Recommended Flow Rates for Continuous Renal Replacement Therapy (CRRT)
The recommended effluent flow rate for CRRT in acute kidney injury is 20-25 mL/kg/h, based on high-quality evidence from large randomized controlled trials. 1
Evidence-Based Dosing Recommendations
- The KDIGO Clinical Practice Guidelines strongly recommend (Level 1A evidence) delivering an effluent volume of 20-25 mL/kg/h for CRRT in acute kidney injury 1
- This recommendation is based on rigorous evidence from large randomized controlled trials, including the RENAL and ATN studies 1
- The prescribed dose should be higher than the target delivered dose, as the actual delivered dose often falls short of what is prescribed 1
- Frequent assessment of the actual delivered dose is recommended to ensure adequate therapy 1
Clinical Trial Evidence Supporting Current Recommendations
- The RENAL (Randomized Evaluation of Normal Versus Augmented Level) study randomly assigned 1,508 patients to CVVHDF at effluent flow rates of either 40 or 25 mL/kg/h 1
- The VA/NIH Acute Renal Failure Trial Network (ATN) study randomly assigned 1,124 patients to either more intensive (CVVHDF at 35 mL/kg/h) or less intensive (CVVHDF at 20 mL/kg/h) therapy 1
- Both studies demonstrated no survival benefit or improvement in kidney function recovery with higher intensity therapy 1
- These findings led to the current recommendation of 20-25 mL/kg/h as the optimal dose 1
Practical Considerations for CRRT Dosing
- The prescribed dose should be higher than the target delivered dose to account for treatment interruptions 1, 2
- Studies show that the actual delivered dose is often only 68% of the prescribed dose due to filter clotting, procedures, and other interruptions 3
- Weight-based dosing should use actual body weight in most patients, but ideal body weight may be more appropriate in severely underweight patients 4
- The dose should be prescribed before starting each session of CRRT 5
Modality-Specific Considerations
- For CVVH (Continuous Venovenous Hemofiltration), the effluent rate refers to the ultrafiltration rate 1, 6
- For CVVHD (Continuous Venovenous Hemodialysis), the effluent rate refers to the dialysate flow rate 1, 6
- For CVVHDF (Continuous Venovenous Hemodiafiltration), the effluent rate is the sum of dialysate and ultrafiltration rates 1, 6
Monitoring and Adjustments
- Regular monitoring of filter performance and delivered dose is essential 1, 2
- Adjustments to the prescription should be made based on the patient's metabolic needs, fluid status, and electrolyte balance 5
- Quality improvement initiatives that include real-time calculation of delivered dose can improve adherence to recommended dosing targets 2
Common Pitfalls to Avoid
- Failing to account for pre-dilution when calculating the effective dose (pre-dilution reduces clearance efficiency) 5, 7
- Not adjusting drug dosing appropriately for the level of CRRT provided (drug clearance during CRRT can be significant) 8
- Using subclavian veins for access, which increases risk of thrombosis and stenosis 5
- Relying solely on static dosing without considering changing patient needs 7
Special Considerations
- Hemodynamically unstable patients and those with acute brain injury may particularly benefit from CRRT over intermittent hemodialysis 5, 6
- Bicarbonate-based replacement fluids are preferred over lactate-based solutions, especially in patients with shock, liver failure, or lactic acidemia 1, 5
- Anticoagulation strategy should be tailored to the patient's bleeding risk 5