From the Guidelines
Hyponatremia is classified into three main types based on volume status: hypovolemic, euvolemic, and hypervolemic hyponatremia, each requiring different management approaches.
Types of Hyponatremia
- Hypovolemic hyponatremia occurs with fluid losses and should be treated with isotonic saline (0.9% NaCl) to restore volume while correcting sodium levels 1.
- Euvolemic hyponatremia, often caused by SIADH, requires fluid restriction (typically 800-1000 mL/day), and may benefit from salt tablets, urea (15-30 g/day), or vasopressin receptor antagonists like tolvaptan (starting at 15 mg daily) 1.
- Hypervolemic hyponatremia, seen in heart failure, cirrhosis, or kidney disease, requires fluid restriction, diuretics (such as furosemide 20-40 mg daily), and sodium restriction (typically <2 g/day) 1.
Management Approaches
- Acute severe hyponatremia (sodium <120 mEq/L with neurological symptoms) requires more urgent correction with hypertonic saline (3% NaCl) at 1-2 mL/kg/hr, carefully monitoring to avoid exceeding correction rates of 8-10 mEq/L in 24 hours and 18 mEq/L in 48 hours to prevent osmotic demyelination syndrome 1.
- Underlying causes like medications (thiazides, SSRIs), adrenal insufficiency, or hypothyroidism must be addressed simultaneously 1.
- Frequent monitoring of serum sodium (every 2-4 hours in severe cases) is essential to guide therapy and prevent overcorrection, which can lead to permanent neurological damage 1. The most recent and highest quality study 1 supports the use of vasopressin receptor antagonists, such as tolvaptan, in the management of hypervolemic hyponatremia, and recommends careful monitoring to avoid overcorrection and prevent osmotic demyelination syndrome.
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 different types of hyponatremia mentioned in the drug label are:
- Euvolemic hyponatremia: characterized by a normal or slightly decreased extracellular fluid volume
- Hypervolemic hyponatremia: characterized by an increased extracellular fluid volume Specific management approaches for these types of hyponatremia are not explicitly stated in the label, but it is mentioned that tolvaptan can be used to treat both euvolemic and hypervolemic hyponatremia. 2
From the Research
Types of Hyponatremia
- Hypovolemic hyponatremia: commonly due to fluid loss 3, 4, 5, 6
- Hypervolemic hyponatremia: commonly due to fluid retention from heart failure, cirrhosis, or renal failure 3, 4, 5, 6
- Euvolemic hyponatremia: most often because of syndrome of inappropriate secretion of antidiuretic hormone (SIADH) 3, 4, 5, 7
- Pseudohyponatremia: due to hyperproteinemia, hyperlipidemia, or hyperglycemia 3, 5
Management Approaches
- Hypovolemic hyponatremia: managed by rehydration with isotonic saline 3, 6
- Hypervolemic hyponatremia: managed by addressing the underlying cause 3, 4, 6
- Euvolemic hyponatremia: managed by restricting free water intake, addressing the underlying cause, and occasionally with drugs (eg, vasopressin receptor antagonists) 3, 4, 7
- Severe or acutely symptomatic hyponatremia: requires urgent treatment with hypertonic saline administration along with monitoring of sodium levels to avoid overly rapid correction 3, 4, 6