Summary of 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.

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