What is the recommended treatment for hypernatremia, including the use of free water (hypotonic fluids) for correction?

Treatment of Hypernatremia with Free Water Flushes

For hypernatremia, free water replacement using hypotonic fluids (such as D5W or enteral water flushes) is the cornerstone of treatment, with correction rates not exceeding 8-10 mmol/L per 24 hours for chronic hypernatremia to prevent cerebral edema. 1, 2

Initial Assessment and Classification

• Determine the acuity of hypernatremia: acute (<24-48 hours) versus chronic (>48 hours), as this fundamentally changes your correction strategy 2, 3
• Assess volume status (hypovolemic, euvolemic, or hypervolemic) to guide fluid selection 3
• Evaluate for underlying causes: diabetes insipidus (central or nephrogenic), excessive sodium intake, renal or extrarenal water losses 1, 3

Free Water Deficit Calculation

Calculate the free water deficit to guide replacement: Free water deficit = 0.6 × body weight (kg) × [(current Na/140) - 1] 1

This calculation provides your target volume for correction, though you'll administer it slowly over 48-72 hours for chronic hypernatremia.

Correction Rate Guidelines: The Critical Safety Parameter

For Chronic Hypernatremia (>48 hours)

Never correct faster than 8-10 mmol/L per 24 hours (approximately 0.4 mmol/L/hour) to prevent osmotic demyelination and cerebral edema 2, 3

• Aim for 0.5 mmol/L/hour maximum correction rate 2
• Monitor serum sodium every 2-4 hours during active correction 1
• The brain has adapted to the hyperosmolar state through intracellular osmolyte accumulation; rapid correction causes water to shift intracellularly, leading to cerebral edema 4

For Acute Hypernatremia (<24 hours)

• Rapid correction is safer and actually improves prognosis by preventing cellular dehydration effects 3
• Can correct more quickly, but still monitor closely 3
• Consider hemodialysis for severe acute hypernatremia requiring rapid normalization 2

Fluid Selection for Free Water Replacement

Primary Options

D5W (5% dextrose in water) is the preferred hypotonic solution for free water replacement 1

• Provides pure free water once glucose is metabolized
• Sodium concentration: 0 mEq/L
• Most effective for correcting hypernatremia

Enteral Free Water Flushes

For patients with enteral access (NG tube, G-tube, PEG), free water flushes are highly effective 1

• Administer 200-400 mL of free water every 4-6 hours via feeding tube
• Adjust volume and frequency based on sodium levels and correction rate
• Monitor for aspiration risk in patients with impaired consciousness

Alternative Hypotonic Solutions

• 0.45% NaCl (half-normal saline) can be used but corrects more slowly 1
• Contains 77 mEq/L sodium, so provides less free water per liter than D5W

Treatment Algorithm Based on Volume Status

Hypovolemic Hypernatremia (Most Common)

1. Initial phase: Restore intravascular volume with isotonic saline (0.9% NaCl) to stabilize hemodynamics 1
2. Once hemodynamically stable: Switch to hypotonic fluids (D5W or 0.45% NaCl) for free water replacement 1
3. Replace ongoing losses appropriately

Euvolemic Hypernatremia (Diabetes Insipidus)

Central diabetes insipidus: Desmopressin (DDAVP) is the primary treatment, combined with free water replacement 2, 3

• Desmopressin dosing: 1-4 mcg IV/SC or 10-20 mcg intranasal
• Continue free water replacement as needed

Nephrogenic diabetes insipidus: Free water replacement is the mainstay, as desmopressin is ineffective 3

• Address underlying causes (discontinue lithium, correct hypokalemia)
• Thiazide diuretics paradoxically help by inducing mild volume depletion

Hypervolemic Hypernatremia (Sodium Excess)

• Loop diuretics (furosemide) to promote sodium excretion 1
• Replace urinary losses with D5W to maintain free water balance
• Consider hemodialysis for severe cases 2

Monitoring Protocol

During active correction, check serum sodium every 2-4 hours initially 1

• Adjust fluid rates if correction is too rapid or too slow
• Monitor for signs of cerebral edema: headache, altered mental status, seizures 4
• Once stable, can extend to every 6-8 hours, then daily

Special Populations and Considerations

Patients with Impaired Thirst Mechanism

• Elderly patients and those with altered mental status cannot request water 1
• Scheduled free water administration is essential, not PRN
• Consider prophylactic free water flushes in high-risk patients (tube feeds without adequate free water)

Patients on Renal Replacement Therapy

When initiating dialysis in chronic hypernatremia, use dialysate with higher sodium concentration to prevent rapid drops 2

• Standard dialysate (140 mmol/L Na) will correct too rapidly
• Customize dialysate sodium to match patient's current level initially

Common Pitfalls to Avoid

Correcting chronic hypernatremia too rapidly causes cerebral edema, seizures, and permanent neurologic damage 2, 4

• The 8-10 mmol/L per 24-hour limit is absolute for chronic cases
• Overzealous correction has higher morbidity than the hypernatremia itself 4

Failing to provide adequate free water in tube-fed patients 1

• Standard tube feeding formulas are hyperosmolar
• Require 200-400 mL free water flushes every 4-6 hours
• This is a preventable cause of hypernatremia

Using isotonic saline throughout correction in hypovolemic hypernatremia 1

• Initial volume resuscitation with normal saline is appropriate
• Must switch to hypotonic fluids once hemodynamically stable
• Continuing isotonic fluids will not correct the hypernatremia

Inadequate monitoring during correction 1

• Serum sodium can change unpredictably
• Every 2-4 hour checks are mandatory during active correction
• Adjust rates based on actual response, not just calculations