Initial Approach to Managing Hyponatremia
The initial approach to managing hyponatremia should begin with determining the patient's volume status (hypovolemic, euvolemic, or hypervolemic) and assessing symptom severity, followed by appropriate targeted therapy based on this classification. 1
Diagnosis and Assessment
Essential Laboratory Tests
- Serum sodium, osmolality
- Urine osmolality and sodium concentration
- Thyroid function tests and cortisol levels
- Fractional excretion of urate (improves diagnostic accuracy for SIADH to 95%) 1
Volume Status Classification
| Volume Status | Urine Osmolality | Urine Sodium | Suggested Diagnosis |
|---|---|---|---|
| Hypovolemic | Variable | <20 mEq/L | Volume depletion |
| Euvolemic | >500 mOsm/kg | >20-40 mEq/L | SIADH |
| Hypervolemic | Elevated | <20 mEq/L | Heart failure, cirrhosis |
Severity Classification
- Mild: 130-134 mmol/L
- Moderate: 125-129 mmol/L
- Severe: <125 mmol/L 2
Treatment Algorithm Based on Volume Status and Symptom Severity
1. Severe Symptomatic Hyponatremia (Any Volume Status)
- Immediate treatment with 3% hypertonic saline as 100-150 mL bolus or continuous infusion 1
- Target correction: 4-6 mEq/L in first 6 hours or until symptoms improve
- Maximum correction: 8 mEq/L in 24 hours, not exceeding 12 mEq/L in 48 hours
- Monitor serum sodium every 2-4 hours during active correction 1, 3
2. Hypovolemic Hyponatremia
- Isotonic (0.9%) saline infusion for plasma volume expansion 1
- Discontinue diuretics or other causative medications
- Reassess sodium levels after volume status correction
3. Euvolemic Hyponatremia (e.g., SIADH)
- Fluid restriction (1-1.5 L/day) 1
- High solute intake (salt and protein)
- Consider oral sodium chloride tablets if no response to fluid restriction
- For refractory cases: consider tolvaptan (starting at 15 mg once daily) or oral urea (30-60 g/day) 1, 4
4. Hypervolemic Hyponatremia (e.g., heart failure, cirrhosis)
- Fluid restriction to 1,000 mL/day for moderate hyponatremia (120-125 mEq/L) 1
- More severe fluid restriction with albumin infusion for severe hyponatremia (<120 mEq/L)
- Treat underlying condition (heart failure, cirrhosis)
- Consider loop diuretics for volume management
Important Considerations and Pitfalls
Correction Rate
- Maximum correction rate for chronic hyponatremia: 8 mEq/L in 24 hours 1
- High-risk patients (alcoholism, malnutrition, liver disease): lower correction rate of 4-6 mEq/L per day
- Too rapid correction can cause osmotic demyelination syndrome (ODS), resulting in dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma, and death 4
Monitoring
- Monitor serum sodium every 4-6 hours during active correction
- Every 2 hours in severe cases
- If correction exceeds 8 mEq/L in 24 hours, consider administering hypotonic fluids or desmopressin to prevent ODS 1
Medication Considerations
- Discontinue medications that may cause or worsen hyponatremia (SSRIs, carbamazepine, thiazide diuretics, NSAIDs) 1
- Tolvaptan should be initiated only in a hospital setting where serum sodium can be closely monitored 4
- Tolvaptan is contraindicated in hypovolemic hyponatremia and should not be used for more than 30 days due to risk of liver injury 4
Special Populations
- Patients with cirrhosis: increased risk of gastrointestinal bleeding with tolvaptan (10% vs 2% with placebo) 4
- Patients with severe malnutrition, alcoholism, or advanced liver disease: use slower correction rates 4
Chronic Management
- For chronic hyponatremia, treat the underlying cause
- Even mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 2
- Regular monitoring of electrolytes during recovery is necessary to prevent complications 1
Remember that early detection and appropriate management of hyponatremia can prevent progression to severe hyponatremia, which can lead to significant morbidity and mortality.