chapter 8

Module 1: Electrolyte Imbalance

Introduction to Electrolytes

  • Body fluids contain electrolytes, chemicals that generate ions when dissolved in water.

  • Ions are electrically charged particles.

    • Cations: positively charged ions.

    • Examples: Sodium (Na⁺), Calcium (Ca²⁺), Hydrogen (H⁺), Potassium (K⁺).

    • Anions: negatively charged ions.

    • Examples: Chloride (Cl⁻), Bicarbonate (HCO₃⁻), Sulfate (SO₄²⁻), Phosphate (PO₄³⁻).

  • Opposite charges of ions attract, forming molecules.

    • Example: Na⁺ + Cl⁻ → NaCl (sodium chloride).

Concentration of Electrolytes

  • Measured in:

    • Milligrams per deciliter (mg/dL): Weight of solute in one-tenth of a liter (dL; equivalent to 100 μL).

    • Milliequivalents per liter (mEq/L): Considers charge equivalency for specific weights of electrolytes.

  • Electroneutrality: Cations and anions must balance in body fluids.

    • 1 mEq of sodium has the same charge as 1 mEq of chloride.

  • Clinical Measurements: Concentrations in plasma (blood fluid) provide insights into electrolyte balance:

    • Plasma contains high sodium, chloride, calcium; low potassium, magnesium, phosphate; moderate bicarbonate.

    • Intracellular fluid (ICF) contains: low calcium; small amounts of sodium, bicarbonate, chloride; moderate phosphate and magnesium; high potassium concentrations.

Electrolyte Transport

  • Plasma membrane: Acts as a barrier between intracellular and extracellular compartments.

  • Transport mechanisms:

    • Active Transport: Requires energy to move ions against concentrations.

    • Passive Transport: Moves ions along concentration gradients without energy.

  • Cation exchange: Movement of one positive ion for another in opposite directions.

  • Anion exchange: Reciprocal transport of negatively charged ions.

  • Mechanisms maintain electrolyte and acid-base balance.

Importance of Calcium

  • Calcium is critical for muscle contraction; must increase intracellular calcium for muscle tension development.

Regulation of Electrolyte Balance

General Importance

  • Essential to maintain metabolic function of cells.

  • Altered electrolytic levels can disrupt action potentials, fluid balance, and acid-base balance.

Altered Sodium Balance

  • Key role of Sodium:

    • Most abundant extracellular cation; primary determinant of blood osmolality.

    • Transported out of the cell against its gradient by the Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in).

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

    • Causes: vomiting, diarrhea, sweating.

    • Symptoms: muscle twitching, weakness, hypotension, tachycardia, oliguria/anuria, altered neural function (nausea, lethargy, seizures, coma).

  • Hypernatremia: Increased sodium levels (>145 mEq/L).

    • Causes: excessive sodium intake, dehydration.

    • Symptoms: agitation, restlessness, decreased consciousness, thirst, hypertension, tachycardia, edema, weight gain.

Altered Potassium Balance

  • Potassium: Most abundant intracellular cation.

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

    • Causes: excessive loss due to diuretics, vomiting, diarrhea.

    • Symptoms: dizziness, hypotension, cardiac arrhythmias, muscle weakness/cramps, decreased motility (nausea, anorexia, abdominal distention).

  • Hyperkalemia: High potassium levels (>5 mEq/L).

    • Causes: medical drug misuse, renal failure, potassium leakage from cells.

    • Symptoms: potential cardiac arrest, abdominal cramping, flaccid paralysis.

Altered Chloride Balance

  • Chloride: Major extracellular anion, often associated with sodium, critical in acid-base balance.

  • Hypochloremia: Low chloride levels (<98 mEq/L).

    • Causes: vomiting, diarrhea, diuretics.

    • Symptoms: excessive tone, tetany, muscle weakness/twitching, shallow breathing.

  • Hyperchloremia: High chloride levels (>108 mEq/L).

    • Causes: dehydration, kidney failure, hemodialysis.

    • Symptoms: hyperchloremic metabolic acidosis, rapid breathing, weakness, headache.

Altered Calcium Balance

  • Calcium: Most stored in bones; some in extracellular fluid.

  • Hypocalcemia: Low calcium levels (<8.5 mg/dL).

    • Causes: medications, thyroid disorders, kidney failure, vitamin D deficiency.

    • Symptoms: anxiety, irritability, muscle cramps/twitching, tetany, arrhythmias.

  • Hypercalcemia: High calcium levels (>10.5 mg/dL).

    • Causes: bone breakdown, overactive parathyroid, excessive intake.

    • Symptoms: thirst, urination issues, digestive problems, muscle weakness, confusion.

Altered Magnesium Balance

  • Magnesium: Similar functions to calcium and potassium; stored in bones.

  • Hypomagnesemia: Low magnesium (<1.5 mEq/L).

    • Causes: malnutrition, burns, alcoholism, diuretics.

    • Symptoms: tetany, seizures, arrhythmias.

  • Hypermagnesemia: High magnesium (>2.5 mEq/L).

    • Causes: excessive intake, renal disease.

    • Symptoms: hypotension, weak reflexes/muscle weakness, respiratory depression.

Altered Phosphate Balance

  • Phosphate: Vital for ATP synthesis, stored in bones.

  • Hypophosphatemia: Low phosphate (<2.5 mg/dL).

    • Causes: burns, malnutrition, kidney disease.

    • Symptoms: muscle weakness, tremors, bone deformities.

  • Hyperphosphatemia: High phosphate (>4.5 mg/dL).

    • Causes: bone disease, fractures, renal failure.

    • Symptoms: often asymptomatic, muscle tetany possible.

Module 2: Fluid Imbalance

Body Water Composition

  • Fluid comprises about 60% of body weight.

    • Intracellular fluid: 40% of total body weight.

    • Extracellular fluid: 20% of total body weight.

Compartments

  • Intracellular Compartment (ICF): 2/3 of body water.

  • Extracellular Compartment (ECF): Remaining 1/3 of body fluid:

    • Interstitial Fluid: 14% of body weight.

    • Plasma Fluid: 5% of body weight.

    • Transcellular Compartment: Contains body fluids in spaces like peritoneal and pleural cavities, not available for exchange.

Fluid Regulation

  • Kidneys: Directly regulate extracellular fluid; indirectly affect intracellular fluid.

  • Osmosis: Water movement through aquaporins based on concentration gradients (low to high particle concentration).

    • Osmotic Pressure: Reflects activity of nondiffusible particles attracting water.

  • Osmolarity (Outside Body): Concentration in 1 L of solution (mOsm/L).

  • Osmolality (Inside Body): Concentration in 1 kg of water (mOsm/kg H₂O).

Fluid Movement

  • Hydrostatic pressure promotes filtration out of capillaries; osmotic pressure promotes reabsorption.

    • Filtration vs. Reabsorption: Controlled by opposing hydrostatic and osmotic pressures in capillaries.

    • Lymphatic System: Drains excess interstitial fluid back into circulation.

Regulation Mechanisms

  • Thirst and Urine Excretion: Regulated by neural and hormonal responses.

    • Thirst Mechanism: Activated by osmoreceptors in hypothalamus due to thirst sensations from dehydration or low volume.

  • Hormonal Control:

    • Renin-Angiotensin-Aldosterone System (RAAS): Activated by low blood pressure, resulting in increased sodium/water reabsorption.

    • Antidiuretic Hormone (ADH): Regulates fluid volume, promoting reabsorption in kidneys.

Tonicity

  • Tonicity: Describes osmotic pressure of solutions:

    • Isotonic: Same osmolality as ICF; no changes in cell size.

    • Hypotonic: Lower osmolality than ICF; cells swell.

    • Hypertonic: Higher osmolality than ICF; cells shrink.

Fluid Imbalance Conditions

Hypovolemia

  • Definition: Decreased body fluid volume.

    • Causes: excessive fluid loss or inadequate intake.

    • Manifestations: thirst, dry membranes, weight loss, hypotension, altered consciousness.

    • Physiological compensation: RAAS activation, sympathetic nervous system increase, fluid intake stimulation.

Dehydration

  • Results from fluid deficit and has several causes including diarrhea and excessive sweating.

  • Can lead to a hypertonic condition with increased blood sodium concentration.

Water Intoxication

  • Known as hypotonic hypovolemia; results from excessive water intake, potentially causing cellular swelling.

Hypervolemia

  • Expansion of extracellular volume (equivalent isotonic condition).

    • Causes: heart failure, cirrhosis, excess fluid replacement, renal issues.

  • Impacts on body: decreased ADH and aldosterone secretion promoting sodium and fluid elimination.

Edema

  • Definition: Accumulation of interstitial fluid.

  • Causes: Increased capillary filtration pressure, decreased osmotic pressure, increased permeability, obstructed lymph flow.

Module 3: Clinical Models

Cirrhosis

Pathophysiology

  • Permanent liver damage disrupting normal blood flow.

  • Common complication: Ascites.

    • Result of enhanced hydrostatic pressure versus osmotic pressure between vascular and interstitial compartments.

Clinical Manifestations

  • Signs of ascites include abdominal distention, discomfort, sodium retention, renal failure.

Diagnosis

  • Assessment of body weight, abdominal girth, urinary sodium concentration, and ascitic fluid analysis for etiology.

Treatment

  • Diuretics for sodium balance, paracentesis for severe ascites, intravenous albumin post-fluid removal.

Dehydration

  • Caused by negative fluid balance, classified based on sodium loss.

    • Isonatremic: Equal solute and water loss.

    • Hyponatremic: More sodium loss than fluid.

    • Hypernatremic: More fluid loss than sodium.

  • Clinical manifestations: changing consciousness, prolonged capillary refill, dry mucous membranes, vital sign alterations.

Laboratory Tests

  • Important tests include sodium, potassium, and chloride concentration, urine osmolality, and specific gravity measures.

Treatment

  • Mild to moderate dehydration managed with oral rehydration solutions; severe cases require intravenous fluids.

Altered Calcium Balance: Hypoparathyroidism

Pathophysiology

  • A condition marked by reduced parathyroid hormone secretion affecting calcium homeostasis.

Clinical Manifestations

  • General symptoms may include hair and skin changes, muscle cramps, seizures.

Treatment

  • Long-term calcium and vitamin D supplementation for balance management.

Summary

  • Maintaining fluid and electrolyte balance is critical for homeostasis as they impact general health and cellular function directly. Fluid composition is significant in terms of weight and functioning and is influenced by a number of conditions ranging from disorders to dietary influences. Changes in electrolyte levels, whether through hyper- or hypoconcentration, require careful monitoring and treatment to prevent systemic failures and ensure optimal body functions.