Hypernatremia Management
No, fluid restriction is NOT appropriate for hypernatremia (sodium 159 mEq/L)—this is the opposite of what is needed. Hypernatremia requires free water replacement, not restriction, as it represents a deficit of water relative to sodium 1, 2.
Critical Distinction: Hypernatremia vs Hyponatremia
Your patient has hypernatremia (sodium 159 mEq/L, which is >145 mEq/L), not hyponatremia. The guidelines you may be thinking of apply to hyponatremia (low sodium), where fluid restriction is sometimes appropriate 3. These are fundamentally opposite conditions requiring opposite treatments 1.
Appropriate Treatment for Hypernatremia
Primary Treatment Approach
Administer free water to correct the water deficit, either orally (if the patient can drink and has intact thirst mechanism) or parenterally with hypotonic fluids 2. The goal is to restore normal plasma osmolality by replacing the free water deficit 1, 2.
Fluid Selection
- Electrolyte-free water is preferred (oral water or D5W intravenously) 2
- Hypotonic saline solutions (0.45% NaCl or 0.2% NaCl) can be used if some sodium replacement is also needed 2
- Oral free water guided by thirst is ideal, though parenteral replacement is usually necessary in critically ill patients 2
Calculate Free Water Deficit
Use standard formulas to estimate the free water deficit and guide initial fluid replacement 2:
- Free water deficit = 0.6 × body weight (kg) × [(current Na/140) - 1]
- This provides a starting point for replacement therapy 2
Correction Rate
- Rate depends on acuity of development 2
- For chronic hypernatremia (>48 hours): correct slowly to avoid cerebral edema—aim for sodium reduction of 10-15 mmol/L per 24 hours 2
- Monitor plasma sodium frequently (every 2-4 hours initially) to ensure appropriate response and adjust fluid replacement rate 2
- Rapid correction of chronic hypernatremia risks cerebral edema from osmotic water shift into brain cells 2
Address Underlying Causes
- Identify and correct the source of water loss (renal vs extrarenal) 2
- Assess for impaired thirst mechanism or restricted water access 2
- Review medications and IV fluids that may contain excessive sodium 2
Why Fluid Restriction Would Be Harmful
Fluid restriction in hypernatremia would worsen the water deficit and further increase sodium concentration, potentially leading to severe neurological complications including altered mental status, seizures, intracranial hemorrhage from vascular rupture, or death 2. The pathophysiology involves osmotic movement of water out of cells, causing intracellular dehydration 2.
Common Pitfall to Avoid
Do not confuse hypernatremia management with hyponatremia management—they require opposite approaches. Hypernatremia needs water administration; hyponatremia often needs fluid restriction 1, 4, 5.