Predict serum sodium change from IV fluid infusion using the Adrogue-Madias formula. Covers NS, hypertonic saline, D5W, LR, and custom fluids.
Managing sodium disorders requires precise knowledge of how intravenous fluids will shift serum sodium. The Adrogue-Madias formula — published in the New England Journal of Medicine — is the standard bedside tool for predicting the expected change in serum sodium per liter of any given IV fluid. It accounts for the patient's total body water (TBW), the sodium concentration of the infusate, and the current serum sodium.
This calculator covers all common IV fluids (D5W, quarter-normal, half-normal, normal saline, lactated Ringer's, Plasma-Lyte, 3% and 5% hypertonic saline) and allows custom fluid compositions. It predicts the change in sodium for any infusion volume, shows a volume-for-target table (how much fluid to achieve a specific sodium correction), and provides a safety assessment comparing the expected correction against evidence-based 24-hour limits.
Overcorrection of hyponatremia risks osmotic demyelination syndrome (ODS), while undercorrection of worsening hypernatremia can lead to cerebral edema. The calculator flags dangerous corrections and reminds clinicians to check serum sodium after every liter.
Sodium disorders are common in hospitalized patients, and incorrect IV fluid selection can worsen dysnatremia or cause dangerous overcorrection. This calculator lets you compare fluids, predict outcomes, and stay within safe correction limits before ordering. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain. Use this clarification to avoid ambiguous interpretation.
Adrogue-Madias: ΔNa = (Infusate Na⁺ − Serum Na⁺) / (TBW + 1) per liter of infusate. TBW = body weight × factor (Male <65y: 0.6; Male ≥65y: 0.5; Female <65y: 0.5; Female ≥65y: 0.45). Total change = ΔNa × volume(L).
Result: ΔNa = +4.5 mEq/L; Predicted Na⁺ = 124.5 mEq/L
TBW = 70 × 0.6 = 42 L. ΔNa per liter = (513 − 120) / (42 + 1) = 9.14. For 500 mL: 9.14 × 0.5 = +4.57 mEq/L. This is within the safe 24h limit of 8 mEq/L for severe hyponatremia.
Three percent NaCl is reserved for symptomatic hyponatremia (seizures, severe confusion, respiratory distress) or serum sodium below 120 mEq/L with symptoms. It should be administered via central or large-bore peripheral line, typically as 100–150 mL boluses in the ED or ICU. Continuous infusion at 15–30 mL/h with q2h sodium checks is the standard inpatient approach. The goal is partial correction — raise sodium enough to resolve acute symptoms, then slow the rate.
To prevent overcorrection in high-risk patients, many nephrologists use a "DDAVP clamp": administer desmopressin 1–2 mcg IV q6–8h alongside the corrective fluid. DDAVP prevents the kidneys from excreting free water, making sodium correction entirely dependent on IV input — giving the clinician full control. If the sodium rises too fast, D5W can be infused to lower it back. This strategy has dramatically reduced ODS incidence in academic centers.
The three most frequent errors: (1) Forgetting that the formula assumes no renal water excretion — patients with high ADH who then receive volume and suppress ADH can rapidly autocorrect as they excrete electrolyte-free water. (2) Not accounting for concurrent potassium replacement, which raises sodium independently. (3) Relying on the initial calculation without rechecking sodium, leading to overcorrection discovered too late.
It predicts the expected change in serum sodium per liter of IV fluid based on the difference between the infusate sodium and serum sodium, divided by total body water plus one. Published by Adrogue and Madias in 2000, it is the most widely used bedside formula for sodium management.
The +1 accounts for the volume of the infused liter itself distributing into total body water. Each liter of infusate expands the volume of distribution by approximately 1 liter.
For chronic hyponatremia (≥48h or unknown duration): no more than 8–10 mEq/L in 24 hours. For patients with high ODS risk (alcoholism, malnutrition, hypokalemia): maximum 6 mEq/L in 24h. For acute hyponatremia (<48h): 1–2 mEq/L per hour is acceptable.
ODS (formerly central pontine myelinolysis) occurs when chronic hyponatremia is corrected too rapidly. Brain cells that adapted to low osmolality are suddenly surrounded by hypertonic extracellular fluid, causing demyelination. Symptoms (dysarthria, dysphagia, quadriparesis) appear 2–6 days after overcorrection.
The standard Adrogue-Madias formula does not include potassium. However, potassium is an effective osmole — giving KCl raises serum sodium similarly to NaCl. A modified version adds infusate K⁺ to Na⁺ in the numerator: ΔNa = (infusate Na + infusate K − serum Na) / (TBW + 1). Keep this in mind for patients receiving KCl simultaneously.
Studies show the formula overestimates sodium change by 15–20% in practice because it doesn't account for ongoing renal free water excretion, insensible losses, or potassium shifts. Always recheck sodium after each liter and recalculate. The formula is a guide, not a guarantee.