Determine Total Body Water Factor
Severe hyponatremia treatment
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Evidence-based calculations Used in clinical settings worldwide Regular monitoring recommended
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3% Saline 500mL
Severe hyponatremia treatment
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0.9% NS 1L for Hypovolemia
Standard isotonic replacement
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Half Normal Saline
Maintenance fluid therapy
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D5W for Hypernatremia
Free water replacement
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Lactated Ringers 2L
Resuscitation fluid
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SIADH Treatment
Euvolemic hyponatremia
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Clinical Scenarios
Click a scenario to load values for common clinical situations:
3% Saline 500mL
Severe hyponatremia treatment
Patient with Na 120, seizures, needs emergent correction
0.9% NS 1L for Hypovolemia
Standard isotonic replacement
Dehydrated patient with mild hyponatremia Na 130
Half Normal Saline
Maintenance fluid therapy
Post-operative patient, Na 140, maintenance fluids
D5W for Hypernatremia
Free water replacement
Elderly nursing home patient with Na 155, dehydration
Lactated Ringers 2L
Resuscitation fluid
Septic patient, volume resuscitation needed
SIADH Treatment
Euvolemic hyponatremia
Patient with SIADH, Na 125, fluid restriction plus 3% saline
Patient Parameters
IV Fluid Selection
Sodium Change Results
+4.6
Expected Sodium Change (mEq/L)
CAUTION
124.6
New Sodium (mEq/L)
42.0
Total Body Water (L)
109
mL per 1 mEq/L Change
875
mL for Safe 24h Max
Infusing 500mL will change sodium by 4.6 mEq/L. New sodium: 124.6 mEq/L. This represents a 57.1% of the safe 24h limit (8 mEq/L).
Recommendations
- Volume for 1 mEq/L change: 109.4 mL
- Volume for safe 8 mEq/L change (24h max): 875.3 mL
- 3% saline: Consider 100-150mL boluses for acute symptoms
- Infusion rate typically 15-30 mL/hr for controlled correction
- Recheck sodium every 2-4 hours during active correction
- Slow or stop correction if approaching 8 mEq/L in 24h
Sodium Change Visualization
Volume for Target Changes
Sodium Levels
Infusate Na Content
Step-by-Step Calculations
Step 1: Determine Total Body Water Factor
Formula: ext{TBW} ext{Factor} ext{based} ext{on} ext{age}, ext{gender}, ext{body} ext{type}
Calculation: Male, normal = 0.6
Result: TBW Factor = 0.6
Step 2: Calculate Total Body Water
Formula: ext{TBW} = ext{Weight} ( ext{kg}) x ext{TBW} ext{Factor}
Calculation: TBW = 70 kg x 0.6
Result: 42.0 L
Step 3: Apply Adrogue-Madias Formula (per 1L)
Formula: ext{Change} ext{per} 1L = rac{ ext{Infusate} ext{Na} - ext{Serum} ext{Na}}{ ext{TBW} + 1}
Calculation: Change = (513 - 120) / (42.0 + 1)
Result: 9.14 mEq/L per liter
Step 4: Calculate Expected Change for Given Volume
Formula: ext{Expected} ext{Change} = ext{Change} ext{per} 1L x ext{Volume} (L)
Calculation: Expected = 9.14 x 0.5 L
Result: 4.57 mEq/L
Step 5: Calculate New Serum Sodium
Formula: ext{New} ext{Na} = ext{Current} ext{Na} + ext{Expected} ext{Change}
Calculation: New Na = 120 + 4.57
Result: 124.6 mEq/L
IV Fluid Sodium Content Reference
| IV Fluid | Na+ (mEq/L) | Tonicity | Common Uses |
| 3% Saline (Hypertonic) | 513 | Hypertonic | Severe symptomatic hyponatremia, cerebral edema |
| 0.9% Normal Saline | 154 | Isotonic | Volume resuscitation, mild hyponatremia |
| Lactated Ringers | 130 | Isotonic | Resuscitation, surgical patients |
| 0.45% Half Normal Saline | 77 | Hypotonic | Maintenance fluids, free water provision |
| D5W (5% Dextrose) | 0 | Hypotonic | Hypernatremia treatment, free water |
Safe Sodium Correction Limits
| Clinical Scenario | 24h Limit | 48h Limit | Notes |
| Chronic Hyponatremia (>48h) | 8 mEq/L | 16-18 mEq/L | Highest ODS risk - strict limits |
| Acute Hyponatremia (<48h) | 10-12 mEq/L | 18-20 mEq/L | Lower ODS risk, can correct faster |
| Severe Symptoms (seizures) | 4-6 mEq/L initial | Then standard | Rapid initial correction to stop symptoms |
| High ODS Risk Patients | 6 mEq/L | 12 mEq/L | Alcoholism, malnutrition, hypokalemia |
What is the Adrogue-Madias Formula?
The Adrogue-Madias formula predicts the change in serum sodium concentration that will result from infusing a liter of any IV fluid. This calculation is essential for safely managing hyponatremia and hypernatremia while avoiding dangerous overcorrection.
Predictive Formula
Accurately predicts sodium change based on infusate sodium, serum sodium, and total body water. Allows precise fluid therapy planning.
Safety Planning
Helps prevent osmotic demyelination syndrome (ODS) by calculating volumes needed to stay within safe correction limits of 8-10 mEq/L per 24 hours.
Fluid Selection
Guides choice of IV fluid based on desired sodium change. Different fluids (3% saline, NS, D5W) have vastly different effects on serum sodium.
How to Use the Adrogue-Madias Formula
Step-by-Step Approach
- 1
Determine Clinical Context
Is this acute (<48h) or chronic (>48h) hyponatremia? Are there symptoms?
- 2
Calculate Total Body Water
TBW = Weight × Factor (0.6 for men, 0.5 for women, lower for elderly/obese)
- 3
Select Appropriate Infusate
3% saline for severe hyponatremia, NS for volume depletion, D5W for hypernatremia
- 4
Apply the Formula
Change in Na = (Infusate Na - Serum Na) / (TBW + 1) per liter infused
- 5
Plan Safe Correction
Calculate volume to achieve target change while staying within safe limits
- 6
Monitor and Adjust
Check sodium every 2-4 hours and adjust infusion rate as needed
When to Use This Calculator
Severe Hyponatremia
Na <120 mEq/L with or without symptoms. Planning 3% saline therapy.
Symptomatic Hyponatremia
Seizures, altered mental status, or severe headache requiring emergent correction.
Hypernatremia Treatment
Planning free water replacement with D5W or hypotonic saline for elevated sodium.
Volume Resuscitation
Predicting sodium changes when giving large volumes of NS or LR for shock.
SIADH Management
Careful correction in euvolemic hyponatremia while avoiding overcorrection.
Monitoring Therapy
Ongoing assessment to ensure correction stays within safe limits over 24-48 hours.
Key Formulas
1. Adrogue-Madias Formula
This gives the change in serum sodium per 1 liter of infusate. Multiply by actual volume (in liters) for total change.
2. Total Body Water (TBW)
TBW Factor: Men 0.6, Women 0.5, Elderly 0.5/0.45, Obese 0.5/0.4
3. Volume for Target Change
Calculate how much infusate is needed to achieve a specific sodium change
4. Safe Correction Rate
Exceeding this rate increases risk of osmotic demyelination syndrome (ODS)
Frequently Asked Questions
Why is slow correction important in hyponatremia?
In chronic hyponatremia (>48 hours), brain cells adapt by losing organic osmolytes. Rapid correction causes water to shift out of brain cells faster than osmolytes can be restored, leading to osmotic demyelination syndrome (ODS). ODS causes irreversible neurological damage including locked-in syndrome. The safe limit is 8-10 mEq/L per 24 hours.
When can I correct sodium faster?
Faster initial correction (1-2 mEq/L per hour for 2-3 hours) is appropriate for acute symptomatic hyponatremia with seizures or severe neurological symptoms. The goal is a 4-6 mEq/L rise to stop acute symptoms, then slow to standard correction rates. Even in emergent situations, the 24-hour limit should still be respected.
What if sodium rises too quickly?
If overcorrection occurs, you can re-lower sodium using D5W infusion (3-6 mL/kg/hr) and/or desmopressin (DDAVP) 1-2 mcg IV. DDAVP prevents water excretion, allowing controlled re-lowering. The goal is to bring the correction back within safe limits. This is especially important in patients with high ODS risk (alcoholism, malnutrition, liver disease).
Does the formula account for ongoing losses?
No, the Adrogue-Madias formula assumes a closed system with no ongoing fluid losses. In reality, patients have insensible losses (600-900 mL/day), urine output, and potentially GI losses. The actual sodium change may differ from predicted. This is why frequent monitoring (every 2-4 hours initially) and recalculation are essential.
Why use TBW + 1 in the formula?
The "+1" in the denominator accounts for the volume of the infusate itself being added to the body water pool. This prevents overestimation of the sodium change. When you infuse 1 liter of fluid, you're not just changing the concentration of existing body water - you're also increasing the total volume.
Clinical Pearls
3% Saline Dosing
For severe symptoms, give 100-150mL 3% saline boluses over 10-20 minutes. Can repeat up to 3 times if symptoms persist. This typically raises sodium by 2-3 mEq/L per bolus.
High-Risk Patients for ODS
Alcoholics, malnourished patients, hypokalemia, liver disease, and elderly require even more conservative correction (6 mEq/L per 24h). These patients have less brain reserve for osmolyte restoration.
Urine Output Matters
If urine output suddenly increases (aquaresis), sodium may rise faster than expected. This commonly happens when the underlying cause (e.g., hypovolemia, pain, nausea) resolves and ADH suppression occurs.
DDAVP Clamp Strategy
Some experts use proactive DDAVP (1-2 mcg q8h) to prevent aquaresis and allow controlled sodium rise with hypertonic saline. This "DDAVP clamp" strategy provides more predictable correction.
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For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
— WHO
— CDC
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