Determine TBW Fraction
Na 130, target 135, 70kg male
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Evidence-based calculations Used in clinical settings worldwide Regular monitoring recommended
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Mild Hyponatremia
Na 130, target 135, 70kg male
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Moderate Hyponatremia
Na 125, target 130, 60kg female
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Severe Hyponatremia
Na 115, target 120, symptomatic
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Hypovolemic Hyponatremia
Na 128, dehydrated patient
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Elderly Female
Na 122, target 128, 55kg elderly
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Hypervolemic Hyponatremia
Heart failure patient with edema
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Clinical Scenarios
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Mild Hyponatremia
Na 130, target 135, 70kg male
Asymptomatic mild hyponatremia
Moderate Hyponatremia
Na 125, target 130, 60kg female
SIADH patient with nausea and headache
Severe Hyponatremia
Na 115, target 120, symptomatic
Seizures requiring urgent correction
Hypovolemic Hyponatremia
Na 128, dehydrated patient
Vomiting and diarrhea causing volume depletion
Elderly Female
Na 122, target 128, 55kg elderly
Thiazide-induced hyponatremia
Hypervolemic Hyponatremia
Heart failure patient with edema
CHF with dilutional hyponatremia
Sodium Values
Patient Characteristics
Clinical Assessment
Sodium Deficit Results
210
Sodium Deficit
mEq
7241
Volume Needed
mL
Total Body Water
42.0 L
TBW Fraction: 60%
Infusion Plan
Safe correction target - within 8 mEq/L
Recommendations
- Do not exceed 8 mEq/L rise in first 24 hours
- Check sodium every 2-4 hours during active correction
- Stop or reduce infusion if correction is too rapid
Sodium Correction Visualization
Deficit & Volume
Expected Correction Trend
Body Water Distribution
Step-by-Step Calculations
Step 1: Determine TBW Fraction
Formula: ext{TBW} ext{Fraction} ext{based} ext{on} ext{sex}, ext{age}, ext{and} ext{body} ext{composition}
Calculation: Base: 0.6, adjusted for adult, normal
Result: 0.60
Step 2: Calculate Total Body Water
Formula: ext{TBW} = ext{Weight} ( ext{kg}) imes ext{TBW} ext{Fraction}
Calculation: 70.0 ร 0.60
Result: 42.0 L
Step 3: Calculate Sodium Deficit
Formula: ext{Deficit} = ext{TBW} imes ( ext{Target} ext{Na} - ext{Current} ext{Na})
Calculation: 42.0 ร (130 - 125)
Result: 210 mEq
Step 4: Calculate Volume of Solution
Formula: ext{Volume} = ext{Deficit} div ( ext{Solution} ext{Na} - ext{Current} ext{Na}) imes 1000
Calculation: 210 รท (154 - 125) ร 1000
Result: 7241 mL
Step 5: Expected Na Change per Liter (Adrogue-Madias)
Formula: \text{Delta} ext{Na} = ( ext{Infusate} ext{Na} - ext{Serum} ext{Na}) div ( ext{TBW} + 1)
Calculation: (154 - 125) รท (42.0 + 1)
Result: 0.7 mEq/L per liter
Sodium Solution Reference
| Solution | Na Content | Tonicity | Typical Use |
| 0.9% NaCl (Normal Saline) | 154 mEq/L | Isotonic | Hypovolemic hyponatremia, volume resuscitation |
| 0.45% NaCl (Half Normal) | 77 mEq/L | Hypotonic | Free water replacement, maintenance |
| 3% NaCl (Hypertonic Saline) | 513 mEq/L | Hypertonic | Severe symptomatic hyponatremia, emergent correction |
| Lactated Ringers | 130 mEq/L | ~Isotonic | Volume resuscitation, surgical patients |
Hyponatremia Classification by Volume Status
Hypovolemic
Total body Na decreased MORE than total body water. Caused by GI losses, diuretics, third spacing.
Treatment: Normal saline (0.9% NaCl)
Euvolemic
Total body water increased with near-normal Na. SIADH, hypothyroidism, adrenal insufficiency, psychogenic polydipsia.
Treatment: Fluid restriction, treat cause
Hypervolemic
Total body water increased MORE than total body Na. CHF, cirrhosis, nephrotic syndrome.
Treatment: Fluid restriction, diuretics, treat cause
Osmotic Demyelination Syndrome Risk Factors
| Risk Factor | Impact | Recommended Limit |
| Chronic hyponatremia (>48 hrs) | HIGH | 8 mEq/L in 24 hours |
| Severe hyponatremia (Na <105) | HIGH | 6 mEq/L in 24 hours |
| Alcoholism / Liver disease | HIGH | 6-8 mEq/L in 24 hours |
| Malnutrition / Hypokalemia | MODERATE | 8 mEq/L in 24 hours |
| Acute (<24-48 hrs) symptomatic | LOWER | Up to 10-12 mEq/L in 24 hours* |
* Acute symptomatic hyponatremia allows faster initial correction to relieve symptoms, but still requires close monitoring
What is Sodium Deficit?
Sodium deficit represents the amount of sodium needed to raise serum sodium from the current level to a target level. It is calculated based on total body water and the difference between current and target sodium concentrations. Understanding sodium deficit is crucial for safe treatment of hyponatremia.
Deficit Formula
Deficit = TBW ร (Target Na - Current Na). Simple but requires accurate TBW estimation.
Correction Risk
Too rapid correction causes osmotic demyelination syndrome (ODS), a devastating neurological complication. Limit to 8-10 mEq/L per 24 hours.
Monitor Closely
Check sodium every 2-4 hours during correction. The body may autocorrect, especially with volume repletion. Adjust therapy based on response.
Key Sodium Deficit Formulas
1. Sodium Deficit
2. Adrogue-Madias Formula
Predicts sodium change per liter of infusate
3. Total Body Water
Male 0.6, Female 0.5, adjust for age and body composition
Frequently Asked Questions
What is osmotic demyelination syndrome?
ODS (formerly central pontine myelinolysis) is a devastating neurological condition caused by too rapid correction of chronic hyponatremia. Symptoms include dysarthria, dysphagia, quadriparesis, and locked-in syndrome. Prevention is key.
How fast should I correct hyponatremia?
For chronic hyponatremia: maximum 8 mEq/L in first 24 hours, 18 mEq/L in 48 hours. For acute symptomatic: can correct 4-6 mEq/L in first 6 hours, then slow down. Higher limits may apply in specific situations with close monitoring.
When should I use 3% saline?
Reserve 3% saline for severe symptomatic hyponatremia (seizures, coma) where rapid initial correction is life-saving. Use 100-150 mL boluses to raise sodium by 1-2 mEq/L quickly. Then switch to slower correction.
What if I overcorrect?
If sodium rises too quickly, immediately lower it back down using D5W (5% dextrose) infusion and/or desmopressin (DDAVP) 2-4 mcg IV. The goal is to keep within safe correction limits. Consult nephrology.
Clinical Pearls
Treat the Cause, Not Just the Number
Always identify the underlying cause of hyponatremia. SIADH needs fluid restriction, hypovolemia needs volume, hypervolemia often needs diuretics with sodium replacement.
Volume Status Changes Everything
Hypovolemic hyponatremia often autocorrects with saline alone. Be vigilant - sodium can rise very rapidly once ADH suppression returns, exceeding safe limits.
High Risk Groups for ODS
Chronic hyponatremia, alcoholism, malnutrition, hypokalemia, liver disease, and Na <105 mEq/L carry higher ODS risk. Be extra conservative in these patients.
Check Potassium Too
Potassium replacement also raises sodium (1 mEq K = 1 mEq Na effect on osmolality). Factor this into your correction calculations, especially with concurrent hypokalemia.
Related Calculators
For informational purposes only โ not medical advice. Consult a healthcare professional before acting on results.
๐ฅ Health Facts
โ WHO
โ CDC
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