From the Guidelines
Hyponatremia can be categorized into hypovolemic, euvolemic, and hypervolemic types, with common cases including SIADH, diuretic use, heart failure, cirrhosis, and nephrotic syndrome. The management of hyponatremia depends on the underlying cause, severity, and chronicity, and treatment options range from fluid restriction to hypertonic saline in severe cases 1.
Causes of Hyponatremia
- Hypovolemic hyponatremia: results from sodium and water losses with greater sodium depletion, as in vomiting, diarrhea, diuretic use, or adrenal insufficiency
- Hypervolemic hyponatremia: occurs in conditions with excess total body water and sodium, such as heart failure, cirrhosis, and nephrotic syndrome
- Euvolemic hyponatremia: often seen in SIADH (Syndrome of Inappropriate Antidiuretic Hormone), where excessive ADH causes water retention despite normal or low serum osmolality
Treatment of Hyponatremia
- Fluid restriction is recommended for patients with hypervolemic hyponatremia, with a goal of restricting fluid intake to 1-1.5 L/day 1
- Hypertonic sodium chloride administration can be considered in patients with severe symptomatic hyponatremia, especially if a transplant is imminent, with a recommended serum sodium increase of up to 5 mmol/L in the first hour and a limit of 8–10 mmol/L every 24 hours thereafter 1
- Plasma expander such as albumin infusion has been tried and reported to be effective in hyponatremia, but the number of patients was very small 1
From the FDA Drug Label
In two double-blind, placebo-controlled, multi-center studies (SALT-1 and SALT-2), a total of 424 patients with euvolemic or hypervolemic hyponatremia (serum sodium <135 mEq/L) resulting from a variety of underlying causes (heart failure, liver cirrhosis, syndrome of inappropriate antidiuretic hormone [SIADH] and others) were treated for 30 days with tolvaptan or placebo, then followed for an additional 7 days after withdrawal.
The cases of hyponatremia mentioned in the study include:
- Euvolemic hyponatremia: caused by various underlying conditions such as
- Heart failure
- Liver cirrhosis
- Syndrome of inappropriate antidiuretic hormone (SIADH)
- Others
- Hypervolemic hyponatremia: also resulting from various underlying causes, with specific serum sodium levels including:
- Serum sodium <135 mEq/L
- Serum sodium <130 mEq/L
- Serum sodium <125 mEq/L 2
From the Research
Cases of Hyponatremia
- Hyponatremia is defined by a serum sodium level of less than 135 mEq/L and most commonly results from water retention 3
- It can be categorized into three types based on fluid volume status: hypovolemic hyponatremia, euvolemic hyponatremia, or hypervolemic hyponatremia 3, 4
- Symptoms and signs of hyponatremia range from mild and nonspecific (such as weakness or nausea) to severe and life-threatening (such as seizures or coma) 3
- Mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 3
- Hyponatremia is a secondary cause of osteoporosis 3
- Severely symptomatic hyponatremia (with signs of somnolence, obtundation, coma, seizures, or cardiorespiratory distress) is a medical emergency that requires treatment with bolus hypertonic saline 3, 5, 6
Treatment of Hyponatremia
- The approach to managing hyponatremia should consist of treating the underlying cause 3
- Urea and vaptans can be effective treatments for the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure 3, 5, 7
- Hypertonic saline is reserved for patients with severely symptomatic hyponatremia 3, 5, 6
- Fluid restriction is the mainstay of management of all types of hypotonic hyponatremia 4, 5
- Rapid correction of chronic hyponatremia may cause osmotic demyelination, a rare but severe neurological condition 3, 4, 5