How do you diagnose and manage hyponatremia (low sodium levels)?

From the Guidelines

Hyponatremia is diagnosed when serum sodium levels fall below 135 mEq/L, with management depending on severity, symptoms, and underlying cause. Initial diagnosis requires serum sodium measurement, assessment of volume status (hypovolemic, euvolemic, or hypervolemic), and evaluation of urine sodium and osmolality. For severe symptomatic hyponatremia (sodium <120 mEq/L with seizures or altered consciousness), administer 3% hypertonic saline at 100-150 mL over 10-20 minutes, which can be repeated until symptoms improve, aiming to increase sodium by 4-6 mEq/L in the first 6 hours and not exceeding 8-10 mEq/L in 24 hours to prevent osmotic demyelination syndrome 1. For chronic hyponatremia, address the underlying cause:

• restrict fluids to 800-1000 mL/day for SIADH;
• use salt tablets and fludrocortisone 0.1 mg daily for salt-wasting conditions;
• administer loop diuretics like furosemide 20-40 mg daily with salt supplementation for hypervolemic states;
• and discontinue offending medications (thiazides, SSRIs, carbamazepine) 1. Vasopressin receptor antagonists like tolvaptan may be used for resistant cases, starting at 15 mg daily 1. Regular monitoring of serum sodium (every 2-4 hours in severe cases) is essential, with correction rates adjusted to prevent neurological complications. Sodium correction that's too rapid can cause permanent neurological damage, while inadequate treatment of severe hyponatremia can lead to cerebral edema and herniation. Key considerations in management include:
• Identifying and treating the underlying cause of hyponatremia
• Avoiding overly rapid correction of sodium levels to prevent osmotic demyelination syndrome
• Using hypertonic saline judiciously in severe cases
• Employing vasopressin receptor antagonists in resistant cases
• Monitoring serum sodium levels closely to adjust treatment as needed.

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 diagnosis of hyponatremia is based on a serum sodium concentration of less than 135 mEq/L.

• Key points for diagnosis and management include:
  • Measuring serum sodium concentrations
  • Assessing the underlying cause of hyponatremia (e.g., heart failure, liver cirrhosis, SIADH)
  • Monitoring patients for signs and symptoms of hyponatremia
  • Avoiding overly rapid correction of serum sodium to prevent osmotic demyelination syndrome
  • Using medications like tolvaptan to increase serum sodium concentrations in patients with euvolemic or hypervolemic hyponatremia 2
  • Monitoring serum sodium levels during treatment to avoid hypernatremia 2
  • Adjusting the dose of tolvaptan or discontinuing treatment if hypernatremia occurs 2

From the Research

Diagnosis of Hyponatremia

• Hyponatremia is defined as a serum sodium concentration of <135 mmol/L 3, 4, 5
• It often develops as a consequence of elevated levels of arginine vasopressin (AVP) hormone 3
• Common clinical conditions that can cause hyponatremia include syndrome of inappropriate secretion of AVP, volume depletion, postoperative states, heart failure, cirrhosis, neuroendocrine disorders, and trauma 3
• A history of concurrent illness and medication use, assessment of extracellular fluid volume, as well as measurement of serum and urine osmolality and urine sodium concentration will help to establish the primary underlying causes 3

Management of Hyponatremia

• Symptomatic hyponatremia must be treated promptly with 3% hypertonic saline to increase the serum sodium by 1-2 mmol/L per hour until symptoms abate, or a total magnitude of correction of 12 mmol/L in 24 hours or 18 mmol/L in 48 hours is achieved 3
• Fluid restriction and loop diuretic are frequently employed to treat volume overload 3
• Vasopressin receptor antagonists provide prompt and effective water diuresis and increase in serum sodium concentration in both euvolemic and hypervolemic hyponatremia 3, 6
• Urea and vaptans can be effective treatments for the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure, but have adverse effects 4
• 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 to reverse hyponatremic encephalopathy by increasing the serum sodium level by 4 mEq/L to 6 mEq/L within 1 to 2 hours but by no more than 10 mEq/L (correction limit) within the first 24 hours 4

Classification of Hyponatremia

• Hyponatremia can be classified into three categories based on fluid volume status: hypovolemic, euvolemic, and hypervolemic 4, 5, 7
• Hypovolemic hyponatremia is treated with normal saline infusions 5
• Euvolemic hyponatremia is treated with restricting free water consumption or using salt tablets or intravenous vaptans 5
• Hypervolemic hyponatremia is treated primarily by managing the underlying cause (e.g., heart failure, cirrhosis) and free water restriction 5