CRRT Sodium Calculator

Sodium management during continuous renal replacement therapy

Na
Clinical Scenario
Rx
CRRT Prescription
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Target Sodium
Sources
Hypernatremia: Yessayan et al. Semin Dial 2021; Tinawi Semin Dial 2021 · Hyponatremia: Rosner & Connor CJASN 2018 · Validation: Fülöp et al. Blood Purif 2019 · Sieving: Zadek et al. Crit Care 2025; Chadha et al. Pediatr Nephrol 2002
For educational purposes only. Not a substitute for clinical judgment.
Verify all calculations independently.
v1.0 · Supplementary material
Σ
Effective Circuit Sodium

The weighted average sodium of all fluids entering the CRRT circuit determines the equilibration point.

Circuit Na⁺ = Σ(flow × [Na⁺]) / Σ(flows)

Includes replacement fluid, dialysate, and citrate anticoagulant (if used). The patient's serum sodium will drift toward this value at steady state.

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Therapeutic Hypernatremia

When Target Na⁺ exceeds the circuit Na⁺, hypertonic saline (3% NaCl, 513 mEq/L) is required to maintain the target.

3% NaCl rate = Total flow × (Target Na − Circuit Na) / (513 − Target Na)

Derived from mass balance: at steady state, sodium input equals sodium output. Solving for the HTS flow rate yields this formula.

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Severe Hyponatremia

When the circuit Na⁺ exceeds the Target Na⁺, D5W (0 mEq/L Na⁺) dilutes the circuit sodium to slow correction and prevent osmotic demyelination.

D5W rate = Total flow × (Circuit Na − Target Na) / Target Na

Same mass balance derivation, solving for D5W volume needed to achieve the target equilibration sodium.

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Assumptions & Limitations
  • Sodium sieving coefficient = 1.0
  • Gibbs-Donnan effect may reduce actual clearance by 2–5% in hypoalbuminemic patients
  • Steady-state model — does not account for transient dynamics
  • Patient fluid intake, UF, and other IV infusions not included
  • Frequent serum Na⁺ monitoring is essential
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References
Primary Formula Sources

Yessayan L, Yee J, Frinak S, Szamosfalvi B. Continuous renal replacement therapy for the management of acid-base and electrolyte imbalances in acute kidney injury. Semin Dial. 2021;34(5):372-383. PMID 34218456
→ Source: 3% NaCl rate formula for therapeutic hypernatremia

Rosner MH, Connor MJ Jr. Management of severe hyponatremia with continuous renal replacement therapies. Clin J Am Soc Nephrol. 2018;13(5):787-789. PMID 29463598
→ Source: D5W rate formula; worked example with ACD-A citrate

Tinawi M. Management of hypernatremia and hyponatremia during continuous renal replacement therapy. Semin Dial. 2021;34(6):499-508. PMID 33063373
→ Independent derivation confirming mass balance approach

Clinical Validation

Fülöp T, Zsom L, Rodríguez RD, et al. Therapeutic hypernatremia management during continuous renal replacement therapy. Blood Purif. 2019;47(1-3):257-265. PMID 30848433
→ Case series: 80–100 mL/hr 3% NaCl rates confirmed empirically

Yessayan L, Yee J, Frinak S, Szamosfalvi B. Treatment of severe hyponatremia in patients with kidney failure. Am J Kidney Dis. 2014;64(2):305-310. PMID 24364893
→ Low-sodium replacement fluid approach

Sieving Coefficient & Citrate Data

Zadek F, Gattin E, Galli A, et al. Sodium sieving coefficient and Gibbs-Donnan effect during CRRT. Crit Care. 2025;29:82. PMID 40059273
→ Na SC slightly <1.0 with albumin; 2–5% conservative bias

Chadha V, Garg U, Warady BA, Alon US. Citrate clearance in children receiving CVVHD. Pediatr Nephrol. 2002;17:819-824. PMID 12376810
→ Citrate SC ≈ 1.0; supports inclusion of citrate Na in calculations

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About

Supplementary tool for: Management of AKI in Acute Brain Injury

Version 1.0 · For educational use only · Based on published mass balance principles