Calculating the impact of various IV fluids on serum sodium levels.
Monitoring the safety of sodium correction to avoid over-correction.
Correction Goal
The goal is usually to alleviate symptoms, not to return to a "normal" range immediately. In chronic cases, a 4–6 mEq/L increase is often sufficient to stop severe symptoms.
Section 2
Formula & Logic
Adrogué-Madias Formula
Change in Serum Na = (Infusate Na - Serum Na) / (TBW + 1)
Total Body Water (TBW) Estimation
Non-elderly Men
Weight × 0.6
Non-elderly Women
Weight × 0.5
Elderly Men
Weight × 0.5
Elderly Women
Weight × 0.45
Common Infusate Na Content
3% Hypertonic Saline
513 mEq/L
0.9% Normal Saline
154 mEq/L
Lactated Ringer’s
130 mEq/L
0.45% Half Normal Saline
77 mEq/L
5% Dextrose (D5W)
0 mEq/L
Section 3
Pearls/Pitfalls
The "Speed Limit"
Maximum Correction: 8–10 mEq/L in any 24-hour period (and < 18 mEq/L in 48 hours). For patients at high risk of ODS (alcoholism, malnutrition, liver disease), keep correction < 6–8 mEq/L/24h.
Osmotic Demyelination Syndrome (ODS)
Previously known as Central Pontine Myelinolysis. Rapid correction of chronic hyponatremia causes water to exit brain cells too quickly, leading to irreversible demyelination of the pons and other brain structures.
Key Gotchas
The formula does NOT account for urinary losses, which can cause Na to rise much faster than predicted (especially as ADH levels drop).
In volume-depleted patients, once fluids are replaced, ADH secretion shuts off, leading to a "water diuresis" that can dangerously accelerate Na correction.
Always use "Corrected Sodium" if the patient is significantly hyperglycemic.
Section 4
Next Steps
Clinical Action Plan
01
Determine chronicity: If > 48h or unknown, treat as chronic.
02
For severe symptoms: Give 100 mL bolus of 3% saline; repeat up to 3x if symptoms persist.
03
Frequent Monitoring: Check Serum Na every 2–4 hours during active correction.
04
The "Desmopressin Clamp": In patients at very high risk for over-correction, some clinicians use DDAVP to prevent water diuresis and lock the Na rise at a predictable rate.
05
If over-correction occurs: Consider giving D5W or DDAVP to lower the sodium back toward the target limit.
Related Tools
Free Water Deficit (Hypernatremia)
Corrected Sodium for Hyperglycemia
FENa (Fractional Excretion of Sodium)
Section 5
Evidence Appraisal
Primary Reference
Hyponatremia.
Adrogué HJ et al. • New England Journal of Medicine (NEJM). 2000;342(21):1581-9. Provides the clinical framework and formulas used globally for sodium management.
Consensus Guidelines
Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations.
Verbalis JG et al. • American Journal of Medicine. 2013;Comprehensive US consensus on safe correction limits and management strategies.
Section 6
Literature
The Madias Formula
Nicolaos Madias and Horacio Adrogué revolutionized electrolyte management by providing a simplified bedside equation. Before this, clinicians relied on complex "sodium deficit" equations that often failed to account for the impact of volume in the infusate.
