What is the treatment for hypernatremia?

Hypernatremia Treatment

For hypernatremia, restore plasma tonicity by replacing free water deficits with hypotonic fluids (5% dextrose or 0.45% NaCl), correcting no faster than 0.4 mmol/L/hour or 10 mmol/L per 24 hours to prevent cerebral edema, while simultaneously addressing the underlying cause. 1, 2

Initial Assessment and Classification

Before initiating treatment, determine the acuity, severity, and volume status of hypernatremia:

• Acute hypernatremia (<24-48 hours) can be corrected more rapidly without risk of cerebral edema 2, 3
• Chronic hypernatremia (>48 hours) requires slow correction at no more than 0.4 mmol/L/hour or 8-10 mmol/L per day to prevent osmotic demyelination syndrome 2, 3
• Severity classification: Mild (145-150 mmol/L), moderate (150-160 mmol/L), severe (>160 mmol/L) 2
• Volume status: Assess for hypovolemic (dehydration, renal/extrarenal losses), euvolemic (diabetes insipidus), or hypervolemic (excessive sodium intake) hypernatremia 1, 2

Fluid Selection and Replacement Strategy

The cornerstone of treatment is free water replacement, with fluid choice depending on severity and route of administration:

Preferred Hypotonic Fluids

• 5% dextrose (D5W) is the optimal choice as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 4
• 0.45% NaCl (half-normal saline) containing 77 mEq/L sodium can be used for moderate hypernatremia, providing both free water and some sodium replacement 4, 1
• 0.18% NaCl (quarter-normal saline) with approximately 31 mEq/L sodium provides greater free water content for more aggressive replacement 4
• Oral free water guided by thirst is ideal when the patient can tolerate oral intake 5

Critical Contraindication

• Never use isotonic saline (0.9% NaCl) in hypernatremic patients, 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 4

Correction Rate Guidelines

The rate of correction is the most critical safety consideration:

For Chronic Hypernatremia (>48 hours)

• Maximum correction rate: 0.4 mmol/L/hour or 8-10 mmol/L per 24 hours 2, 3
• Slower correction prevents cerebral edema from rapid osmotic shifts 2, 3
• Close laboratory monitoring every 2-4 hours during active correction is essential 3, 5

For Acute Hypernatremia (<24 hours)

• Rapid correction improves prognosis by preventing cellular dehydration effects 2
• Hemodialysis is an effective option to rapidly normalize sodium levels in severe acute cases 3
• Even in acute cases, frequent sodium monitoring is mandatory 5

Initial Fluid Administration Rates

Calculate maintenance fluid requirements based on patient weight:

• Children: 100 mL/kg/24 hours for first 10 kg, 50 mL/kg/24 hours for 10-20 kg, 20 mL/kg/24 hours for remaining weight 4
• Adults: 25-30 mL/kg/24 hours 4
• Use calculators to estimate free water deficit and guide replacement to avoid overly rapid correction 1, 5

Treatment Based on Underlying Etiology

Hypovolemic Hypernatremia (Dehydration)

• Replace free water losses with hypotonic fluids 1, 2
• Address ongoing losses from diarrhea, vomiting, or excessive sweating 4
• Restore intravascular volume while correcting sodium concentration 2

Euvolemic Hypernatremia (Diabetes Insipidus)

• Central (neurogenic) diabetes insipidus: Administer desmopressin (Minirin) to reduce renal free water losses 3
• Nephrogenic diabetes insipidus: Requires ongoing hypotonic fluid administration to match excessive free water losses 4
• Identify and treat underlying causes (medications like lithium, hypokalemia, traumatic/vascular/infectious CNS events) 2

Hypervolemic Hypernatremia (Sodium Excess)

• Often iatrogenic from hypertonic NaCl or NaHCO3 solutions 2
• May indicate primary hyperaldosteronism in chronic cases 2
• Focus on eliminating excess sodium intake while providing free water 2

Clinical Monitoring and Safety

Symptoms to Monitor

• Mild symptoms: Confusion, thirst (in awake patients) 3
• Severe symptoms: Coma, central nervous system dysfunction, abnormal cognitive and neuromuscular function 3, 5
• Advanced complications: Hemorrhagic complications or death from vascular stretching and rupture 5

Laboratory Monitoring

• Check plasma sodium every 2-4 hours during active correction 3, 5
• Assess urine osmolality to guide differential diagnosis 3
• Monitor for signs of cerebral edema if correction is too rapid 2, 3

Common Pitfalls to Avoid

• Overly rapid correction of chronic hypernatremia causes cerebral edema—never exceed 8-10 mmol/L per day 2, 3
• Using isotonic saline worsens hypernatremia by delivering excessive osmotic load 4
• Inadequate free water prescription in ICU patients leads to iatrogenic hospital-acquired hypernatremia, which is preventable 6, 5
• Starting renal replacement therapy without considering the rapid sodium drop in patients with chronic hypernatremia 3
• Failing to address underlying causes such as impaired thirst mechanism, lack of water access, or diabetes insipidus 1, 6

Special Populations

ICU Patients

• At high risk due to sedation, intubation, altered mental status, and fluid restriction 5
• Parenteral fluid replacement usually necessary 5
• Routinely assess free water requirements and prescribe judicious electrolyte-free water replacement 5

Patients with Renal Concentrating Defects

• Require ongoing hypotonic fluid administration to match excessive free water losses 4
• Isotonic fluids will exacerbate hypernatremia and must be avoided 4