Free Water Deficit Calculator
Calculate free water deficit for hypernatremia treatment planning.
Affects total body water calculation
Affects total body water percentage
Acceptable range: 2-330 lbs
Use only if sodium >140 - Acceptable range: 100-200 mEq/L
Target sodium level (typically 140 mEq/L)
Results
Enter values and click Calculate to see results
Methodology
This calculator estimates free water deficit using the formula: FWD = TBW × [(Na_current / Na_desired) - 1], where total body water (TBW) is calculated based on sex, age, and weight. Adult males: 60% of body weight, adult females: 50%, elderly males: 50%, elderly females: 45%, children: 60%. The calculator provides severity assessment and correction rate recommendations based on current sodium levels.
Important Disclaimers:
- This calculator is for educational purposes only and should not replace clinical judgment
- Hypernatremia requires immediate medical evaluation and treatment
- Correction rates may need adjustment based on chronicity and patient factors
- Continuous monitoring of sodium levels and neurological status is essential
- Individual patient factors may require modified treatment approaches
- Always consult healthcare providers for treatment decisions and monitoring
About This Calculator
1. How does the Free Water Deficit Calculator work?
This calculator uses the formula: Free Water Deficit = Total Body Water × [(Current Sodium / Desired Sodium) - 1]. Total body water is estimated based on sex, age, and weight using standard coefficients: adult males 60%, adult females 50%, elderly males 50%, elderly females 45%, and children 60% of body weight.
2. When should I use this calculator?
Use this calculator for hypernatremia (sodium >140 mEq/L) to estimate the free water deficit. It's most useful for planning fluid replacement therapy in patients with pure water deficit. Do not use for hyponatremia or when significant sodium excess is present.
3. What are the different severity levels of hypernatremia?
Mild hypernatremia (141-149 mEq/L) requires gradual correction over 24-48 hours. Moderate hypernatremia (150-159 mEq/L) needs more careful monitoring and correction. Severe hypernatremia (≥160 mEq/L) is life-threatening and requires immediate intervention with intensive monitoring.
4. How fast should hypernatremia be corrected?
Generally, sodium should be corrected at 0.5-1 mEq/L per hour, with a maximum of 8-10 mEq/L per day. Severe hypernatremia may initially be corrected at 1-2 mEq/L per hour. Too rapid correction can cause cerebral edema and neurological complications.
5. What causes hypernatremia?
Hypernatremia usually results from free water deficit due to inadequate intake (altered mental status, lack of access) or excessive losses (diabetes insipidus, osmotic diuresis, diarrhea, fever, sweating). It's more common in infants, elderly, and hospitalized patients.
6. What are the limitations of this calculator?
This calculator estimates total body water using standard formulas which may not apply to all patients. It assumes pure water deficit and doesn't account for ongoing losses or concurrent sodium excess. Individual patient factors, chronicity of hypernatremia, and clinical condition may require modified correction approaches. Always use clinical judgment and continuous monitoring.