL/day)
  • Increases with increased respiratory activity, skin damage, and dry air

• Hyperventilation:

  • Excessive carbon dioxide elimination (results in respiratory alkalosis).

• Hypoventilation:

  • Retention of carbon dioxide potentially more dangerous (causes respiratory acidosis).

Electrolytes

• Chemicals dissociating into charged ions (cations and anions) when dissolved

• Maintain fluid and acid-base balance

• Crucial for nerve excitability, blood clotting, and cellular metabolism

• Composition and concentration vary in fluid compartments (measured as mEq/L)

• Electrolytes in Body Fluid:

  • Regulate cell membrane permeability enabling transfer of materials -Maintain acid-base balance
  • Promote nerve and muscle irritability/excitability via electrical energy transmission
  • Maintain fluid osmolarity.

Mechanisms regulating fluid and electrolyte balance

• Proteins and electrolytes

  • Maintain water in compartments
  • Serum albumin (intravascular), sodium (interstitial), and potassium (intracellular) are major forces holding water in compartments

• Kidneys

  • Most important regulatory mechanism
  • Regulated by antidiuretic hormone (ADH) controlling H2O reabsorption/excretion
  • Regulated by aldosterone promoting sodium retention and potassium excretion
  • Regulate total ECF, electrolyte concentration, acid-base balance and blood pressure

• Gastrointestinal tract

  • Selective absorption of water and solutes generally in the small intestine
  • Absorbs about 7 – 9 L of secretions daily
  • Some fluid and electrolytes lost in excessive vomiting and diarrhea

• Thirst

  • Stimulated by decreased extracellular fluid volume
  • Indicating physiological need for water
  • Stimulated by increased osmotic pressure, reduced ECF, and dry mouth

• Lungs

  • Water lost during inhalation and exhalation (small amount)
  • More water loss with increased respiration rate and depth.

• Skin

  • Water loss through perspiration

• Hormonal control:

  • Three primary hormones regulate fluid and electrolytes balances:
    • ADH: Controls water reabsorption, decreasing urine output
    • Aldosterone: Promotes sodium reabsorption and potassium excretion
    • Parathormone: Regulates calcium and phosphorus balance

Specific Electrolytes

Sodium

• Major cation in ECF

• Regulates fluid volume, ECF osmotic pressure, cellular membrane potential, blood volume and vascular bed size

• Normal level: 135-145 mEq/L

• Hyponatremia: decreased sodium levels in blood (<135mEq/L)

  • Causes: inadequate intake, excessive loss of fluids (vomiting/diarrhea), diuretics, hormonal imbalances, excess fluid administration (e.g., 5% D/W; can be linked to water intoxication).
  • Classifications: hypovolemic (decreased total body water), euvolemic (normal total body water), and hypervolemic (increased total body water)

• Hypernatremia: increased sodium levels in blood (>145 mEq/L)

  • Causes: decreased water intake, excessive water loss, and administration of hypertonic fluids

Potassium

• Major cation in ICF

• Maintains intracellular homeostasis, resting membrane potential, nerve impulse conduction, skeletal muscle function, heart function, protein and CHO metabolism

• Normal level: 3.5-5.0 mEq/L

• Hypokalemia: decreased potassium levels (<3.5 mEq/L)

  -Causes: poor dietary intake, use of potassium-wasting diuretics or corticosteroids, excessive loss of GI tract fluids (severe vomiting/diarrhea), prolonged stress or fever, hormonal imbalances

  • Clinical observation: smooth muscle issues (decreased bowel movements/constipation), decreased cardiac impulses (hypotension/ irregular pulse), respiratory depression (shallow/ineffective respirations)

• Hyperkalemia: increased potassium levels (>5.0 mEq/L)

  -Causes: kidney failure, excessive potassium intake, leakage of potassium from cells (burns/trauma), medication side effects (e.g., ACE inhibitors) -Clinical observation: muscle irritability, pain, and paralysis at increasingly severe levels; cardiac abnormalities (ECG changes)

Calcium

• Most abundant electrolyte in the body (mostly stored in bones/teeth)

• Maintains normal level in ECF (1% of total); necessary for neuromuscular activity/function, blood clotting, decreasing capillary permeability, normal muscle contractility, nerve impulses, bones and tooth development

• Hypocalcemia: decreased blood calcium levels (<9 mg/dL or 2.25 mmol/L)

  -Causes: low Vitamin D levels, parathyroid hormone deficit, malabsorption disorders, chronic diarrhea, renal diseases, medications (bisphosphonates), and immobilization -Clinical Observation: Tingling/numbness, muscle cramps, spasms of smooth and skeletal muscles, and seizures

• Hypercalcemia: increased blood calcium levels (>5.3 mEq/L)

  -Causes: hyperparathyroidism, over-consumption of calcium supplements, malignancies, immobilization/decalcification -Clinical Observation: Fatigue, decreased neuromuscular excitability, nausea/vomiting, anorexia, deep bone pain, kidney stones, and ECG changes.