How is hyponatremia treated?

Treatment of Hyponatremia

The treatment of hyponatremia should be guided by the patient's volume status, severity of symptoms, and rate of onset, with fluid restriction of 1-1.5 L/day as first-line treatment for euvolemic hyponatremia (SIADH) and correction rates not exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment and Classification

Volume Status Assessment

• Hypovolemic: Orthostatic hypotension, dry mucous membranes, tachycardia, urine sodium <20 mEq/L
  • Common causes: GI losses, diuretics, cerebral salt wasting (CSW), adrenal insufficiency
• Euvolemic: No edema, normal vital signs, urine sodium >20-40 mEq/L
  • Common causes: SIADH, hypothyroidism, adrenal insufficiency
• Hypervolemic: Edema, ascites, elevated JVP, urine sodium <20 mEq/L
  • Common causes: Heart failure, cirrhosis, renal failure 1

Severity Classification

• Mild: 126-135 mEq/L (often asymptomatic)
• Moderate: 120-125 mEq/L (nausea, headache, confusion)
• Severe: <120 mEq/L (risk of seizures, coma, respiratory arrest) 1

Treatment Algorithm Based on Presentation

1. Severe Symptomatic Hyponatremia (Seizures, Coma, Respiratory Distress)

• Emergency treatment with 3% hypertonic saline to increase serum sodium by 4-6 mEq/L within 1-2 hours 1, 2
• Then slow correction rate to avoid osmotic demyelination syndrome
• Maximum correction rate: 8 mmol/L in 24 hours 1
• Monitor sodium levels every 2 hours initially, then every 4 hours during treatment 1

2. Euvolemic Hyponatremia (SIADH)

• First-line: Fluid restriction of 1-1.5 L/day 1
• If inadequate response:
  • Consider tolvaptan (vasopressin receptor antagonist) starting at 15 mg once daily for short-term treatment (≤30 days) 1, 3
  • Tolvaptan has been shown to effectively increase serum sodium levels in patients with euvolemic hyponatremia, with mean increases of 4.0 mEq/L by day 4 and 6.2 mEq/L by day 30 3
  • Caution: Monitor for overly rapid correction and hypernatremia 1

3. Hypovolemic Hyponatremia

• Isotonic saline (0.9% NaCl) to restore volume status 4, 2
• For CSW: Consider mineralocorticoids (fludrocortisone) to correct negative sodium balance 1

4. Hypervolemic Hyponatremia

• Treat underlying condition (heart failure, cirrhosis, renal failure)
• Fluid restriction (1-1.5 L/day) 1
• Loop diuretics to treat volume overload 5
• For cirrhotic patients:
  • Serum sodium 121-125 mmol/L: Consider stopping diuretics and observe
  • Serum sodium <120 mmol/L: Stop diuretics and consider volume expansion with colloid or saline 1

Critical Considerations and Pitfalls

Correction Rate

• Avoid increasing serum sodium by >8-10 mmol/L/day to prevent osmotic demyelination syndrome 1
• Chronic hyponatremia (>48 hours) requires slower correction than acute hyponatremia (<48 hours) 1
• Overly rapid correction can lead to central pontine myelinolysis, which can result in parkinsonism, quadriparesis, or death 2

Special Populations

• Neurosurgical patients: At high risk for complications from hyponatremia (cerebral edema, mental status changes, seizures) and from inappropriate treatment 6
• Cirrhotic patients: Avoid water restriction in patients with uncomplicated ascites 1
• Hypothyroidism: Primary treatment with thyroid hormone replacement therapy 1
• Heart failure: Optimize heart failure medications including ACE inhibitors, beta-blockers, and mineralocorticoid receptor antagonists 1

Monitoring

• Frequent assessment of volume status and electrolytes is essential during treatment 1
• Untreated hyponatremia can lead to severe complications including seizures, coma, and death, especially when serum sodium levels fall below 120 mEq/L 1, 2
• Even mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 2

By following this structured approach based on volume status, symptom severity, and underlying cause, clinicians can effectively manage hyponatremia while minimizing the risk of complications from both the condition itself and its treatment.