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Electrolyte Shifts and Acid-Base Imbalance

Key Points on Electrolyte Shifts and Acid-Base Imbalance

  1. Electrolyte Absorption in the Gut:
    • Sodium is absorbed both trans-cellularly and para-cellularly in the ileum and colon.
    • Ileum: Absorbs less chloride but more potassium than the colon.
    • Electrolyte Losses in Metabolic Acidosis: Potassium, calcium, and magnesium loss can occur, leading to hypokalemia, hypocalcemia, and hypomagnesemia.
  2. Mechanism of Hyperchloremic Acidosis:
    • Ammonium ions dissociate into ammonia and hydrogen.
    • Ammonium substitutes potassium in potassium channels, while hydrogen is exchanged for sodium.
    • Absorption of chloride with ammonium leads to hyperchloremic acidosis and bicarbonate loss.
  3. Hypocalcemia:
    • Results from renal wasting and bone demineralization due to chronic metabolic acidosis.
    • Calcium is released from bone to buffer the acidosis, but continued acidosis prevents renal calcium reabsorption.
  4. Jejunum in Urinary Diversion:
    • Use of the jejunum in urinary diversion can lead to hyponatremia, hypochloremia, hyperkalemia, and acidosis in up to 40% of cases.
    • This condition arises from increased secretion of sodium and chloride, coupled with reabsorption of hydrogen and potassium.
  5. Water Transport and Intestinal Permeability:
    • Water follows an osmotic gradient, and the permeability of intercellular junctions determines the extent of fluid movement.
    • Stomach: Very leaky, but bidirectional currents cancel each other out.
    • Jejunum: Highly leaky, leading to higher metabolic complication rates.
    • Colon: Least leaky, making it the most efficient segment for diversion.
  6. Acid-Base Imbalance in Different Segments:
    • Ileal/Colonic Diversion: Leads to hyperchloremic metabolic acidosis due to the exchange of hydrogen and chloride for sodium and bicarbonate.
    • Patients with reservoirs (as opposed to simple conduits) are at higher risk due to prolonged urine contact and larger surface area.
  7. Symptoms and Presentation:
    • Symptoms of electrolyte disturbances include lethargy, nausea, vomiting, dehydration, muscle weakness, and anorexia.
    • Metabolic acidosis in jejunal and ileal segments may lead to weakness, anorexia, vomiting, and other complications.
    • Hypochloremic, hypokalemic metabolic acidosis occurs when the stomach is used, especially in dehydrated or renal failure patients. Symptoms include seizures, respiratory issues, and ventricular arrhythmias.

Important Concepts:

  • Electrolyte Imbalance: Particularly potassium, calcium, and magnesium shifts in metabolic acidosis.
  • Chronic Acidosis: Leads to hyperchloremic acidosis due to ammonium absorption.
  • Segment-Specific Risks: Jejunum poses higher risks of severe electrolyte disturbances, while the colon is more stable.
  • Clinical Presentation: Varies depending on the affected segment and severity of electrolyte shifts or acidosis.