How to manage hypernatremia?

Management of Hypernatremia

Hypernatremia (Na >145 mmol/L) should be corrected at a rate of 10-15 mmol/L per 24 hours using hypotonic fluids, with the specific fluid choice and rate depending on volume status and chronicity. 1

Initial Assessment

Before initiating treatment, determine the following critical parameters:

• Volume status - Assess for signs of hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor) versus hypervolemia (edema, ascites) versus euvolemia 2, 1
• Chronicity - Acute hypernatremia (<48 hours) can be corrected more rapidly (up to 1 mmol/L/hour if severely symptomatic), while chronic hypernatremia (>48 hours) requires slower correction to prevent cerebral edema 1
• Body weight and composition - Essential for calculating fluid deficits 2
• Urine output, specific gravity, and osmolality - Helps differentiate causes 2
• Blood electrolytes, acid-base status, hematocrit, and blood urea nitrogen - Complete metabolic assessment 2

Fluid Selection Based on Clinical Scenario

Hypotonic Fluid Options

For most cases of hypernatremia requiring correction, use hypotonic fluids: 1

• 0.45% NaCl (half-normal saline) - Contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia 1
• 0.18% NaCl (quarter-normal saline) - Contains ~31 mEq/L sodium, provides more aggressive free water replacement for severe cases 1
• D5W (5% dextrose in water) - Provides pure free water replacement, useful for severe hypernatremia or when no sodium is needed 1

Critical Contraindication

Never use isotonic saline (0.9% NaCl) as initial therapy in hypernatremia, especially in patients with nephrogenic diabetes insipidus or renal concentrating defects, as this will worsen hypernatremia. 1

Correction Rate Guidelines

Chronic Hypernatremia (>48 hours)

The recommended reduction rate is 10-15 mmol/L per 24 hours. 2, 1 This slower approach is critical because:

• Brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions 1
• Rapid correction causes cerebral edema, seizures, and permanent neurological injury 2, 1
• Corrections faster than 48-72 hours have been associated with increased risk of pontine myelinolysis 2

Acute Hypernatremia (<48 hours)

• Can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic 1
• Lower risk of cerebral edema with faster correction since osmolyte adaptation has not occurred 1

Treatment Based on Volume Status

Hypovolemic Hypernatremia

• Administer hypotonic fluids to replace free water deficit 1
• Avoid isotonic saline as initial therapy 1
• Match fluid composition to ongoing losses (severe burns, voluminous diarrhea) while providing adequate free water 1

Hypervolemic Hypernatremia (e.g., Cirrhosis)

• Focus on attaining negative water balance rather than aggressive fluid administration 1
• Discontinue intravenous fluid therapy and implement free water restriction 1
• Close monitoring of serum sodium and fluid status required 1

Euvolemic Hypernatremia

• Low salt diet (<6 g/day) and protein restriction (<1 g/kg/day) may be beneficial 1
• Regular monitoring of serum electrolytes and renal function essential 1

Special Populations

Heart Failure Patients

• Sodium and fluid restriction - Limit fluid intake to around 2 L/day for most hospitalized patients 1
• Consider stricter fluid restriction for diuretic-resistant or significantly hypernatremic patients 1
• For persistent severe hypernatremia with cognitive symptoms, vasopressin antagonists (tolvaptan, conivaptan) may be considered for short-term use 1

Nephrogenic Diabetes Insipidus

• Requires ongoing hypotonic fluid administration to match excessive free water losses 1
• Isotonic fluids will cause or worsen hypernatremia in these patients 1
• Hypotonic fluids are essential as initial and maintenance therapy 1

Pediatric Patients (Especially Neonates)

• Hypernatremia in very low birth weight infants mostly results from incorrect replacement of transepidermal water loss, inadequate water intake, or excessive sodium intake 2
• Assess infant's intravascular volume and hydration status before treatment 2
• In symptomatic hypovolemia, replace plasma volume first 2

Monitoring During Treatment

• Serum electrolytes and weight - Monitor daily for the first days of treatment, then adjust intervals based on clinical stability 2
• Fluid and electrolyte balance - Track urine output, urine specific gravity/osmolarity, and urine electrolyte concentrations 2
• Neurological status - Watch for signs of cerebral edema (confusion, seizures, altered mental status) if correction is too rapid 2, 1
• Renal function and urine osmolality - Essential for ongoing assessment 1

Common Pitfalls to Avoid

• Correcting chronic hypernatremia too rapidly - Leads to cerebral edema, seizures, and neurological injury 2, 1
• Using isotonic saline in patients with renal concentrating defects - Exacerbates hypernatremia 1
• Inadequate monitoring during correction - Can result in overcorrection or undercorrection 2
• Failing to identify and treat underlying cause - Hypernatremia is often iatrogenic, especially in vulnerable populations 2