Free Water Deficit
Calculate fluid replacement needed for hypernatremia correction.
Patient Parameters
TBW factor: 60% of body weight
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0.0 L
Water needed to normalize sodium
Moderate Hypernatremia
Total Body Water
42.0 L
Sodium Excess
15 mEq/L
Target Na (48h)
140 mEq/L
Max Rate
10-12 mEq/24h
Formula & Calculation
Free Water Deficit = TBW × [(Current Na / 140) - 1]
= 42.0 × [(155 / 140) - 1] = 0.00 L
• TBW (male) = Weight × 0.6 = 70 × 0.6 = 42.0 L
• TBW (female) = Weight × 0.5 = 70 × 0.5 = 35.0 L
• Elderly: Use 0.5 (male) or 0.45 (female)
⚠️ Remember: This is the deficit only. Add ongoing losses (insensible ~500mL/day, urine output, GI losses). Correct slowly: 10-12 mEq/L/day for chronic hypernatremia.
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