Sodium Correction Calculator
Calculate how much sodium is needed to correct hyponatremia safely. Enter current sodium, target sodium, and patient weight. Includes correction for hyperglycemia.
Understanding Sodium and Total Body Water
Sodium is the main determinant of serum osmolality and controls water distribution between cells and blood. Normal sodium is 135-145 mEq/L. When sodium drops, water moves into cells, causing them to swell. Brain cell swelling in severe hyponatremia causes confusion, seizures, and coma.
The sodium deficit formula estimates how much sodium is needed to raise serum sodium to a target. It uses total body water (TBW), calculated as a percentage of body weight. Men have more muscle and less fat, so TBW is about 60% of weight. Women and elderly patients have lower TBW (~50%).
Formula: Sodium deficit (mEq) = TBW × (target Na - current Na). For example, a 70 kg man with sodium of 125 mEq/L targeting 130 mEq/L needs: (70 × 0.6) × (130 - 125) = 42 × 5 = 210 mEq of sodium.
Medical disclaimer: This calculator is for educational purposes only. Sodium correction requires expert medical management. Rapid correction can cause permanent neurological damage or death. Only qualified healthcare providers should treat hyponatremia.
Safe Sodium Correction Strategies
The most critical rule in hyponatremia management is slow correction. Raising sodium by more than 8-10 mEq/L in 24 hours risks osmotic demyelination syndrome, a devastating neurological condition that can occur 2-7 days after overly rapid correction.
For chronic hyponatremia (duration >48 hours or unknown), target a correction rate of 4-6 mEq/L per 24 hours. For acute hyponatremia (<48 hours) with severe symptoms like seizures, a faster initial correction of 1-2 mEq/L per hour for 3-4 hours is acceptable, followed by slower correction.
Treatment modalities include hypertonic saline (3% NaCl) for symptomatic patients, normal saline for euvolemic or hypovolemic hyponatremia, and fluid restriction with or without loop diuretics for hypervolemic hyponatremia (heart failure, cirrhosis).
Frequent sodium monitoring is essential. Check sodium every 2-4 hours during active correction and every 6 hours thereafter. If sodium rises too quickly, give hypotonic fluids (0.45% saline or even D5W) to prevent overshoot and reduce demyelination risk.
Causes and Types of Hyponatremia
Hyponatremia is classified by volume status. Hypovolemic hyponatremia (low total body sodium and water) occurs with vomiting, diarrhea, diuretics, and salt-wasting nephropathy. Urine sodium is low (<20 mEq/L) unless kidneys are the cause.
Euvolemic hyponatremia (normal sodium, excess water) is caused by SIADH (syndrome of inappropriate antidiuretic hormone). ADH is secreted despite low serum osmolality, causing water retention. Causes include lung cancer, CNS disorders, and drugs like SSRIs, carbamazepine, and cyclophosphamide.
Hypervolemic hyponatremia (excess sodium and water, but water gain exceeds sodium gain) occurs in heart failure, cirrhosis, and nephrotic syndrome. Urine sodium is low (<20 mEq/L) as the kidneys retain sodium to compensate for perceived low volume.
Hyperglycemia causes pseudohyponatremia. High glucose pulls water from cells, diluting sodium. Corrected sodium = measured sodium + 1.6 × (glucose - 100) / 100. If glucose is 500 mg/dL and sodium is 130 mEq/L, corrected sodium is 130 + 1.6 × 4 = 136.4 mEq/L—actually normal.
Frequently Asked Questions
What is hyponatremia?
Hyponatremia is serum sodium below 135 mEq/L. It's the most common electrolyte disorder, caused by water retention, sodium loss, or both. Symptoms range from nausea and confusion to seizures and coma in severe cases (<120 mEq/L).
How fast can I correct sodium?
The safe correction rate is 6-8 mEq/L per 24 hours, with a maximum of 10-12 mEq/L in the first 24 hours for severe symptomatic hyponatremia. Faster correction risks osmotic demyelination syndrome, a devastating neurological complication.
What is osmotic demyelination syndrome?
Osmotic demyelination (formerly called central pontine myelinolysis) occurs when sodium is corrected too quickly. Brain cells adapted to low sodium shrink rapidly, damaging myelin. Patients develop locked-in syndrome, quadriplegia, dysphagia, and dysarthria.
Why does hyperglycemia affect sodium?
High glucose draws water from cells into blood, diluting sodium. For every 100 mg/dL rise in glucose above 100, sodium drops about 1.6 mEq/L. Correcting sodium for glucose reveals true sodium status.
How do I calculate total body water?
Total body water (TBW) = weight × factor. For men, factor = 0.6 (60% of weight). For women, factor = 0.5 (50%). Elderly and obese patients have less TBW; infants have more (~0.7).