How to manage a patient with hypernatremia on D5 1/2 NS?

Management of Hypernatremia in a Patient on D5½NS

Immediate Action Required: Change the IV Fluid

Your patient with sodium 161 mEq/L on D5½NS (half-normal saline) is receiving the wrong fluid—this solution contains 77 mEq/L of sodium and will worsen or maintain hypernatremia rather than correct it. 1

Switch to Appropriate Hypotonic Fluids

Discontinue D5½NS immediately and switch to D5W (5% dextrose in water) as the primary rehydration fluid because it delivers no renal osmotic load and allows slow, controlled decrease in plasma osmolality. 1

Alternative hypotonic options include:

• D5W (0 mEq/L sodium): Most aggressive free water replacement, preferred for severe hypernatremia 1
• 0.18% NaCl (quarter-normal saline, ~31 mEq/L sodium): Provides more aggressive free water replacement 1
• 0.45% NaCl should NOT be used as it still contains 77 mEq/L sodium—the same as what the patient is currently receiving 1

Critical Correction Rate Guidelines

Target correction rate: 10-15 mmol/L per 24 hours maximum to avoid cerebral edema, seizures, and permanent neurological injury. 1 For chronic hypernatremia (>48 hours), slower correction is critical because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions. 1

• Acute hypernatremia (<48 hours): Can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic 1
• Chronic hypernatremia (>48 hours): Maximum 0.5 mmol/L/hour or 10-15 mmol/L per 24 hours 1

Calculate Free Water Deficit and Replacement Rate

Determine the volume of free water needed and infusion rate to achieve target correction of 10-15 mmol/L over 24 hours. 1 Monitor serum sodium every 2-4 hours initially during active correction. 1

Assess and Address Underlying Cause

Evaluate for:

• Renal concentrating defects (nephrogenic diabetes insipidus): These patients require ongoing hypotonic fluid administration to match excessive free water losses—isotonic fluids will cause or worsen hypernatremia 1
• Inadequate fluid intake: Impaired thirst mechanism or lack of access to water 2, 3
• Excessive water losses: Diarrhea, vomiting, burns, or osmotic diuresis 1, 3
• Iatrogenic causes: Review all IV fluids and medications 4

Special Considerations and Monitoring

• Never use isotonic saline (0.9% NaCl) in hypernatremia as it delivers excessive osmotic load, requiring 3 liters of urine to excrete the osmotic load from just 1 liter of isotonic fluid, which risks worsening hypernatremia 1
• Monitor for complications: Hypernatremia is associated with hyperchloremia, which may impair renal function 1
• Track ongoing losses: Match fluid composition to ongoing losses (diarrhea, polyuria) while providing adequate free water 1
• Assess volume status: Determine if hypovolemic (most common) vs. hypervolemic to guide additional management 1, 3

Common Pitfall to Avoid

The most critical error is continuing half-normal saline (D5½NS) in a hypernatremic patient—this fluid contains too much sodium (77 mEq/L) to effectively correct hypernatremia and may perpetuate the problem. 1 Switch to D5W immediately for optimal free water replacement.