📋 Clinical Utility: Calculates free water deficit to guide correction of hypernatremia.
Target Na⁺: 140-145 mEq/L
⚠️ Correction Rate: Max 10-12 mEq/L/day to avoid cerebral edema.
📖 Understanding Free Water Deficit
Interpretation Guidelines
- 145-150 mEq/L: Mild hypernatremia
- 150-155 mEq/L: Moderate hypernatremia
- 155-160 mEq/L: Severe hypernatremia
- > 160 mEq/L: Extreme hypernatremia
Correction Principles
- Rate: Max 10-12 mEq/L/day
- Fluid: Free water (oral, D5W, or 0.45% saline)
- Monitor: Sodium every 2-4 hours
- Risk: Cerebral edema if corrected too fast
- Ongoing losses: Account for continuing water losses
💡 Clinical Pearl: For every 1 mEq/L decrease in sodium,
the brain adapts with organic osmolyte accumulation. Correct slowly
to prevent cerebral edema. In chronic hypernatremia (> 48 hours),
correction rate should be even slower (6-8 mEq/L/day).
📖 Free Water Deficit Formula:
Water Deficit (L) = TBW × ((Current Na⁺ / Target Na⁺) - 1)
TBW Calculation (Watson):
Male: TBW = 2.447 - 0.09156 × Age + 0.1074 × Height + 0.3362 × Weight
Female: TBW = -2.097 + 0.1069 × Height + 0.2466 × Weight
Additional Considerations:
• Add ongoing fluid losses (urine, insensible, GI) to replacement plan
• Use 0.45% saline for patients with volume depletion
• Use D5W for patients with adequate volume status
• Monitor serum sodium every 2-4 hours during correction
Water Deficit (L) = TBW × ((Current Na⁺ / Target Na⁺) - 1)
TBW Calculation (Watson):
Male: TBW = 2.447 - 0.09156 × Age + 0.1074 × Height + 0.3362 × Weight
Female: TBW = -2.097 + 0.1069 × Height + 0.2466 × Weight
Additional Considerations:
• Add ongoing fluid losses (urine, insensible, GI) to replacement plan
• Use 0.45% saline for patients with volume depletion
• Use D5W for patients with adequate volume status
• Monitor serum sodium every 2-4 hours during correction