15. FLUIDS AND ELECTROLYTES BALANCE

Fluids and electrolytes balance is essential for maintaining normal physiological functions in the human body. Proper balance ensures stable cellular activity, nerve conduction, muscle function, acid–base equilibrium, and normal hydration. Disturbances in fluid or electrolyte levels can lead to serious clinical conditions requiring immediate attention. Understanding these principles is vital for clinical pharmacists and healthcare professionals involved in patient management.

Body Fluid Compartments

Total body water constitutes around 60% of body weight in adults. It is distributed into major compartments:

1. Intracellular Fluid (ICF)

  • Accounts for about two-thirds of total body water.
  • Rich in potassium (K⁺) and phosphate (PO₄³⁻).

2. Extracellular Fluid (ECF)

  • One-third of total body water.
  • Divided into interstitial fluid and plasma.
  • Rich in sodium (Na⁺) and chloride (Cl⁻).

Major Electrolytes and Their Functions

Sodium (Na⁺)

Essential for maintaining ECF volume, osmotic balance, and nerve impulse transmission.

Potassium (K⁺)

Key intracellular cation involved in neuromuscular function and cardiac rhythm.

Chloride (Cl⁻)

Maintains acid–base balance and osmotic pressure.

Bicarbonate (HCO₃⁻)

Primary buffer regulating acid–base balance.

Calcium (Ca²⁺)

Required for muscle contraction, blood clotting, and bone strength.

Magnesium (Mg²⁺)

Important for enzyme activity, neuromuscular function, and ATP production.

Fluid Imbalances

Fluid balance disorders are classified into two major types: dehydration and fluid overload.

1. Dehydration

Occurs due to reduced body water.

  • Causes: vomiting, diarrhea, fever, burns, diuretics.
  • Symptoms: dry mouth, tachycardia, low BP, weight loss.
  • Severe dehydration can lead to shock.

2. Fluid Overload (Hypervolemia)

Excess fluid accumulation.

  • Causes: renal failure, heart failure, excessive IV fluids.
  • Symptoms: edema, shortness of breath, hypertension.

Electrolyte Imbalances

1. Hyponatremia (Low Sodium)

  • Causes: SIADH, renal failure, diuretics, heart failure.
  • Symptoms: confusion, seizures, headache.
  • Severe cases require hypertonic saline.

2. Hypernatremia (High Sodium)

  • Causes: dehydration, diabetes insipidus.
  • Symptoms: thirst, irritability, altered mental status.

3. Hypokalemia (Low Potassium)

  • Causes: vomiting, diarrhea, thiazide/loop diuretics.
  • Symptoms: muscle weakness, arrhythmias.
  • Treated with oral or IV potassium.

4. Hyperkalemia (High Potassium)

  • Causes: renal failure, ACE inhibitors, potassium-sparing diuretics.
  • Symptoms: peaked T waves, arrhythmias, muscle paralysis.
  • Treatments: calcium gluconate, insulin + glucose, dialysis.

5. Hypocalcemia (Low Calcium)

  • Causes: vitamin D deficiency, hypoparathyroidism.
  • Symptoms: tetany, muscle spasms, numbness.

6. Hypercalcemia (High Calcium)

  • Causes: hyperparathyroidism, malignancies.
  • Symptoms: polyuria, kidney stones, confusion.

7. Hypomagnesemia

  • Causes: alcoholism, malnutrition, diuretics.
  • Symptoms: tremors, seizures, arrhythmias.

8. Hypermagnesemia

  • Causes: renal failure, magnesium-containing antacids.
  • Symptoms: hypotension, respiratory depression.

Acid–Base Balance

The body maintains pH between 7.35 and 7.45 through respiratory and metabolic mechanisms.

Metabolic Acidosis

  • Causes: renal failure, ketoacidosis, diarrhea.
  • Low bicarbonate (HCO₃⁻).

Metabolic Alkalosis

  • Causes: vomiting, diuretics.
  • High bicarbonate.

Respiratory Acidosis

  • Causes: COPD, respiratory depression.
  • High CO₂ levels.

Respiratory Alkalosis

  • Causes: anxiety, hyperventilation.
  • Low CO₂ levels.

Clinical Assessment of Fluid and Electrolyte Balance

1. Physical Examination

  • Skin turgor
  • Blood pressure
  • Edema
  • Jugular venous pressure

2. Laboratory Tests

  • Serum electrolytes (Na⁺, K⁺, Cl⁻, HCO₃⁻)
  • Renal function tests
  • Arterial blood gases (ABG)

3. Intake and Output Charting

Monitors hydration status and guides management.

Management of Fluid and Electrolyte Disorders

1. Intravenous (IV) Fluids

  • Isotonic: 0.9% saline, Ringer’s lactate (used for dehydration, shock)
  • Hypotonic: 0.45% saline (used in hypernatremia)
  • Hypertonic: 3% saline (used for severe hyponatremia)

2. Electrolyte Replacement Therapy

  • Oral or IV potassium for hypokalemia.
  • Calcium gluconate for hypocalcemia.
  • Magnesium sulfate for hypomagnesemia.

3. Correcting Underlying Causes

  • Treat vomiting, diarrhea, kidney disease.
  • Adjust medications causing electrolyte disturbances.
  • Dialysis in severe renal failure.

Detailed Notes:

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