How to treat a patient with severe hypernatremia?

Treatment of Severe Hypernatremia

For severe hypernatremia, immediately initiate hypotonic fluid replacement (0.45% NaCl or D5W) with a maximum correction rate of 10-15 mmol/L per 24 hours for chronic cases (>48 hours), while simultaneously addressing the underlying cause such as free water deficit, diabetes insipidus, or excessive sodium intake. 1, 2

Initial Assessment and Diagnostic Approach

Before initiating treatment, rapidly determine three critical factors:

• Chronicity: Acute (<48 hours) vs chronic (>48 hours) hypernatremia, as this dictates correction speed 1, 3
• Volume status: Assess for hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor) vs hypervolemia (edema, ascites, jugular venous distention) 1, 4
• Urine osmolality and sodium: Measure to differentiate renal vs extrarenal water losses and identify diabetes insipidus 4, 5

A urine osmolality inappropriately low (<300 mOsm/kg) in the setting of hypernatremia suggests diabetes insipidus or impaired renal concentrating ability 1. Urine sodium <20 mmol/L indicates extrarenal losses, while >20 mmol/L suggests renal losses 4.

Fluid Selection and Administration Strategy

Never use isotonic saline (0.9% NaCl) as initial therapy for hypernatremia, as this will worsen the condition by delivering excessive osmotic load. 1, 2

Preferred Hypotonic Fluids:

• D5W (5% dextrose in water): First-line choice as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 1
• 0.45% NaCl (half-normal saline): Contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia 1, 2
• 0.18% NaCl (quarter-normal saline): Contains ~31 mEq/L sodium, providing more aggressive free water replacement for severe cases 1

Initial Fluid Administration Rates:

• Adults: 25-30 mL/kg/24 hours as baseline maintenance 1
• Calculate free water deficit: Use the formula: Free water deficit = 0.5 × body weight (kg) × [(current Na/140) - 1] 1, 4
• Add ongoing losses: Account for insensible losses (typically 500-1000 mL/day) and any measured losses 4, 5

Critical Correction Rate Guidelines

The single most important safety principle: For chronic hypernatremia (>48 hours), never exceed 10-15 mmol/L correction per 24 hours to prevent cerebral edema, seizures, and permanent neurological injury. 1, 3, 2

Correction Rates by Chronicity:

• Chronic hypernatremia (>48 hours): Maximum 10-15 mmol/L per 24 hours 1, 3
• Acute hypernatremia (<48 hours): Can correct more rapidly, up to 1 mmol/L/hour if severely symptomatic 1, 6
• Corrections faster than 48-72 hours: Associated with increased risk of pontine myelinolysis 1

The rationale for slow correction in chronic cases is that brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions; rapid correction causes these cells to swell, leading to cerebral edema 1, 3.

Monitoring Protocol

Check serum sodium every 2-4 hours initially during active correction, then every 6-12 hours once stable. 1, 4

Additional monitoring includes:

• Daily weights: Track fluid balance and treatment response 1, 4
• Vital signs: Monitor supine and standing blood pressure for volume status 1
• Urine output and specific gravity: Assess ongoing losses and renal concentrating ability 1, 4
• Neurological status: Watch for confusion, seizures, or altered mental status indicating cerebral edema from overcorrection 1, 2

Treatment Based on Underlying Etiology

Hypovolemic Hypernatremia (Most Common):

• Replace volume deficit first with hypotonic fluids 1, 2
• Address ongoing losses: Match fluid composition to losses (GI, renal, insensible) 4, 5
• Avoid isotonic saline: This worsens hypernatremia in patients with impaired renal concentrating ability 1

Diabetes Insipidus:

• Central DI: Administer desmopressin (DDAVP) 1-2 mcg IV/SC or 10-20 mcg intranasally 3, 4
• Nephrogenic DI: Requires ongoing hypotonic fluid administration to match excessive free water losses; desmopressin is ineffective 1, 4
• Never use isotonic fluids: This will cause or worsen hypernatremia in these patients 1

Hypervolemic Hypernatremia (Rare):

• Discontinue IV fluids and implement free water restriction 1
• Consider diuretics: To promote renal sodium excretion if sodium overload is present 6, 5
• In cirrhosis: Focus on negative water balance rather than aggressive fluid administration 1

Special Clinical Scenarios

Severe Symptoms (Confusion, Seizures, Coma):

• Combine IV hypotonic fluids with free water via nasogastric tube if patient cannot drink 1
• Target 10-15 mmol/L correction per 24 hours even with severe symptoms to avoid cerebral edema 1, 2
• Consider hemodialysis: For acute hypernatremia (<24 hours) requiring rapid normalization 3

Heart Failure Patients:

• Fluid restriction (1.5-2 L/day) may be needed after initial correction 1
• Avoid excessive fluid administration: Balance hypernatremia correction with volume overload risk 1
• Consider vasopressin antagonists: Tolvaptan or conivaptan for short-term use in persistent severe hypernatremia with cognitive symptoms 1

Traumatic Brain Injury:

• Prolonged induced hypernatremia to control ICP is NOT recommended: Requires intact blood-brain barrier and may worsen cerebral contusions 1
• Risk of "rebound" ICP elevation: During correction as brain cells have synthesized intracellular osmolytes 1

Common Pitfalls to Avoid

• Using isotonic saline in nephrogenic diabetes insipidus or renal concentrating defects: This exacerbates hypernatremia 1, 2
• Correcting chronic hypernatremia too rapidly: Leads to cerebral edema, seizures, and permanent neurological injury 1, 3, 2
• Inadequate monitoring during correction: Results in overcorrection or undercorrection 1, 4
• Failing to identify and treat underlying cause: Hypernatremia is often iatrogenic, especially in vulnerable populations 1, 5
• Starting renal replacement therapy without adjusting for chronic hypernatremia: Can cause rapid sodium drop 3

Additional Therapy Considerations

For patients with ongoing excessive losses (severe burns, voluminous diarrhea), hypotonic fluids must match the composition of losses while providing adequate free water 1. In older adults, be particularly cautious as they have reduced renal function affecting sodium and water handling, and cognitive impairment may prevent recognition of thirst 1.

Monitor for hyperchloremia during treatment, as hypernatremia is often associated with elevated chloride levels that may impair renal function. 1