Hyponatraemia (Hyponatremia) - classification, causes, pathophysiology, treatment

Summary of Hyponatraemia (Hyponatremia)

Hyponatremia is defined as a serum Sodium concentration below 130 mmol/L and affects 1-15% of hospital patients. While most cases require no treatment, acute Hyponatremia can be life-threatening. Sodium plays a crucial role in the body, being the main cation in extracellular fluid, and is involved in various physiological processes.

Key Concepts and Classifications:

• Sodium Distribution:
  • Extracellular Fluid: 145 mmol/L (intravascular and interstitial compartments).
  • Intracellular Fluid: 12 mmol/L.
• Sodium-Potassium Pump: Maintains higher Sodium levels in extracellular space by exchanging Sodium for potassium.
• Classification of Hyponatremia by Volume Status:
  • Hypervolemic Hyponatremia: Low serum Sodium with fluid overload (e.g., Congestive Heart Failure, Liver Cirrhosis).
  • Euvolemic Hyponatremia: Low serum Sodium with normal fluid status (e.g., Syndrome of Inappropriate ADH Secretion).
  • Hypovolemic Hyponatremia: Low serum Sodium with dehydration (e.g., due to Diuretics, vomiting, diarrhea).

Causes of Hyponatremia:

• Pseudo Hyponatremia: Falsely low Sodium readings due to factors like hyperglycemia, mannitol use, hyperlipidemia, and hyperproteinemia.
• True Causes:
  • Hypervolemic:
    • Congestive Heart Failure: Increased ADH release due to low arterial blood flow.
    • Liver Cirrhosis: Low albumin leading to fluid shifts.
    • Nephrotic syndrome: Protein leakage affecting fluid balance.
    • Chronic renal failure and hypothyroidism: Reduced filtration and hormonal imbalances.
  • Euvolemic:
    • Syndrome of Inappropriate ADH Secretion: Excessive ADH leads to water retention and dilution of Sodium.
    • Beer potomania: Chronic alcohol consumption leading to fluid overload and low solute concentration.
  • Hypovolemic:
    • Diuretics: Increase Sodium and water excretion.
    • Vomiting and diarrhea: Loss of water and electrolytes.
    • Sweating, burns, pancreatitis: Loss of fluids from the body.

Clinical Presentation:

Symptoms typically arise when serum Sodium drops below 120 mmol/L, including headaches, lethargy, malaise, nausea, and vomiting. Rapid drops can lead to cerebral edema and pulmonary edema.

Diagnosis and Management:

Diagnosis involves measuring serum osmolality, urine osmolality, and urine Sodium concentration. Management depends on the cause and severity:

• Mild, asymptomatic cases may require no treatment.
• Severe cases need fluid restriction and possibly hypertonic saline to increase Sodium levels slowly, avoiding rapid correction to prevent complications like central pontine myelinolysis.

Researchers/Sources Featured:

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