Fluid and Electrolyte Balance - Pharmacy Notes

Fluid and Electrolyte Balance - Graduate Pharmacy Notes

INTRODUCTION

Fluid and electrolyte balance is fundamental to maintaining homeostasis and ensuring optimal functioning of all physiological systems. This equilibrium regulates cellular hydration, nerve conduction, muscle contraction, acid–base status, and cardiovascular stability. Disruptions can lead to severe clinical consequences including dehydration, electrolyte disorders, shock, arrhythmias, renal dysfunction, and impaired neuromuscular activity.

BODY FLUID COMPARTMENTS

Total body water (TBW) is compartmentalized into intracellular fluid (ICF) and extracellular fluid (ECF).

  • ICF: ~66% of TBW, rich in K+, Mg2+, PO42-.
  • ECF: ~33% of TBW, subdivided into:
    • Interstitial fluid (ISF) - 75% of ECF
    • Plasma - 20 - 25% of ECF
    • Transcellular fluid - intake → hypovolemia, ↑ plasma osmolarity, thirst, ADH release, risk of shock.

      Overhydration: Excessive water intake/retention → hypervolemia, ↓ plasma osmolarity, cellular swelling (cerebral edema).

      Electrolyte Imbalances

      • Hyponatremia: Low Na+ → cerebral edema, neurological symptoms.
      • Hypernatremia: High Na+ → cellular dehydration, irritability, mortality risk.
      • Hypokalemia: Low K+ → muscle weakness, arrhythmias.
      • Hyperkalemia: High K+ → life-threatening cardiac conduction issues.
      • Hypocalcemia: Low Ca2+ → tetany, muscle spasms, cardiac abnormalities.
      • Hypercalcemia: High Ca2+ → fatigue, constipation, kidney stones, arrhythmias.

      Acid - Base Disorders

      • Metabolic acidosis: ↓HCO3- or ↑ acids → compensatory hyperventilation.
      • Metabolic alkalosis: ↑ HCO3- → hypoventilation, neuromuscular excitability.
      • Respiratory acidosis: ↑ CO2 due to hypoventilation.
      • Respiratory alkalosis: ↓ CO2 due to hyperventilation.
      CLINICAL & THERAPEUTIC IMPLICATIONS

      IV Fluids & Oral Rehydration Therapy (ORT): Tailored to correct hypovolemia, dehydration, electrolyte abnormalities. ORT uses glucose-mediated Na+ transport for mild-moderate dehydration.

      Diuretics: Loop, thiazide, K+-sparing diuretics manage hypervolemia, hypertension, electrolyte disorders.

      Critical Care: Precise fluid therapy, monitoring of urine output, electrolytes, hemodynamics, organ function to avoid overload, AKI, acid–base disturbances.

      CONCLUSION

      Fluid and electrolyte balance is essential for physiological stability. Understanding osmotic gradients, hormonal systems (ADH, RAAS, natriuretic peptides), renal processes, and electrolyte functions is critical for clinical management. Disturbances manifest as dehydration, overhydration, electrolyte disorders, and acid–base imbalances. Therapeutic strategies include tailored IV fluids, ORT, diuretics, and intensive monitoring. Future research should integrate molecular insights with precision medicine to improve outcomes.