What is the appropriate workup and treatment for hyponatremia (low sodium levels)?

From the Guidelines

The workup and treatment of hyponatremia should begin with determining the underlying cause through assessment of volume status, serum osmolality, and urine studies, with the goal of safely normalizing sodium levels while addressing the underlying cause. Initial evaluation includes measuring serum sodium, osmolality, urine sodium and osmolality, thyroid and adrenal function tests, and medication review 1. Treatment depends on severity, chronicity, and etiology. For severe symptomatic hyponatremia (sodium <120 mEq/L with seizures or altered mental status), administer 3% hypertonic saline at 100-150 mL over 10-20 minutes, which can be repeated, aiming for a sodium correction rate of 4-6 mEq/L in the first 24 hours to avoid osmotic demyelination syndrome 1. For moderate hyponatremia, fluid restriction to <1-1.5 L/day is often effective for SIADH, while isotonic fluids are appropriate for hypovolemic hyponatremia. Specific treatments include discontinuing offending medications, treating underlying conditions, and using pharmacologic agents like tolvaptan (starting at 15 mg daily) for euvolemic hyponatremia or demeclocycline (300-600 mg twice daily) for SIADH when fluid restriction is ineffective 1. Regular monitoring of serum sodium (every 2-4 hours initially for severe cases) is essential to ensure appropriate correction rates and prevent complications.

Some key points to consider in the management of hyponatremia include:

• Hypovolemic hyponatremia requires plasma volume expansion with saline solution and correction of the causative factor 1
• Hypervolemic hyponatremia requires attainment of a negative water balance, with non-osmotic fluid restriction being helpful in preventing a further decrease in serum sodium levels, but seldom effective in improving natremia 1
• Hypertonic sodium chloride administration may improve natremia but enhances volume overload and worsens the amount of ascites and edema, and should be limited to severely symptomatic hyponatremia or in patients expected to undergo liver transplant within a few days 1
• Albumin infusion appears to improve serum sodium concentration, but more information is needed 1

Overall, the management of hyponatremia requires a careful assessment of the underlying cause and a tailored approach to treatment, with the goal of safely normalizing sodium levels while addressing the underlying cause.

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)

Patients should be in a hospital for initiation and re-initiation of therapy to evaluate the therapeutic response and because too rapid correction of hyponatremia can cause osmotic demyelination resulting in dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma and death

The appropriate workup for hyponatremia includes:

• Evaluating the patient's volume status to determine if they are hypovolemic, euvolemic, or hypervolemic
• Measuring serum sodium levels
• Assessing for symptoms of hyponatremia, such as headache, nausea, vomiting, and seizures
• Identifying the underlying cause of hyponatremia, such as heart failure, liver cirrhosis, or SIADH

The appropriate treatment for hyponatremia includes:

• Fluid restriction: restricting fluid intake to ≤1.0 liter/day
• Tolvaptan: initiating therapy in a hospital setting, with a starting dose of 15 mg once daily, and titrating up to a maximum dose of 60 mg once daily as needed to achieve the desired level of serum sodium
• Monitoring: frequently monitoring serum electrolytes and volume status, and avoiding overly rapid correction of serum sodium to prevent osmotic demyelination syndrome 2

From the Research

Diagnosis and Evaluation of Hyponatremia

• Hyponatremia is defined as a serum sodium level of less than 135 mEq/L 3, 4, 5, 6
• The condition can be categorized based on the patient's fluid volume status: hypovolemic, euvolemic, or hypervolemic hyponatremia 3, 4, 5, 6
• Symptoms of hyponatremia range from mild and nonspecific (such as weakness or nausea) to severe and life-threatening (such as seizures or coma) 3, 4, 5, 6
• The severity of symptoms depends on the rapidity of development, duration, and severity of hyponatremia 3, 4, 5, 6

Treatment of Hyponatremia

• Treatment should focus on correcting the underlying cause of hyponatremia 3, 4, 5, 6
• For hypovolemic hyponatremia, treatment involves normal saline infusions 4, 6
• For euvolemic hyponatremia, treatment includes restricting free water consumption or using salt tablets or intravenous vaptans 3, 4, 6
• For hypervolemic hyponatremia, treatment primarily involves managing the underlying cause (e.g., heart failure, cirrhosis) and free water restriction 3, 4, 6
• Severely symptomatic hyponatremia requires emergency treatment with bolus hypertonic saline to increase the serum sodium level by 4-6 mEq/L within 1-2 hours, but not exceeding a correction limit of 10 mEq/L within the first 24 hours 3, 4, 6

Special Considerations

• Overly rapid correction of hyponatremia can cause osmotic demyelination, a rare but severe neurological condition 3, 4, 5, 6
• The use of urea and vaptans can be effective in managing the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure, but have adverse effects 3, 7
• Tolvaptan, an oral selective V(2)-receptor antagonist, can be used to treat clinically significant hypervolemic/euvolemic hyponatremia, including in patients with heart failure 7