How do you treat hypernatremia in patients, particularly the elderly and those with underlying medical conditions?

Treatment of Hypernatremia

For hypernatremia, administer hypotonic fluids (0.45% NaCl or D5W) to replace free water deficit, with a maximum correction rate of 10-15 mmol/L per 24 hours for chronic cases, and avoid isotonic saline as it will worsen hypernatremia, especially in patients with renal concentrating defects. 1

Initial Assessment and Correction Rate

Distinguish between acute (<48 hours) and chronic (>48 hours) hypernatremia, as this determines your correction rate. 1

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

Fluid Selection Strategy

Never use isotonic saline (0.9% NaCl) as initial therapy—it will worsen hypernatremia. 1

Hypotonic Fluid Options:

• 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, preferred when no sodium is needed 1

Initial Fluid Administration Rates:

• Adults: 25-30 mL/kg/24 hours 1
• Hypovolemic hypernatremia: Initial rate 4-14 mL/kg/h 1

Volume Status-Based Approach

Hypovolemic Hypernatremia:

Replace free water deficit with hypotonic fluids at 4-14 mL/kg/h initially. 1

• Avoid isotonic saline as it delivers excessive osmotic load requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid 1
• For severe burns or voluminous diarrhea, match fluid composition to ongoing losses while providing adequate free water 1

Euvolemic Hypernatremia:

• Consider low salt diet (<6 g/day) and protein restriction (<1 g/kg/day) 1
• Address underlying cause (diabetes insipidus, inadequate water intake) 1

Hypervolemic Hypernatremia (Cirrhosis):

Focus on achieving 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

Special Populations and Conditions

Elderly Patients:

• Higher risk for complications due to reduced renal function affecting sodium and water handling 1
• Cognitive impairment may prevent recognition of thirst or ability to access fluids 1
• More cautious correction rates recommended 1

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 short-term 1

Nephrogenic Diabetes Insipidus:

Ongoing hypotonic fluid administration required to match excessive free water losses. 1

• Isotonic saline will cause or worsen hypernatremia in these patients 1
• Never use isotonic fluids in patients with renal concentrating defects 1

Monitoring Protocol

Daily monitoring of serum electrolytes and weight is essential for the first days of treatment. 1

• Check serum sodium every 2-4 hours initially during active correction 1
• Then every 6-12 hours once stable 1
• Monitor urine output, specific gravity/osmolarity, and urine electrolyte concentrations 1
• Track fluid and electrolyte balance meticulously 1
• Assess renal function and urine osmolality regularly 1

Critical Pitfalls to Avoid

Correcting chronic hypernatremia faster than 10-15 mmol/L per 24 hours risks cerebral edema and seizures. 1

• Using isotonic saline in nephrogenic diabetes insipidus or renal concentrating defects exacerbates hypernatremia 1
• Inadequate monitoring during correction can result in overcorrection or undercorrection 1
• Failing to identify and treat the underlying cause (often iatrogenic in vulnerable populations) 1
• Prolonged induced hypernatremia to control ICP in traumatic brain injury is NOT recommended as it may worsen cerebral contusions 1

Calculating Free Water Deficit

Use the formula: Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg) to determine fluid requirements. 1

This helps guide the total volume of hypotonic fluid needed for correction 1