What is the recommended protocol for treating hypernatremia, including assessment of volume status, calculation of free‑water deficit, safe correction rates, fluid selection, and monitoring?

Hypernatremia Treatment Protocol

Initial Assessment and Volume Status Determination

Hypernatremia (serum sodium >145 mmol/L) requires immediate assessment of volume status, chronicity, and symptom severity to guide treatment. 1, 2

Volume Status Classification

• Hypovolemic hypernatremia: Look for orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins, and tachycardia 1
• Euvolemic hypernatremia: Absence of volume depletion or overload signs; suspect diabetes insipidus (central or nephrogenic) 3, 4
• Hypervolemic hypernatremia: Peripheral edema, ascites, jugular venous distention; often iatrogenic from hypertonic saline or sodium bicarbonate administration 3

Diagnostic Workup

• Measure urine osmolality and urine sodium to differentiate causes 1, 2
• Urine osmolality <300 mOsm/kg with hypernatremia suggests diabetes insipidus 4
• Urine osmolality >600 mOsm/kg indicates appropriate renal response to extrarenal water losses 4
• Check serum glucose to exclude pseudohypernatremia (correct sodium by adding 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL) 3
• Assess BUN, creatinine, hematocrit to evaluate hydration status and renal function 1

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Calculating Free Water Deficit

Use the following formula to determine water replacement needs: 1

Free water deficit = Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg)

• For men: Total body water = 0.6 × body weight (kg)
• For women: Total body water = 0.5 × body weight (kg)
• For elderly: Total body water = 0.45 × body weight (kg) 4

This calculation provides the baseline deficit; add ongoing losses (insensible losses ~500-1000 mL/day plus any measured losses from urine, drains, or diarrhea). 4

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Safe Correction Rates

Chronic Hypernatremia (>48 hours)

Maximum correction rate: 10-15 mmol/L per 24 hours (approximately 0.4-0.6 mmol/L/hour). 1, 2, 3, 5

• Slower correction 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 1, 2, 5
• Corrections faster than 48-72 hours increase risk of pontine myelinolysis 1

Acute Hypernatremia (<24-48 hours)

Can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic, as brain adaptation has not yet occurred. 1

• For acute symptomatic cases, hemodialysis is an effective option to rapidly normalize sodium levels 5

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Fluid Selection

Hypovolemic Hypernatremia

Administer hypotonic fluids to replace free water deficit: 1, 4

• 0.45% NaCl (half-normal saline): Contains 77 mEq/L sodium, 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): Preferred as primary rehydration fluid because it delivers no renal osmotic load and allows slow, controlled decrease in plasma osmolality 1

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

Initial Fluid Administration Rates

• Adults: 25-30 mL/kg/24 hours initially, then 4-14 mL/kg/h based on clinical response 1
• 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
• High-risk populations (infants, malnourished): Consider smaller-volume frequent boluses (10 mL/kg) due to reduced cardiac output capacity 1

Euvolemic Hypernatremia (Diabetes Insipidus)

• Central diabetes insipidus: Desmopressin (DDAVP) plus hypotonic fluid replacement 5, 4
• Nephrogenic diabetes insipidus: Requires ongoing hypotonic fluid administration to match excessive free water losses; desmopressin is ineffective 1, 4

Hypervolemic Hypernatremia

• Discontinue intravenous fluid therapy and implement free water restriction 1
• Focus on attaining negative water balance rather than aggressive fluid administration 1
• In cirrhotic patients, evaluate for hypovolemic vs. hypervolemic state before treatment 1

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Monitoring Protocol

Initial Phase (First 24-48 Hours)

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

• Monitor daily weight, supine and standing vital signs 1
• Track fluid input and output meticulously 1
• Measure urine output, specific gravity/osmolarity, and urine electrolyte concentrations 1
• Assess serum electrolytes (sodium, potassium, chloride, bicarbonate), BUN, creatinine, hematocrit 1, 4

Ongoing Monitoring

• Daily monitoring of serum electrolytes and weight for first several days, then adjust intervals based on clinical stability 1
• Watch for signs of cerebral edema: headache, confusion, seizures, altered mental status 1, 2
• Monitor renal function closely, as hypernatremia is associated with hyperchloremia which may impair renal function 1

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Special Populations and Considerations

Heart Failure Patients

• Fluid restriction (1.5-2 L/day) may be needed after initial correction 1
• Combine IV hypotonic fluids with free water via nasogastric tube if needed, targeting 10-15 mmol/L correction per 24 hours 1
• Diuretics remain essential for volume management but must be carefully balanced with hypernatremia correction 1
• Sodium restriction to <2 g daily and fluid limitation to 1.5-2 L/day 1

Cirrhotic Patients

• Evaluate for hypovolemic vs. hypervolemic state before treatment 1
• Hypovolemic: Provide fluid resuscitation with hypotonic solutions 1
• Hypervolemic: Focus on negative water balance, discontinue IV fluids, implement free water restriction 1

Older Adults

• Higher risk for complications due to reduced renal function, cognitive impairment preventing thirst recognition, and inability to access fluids 1
• Use more conservative fluid rates and monitor closely for worsening azotemia 1
• In patients with chronic kidney disease, closely monitor for worsening azotemia during correction 1

Traumatic Brain Injury

Prolonged induced hypernatremia to control intracranial pressure is NOT recommended—it requires an intact blood-brain barrier and may worsen cerebral contusions. 1

• Risk of "rebound" ICP elevation during correction exists as brain cells synthesize intracellular osmolytes 1
• Weak relationship between serum sodium and ICP 1

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Common Pitfalls to Avoid

• Correcting chronic hypernatremia too rapidly leads to cerebral edema, seizures, and neurological injury 1, 2
• Using isotonic saline in nephrogenic diabetes insipidus or renal concentrating defects exacerbates hypernatremia 1
• Inadequate monitoring during correction results in overcorrection or undercorrection 1
• Failing to identify and treat the underlying cause, which is often iatrogenic, especially in vulnerable populations 1
• Starting renal replacement therapy without considering sodium concentration can cause rapid drops in chronic hypernatremia 5