Initial Fluid Management for Severe Hyponatremia
For severe symptomatic hyponatremia (seizures, altered mental status, coma), immediately administer 3% hypertonic saline as 100-150 mL IV boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms resolve, with a target correction of 6 mmol/L over 6 hours—never exceeding 8 mmol/L total correction in 24 hours. 1, 2, 3
Algorithmic Approach Based on Clinical Presentation
Severe Symptomatic Hyponatremia (Medical Emergency)
Symptoms: Seizures, coma, confusion, altered consciousness, respiratory distress 4
Immediate Action:
- 3% hypertonic saline (513 mEq/L sodium) as bolus therapy 1, 2
- Administer 100-150 mL IV bolus over 10 minutes 3
- Can repeat up to 3 times at 10-minute intervals 3
- Target: Increase sodium by 6 mmol/L over first 6 hours OR until symptoms resolve 1
- Critical limit: Maximum 8 mmol/L correction in 24 hours 1, 2, 3
Monitoring:
- Check serum sodium every 2 hours during initial correction 1
- Switch to every 4 hours after symptom resolution 1
Hypovolemic Hyponatremia (Volume Depleted)
Clinical signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
Diagnostic clue: Urine sodium <30 mmol/L predicts 71-100% response to saline 1
Fluid choice:
- 0.9% normal saline (isotonic) for volume repletion 1, 5
- Initial rate: 15-20 mL/kg/hour, then 4-14 mL/kg/hour based on response 1
- Discontinue diuretics immediately 1
- Still respect 8 mmol/L/24-hour correction limit 1
Euvolemic Hyponatremia (SIADH)
Clinical presentation: No edema, normal blood pressure, normal skin turgor, moist mucous membranes 1
Diagnostic criteria: Urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg 1
Management hierarchy:
- Severe symptoms: 3% hypertonic saline as above 1
- Mild/asymptomatic: Fluid restriction to 1 L/day 1, 3
- If no response: Add oral sodium chloride 100 mEq (936 mg) three times daily 1, 6
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Clinical signs: Peripheral edema, ascites, jugular venous distention 1
Fluid management:
- Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 5
- Avoid hypertonic saline unless life-threatening symptoms present 1
- Consider albumin infusion in cirrhotic patients 1
- Temporarily discontinue diuretics if sodium <125 mmol/L 1
Critical Safety Considerations
Osmotic Demyelination Syndrome Prevention
Never exceed these correction rates: 1, 2, 7
- Standard patients: 8 mmol/L per 24 hours maximum
- High-risk patients: 4-6 mmol/L per 24 hours maximum
High-risk populations requiring slower correction: 1
- Advanced liver disease
- Alcoholism
- Malnutrition
- Prior encephalopathy
- Severe hyponatremia (<120 mmol/L)
If Overcorrection Occurs
Immediate intervention: 1
- Discontinue current fluids
- Switch to D5W (5% dextrose in water)
- Consider desmopressin to slow/reverse sodium rise
- Goal: Bring total 24-hour correction to ≤8 mmol/L from baseline
Common Pitfalls to Avoid
- Never use fluid restriction for severe symptomatic hyponatremia—this is a medical emergency requiring hypertonic saline 1
- Never use normal saline for SIADH—it can worsen hyponatremia through dilution 1
- Never use hypertonic saline in hypervolemic states without life-threatening symptoms—it worsens fluid overload 1
- Never ignore mild hyponatremia (130-135 mmol/L)—it increases fall risk 21% vs 5% and mortality 60-fold 1, 4, 2
- Never use fluid restriction in cerebral salt wasting—it worsens outcomes 1
Sample Order Sets
For Severe Symptomatic Hyponatremia:
- 3% NaCl 150 mL IV bolus over 10 minutes now
- May repeat x2 at 10-minute intervals if symptoms persist
- Check serum sodium q2h x 12 hours, then q4h
- ICU admission for continuous monitoring 1
For Hypovolemic Hyponatremia:
- 0.9% NaCl 1000 mL IV at 100-150 mL/hour
- Check serum sodium q4-6h
- Discontinue diuretics
- Target correction: 6-8 mmol/L per 24 hours 1
For SIADH (Mild Symptoms):