CRRT Calculator

CRRT UF Rate Calculator

UF Rate Calculator

Built by Mark Sescon.

Overall Goal
Hourly Goal
Overall + Unscheduled
Fluid Balance
mL
If hourly goal given, multiply by 24 first
mL
hours
Intake / Output
Enteral, IV, additional fluids
mL/hr
Urine, stool, OG suction (excl. CRRT)
mL/hr
Suggested UF Rate
—
UF = (Fc − G) / t + (I − O)
Hourly Goal
Negative = net removal (e.g. −200)
mL/hr
Intake / Output
Enteral, IV, additional fluids
mL/hr
Urine, stool, OG suction (excl. CRRT)
mL/hr
Suggested UF Rate
—
UF = Grate + (I − O)
Fluid Balance
mL
If hourly goal given, multiply by 24 first
mL
hours
Intake / Output
Enteral, IV, continuous fluids
mL/hr
PRBCs, boluses, antibiotics — enter total volume as lump sum
mL
Urine, stool, OG suction (excl. CRRT)
mL/hr
Suggested UF Rate
—
UF = (Fc − G + Iuns) / t + (I − O)

Background

Last year I built two CRRT calculators that I was genuinely proud of. Both were feature-rich and highly functional but honestly, ultra complex. One was literally called UltraCalc.

When renewed interest came around for the basic version of the CRRT calculator, I took it as an opportunity to go back to the drawing board. Rather than maintaining two separate tools, I decided to merge them, keeping the mathematical rigor of UltraCalc while stripping out the parts that were more niche than necessary. Things like shift-based time remaining calculations were cool in theory, but in practice they added friction without adding much clinical value at the bedside.

The result is something I'm happier with than either of the originals. It's leaner, cleaner, and covers the three scenarios that actually come up during a shift:

  • Overall Goal: Calculating a UF rate to hit a target fluid balance over a defined time window

  • Hourly Goal: When you just want to know the UF for an hourly goal.

  • Overall Goal with Unscheduled Intake: Accounting for antibiotics, PRN fluids, blood products, and anything else that doesn't fit neatly into a continuous drip rate

The underlying math is the same. The experience of using it is just a lot better.

The Math

Module 1 — Overall Goal

UF = (FB₀ − G) / t + (Iavg − Oavg)

Where:

  • FB₀ = Current fluid balance (mL)
  • G = Goal fluid balance (mL)
  • t = Time remaining (hours)
  • Iavg = Average hourly intake (mL/hr)
  • Oavg = Average hourly output, excluding CRRT (mL/hr)

Module 2 — Hourly Goal

UF = Grate + (Iavg − Oavg)

Where:

  • Grate = Prescribed hourly fluid balance goal (mL/hr)
  • Iavg = Average hourly intake (mL/hr)
  • Oavg = Average hourly output, excluding CRRT (mL/hr)

Module 3 — Overall Goal with Unscheduled Intake

UF = [(FB₀ − G) + Iuns]/t + (Iavg − Oavg)

Where:

  • FB₀ = Current fluid balance (mL)
  • G = Goal fluid balance (mL)
  • t = Time remaining (hours)
  • Iavg = Average hourly intake — continuous drips, feeds (mL/hr)
  • Iuns = Unscheduled intake — antibiotics, boluses, blood products (total expected volume ÷ t)
  • Oavg = Average hourly output, excluding CRRT (mL/hr)