What fluid is recommended to correct hypernatremia in a patient?

Fluid Selection for Hypernatremia Correction

For hypernatremic dehydration, use 5% dextrose (D5W) as the primary fluid because it delivers no renal osmotic load and allows controlled reduction of plasma osmolality—avoid isotonic saline (0.9% NaCl) as it will worsen hypernatremia. 1

Why Isotonic Saline is Contraindicated

Salt-containing solutions, especially 0.9% NaCl, must be avoided in hypernatremia because their tonicity (300 mOsm/kg H₂O) exceeds typical urine osmolality in conditions like nephrogenic diabetes insipidus (100 mOsm/kg H₂O) by approximately 3-fold 1. This means around 3 liters of urine are needed to excrete the renal osmotic load from just 1 liter of isotonic fluid, risking serious worsening of hypernatremia 1. In patients with renal concentrating defects, isotonic fluids will exacerbate hypernatremia rather than correct it 2.

Primary Fluid Recommendations

First-Line: 5% Dextrose (D5W)

• D5W is the preferred choice because it provides pure free water replacement without any renal osmotic load 1, 2
• Application at physiological maintenance rates results in slow, controlled decrease in plasma osmolality 1
• For adults: 25-30 mL/kg/24 hours 1
• For children: 100 mL/kg/24h for first 10 kg, 50 mL/kg/24h for 10-20 kg, 20 mL/kg/24h for remaining weight 1

Alternative Hypotonic Solutions

When D5W alone is insufficient or additional electrolytes are needed:

• 0.45% NaCl (half-normal saline): Contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia 2
• 0.18% NaCl (quarter-normal saline): Contains ~31 mEq/L sodium, providing more aggressive free water replacement for severe cases 2

Correction Rate Guidelines

The maximum correction rate should not exceed 10-15 mmol/L per 24 hours for chronic hypernatremia (>48 hours duration) to prevent cerebral edema 2. Slower correction is critical because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions, and rapid correction can cause cerebral edema, seizures, and permanent neurological injury 2.

However, recent evidence suggests faster correction may be safe in specific circumstances:

• Acute hypernatremia (<48 hours) can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic 2
• A 2025 meta-analysis found faster correction (>0.5 mmol/L/h) within the first 24 hours of diagnosis was associated with lower mortality (OR 0.48) without major neurological complications when rates stayed <1 mmol/L/h 3
• A 2019 study of critically ill patients found no increased mortality or cerebral edema with rapid correction rates >0.5 mmol/L/hour 4

Despite this emerging evidence, guidelines still recommend the conservative 10-15 mmol/L per 24 hours approach, particularly for chronic hypernatremia 2.

Special Clinical Scenarios

Nephrogenic Diabetes Insipidus

• Requires ongoing hypotonic fluid administration to match excessive free water losses 1, 2
• Never use isotonic saline as it will cause or worsen hypernatremia in these patients 2
• Continue hypotonic fluids even after initial correction to prevent recurrence 1

Severe Burns or Voluminous Diarrhea

• Hypotonic fluids required to match ongoing free water losses 2
• Fluid composition should match losses while providing adequate free water 2

Combined Approach for Severe Cases

For severe hypernatremia with altered mental status, combine IV hypotonic fluids with free water via nasogastric tube, targeting 10-15 mmol/L correction per 24 hours 2.

Critical Monitoring Requirements

• Check serum sodium every 2-4 hours initially during active correction, then every 6-12 hours 2
• Monitor daily weight, vital signs, and fluid balance meticulously 2
• Track urine output, specific gravity, and osmolality 2
• Assess for signs of cerebral edema: altered mental status, seizures, neurological deterioration 2

Common Pitfalls to Avoid

• Using isotonic saline as initial therapy—this is the most critical error and will worsen hypernatremia, particularly in patients with impaired renal concentrating ability 1, 2
• Correcting chronic hypernatremia too rapidly (>10-15 mmol/L per 24 hours), which can cause cerebral edema 2
• Inadequate monitoring during correction, risking overcorrection or undercorrection 2
• Failing to provide ongoing free water replacement in conditions with persistent losses 1