Treatment of Hyponatremia
The treatment of hyponatremia should be based on the underlying cause, severity, chronicity, and volume status of the patient, with fluid restriction as first-line therapy for most cases of euvolemic and hypervolemic hyponatremia. 1
Classification and Initial Assessment
Hyponatremia is classified based on volume status:
Hypovolemic hyponatremia:
- Clinical signs: Orthostatic hypotension, tachycardia, dry mucous membranes
- Lab findings: Urine sodium typically <20 mEq/L (unless on diuretics)
- Common causes: Fluid losses (GI, renal, skin)
Euvolemic hyponatremia:
- Clinical signs: No signs of volume depletion or excess
- Lab findings: Urine sodium >20-40 mEq/L, urine osmolality >500 mOsm/kg (in SIADH)
- Common causes: SIADH, hypothyroidism, medications
Hypervolemic hyponatremia:
- Clinical signs: Edema, ascites, elevated jugular venous pressure
- Lab findings: Urine sodium typically <20 mEq/L in heart failure or cirrhosis
- Common causes: Heart failure, cirrhosis, renal failure
Severity-Based Management
Mild Hyponatremia (126-135 mEq/L)
- Often does not require specific management apart from monitoring and water restriction 2
- Identify and address underlying cause
Moderate Hyponatremia (120-125 mEq/L)
- Water restriction to 1,000 mL/day
- Cessation of diuretics
- Treat underlying cause 2
Severe Hyponatremia (<120 mEq/L)
- More severe water restriction
- Albumin infusion recommended for cirrhotic patients 2
- Consider hypertonic saline for symptomatic patients
Treatment Based on Volume Status
Hypovolemic Hyponatremia
- Administer isotonic saline (0.9% NaCl) to restore intravascular volume 1
- Correct the underlying cause of volume depletion
- Discontinue diuretics if applicable
Euvolemic Hyponatremia
- Fluid restriction (1-1.5 L/day) as first-line therapy 1
- Discontinue medications that may cause hyponatremia
- For SIADH:
Hypervolemic Hyponatremia
- Fluid restriction is the cornerstone of treatment
- Diuretic therapy:
- Loop diuretics for heart failure
- Spironolactone (100-400 mg/day) for cirrhosis 1
- Albumin infusion for severe hyponatremia in cirrhosis 2
- Vasopressin antagonists may be considered for short-term use (≤30 days) 2, 3
Special Considerations for Symptomatic Hyponatremia
For patients with severe symptoms (seizures, coma, cardiorespiratory distress):
- Hypertonic saline (3% NaCl) administration 1
- Target correction of 4-6 mEq/L in first 6 hours to reverse life-threatening symptoms
- Critical safety point: Do not exceed correction rate of 8 mEq/L per 24 hours to avoid osmotic demyelination syndrome (ODS) 2
- For high-risk patients (alcoholism, malnutrition, liver disease), limit correction to 4-6 mEq/L per day 2
Use of Vasopressin Receptor Antagonists (Vaptans)
- May be considered for euvolemic or hypervolemic hyponatremia resistant to fluid restriction 2, 3
- Must be initiated in a hospital setting where serum sodium can be closely monitored 3
- Contraindicated in hypovolemic hyponatremia 3
- Limited to short-term use (≤30 days) due to risk of liver injury 2, 3
- Avoid fluid restriction during first 24 hours of therapy 3
Monitoring and Safety
- Monitor serum sodium every 4-6 hours during active correction, every 2 hours in severe cases 1
- If correction exceeds 8 mEq/L in 24 hours, consider administration of hypotonic fluids or desmopressin to prevent ODS 2
- Watch for signs of ODS: dysarthria, dysphagia, altered mental status, quadriparesis 2
- Correct hypokalemia concurrently, as it affects sodium balance 1
Common Pitfalls to Avoid
- Overly rapid correction of chronic hyponatremia leading to ODS
- Inappropriate use of hypertonic saline in asymptomatic patients
- Failure to identify and treat the underlying cause
- Using vaptans in hypovolemic patients or those unable to sense thirst
- Prolonged use of vaptans beyond 30 days due to risk of liver injury
By following this approach based on volume status and severity, while carefully monitoring correction rates, clinicians can effectively manage hyponatremia while minimizing the risk of complications.