15. ELECTROLYTE REPLENISHERS

Introduction to Electrolyte Replenishers and Replacement Therapy

The human body maintains a delicate balance of electrolytes and fluids for normal physiological functions. These electrolytes are distributed across different body compartments to regulate processes like pH balance, osmotic pressure, and cellular activity. When illness, dehydration, or prolonged fever disrupts this equilibrium, external administration of electrolytes becomes essential — a process known as Replacement Therapy.

Body Fluid Compartments

  1. Intracellular Fluid: Present inside cells (cytoplasm); constitutes 40–50% of body weight (~30 L).
  2. Interstitial Fluid: Found between cells; constitutes 12–15% of body weight (~10 L).
  3. Vascular Fluid (Plasma): Found in blood; constitutes 4–5% of body weight (~3–5 L).

The interstitial fluid and plasma together are known as the extracellular fluid. Electrolyte concentration in these fluids is maintained through regulatory mechanisms involving ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, SO₄²⁻, HCO₃⁻, and phosphates.

Electrolyte Replacement Solutions

1. Rapid Initial Replacement Solution

Used for quick restoration of electrolytes in acute losses.

  • Sodium: 130–150 mEq/L
  • Chloride: 98–110 mEq/L
  • Bicarbonate: 28–55 mEq/L
  • Potassium: 4–12 mEq/L
  • Calcium: 3–15 mEq/L
  • Magnesium: 3 mEq/L

2. Subsequent Replacement Solution

Used for gradual replenishment after initial recovery.

  • Sodium: 40–120 mEq/L
  • Chloride: 30–105 mEq/L
  • Bicarbonate: 16–53 mEq/L
  • Potassium: 16–35 mEq/L
  • Calcium: 10–15 mEq/L
  • Magnesium: 3–6 mEq/L
  • Phosphate: 0–13 mEq/L

Important Electrolyte Replenishers

1. Sodium Chloride (NaCl)

  • Purity Limit: 99–105% (dried at 130°C)
  • Preparation: Obtained by dissolving impure salt in water and purifying with hydrochloric gas; industrially by evaporating purified saline or rock salt.
  • Properties: White, odorless, saline-tasting crystalline powder; freely soluble in water.
  • Assay: Precipitation titration (Volhard’s method) using AgNO₃ and thiocyanate.
  • Uses: Major source of Na⁺ and Cl⁻ ions; used in 0.9% isotonic saline, Ringer’s solution, and irrigation fluids.

2. Potassium Chloride (KCl)

  • Purity Limit: Not less than 99.5% (dried at 130°C)
  • Preparation:
    1. From mineral carnallite (KCl·MgCl₂·6H₂O) by crystallization.
    2. By reacting HCl with potassium carbonate/bicarbonate.
  • Properties: Colorless, prismatic crystals with saline taste; soluble in water.
  • Assay: Precipitation titration with AgNO₃ using potassium chromate indicator.
  • Uses: Used as electrolyte replenisher in hypokalemia, and as component of Ringer’s and ORS formulations.

3. Calcium Gluconate (C₁₂H₂₂O₁₄Ca·H₂O)

  • Purity Limit: 99–103%
  • Preparation: Produced by oxidation of glucose to gluconic acid in the presence of calcium carbonate.
  • Properties: White, odorless crystalline powder; slightly soluble in water.
  • Assay: Complexometric titration with EDTA.
  • Uses: Treats hypocalcemia; less irritant than calcium chloride.

Acid–Base Imbalance

Normal blood pH ranges between 7.35 and 7.45.

  • Acidosis: pH below 7.35 due to decreased bicarbonate (22–26 mEq/L).
  • Alkalosis: pH above 7.45 due to increased bicarbonate levels, often from excessive diuretic use.

Acidosis causes CNS depression, while alkalosis leads to CNS hyperexcitability.

Electrolytes Used in Acid–Base Therapy

1. Sodium Acetate (CH₃COONa·3H₂O)

  • Purity Limit: 99–101%
  • Preparation: Neutralizing acetic acid with sodium carbonate or bicarbonate.
  • Assay: Non-aqueous titration using perchloric acid.
  • Uses: Component of peritoneal dialysis fluids; used as an alkalinizing agent.

2. Potassium Acetate (CH₃COOK)

  • Purity Limit: 99%
  • Preparation: Formed by neutralizing acetic acid with potassium carbonate or bicarbonate.
  • Assay: Acid–base back titration using sulfuric acid and NaOH.
  • Uses: Acts as diuretic and urinary alkalizer; useful in metabolic acidosis.

3. Sodium Citrate (Na₃C₆H₅O₇)

  • Purity Limit: 99–101%
  • Preparation: Obtained by neutralizing citric acid with sodium bicarbonate.
  • Assay: Non-aqueous titration with perchloric acid.
  • Uses: Used as buffer, antacid, systemic alkalizer, anticoagulant, and expectorant.

Electrolyte Combination Therapy

In surgical or critical care patients, maintaining electrolyte balance is crucial. Combination solutions containing multiple electrolytes are administered to restore fluid and ion balance effectively.

Examples:

  • Compound Sodium Chloride Injection:
    Sodium chloride – 8.6 g, Potassium chloride – 0.3 g, Calcium chloride – 0.3 g, Water for injection up to 1000 mL. The solution is filtered and sterilized by autoclaving.
  • Oral Rehydration Salts (ORS):
    Used in dehydration and diarrhea to replenish electrolytes. WHO-recommended formulations (Formula 2 and 3) are most commonly used.

Detailed Notes:

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