- Enter the net ultrafiltration volume removed from the patient in mL. This is the net fluid taken off (after replacement / dialysate accounting), not the gross effluent.
- Enter the number of hours that volume was removed over. To enter a rate in mL/hr directly, leave hours at 1 and type the mL/hr value in the volume field.
- Enter the patient's body weight (kg). The net UF rate (mL/hr), the weight-normalized rate (mL/kg/hr), and the intensity category update automatically.
- Read the intensity band: < 1.01 mL/kg/hr = low; 1.01–1.75 = moderate (often the target); > 1.75 = high (associated with increased mortality and hemodynamic instability).
All computation runs in your browser; no values are stored or transmitted.
When to Use
Use this in any critically ill adult with acute kidney injury (or fluid overload) receiving CRRT, to quantify how intensely fluid is being removed and to titrate decongestion to a safe, even pace. After accounting for replacement fluid and dialysate, express the net fluid removed as a rate (mL/hr) and normalize it to body weight (mL/kg/hr). Judging that normalized rate against the Murugan/RENAL thresholds tells you whether removal is too gentle (risk of persistent fluid overload), in the usual target band, or aggressive enough to raise the risk of hemodynamic instability and mortality.
Appropriate population
Critically ill adults with AKI on continuous renal replacement therapy (CVVH, CVVHD, CVVHDF) who require fluid removal. Most useful when setting or reviewing the prescribed net UF goal during ICU rounds, when titrating to even, gradual decongestion, and when reconciling fluid balance with hemodynamics over the prior hours of therapy.
When NOT to rely on it
This describes CRRT net fluid-removal intensity only — it is not the intermittent-hemodialysis UF-rate limit (the HD safety threshold is roughly an order of magnitude higher, ~13 mL/kg/hr). It also is not the CRRT effluent dose (clearance), which is a different number with its own 20–25 mL/kg/hr target. The thresholds derive from observational data; they inform, but do not replace, bedside hemodynamic judgment. A rate inside the "moderate" band can still be too fast for an unstable patient, and a "low" rate may be deliberate during shock.
Pearls & Pitfalls
Net UF rate is NOT the CRRT dose
This is the single most common confusion. Net ultrafiltration rate (mL/kg/hr) is the fluid-removal / decongestion intensity — how fast the patient is losing volume. The CRRT effluent dose (also in mL/kg/hr) is the clearance / solute-removal prescription, with a target of 20–25 mL/kg/hr. They share units but answer different questions. Use the CRRT Dose & Effluent Flow calculator for the dose.
The thresholds, at a glance
From the RENAL secondary analysis (Murugan et al.): < 1.01 mL/kg/hr = low-intensity net UF (risk of inadequate decongestion / persistent fluid overload); 1.01–1.75 mL/kg/hr = moderate (often the target); > 1.75 mL/kg/hr = high-intensity, independently associated with increased mortality and hemodynamic instability. Note these CRRT numbers are roughly an order of magnitude lower than the ~13 mL/kg/hr intermittent-HD UF-rate ceiling.
Pitfalls
(1) Use the net volume removed from the patient, not the gross ultrafiltrate / effluent — failing to subtract replacement and dialysate inflows hugely overestimates the rate. (2) Thresholds are associations, not hard limits: individualize to hemodynamics. A "moderate" rate may still destabilize a vasoplegic patient, while a "high" rate may be justified for life-threatening pulmonary edema if tolerated. (3) Dosing weight matters — for very obese or markedly edematous patients consider whether actual, ideal, or adjusted weight best reflects the physiology. (4) Avoid the opposite error too: chronically running at a "low" rate may leave a dangerous, unresolved fluid overload.
Why Use It
Fluid management is one of the highest-stakes decisions in critically ill patients on CRRT. Both extremes are harmful: persistent fluid overload is associated with worse organ recovery and mortality, while removing fluid too aggressively provokes hypotension, organ hypoperfusion, and — in observational data — excess mortality. The net ultrafiltration rate, normalized to body weight, turns a raw fluid-balance number into a comparable measure of decongestion intensity that can be titrated. The Murugan/RENAL analyses showed that a high net UF rate (> 1.75 mL/kg/hr) was independently associated with higher mortality, giving clinicians a concrete, evidence-based reference point for prescribing and reviewing fluid removal — aiming for an even, gentle decongestion individualized to the patient's hemodynamics.
Net Ultrafiltration Rate — CRRT Fluid Removal Intensity
Enter the net fluid volume removed and the hours it was removed over (leave hours at 1 to enter a rate in mL/hr directly), plus the patient's weight. The net UF rate, the weight-normalized rate (mL/kg/hr), and the intensity category appear below.
⚕ Thresholds from Murugan et al., RENAL secondary analysis (JAMA Netw Open. 2019). This is the net ultrafiltration rate (decongestion intensity) during CRRT — NOT the CRRT effluent dose (clearance, target 20–25 mL/kg/hr) and NOT the intermittent-HD UF limit (~13 mL/kg/hr). Individualize to hemodynamics. For licensed clinicians; not a substitute for individualized assessment.
Next Steps
Use the weight-normalized rate to set or review the net UF goal, always individualized to hemodynamics.
- Low intensity (< 1.01 mL/kg/hr): confirm this is intentional. If the patient remains fluid-overloaded and hemodynamically tolerant, consider increasing the net UF goal toward gentle, even decongestion.
- Moderate intensity (1.01–1.75 mL/kg/hr): often the target band. Continue to titrate to hemodynamics, MAP, vasopressor trend, and serial fluid balance.
- High intensity (> 1.75 mL/kg/hr): associated with increased mortality and hemodynamic instability — reassess. Confirm the rate is truly necessary, watch closely for hypotension and organ hypoperfusion, and consider dialing back toward the moderate band unless removal is life-saving (e.g., refractory pulmonary edema) and tolerated.
- Remember this is decongestion intensity, not clearance — set the solute dose separately with the CRRT Dose & Effluent Flow calculator (target 20–25 mL/kg/hr), and compare with the intermittent-HD UF rate when transitioning modalities.
Evidence & References
Formula
| Quantity | Formula |
|---|---|
| Net UF rate (mL/hr) | net UF volume removed (mL) ÷ hours |
| Net UF rate, normalized (mL/kg/hr) | net UF rate (mL/hr) ÷ weight (kg) |
Intensity Thresholds (Murugan / RENAL)
| Normalized net UF rate | Intensity |
|---|---|
| < 1.01 mL/kg/hr | Low — risk of inadequate decongestion / persistent fluid overload |
| 1.01–1.75 mL/kg/hr | Moderate — often the target range |
| > 1.75 mL/kg/hr | High — independently associated with increased mortality and hemodynamic instability |
These CRRT net-UF thresholds are roughly an order of magnitude lower than the ~13 mL/kg/hr intermittent-hemodialysis UF-rate ceiling, and are distinct from the CRRT effluent dose (clearance) target of 20–25 mL/kg/hr.
References
- Murugan R, Kerti SJ, Chang CH, et al. Association of Net Ultrafiltration Rate With Mortality Among Critically Ill Adults With Acute Kidney Injury Receiving Continuous Venovenous Hemodiafiltration: A Secondary Analysis of the RENAL Trial. JAMA Netw Open. 2019;2(6):e195418.
- Murugan R, Balakumar V, Kerti SJ, et al. Net ultrafiltration intensity and mortality in critically ill patients with fluid overload. Crit Care. 2018;22(1):223.
- Naorungroj T, Neto AS, Zwakman-Hessels L, et al. Mediators of the Impact of Net Ultrafiltration Rate on Outcomes During Continuous Renal Replacement Therapy. Crit Care Med. 2020;48(10):e934–e942.
