Treatment of Severe Symptomatic Hyponatremia with Presyncope (Sodium 115 mmol/L)
Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over the first 6 hours or until presyncope resolves, but never exceed 8 mmol/L total correction in 24 hours. 1
Immediate Emergency Management
Presyncope at a sodium of 115 mmol/L represents severe symptomatic hyponatremia requiring urgent intervention—this is a medical emergency that demands hypertonic saline, not fluid restriction. 1, 2
Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, which can be repeated up to three times at 10-minute intervals until symptoms improve. 1 The initial goal is to correct sodium by 6 mmol/L over 6 hours or until severe symptoms (presyncope) resolve. 1, 2
Why This Approach
- Presyncope indicates cerebral dysfunction from severe hyponatremia and requires rapid initial correction to prevent progression to seizures, coma, or death 1, 3
- The 6 mmol/L target over 6 hours reverses hyponatremic encephalopathy while staying within safe limits 1, 2
- After achieving 6 mmol/L correction in the first 6 hours, you have only 2 mmol/L remaining allowance for the next 18 hours to stay under the 8 mmol/L/24-hour ceiling 2
Critical Safety Parameters
The absolute maximum correction is 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome (ODS). 1, 2, 4 Exceeding this limit risks devastating neurological complications including dysarthria, dysphagia, quadriparesis, and locked-in syndrome appearing 2-7 days after overcorrection. 1, 4
Monitoring Protocol
- Check serum sodium every 2 hours during the initial correction phase until symptoms resolve 1, 2
- Switch to every 4-hour monitoring after severe symptoms abate 1, 2
- Track neurological status continuously using Glasgow Coma Scale, pupillary response, and motor function 4
Transition After Symptom Resolution
Discontinue 3% saline when presyncope resolves, then transition to management based on volume status and underlying etiology. 2
Post-Acute Management
- Implement fluid restriction to 1 L/day if SIADH is confirmed (euvolemic hyponatremia) 1, 2
- Continue volume and sodium replacement if cerebral salt wasting is diagnosed (hypovolemic with high urine sodium despite volume depletion) 1
- Never use fluid restriction in cerebral salt wasting—this worsens outcomes and can precipitate cerebral ischemia 1
Target Sodium Level
Continue treatment until sodium reaches 125-130 mmol/L, not normal range. 1, 5 The therapeutic goal is mild hyponatremia, not normonatremia, as acute correction to normal values increases ODS risk. 5
High-Risk Considerations
If this patient has advanced liver disease, chronic alcoholism, malnutrition, or prior encephalopathy, use even more conservative correction rates of 4-6 mmol/L per day with an absolute maximum of 8 mmol/L in 24 hours. 1, 4 These populations have a 0.5-1.5% risk of ODS even with careful correction. 1
Common Pitfalls to Avoid
- Never use fluid restriction as initial treatment for presyncope with severe hyponatremia—this is a medical emergency requiring hypertonic saline 1, 2
- Never exceed 8 mmol/L correction in 24 hours regardless of symptom improvement—overcorrection causes ODS 1, 2, 4
- Never aim for normonatremia acutely—target 125-130 mmol/L only 5
- Never apply rapid correction (>1 mmol/L/hour) beyond the initial 6-hour window unless hyponatremia is confirmed acute (<48 hours onset) 2
Management of Overcorrection
If sodium rises excessively (>8 mmol/L in 24 hours), immediately stop all saline and switch to D5W (5% dextrose in water) to prevent further sodium increase. 1, 4 Consider desmopressin administration to slow or reverse the rapid rise and bring total 24-hour correction back to ≤8 mmol/L from baseline. 1, 4
Assessment for ODS
If the patient remains unconscious after appropriate correction or develops new neurological deficits 2-7 days post-treatment, obtain urgent brain MRI to evaluate for pontine and extrapontine myelinolysis, though MRI changes may lag clinical symptoms by several days. 4