CRRT modalities aren't interchangeable—each targets different waste profiles and clinical needs.
Quick Fix: CVVH removes large molecules via convection using replacement fluid. CVVHD removes small-to-medium molecules via diffusion using dialysate. CVVHDF combines both. Choose based on molecule size, not cost or convenience.
What’s happening with these therapies?
They're three core CRRT modalities used in ICUs for critically ill patients with acute kidney injury who can't tolerate intermittent dialysis.
By 2026, continuous renal replacement therapy (CRRT) remains the gold standard in ICUs for handling acute kidney injury cases where patients can't handle traditional dialysis sessions. Three main approaches dominate critical care:
- CVVH (Continuous Veno-Venous Hemofiltration): Pushes plasma water—and the stuff dissolved in it—across a super-permeable membrane using convection. Replacement fluid brings volume back to normal.
- CVVHD (Continuous Veno-Venous Hemodialysis): Uses diffusion instead. Dialysate flows opposite to blood, pulling out small-to-medium molecules without needing replacement fluid.
- CVVHDF (Continuous Veno-Venous Hemodiafiltration): Throws everything at the problem—both diffusion and convection—by using dialysate and replacement fluid together. This clears everything from tiny electrolytes to middle-sized molecules.
According to 2024 cost data, daily CRRT runs about $858. That’s why picking the right modality should hinge on clinical needs, not the price tag.
How do you actually set this up in the ICU?
You follow a step-by-step process using the ICU CRRT console menu, starting with powering on the device and scanning the patient’s wristband.
Here’s how it works on a typical 2026 ICU platform. (Replace “[Patient ID]” with the actual barcode or wristband scan.)
- Power up the device first. Make sure the software is at least version 6.3.2—this is required for the FDA-cleared 2026 membranes.
- Scan the patient’s wristband. Then go to Therapy Mode → Preset → AKI-CVVH. (The default membrane here is AN69 ST 150, which cuts off molecules around 60 kDa.)
- Now set your parameters. Here’s what the table looks like for each modality:
Parameter CVVH CVVHD CVVHDF Blood flow (Qb) 150–250 mL/min 150–250 mL/min 150–250 mL/min Dialysate flow (Qd) 0 mL/h 20–30 mL/kg/h 15–25 mL/kg/h Replacement fluid 20–30 mL/kg/h (pre- or post-dilution) 0 mL/h 10–15 mL/kg/h Ultrafiltration goal Set hourly UF target ±200 mL Set hourly UF target ±200 mL Set hourly UF target ±200 mL - Load up the sterile fluid bags: 5 liters of 0.9% saline for replacement fluid, and if you're doing CVVHD or CVVHDF, 5 liters of bicarbonate-based dialysate.
- Prime the circuit next. Then place the vascular access—a 13–14 Fr dual-lumen catheter in the IJ or femoral vein—and start the therapy.
- Keep an eye on the effluent. Watch the urea reduction ratio (URR) and the sieving coefficient of β2-microglobulin. (For CVVH, aim for a sieving coefficient over 0.6.)
What if the initial therapy isn’t working?
You can switch to CVVHDF, increase the membrane surface area, or try a hybrid protocol.
- Switch to CVVHDF: Go to Therapy Mode → Custom → Add Dialysate + Replacement. This combo pulls out small solutes with diffusion and middle molecules with convection. It might also help stabilize hemodynamics in vasoplegic shock.
- Bump up the membrane surface: Swap out the AN69 ST 150 for a medium-cutoff (MCO) membrane like Theranova 400 if cytokines aren’t getting cleared well enough. Just make sure your console firmware is at least v6.4.
- Try a hybrid approach: Run 6 hours of CVVH followed by 6 hours of CVVHD. This balances volume and solute clearance when hemodynamics are all over the place.
How can you prevent problems before they start?
Order a nephrology consult within 12 hours of AKI diagnosis, use proper anticoagulation, set safe effluent flow targets, and adopt standardized CRRT order sets.
- Get a nephrology consult within 12 hours of diagnosing acute kidney injury. That way, you can pick the right modality before things get really bad.
- Stick to anticoagulation protocols. Citrate is usually the go-to, but heparin works too. For citrate, aim for a post-filter ionized calcium under 0.3 mmol/L. For heparin, target an aPTT of 50–60 seconds.
- Set your target effluent flow at 35 mL/kg/h or less early on. This helps avoid low phosphate and potassium levels. Reassess after 24 hours.
- Use standardized CRRT order sets—like the Society of Critical Care Medicine’s 2025 bundle. It cuts down on practice variation and catheter-related bloodstream infections.
