What is the treatment for hypernatremia?

Treatment of Hypernatremia

For hypernatremia, administer hypotonic fluids (0.45% NaCl or D5W) to replace free water deficit, targeting a correction rate of 10-15 mmol/L per 24 hours for chronic cases, while avoiding isotonic saline which will worsen the condition. 1

Initial Assessment

Before initiating treatment, rapidly assess several key parameters 2:

• Confirm true hypernatremia by excluding pseudohypernatremia and calculating glucose-corrected sodium (add 1.6 mEq/L to measured sodium for each 100 mg/dL glucose above 100 mg/dL) 2
• Determine volume status through physical examination looking for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemic), versus edema, ascites, or jugular venous distention (hypervolemic) 1, 2
• Measure urine osmolality and sodium to differentiate causes - concentrated urine (>600 mOsm/kg) suggests extrarenal losses, while dilute urine (<300 mOsm/kg) suggests diabetes insipidus 2
• Distinguish acute (<48 hours) from chronic (>48 hours) hypernatremia, as this fundamentally changes correction rates 3, 4

Fluid Replacement Strategy

Choice of Replacement Fluid

Never use isotonic saline (0.9% NaCl) as initial therapy for hypernatremia, especially in patients with nephrogenic diabetes insipidus, as this will worsen the condition. 1

The appropriate hypotonic fluids include 1, 5:

• 0.45% NaCl (half-normal saline) - contains 77 mEq/L sodium, appropriate for moderate hypernatremia
• 0.18% NaCl (quarter-normal saline) - contains 31 mEq/L sodium, provides more aggressive free water replacement
• D5W (5% dextrose in water) - provides pure free water replacement for severe cases

For patients with severe hypernatremia and altered mental status, combine IV hypotonic fluids with free water via nasogastric tube 1

Correction Rate Guidelines

The correction rate is critical and depends on acuity 3, 4:

• Chronic hypernatremia (>48 hours): Correct slowly at 10-15 mmol/L per 24 hours (maximum 0.4 mmol/L per hour) to prevent cerebral edema 1, 3, 4
• Acute hypernatremia (<24-48 hours): Can be corrected more rapidly, up to 1 mmol/L per hour if severely symptomatic 1, 4

Correcting chronic hypernatremia too rapidly causes cerebral edema, seizures, and permanent neurological injury because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions. 1, 3

Treatment Based on Volume Status

Hypovolemic Hypernatremia

• Replace free water deficit with hypotonic fluids (0.45% NaCl or 0.18% NaCl) 1
• Address underlying cause - extrarenal losses (diarrhea, burns, excessive sweating) or renal losses 4, 2
• In patients with severe burns or voluminous diarrhea, match fluid composition to ongoing losses while providing adequate free water 1

Euvolemic Hypernatremia

• Diabetes insipidus is the primary cause - differentiate central from nephrogenic 4, 2
• For central diabetes insipidus: administer desmopressin (Minirin) along with hypotonic fluid replacement 3
• For nephrogenic diabetes insipidus: provide ongoing hypotonic fluid administration to match excessive free water losses 1
• Consider low salt diet (<6 g/day) and protein restriction (<1 g/kg/day) 1

Hypervolemic Hypernatremia

• In cirrhosis: Discontinue intravenous fluid therapy and implement free water restriction, focusing on achieving negative water balance rather than aggressive fluid administration 1
• In heart failure: Implement sodium and fluid restriction, limiting fluid intake to 1.5-2 L/day after initial correction 1
• For persistent severe hypernatremia with cognitive symptoms, consider vasopressin antagonists (tolvaptan, conivaptan) for short-term use 1

Monitoring Requirements

• Check serum sodium every 2-4 hours initially during active correction to ensure target correction rate is not exceeded 1, 3
• Monitor for neurological symptoms - confusion, seizures, altered mental status indicating either inadequate correction or overly rapid correction 5, 3
• Assess renal function, urine osmolality, and electrolyte balance regularly 1, 2
• Track fluid balance meticulously, including insensible losses 2

Special Populations and Pitfalls

• Patients with renal concentrating defects (nephrogenic diabetes insipidus) require hypotonic fluids; isotonic saline will exacerbate hypernatremia 1
• Traumatic brain injury patients: Prolonged induced hypernatremia to control intracranial pressure is not recommended, as it requires an intact blood-brain barrier and may worsen cerebral contusions 1
• Starting renal replacement therapy: In patients with chronic hypernatremia, dialysis can cause rapid sodium drops - use modified dialysate or adjust treatment parameters 3
• Hypernatremia with hyperchloremia may impair renal function and requires monitoring 1