What are the causes and treatments of hyponatremia (low sodium levels)?

From the Guidelines

Hyponatremia should be treated when serum sodium is lower than 130 mmol/L, with the goal of correcting the sodium level by no more than 8 mmol/L per day to prevent osmotic demyelination syndrome, as recommended by the most recent and highest quality study 1.

Causes and Classification of Hyponatremia

Hyponatremia can be classified into three main categories: hypovolemic, euvolemic, and hypervolemic, each with different underlying causes and treatment approaches.

• Hypovolemic hyponatremia is characterized by a decrease in extracellular fluid volume, often due to excessive diuretic use, gastrointestinal losses, or renal losses.
• Euvolemic hyponatremia is associated with an intact extracellular fluid volume, commonly seen in the syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypothyroidism, or adrenal insufficiency.
• Hypervolemic hyponatremia is marked by an increase in extracellular fluid volume, typically observed in conditions like heart failure, cirrhosis, or nephrotic syndrome.

Treatment Approaches

Treatment of hyponatremia depends on the severity, cause, and rapidity of onset.

• For mild cases (sodium 130-134 mmol/L), restricting fluid intake to 1-1.5 liters daily may be sufficient, as suggested by 1.
• For moderate to severe cases, intravenous sodium chloride solution is typically administered, with 3% hypertonic saline reserved for severe symptomatic cases (sodium <120 mmol/L with neurological symptoms) 1.
• Underlying causes must be addressed, which may include adjusting medications like diuretics, treating SIADH with fluid restriction or medications such as tolvaptan, or managing conditions like heart failure or cirrhosis 1.

Important Considerations

• Correction rates should not exceed 8-10 mmol/L in 24 hours to prevent osmotic demyelination syndrome, a potentially life-threatening complication 1.
• The use of vasopressin antagonists, such as tolvaptan, may be considered in the short term to improve serum sodium concentration in hypervolemic, hyponatremic states, but their long-term safety and benefit remain unknown 1.
• Frequent monitoring is necessary when correcting the serum sodium concentration to avoid overcorrection and its associated risks 1.

From the FDA Drug Label

Tolvaptan tablets are indicated for the treatment of clinically significant hypervolemic and euvolemic hyponatremia (serum sodium <125 mEq/L or less marked hyponatremia that is symptomatic and has resisted correction with fluid restriction), including patients with heart failure and Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

• Hyponatremia treatment: Tolvaptan is used to treat hyponatremia, specifically hypervolemic and euvolemic hyponatremia.
• Serum sodium levels: The treatment is indicated for patients with serum sodium levels <125 mEq/L or those with less marked hyponatremia that is symptomatic and has resisted correction with fluid restriction.
• Patient population: Tolvaptan is used in patients with heart failure and Syndrome of Inappropriate Antidiuretic Hormone (SIADH) 2, 2.

From the Research

Definition and Prevalence of Hyponatremia

• Hyponatremia is defined as a serum sodium concentration <135 mmol/L 3, 4, 5, 6
• It is the most common electrolyte disorder, affecting approximately 5% of adults and 35% of hospitalized patients 3
• Hyponatremia can lead to a wide spectrum of clinical symptoms, from mild to severe or even life-threatening, and is associated with increased mortality, morbidity, and length of hospital stay 4, 5, 6

Causes and Classification of Hyponatremia

• Hyponatremia most commonly results from water retention 3
• It can be classified into three categories based on fluid volume status: hypovolemic hyponatremia, euvolemic hyponatremia, and hypervolemic hyponatremia 3, 5
• The approach to managing hyponatremia should consist of treating the underlying cause 3

Symptoms and Signs of Hyponatremia

• 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
• Symptom severity depends on the rapidity of development, duration, and severity of hyponatremia 3
• Mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 3

Treatment of Hyponatremia

• Urea and vaptans can be effective treatments for the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure, but have adverse effects 3
• Tolvaptan is a vasopressin antagonist that has been shown to be safe and effective for the treatment of patients with hyponatremia 5, 7
• Severely symptomatic hyponatremia (with signs of somnolence, obtundation, coma, seizures, or cardiorespiratory distress) is a medical emergency and should be treated with bolus hypertonic saline 3
• The correction limit for hyponatremia is 10 mEq/L within the first 24 hours, and overly rapid correction can cause osmotic demyelination, a rare but severe neurological condition 3