Hyponatremia Correction with 3% Normal Saline: Dose Calculation
For severe symptomatic hyponatremia, administer 3% hypertonic saline as 100-150 mL intravenous boluses over 10 minutes, which can be repeated up to three times at 10-minute intervals, with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve—never exceeding 8 mmol/L total correction in 24 hours. 1, 2, 3
Calculating Sodium Deficit
The sodium deficit formula provides an estimate of the amount of sodium needed: 1
Sodium deficit (mEq) = Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
- For severe symptoms: target a 6 mEq/L increase over the first 6 hours 1, 2
- After achieving 6 mEq/L correction, limit additional correction to only 2 mEq/L in the following 18 hours 2
- This ensures the total 24-hour correction does not exceed 8 mmol/L 1, 2, 3
Bolus vs Continuous Infusion Approach
The rapid intermittent bolus administration of 3% saline is preferred over continuous infusion for symptomatic hyponatremia. 4
Bolus Dosing Protocol:
- 100-150 mL bolus over 10 minutes 1, 3
- Can repeat up to 3 times at 10-minute intervals 1
- Recent evidence suggests 250 mL boluses are more effective than 100 mL (52% vs 32% achieving ≥5 mmol/L rise within 4 hours) without increasing overcorrection risk 5
Alternative Continuous Infusion Calculation:
If continuous infusion is used, the initial rate can be estimated: 6
Infusion rate (mL/kg/hour) = Body weight (kg) × Desired rate of sodium increase (mmol/L/hour) 6
- For severe symptoms: aim for 1-2 mmol/L per hour initially 6
- Once symptoms resolve, slow the rate dramatically 2
Critical Monitoring Requirements
Severe Symptoms (seizures, coma, altered mental status):
- Check serum sodium every 2 hours during initial correction 1, 2
- Continue until severe symptoms resolve 1, 2
After Symptom Resolution:
Discontinuation Criteria
Stop 3% saline when: 2
- Severe symptoms have resolved 2
- 6 mmol/L correction achieved in first 6 hours 2
- Total correction approaches 8 mmol/L in 24 hours 2
After discontinuation: 2
- Implement fluid restriction to 1 L/day 2
- Continue monitoring sodium every 4 hours 2
- Treat underlying cause (SIADH, cerebral salt wasting, etc.) 1, 2
High-Risk Populations Requiring Slower Correction
Limit correction to 4-6 mmol/L per day (maximum 8 mmol/L in 24 hours) in: 1, 3
- Advanced liver disease 1, 3
- Alcoholism 1, 3
- Malnutrition 1, 3
- Prior encephalopathy 1
- Chronic hyponatremia (>48 hours duration) 1, 2
Common Pitfalls to Avoid
Never exceed 8 mmol/L correction in 24 hours—this causes osmotic demyelination syndrome, a devastating neurological complication that can result in parkinsonism, quadriparesis, or death. 1, 3, 4
Do not use continuous infusion without frequent monitoring—bolus therapy allows better control and reduces overcorrection risk. 4
Rapid correction (>1 mmol/L/hour) should only be used for severely symptomatic acute hyponatremia (<48 hours)—chronic hyponatremia requires slower correction after initial symptom control. 2, 7
If overcorrection occurs, immediately discontinue hypertonic saline, switch to D5W (5% dextrose in water), and consider desmopressin to reverse the rapid rise. 1
Special Considerations
For neurosurgical patients with subarachnoid hemorrhage at risk of vasospasm, treatment may continue even for sodium levels 131-135 mmol/L, and fluid restriction should never be used. 2
The 3% saline concentration contains 513 mEq/L of sodium with an osmolarity of approximately 1026 mOsm/L, making it highly effective for rapid correction. 1