From the Research
Diagnosis of Hyponatremia
The diagnosis of hyponatremia involves a systematic approach to laboratory diagnosis, including measurement of the effective serum tonicity (serum osmolality less serum urea level) 1. The following steps can be taken:
- Measure serum osmolality and urine osmolality to determine whether water excretion is normal or impaired
- Assess extracellular volume status on physical examination to provide useful clues as to the pathogenesis of hyponatremia
- Determine the urine sodium level to indicate whether the patient has hypovolemia or the syndrome of inappropriate antidiuretic hormone secretion
Classification of Hyponatremia
Hyponatremia can be classified based on volume status, including:
- Hypovolemic hyponatremia: treated with normal saline infusions 2, 3
- Euvolemic hyponatremia: treated with restricting free water consumption or using salt tablets or intravenous vaptans 2, 3
- Hypervolemic hyponatremia: treated primarily by managing the underlying cause (e.g., heart failure, cirrhosis) and free water restriction 2, 3
Treatment of Hyponatremia
The treatment of hyponatremia depends on the severity of symptoms and the underlying cause. The following treatments can be used:
- Fluid restriction for euvolemic hyponatremia
- Isotonic saline for hypovolemic hyponatremia
- Diuresis for hypervolemic hyponatremia
- Hypertonic saline for severe symptomatic hyponatremia 4, 2, 5
- Vaptans for euvolemic and hypervolemic hyponatremia 4, 3
Monitoring and Correction of Sodium Levels
It is essential to monitor sodium levels closely to avoid overly rapid correction, which can cause osmotic demyelination syndrome 2, 5. The correction rate should be sufficient to reduce symptoms but not at an excessive rate that would create a risk of osmotic injury. Calculators can be used to guide fluid replacement and avoid overly rapid correction of sodium concentration 2.