How is hypernatremia treated?

Management of Hypernatremia (Sodium 168 mmol/L)

For a sodium level of 168 mmol/L, you should administer hypotonic fluids (0.45% NaCl or D5W) with a correction rate not exceeding 10-15 mmol/L per 24 hours to avoid cerebral edema and neurological injury. 1, 2

Immediate Assessment

Before initiating treatment, determine three critical factors:

• Duration of hypernatremia: Acute (<24-48 hours) vs. chronic (>48 hours) - this dictates correction speed 2, 3
• Volume status: Check for signs of hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor), hypervolemia (edema, jugular venous distention), or euvolemia 2
• Urine osmolality: Obtain to differentiate between diabetes insipidus (inappropriately dilute urine) vs. extrarenal losses (concentrated urine >600 mOsm/kg) 2

Treatment Algorithm Based on Duration

Chronic Hypernatremia (Most Likely Scenario)

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

• Use 0.45% NaCl (half-normal saline) as the primary fluid, which contains 77 mEq/L sodium 4
• Alternatively, use D5W (5% dextrose in water) for more aggressive free water replacement 4, 1
• Never exceed 8-10 mmol/L reduction per day to prevent cerebral edema, seizures, and permanent neurological injury 1, 3
• Monitor serum sodium every 2-4 hours initially, then every 6 hours once stable 1, 3

Acute Hypernatremia (<24 hours)

• Rapid correction is safe and improves prognosis by preventing cellular dehydration 2
• Hemodialysis is an effective option for rapid normalization if needed 3
• Still monitor closely to avoid overly rapid drops if transitioning to maintenance therapy 3

Treatment Based on Volume Status

Hypovolemic Hypernatremia (Most Common)

• First priority: Restore intravascular volume with isotonic saline (0.9% NaCl) until hemodynamically stable 2, 5
• Second step: Switch to hypotonic fluids (0.45% NaCl or D5W) to correct the free water deficit 4, 5
• Common causes: Renal losses (osmotic diuresis, diuretics) or extrarenal losses (diarrhea, burns, excessive sweating) 2

Euvolemic Hypernatremia (Diabetes Insipidus)

• Central diabetes insipidus: Administer desmopressin (DDAVP) 1-2 mcg IV/SC or 10-20 mcg intranasally 2, 3
• Nephrogenic diabetes insipidus: Requires hypotonic fluid replacement to match ongoing free water losses; desmopressin is ineffective 4, 2
• Identify underlying cause: Central DI from trauma/surgery/infection; nephrogenic DI from lithium, hypokalemia, hypercalcemia 2

Hypervolemic Hypernatremia (Rare)

• Acute: Usually iatrogenic from hypertonic saline or sodium bicarbonate administration 2
• Chronic: Consider primary hyperaldosteronism 2
• Treatment: Diuretics (furosemide) to promote sodium excretion plus hypotonic fluid replacement 2, 6

Calculating Free Water Deficit

Use this formula to estimate the volume of free water needed:

Free water deficit (L) = 0.6 × body weight (kg) × [(current Na ÷ 140) - 1] 5

For a 70 kg patient with Na 168:

• Free water deficit = 0.6 × 70 × [(168 ÷ 140) - 1] = 8.4 liters

This represents the total deficit, not the amount to replace in 24 hours. Correct gradually over multiple days based on the 10-15 mmol/L per day limit 1, 2.

Critical Monitoring Parameters

• Serum sodium: Every 2-4 hours during active correction, then every 6 hours 1, 3
• Daily weights: Track fluid balance 1
• Neurological status: Watch for confusion, seizures, altered consciousness 2, 5
• Urine output and osmolality: Reassess if correction is inadequate 2

Common Pitfalls to Avoid

• Too rapid correction of chronic hypernatremia: This causes cerebral edema, seizures, and permanent brain injury from rapid fluid shifts into brain cells 1, 2, 3
• Using isotonic saline (0.9% NaCl) throughout: This will not correct hypernatremia and may worsen it in patients with impaired free water excretion 4, 2
• Inadequate monitoring: Both undercorrection and overcorrection are associated with poor outcomes 1
• Starting renal replacement therapy without adjusting dialysate: Can cause dangerously rapid sodium drops in chronic hypernatremia 3
• Ignoring underlying cause: Failure to identify and treat diabetes insipidus, medication effects, or ongoing losses leads to recurrence 2, 5

Prognosis Factors

• Age: Very young patients tolerate hypernatremia better than adults 7
• Initial sodium level: Sodium >200 mmol/L carries extremely high mortality 7
• Severity of symptoms: Seizures, coma, and altered consciousness indicate severe cellular dehydration and worse prognosis 5, 7
• Independent mortality risk: Hypernatremia itself is an independent risk factor for death in critically ill patients 6