Correction of Hypernatremia in Subarachnoid Hemorrhage
In SAH patients with hypernatremia, correct sodium slowly using hypotonic fluids (0.45% NaCl or D5W) at a rate not exceeding 10-12 mmol/L per 24 hours, while maintaining euvolemia to prevent cerebral ischemia and vasospasm.
Understanding the Unique Challenge in SAH
Hypernatremia in SAH presents a paradoxical management challenge. While mild hypernatremia (145-155 mmol/L) is sometimes deliberately targeted for cerebral edema control 1, excessive hypernatremia (>150 mmol/L) is independently associated with poor outcomes and increased mortality 2. The key distinction is that SAH patients require careful volume management—they need adequate intravascular volume to prevent vasospasm while simultaneously correcting elevated sodium 3.
Correction Strategy
Fluid Selection
- Use hypotonic fluids such as 0.45% NaCl (half-normal saline) or D5W (5% dextrose in water) as the primary correction fluid 1, 4
- Avoid isotonic saline (0.9% NaCl) as it will worsen hypernatremia in patients unable to excrete free water appropriately 1
- D5W provides pure free water replacement without additional sodium load 1
Correction Rate
- Maximum correction: 10-12 mmol/L per 24 hours for standard-risk patients 5
- Target rate: 0.5 mmol/L per hour or less to minimize risk of cerebral edema 5, 4
- Extend correction over 48-72 hours for severe hypernatremia to prevent complications 4
- Evidence from critically ill patients shows that rapid correction (>0.5 mmol/L per hour) was not associated with increased mortality or cerebral edema, but slower correction remains the safer approach 5
Critical SAH-Specific Considerations
Volume Status Management
- Maintain euvolemia or mild hypervolemia throughout correction to prevent vasospasm 3, 6
- Never restrict fluids in SAH patients, even when correcting hypernatremia—this increases vasospasm risk 3
- Monitor for rapid natriuresis, which can precede symptomatic vasospasm 6
Monitoring Protocol
- Check serum sodium every 4-6 hours during active correction 1
- Assess volume status continuously using CVP, fluid balance, and clinical examination 3
- Watch for neurological deterioration that may indicate cerebral edema from overly rapid correction 7, 4
- Monitor for signs of vasospasm (new focal deficits, decreased consciousness) 2, 6
Common Pitfalls to Avoid
- Using isotonic saline for hypernatremia correction will fail to lower sodium and may worsen the problem 1
- Correcting too rapidly (>12 mmol/L per 24 hours) risks cerebral edema, though this appears less common in adults than previously thought 5, 4
- Fluid restriction to correct hypernatremia is contraindicated in SAH due to vasospasm risk 3
- Ignoring mild hypernatremia (150-155 mmol/L) when it develops iatrogenically—this range may be acceptable for cerebral edema management but requires close monitoring 1, 2
Special Populations
Patients with Cerebral Salt Wasting
- If CSW is present (common in SAH), aggressive sodium and volume replacement with isotonic or hypertonic saline is appropriate for hyponatremia 3, 2
- CSW occurred in 3.5% of SAH patients in one series, more commonly than SIADH (0.3%) 2
- Fludrocortisone 0.1-0.2 mg daily may be added for severe CSW 3
High-Risk Features
- Severe hypernatremia (>155 mmol/L) was present in 11.9% of SAH patients and associated with significantly higher mortality 2
- Hypernatremia was an independent risk factor for poor outcome (OR for mortality and morbidity) 2
- Children may be at higher risk for cerebral edema with rapid sodium shifts 7
Practical Algorithm
- Confirm hypernatremia (Na >150 mmol/L) and assess volume status
- Calculate free water deficit but replace over 48-72 hours, not acutely 4
- Start 0.45% NaCl or D5W at a rate targeting 0.5 mmol/L per hour reduction 5, 4
- Maintain adequate volume with additional isotonic fluids if needed to prevent hypovolemia 3
- Check sodium every 4-6 hours and adjust infusion rate to stay within safe limits 1
- Continue monitoring for 48-72 hours until sodium normalizes 4