What is the recommended approach for increasing free water intake to correct sodium imbalance in hypernatremia?

Increasing Free Water Intake for Hypernatremia Correction

For hypernatremia correction, increase free water administration using hypotonic fluids such as 5% dextrose (D5W) or 0.45% NaCl, with a maximum correction rate of 0.4 mmol/L/hour or 10 mmol/L per 24 hours to prevent cerebral edema. 1, 2, 3

Fluid Selection for Free Water Replacement

Primary hypotonic fluid options:

• 5% dextrose in water (D5W) is the preferred choice because it delivers no renal osmotic load and allows slow, controlled decrease in plasma osmolality 4
• 0.45% NaCl (half-normal saline) contains 77 mEq/L sodium with osmolarity of 154 mOsm/L, appropriate for moderate hypernatremia 4
• 0.18% NaCl (quarter-normal saline) contains 31 mEq/L sodium, providing greater free water content for more aggressive replacement 4

Critical contraindication: Avoid isotonic saline (0.9% NaCl) in hypernatremia as it delivers excessive osmotic load—requiring 3 liters of urine to excrete the osmotic load from just 1 liter of isotonic fluid, which worsens hypernatremia 4

Correction Rate Guidelines

For chronic hypernatremia (>48 hours):

• Maximum correction rate: 0.4 mmol/L/hour or 8-10 mmol/L per 24 hours 1, 2, 3, 5
• Slower correction prevents cerebral edema from rapid osmotic shifts 1, 2

For acute hypernatremia (<24-48 hours):

• Rapid correction improves prognosis by preventing cellular dehydration effects 2
• Hemodialysis is an effective option for rapidly normalizing sodium levels in acute cases 5

Initial Fluid Administration Rates

For adults:

• Initial rate: 25-30 mL/kg/24 hours 4

For children:

• First 10 kg: 100 mL/kg/24 hours 4
• 10-20 kg: 50 mL/kg/24 hours 4
• Remaining weight: 20 mL/kg/24 hours 4

Special Clinical Scenarios

Hypervolemic hypernatremia (heart failure, cirrhosis):

• Use loop diuretics (furosemide) to promote free water excretion and reduce volume overload 1
• Monitor serum sodium frequently during correction 1
• In cirrhotic patients, avoid rapid sodium changes and consider free water restriction in addition to diuretics 1
• Monitor for hepatorenal syndrome during diuretic therapy in cirrhosis 1
• Monitor for decreased cardiac output during fluid removal in heart failure 1

Nephrogenic diabetes insipidus:

• Requires ongoing hypotonic fluid administration to match excessive free water losses 4
• Isotonic fluids worsen hypernatremia in these patients 4

Excessive water losses (diarrhea, vomiting):

• Replace ongoing losses with hypotonic fluids 4
• Ensure access to free water for inadequate intake 4

Monitoring Requirements

• Check serum sodium levels frequently during correction to avoid cerebral edema 1
• Close laboratory controls are essential throughout treatment 5
• When starting renal replacement therapy in chronic hypernatremia, avoid rapid sodium drops 5

Common Pitfalls to Avoid

• Never use isotonic saline for hypernatremia correction—it worsens the condition by delivering excessive osmotic load 4
• Never correct chronic hypernatremia faster than 8-10 mmol/L per 24 hours—rapid correction causes cerebral edema 1, 2, 5
• Never ignore volume status—hypervolemic patients require diuresis, not just free water 1