Sodium Deficit Calculator

Na⁺ Deficit = TBW × (Target Na⁺ − Current Na⁺)

Calculate the sodium deficit in hyponatremia with built-in safe correction rate monitoring. Prevent osmotic demyelination syndrome by following evidence-based correction guidelines. Enter your values below for instant results.

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Calculate Sodium Deficit

Enter patient weight, sex, current sodium, and target sodium for deficit calculation with safety monitoring.

Patient Data

Weight in kg, sodium in mEq/L

Results

Enter values and click Calculate to see your results

Formula & Calculation

Sodium Deficit Formula

How sodium replacement needs are calculated.

Deficit Calculation

Na⁺ Deficit = TBW × (Target Na⁺ − Current Na⁺)

Total Body Water (TBW) is estimated as Weight × 0.6 for males and Weight × 0.5 for females. The deficit represents the total mEq of sodium needed to reach the target level, assuming a closed system.

Safe Correction

Max Correction: 8–10 mEq/L per 24 hours

Regardless of the total deficit, correction must be slow to prevent osmotic demyelination syndrome (ODS). The safe rate is ≤8 mEq/L in 24 hours for chronic hyponatremia. Acute hyponatremia (<48h) can be corrected faster.

Step-by-Step Calculation

1
Calculate TBW. For a 70 kg male: TBW = 70 × 0.6 = 42 L.
2
Determine the sodium gap. Target Na⁺ − Current Na⁺ = 135 − 125 = 10 mEq/L.
3
Compute the deficit. Na⁺ Deficit = 42 × 10 = 420 mEq.
4
Plan safe correction. Correct ≤8 mEq/L in first 24h (safe target = 133 mEq/L). This may require multiple days for full correction.

Live Calculation Preview

Updates in real-time as you change values above.

Understanding the Basics

What is Hyponatremia?

The most common electrolyte disorder explained.

Sodium & Body Water

Sodium is the primary extracellular cation and the main determinant of serum osmolality. Hyponatremia (Na⁺ <135 mEq/L) usually reflects excess water relative to sodium, not sodium depletion alone. The body responds to osmolality changes by shifting water across cell membranes.

Why Safe Correction Matters

In chronic hyponatremia, brain cells adapt by losing intracellular osmolytes. If sodium is corrected too rapidly, the now-hypotonic brain cells shrink as water moves out, causing osmotic demyelination syndrome (ODS). This devastating condition causes irreversible neurological damage. The golden rule: correct slowly, no more than 8 mEq/L in 24 hours.

Current Na⁺ level
Target Na⁺ level
Correction rate risk
Reference Values

Sodium & Hyponatremia Reference

Classification and reference ranges for serum sodium.

ClassificationNa⁺ LevelUnitNotes
Normal Sodium135 – 145mEq/LTarget range for correction
Mild Hyponatremia125 – 134mEq/LOften asymptomatic; fluid restrict
Moderate Hyponatremia120 – 124mEq/LNausea, confusion; careful correction
Severe Hyponatremia< 120mEq/LMedical emergency — seizures, coma
TBW Factor (Male)0.6× weight(kg)Higher water fraction
TBW Factor (Female)0.5× weight(kg)Lower water fraction

Where Does the Current Na⁺ Fall?

This gauge shows the hyponatremia severity and correction rate safety.

Clinical Interpretation

Hyponatremia Management

Clinical approach based on severity.

🔴

Severe Hyponatremia

Na⁺ < 120 mEq/L
  • Medical emergency if symptomatic
  • Seizures, obtundation, coma possible
  • May need hypertonic saline (3% NaCl)
  • Correct ≤8 mEq/L in 24h (max 10)
  • Frequent Na⁺ monitoring q2-4h
🟢

Mild Hyponatremia

Na⁺ 125–134 mEq/L
  • Often asymptomatic or subtle symptoms
  • First-line: fluid restriction (<1L/day)
  • Identify and treat underlying cause
  • Correct slowly — ≤8 mEq/L in 24h
  • Monitor Na⁺ daily during correction
🔵

Causes of Hyponatremia

Key etiologies to consider
  • SIADH (most common inpatient cause)
  • Heart failure, cirrhosis (hypervolemic)
  • Diuretics (especially thiazides)
  • Psychogenic polydipsia
  • Adrenal insufficiency, hypothyroidism
Treatment Approach

Sodium Correction Strategies

Evidence-based approaches to hyponatremia correction.

Key Principles

  • Identify the cause first — Treatment depends on volume status: hypovolemic (give NS), euvolemic (fluid restrict), or hypervolemic (fluid restrict + diuretics).
  • Acute vs chronic — Hyponatremia developing in <48 hours can be corrected more rapidly. Chronic hyponatremia (>48h or unknown duration) must be corrected slowly.
  • 3% saline for emergencies — For seizures or severe symptoms, give 100 mL of 3% NaCl over 10 minutes (can repeat ×2). This raises Na⁺ by ~2 mEq/L per bolus.
  • Monitor and desmopressin clamp — If correction is too rapid (approaching 8 mEq/L), desmopressin (DDAVP) can be given to slow or stop the rise, along with D5W infusion.
  • Check sodium frequently — During active correction, check serum Na⁺ every 2–4 hours to ensure safe rate of rise.
Common Questions

Frequently Asked Questions

Answers to common questions about sodium deficit and hyponatremia.

Hyponatremia is defined as a serum sodium concentration below 135 mEq/L. It is the most common electrolyte disorder in hospitalized patients, affecting up to 30% of inpatients. It usually reflects excess body water relative to sodium rather than true sodium depletion. The clinical significance ranges from asymptomatic to life-threatening depending on severity and rate of development.
For chronic hyponatremia (duration >48 hours or unknown): correct no more than 8 mEq/L in 24 hours and no more than 18 mEq/L in 48 hours. Some experts recommend even slower rates (6 mEq/L per 24h) in high-risk patients (alcoholics, malnourished, hypokalemic, liver disease). For acute hyponatremia (<48h) with severe symptoms, faster correction with hypertonic saline is acceptable.
ODS (formerly central pontine myelinolysis) is a devastating neurological condition caused by overly rapid correction of chronic hyponatremia. When the brain has adapted to low osmolality by losing intracellular osmolytes, rapid correction causes brain cells to shrink, damaging myelin sheaths. Symptoms appear 2–6 days after overcorrection and include dysarthria, dysphagia, quadriparesis, behavioral changes, and in severe cases, locked-in syndrome. It is largely irreversible.
Causes are classified by volume status: Hypovolemic (dehydration, diuretics, vomiting, diarrhea), Euvolemic (SIADH — most common inpatient cause, hypothyroidism, adrenal insufficiency, psychogenic polydipsia), and Hypervolemic (heart failure, cirrhosis, nephrotic syndrome). Medications are a common cause — especially thiazide diuretics, SSRIs, carbamazepine, and desmopressin.
Severe symptomatic hyponatremia (seizures, coma) is treated with 3% hypertonic saline: bolus 100 mL IV over 10 minutes, repeated up to 3 times. Goal is to raise Na⁺ by 4–6 mEq/L in the first few hours to resolve symptoms. After stabilization, switch to slow correction (≤8 mEq/L total in 24h). If overcorrection occurs, use desmopressin (DDAVP) 1–2 mcg IV + D5W to lower Na⁺ back down ("re-lowering" strategy).
Syndrome of Inappropriate Antidiuretic Hormone (SIADH) is the most common cause of euvolemic hyponatremia. ADH (vasopressin) causes the kidneys to retain free water, diluting serum sodium. Common causes include CNS disorders (stroke, infection, trauma), pulmonary diseases (pneumonia, lung cancer), medications (SSRIs, carbamazepine), pain, nausea, and malignancies. Diagnosis requires: hyponatremia, low serum osmolality, concentrated urine (>100 mOsm/kg), euvolemia, and normal adrenal/thyroid function.