Osmotic Demyelination Syndrome (Central Pontine Myelinolysis)
The primary complication of rapid correction of severe hyponatremia in children is osmotic demyelination syndrome (ODS), also known as central pontine myelinolysis, which occurs when sodium correction exceeds 8 mmol/L in 24 hours. 1, 2
Critical Correction Rate Limits
The absolute maximum sodium correction rate is 8 mmol/L per 24 hours to prevent osmotic demyelination syndrome. 1, 2, 3 This limit applies regardless of symptom severity or clinical urgency. 2
For pediatric patients with severe hyponatremia:
- Initial correction target: 4-6 mmol/L over the first 6 hours if symptomatic 3
- Total 24-hour limit: Never exceed 8 mmol/L 1, 2, 3
- Chronic or unknown duration hyponatremia: Limit to 6-8 mmol/L per 24 hours 3
High-Risk Populations Requiring Even Slower Correction
Children with the following conditions require more cautious correction at 4-6 mmol/L per day maximum: 1, 2
- Advanced liver disease 1, 2
- Malnutrition 1, 2
- Alcoholism (less common in pediatrics but relevant for adolescents) 1, 2
- Hypokalemia 4
- Hypophosphatemia 4
Notably, 5 of 7 patients who developed osmotic demyelination syndrome did so despite correction rates ≤8 mmol/L per 24 hours, and 6 of 7 had identifiable risk factors. 4 This underscores that the 8 mmol/L limit is a ceiling, not a target, and high-risk patients need even slower correction.
Clinical Manifestations of Osmotic Demyelination Syndrome
Symptoms typically appear 2-7 days after rapid correction and include: 2
- Dysarthria (difficulty speaking) 2
- Dysphagia (difficulty swallowing) 2
- Oculomotor dysfunction (eye movement abnormalities) 2
- Quadriparesis (weakness in all four limbs) 2
- Altered mental status 2
- Seizures 1
Monitoring Requirements During Correction
Frequency of sodium monitoring must be aggressive to prevent overcorrection: 3
- Severe symptoms or active correction: Every 2 hours 3
- Moderate symptoms: Every 4 hours 3
- Mild/asymptomatic: Every 6-12 hours initially, then daily 3
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours, immediate intervention is required: 2
- Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 2
- Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 2
- Goal: Relower sodium to bring total 24-hour correction to no more than 8 mmol/L from starting point 2
Special Considerations in Pediatric Acute Kidney Injury
For children with severe hyponatremia and AKI requiring renal replacement therapy, continuous venovenous hemofiltration (CVVH) with customized low-sodium replacement fluid allows controlled sodium correction. 5, 6 Standard dialysis solutions will cause dangerously rapid correction. 6
Replacement fluids must be modified daily to create hypotonic solutions with successively higher sodium concentrations, allowing gradual correction over a week while managing AKI complications. 5
Common Pitfalls to Avoid
- Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this is the single most important principle 2
- Inadequate monitoring during active correction leads to unrecognized overcorrection 2
- Using isotonic saline in hypervolemic hyponatremia without life-threatening symptoms can paradoxically worsen hyponatremia 2
- Failing to identify high-risk patients who need even slower correction (4-6 mmol/L per day) 1, 2
Mortality Considerations
While limiting correction rates prevents osmotic demyelination syndrome, recent evidence suggests correction rates <6 mmol/L per 24 hours may be associated with higher in-hospital mortality. 4 This creates a therapeutic window: aim for 6-8 mmol/L per 24 hours in average-risk patients, but never exceed 8 mmol/L, and use 4-6 mmol/L per day in high-risk patients. 2, 4
The risk of osmotic demyelination syndrome in properly managed cases is estimated at 0.5-1.5%, but this risk increases dramatically with overcorrection or in patients with multiple risk factors. 2, 4