Management of Hyponatraemia in an Infant with SIADH
For an infant with SIADH-related hyponatraemia, fluid restriction is the cornerstone of initial management, with the specific approach determined by symptom severity and serum sodium level. 1, 2
Initial Assessment
Determine the severity of hyponatraemia and presence of symptoms:
- Severe symptomatic hyponatraemia (seizures, altered mental status, coma) requires immediate ICU admission with 3% hypertonic saline 1, 2
- Asymptomatic or mildly symptomatic hyponatraemia should be managed with fluid restriction as first-line therapy 1, 2, 3
- Serum sodium <131 mmol/L warrants full diagnostic workup and treatment 1
Management Based on Symptom Severity
For Severe Symptomatic Hyponatraemia
Administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 2
- Transfer to ICU for close monitoring 2
- Monitor serum sodium every 2 hours initially 1, 2
- Never exceed total correction of 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2, 4
- After symptom resolution, transition to fluid restriction 1
For Asymptomatic or Mildly Symptomatic Hyponatraemia
Implement strict fluid restriction to 1 L/day (or age-appropriate equivalent for infants). 1, 2, 3
- This is the primary treatment for SIADH 1, 2
- Adjust fluid restriction based on serum sodium response 1
- Initial fluid restriction should be 500 ml/day in some protocols, adjusted according to sodium levels 5
- Monitor serum sodium every 4-6 hours during initial correction 1
Pediatric-Specific Considerations
In infants and neonates, fluid restriction remains the safest initial approach, even with severe hyponatraemia (sodium as low as 115 mmol/L), provided the infant is not acutely symptomatic. 6
- Aggressive sodium supplementation alone without fluid restriction is often ineffective 6
- Fluid restriction should be initiated promptly when SIADH is diagnosed 6, 3
- Hypertonic saline should be reserved only for severely symptomatic patients 3
Second-Line Treatment Options
If fluid restriction fails to correct hyponatraemia after 24-48 hours:
Oral urea is considered a very effective and safe second-line treatment for chronic SIADH in infants. 5, 7
- Urea induces osmotic water diuresis 7
- Long-term oral urea treatment has been shown to be successful and well-tolerated in infants with chronic SIADH 7
- Allows easier water and sodium control and may permit decreased fluid restriction 7
- Dosing should be individualized based on response 7
Critical Safety Parameters
The correction rate must not exceed 8 mmol/L in 24 hours (or 0.5 mmol/L per hour) to prevent osmotic demyelination syndrome. 1, 2, 4, 8
- In infants with severe malnutrition or other risk factors, even slower correction rates (4-6 mmol/L per day) may be advisable 1, 4
- Target a mildly hyponatraemic range (125-130 mmol/L) initially, rather than complete normalization 8
- Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, lethargy, seizures) typically occurring 2-7 days after rapid correction 1
Common Pitfalls to Avoid
- Do not use aggressive sodium supplementation without fluid restriction - this approach is ineffective in SIADH and may worsen hyponatraemia 6
- Do not correct chronic hyponatraemia rapidly - rates >12 mEq/L per 24 hours can cause osmotic demyelination 4, 8
- Do not ignore mild hyponatraemia (130-135 mmol/L) - even mild hyponatraemia increases morbidity 1
- Do not use tolvaptan in infants - it should be initiated only in a hospital setting and is not typically used in pediatric populations 4
Monitoring Protocol
- Check serum sodium every 2 hours during acute correction of symptomatic hyponatraemia 1, 2
- Check serum sodium every 4-6 hours for asymptomatic patients on fluid restriction 1
- Assess volume status and urine output regularly 1
- Calculate sodium deficit if needed: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1