What should be done to correct sodium levels in patients with Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) due to hyponatremia?

Management of Sodium Levels in SIADH

For patients with SIADH, tolvaptan should be initiated at 15 mg once daily and titrated up to 30 mg after 24 hours as needed, with treatment limited to 30 days to minimize liver injury risk. 1, 2

Assessment and Classification

• Determine severity of hyponatremia:

  • Mild (130-135 mmol/L)
  • Moderate (125-129 mmol/L)
  • Severe (<125 mmol/L)

• Assess for symptoms:

  • Severe symptoms: seizures, altered consciousness, coma
  • Moderate symptoms: nausea, confusion, headache
  • Mild/asymptomatic: minimal or no symptoms

Treatment Algorithm for SIADH

First-line Treatment Options

1. Fluid Restriction:

   • Initial restriction of 500-1000 mL/day 3
   • Efficacy is modest - increases sodium by approximately 3-4 mmol/L after 3 days 4
   • Only about 61% of patients reach sodium ≥130 mmol/L after 3 days of restriction 4

2. For Symptomatic Severe Hyponatremia:

   • 3% hypertonic saline as 100-150 mL bolus or continuous infusion 3
   • Critical safety point: Correction rate should not exceed 8 mEq/L in 24 hours to prevent osmotic demyelination syndrome 1
   • Target correction rate of 4-6 mEq/L per day is safer 1

Second-line Treatment (When Fluid Restriction Fails)

Tolvaptan (Vasopressin Receptor Antagonist):

• Starting dose: 15 mg once daily 1, 2
• Can be increased to 30 mg after 24 hours, and maximum 60 mg daily as needed 2
• Important: Must be initiated in hospital setting with close monitoring of serum sodium 2
• Measure sodium at 0,6,24, and 48 hours after starting treatment 5
• Limit treatment duration to 30 days to minimize risk of liver injury 1, 2
• Avoid fluid restriction during first 24 hours of therapy 2

Alternative Options

1. Urea:

   • Effective and safe second-line treatment 1, 3
   • Advantage: Does not increase ascites or edema, lower risk of liver injury compared to vaptans 1

2. Demeclocycline:

   • Consider when other options have failed 5

Important Monitoring and Safety Considerations

1. Prevention of Overcorrection:

   • Monitor serum sodium frequently, especially in first 24-48 hours
   • If correction exceeds 8 mEq/L in 24 hours, consider administering desmopressin to slow correction 1
   • High-risk patients for osmotic demyelination syndrome include those with alcoholism, malnutrition, liver disease 1

2. Contraindications to Tolvaptan:

   • Liver disease (risk of gastrointestinal bleeding) 1, 2
   • Inability to sense or respond to thirst 2
   • Hypovolemic hyponatremia 2
   • Patients taking strong CYP3A inhibitors 2
   • Anuria 2

3. After Treatment Discontinuation:

   • Resume fluid restriction after stopping tolvaptan 2
   • Monitor for hyponatremic relapse, especially if treatment stopped for >5-6 days 5

Special Considerations

• For chronic asymptomatic hyponatremia: Fluid restriction may be sufficient 6
• For acute symptomatic hyponatremia: More rapid correction with hypertonic saline is warranted 6
• In elderly patients: Particularly susceptible to hyponatremia symptoms including cognitive impairment and falls 1

Remember that the goal is not necessarily normalization of sodium levels but rather achieving mild hyponatremia (approximately 125-130 mmol/L) to relieve symptoms while avoiding complications of overcorrection 6, 3.