CRRT Filter Duration and Replacement
In adult patients receiving CRRT, filters should be changed routinely at 48-72 hours to maintain adequate solute clearance, though filters may function acceptably for up to 72 hours with proper anticoagulation. 1
Evidence-Based Filter Lifespan Recommendations
Routine Replacement Timing
- Filters should be changed at 48-72 hours on a routine basis to prevent progressive decline in delivered dose that occurs over time 1
- Without anticoagulation, circuit life may be less than 24 hours, making it difficult to deliver adequate renal support 2
- Failure before 8 hours is associated with inadequate renal support and should trigger clinical review of circuit setup and catheter function 3
Filter Performance Over Time
- Prescribed clearance progressively overestimates actually delivered clearance as filter function declines, with the difference increasing over time 1
- Small molecule (urea, creatinine) clearance remains relatively stable for the first 48 hours, but middle molecule clearance (beta-2 microglobulin) begins to decline significantly by 72 hours 4
- The mean filter lifespan across studies is approximately 37.7 hours (SD 17.6) when using standard anticoagulation protocols 1
Factors That Extend Filter Life
Anticoagulation Strategy (Most Important)
- Regional citrate anticoagulation provides the longest filter life (median 48 hours, IQR 20.3-75.0 hours) compared to heparin (median 5.9 hours, IQR 8.5-27.0 hours) or no anticoagulation (median 17.5 hours, IQR 9.5-32 hours) 5
- Citrate anticoagulation also delivers higher actual dialysis doses due to improved filter efficacy 5
- CVVHD (dialysis mode) provides significantly longer filter lifespan (median 37 hours, IQR 19.5-72.5) compared to CVVH (hemofiltration mode) (median 19 hours, IQR 12.5-28) 4
Blood Flow Rate
- Higher blood flow rates predict longer filter lifespan in multivariable analyses (p=0.03 for all filters, p=0.04 for non-electively ceased filters) 6
- Optimizing blood flow through proper catheter selection and positioning is critical for filter longevity 6
Patient Factors
- Lower platelet counts are associated with longer filter life (p=0.003 for all filters, p<0.001 for non-electively ceased filters), likely reflecting reduced thrombotic tendency 6
- Vascular catheter design may influence filter lifespan, though the specific optimal design remains unclear 6
Monitoring Filter Function
Clinical Indicators for Early Replacement
- Rising transmembrane pressure is significantly correlated with declining filter performance (Spearman's rho 0.44, p<0.001) 1
- Document actual filter life (elapsed hours) at the bedside as a quality measure 3
- Monitor effluent urea nitrogen/blood urea nitrogen ratios to assess filter efficacy 5
When to Replace Before Scheduled Time
- Replace immediately if transmembrane pressure rises significantly above baseline 1
- Replace if circuit clots or blood flow becomes inadequate despite troubleshooting 3
- Replace if filter life is consistently <8 hours, as this indicates inadequate therapy delivery 3
Common Pitfalls to Avoid
- Do not rely solely on prescribed dose as a measure of adequate therapy—prescribed clearance overestimates delivered clearance by 9.3% on average (95% CI: -4.4% to 32.3%), with the gap widening over time 1
- Do not extend filters beyond 72 hours routinely, as solute clearance efficiency declines progressively even if the circuit remains patent 1, 4
- Do not assume heparin provides adequate anticoagulation—it results in significantly shorter filter life compared to citrate without reducing bleeding complications 5
- Avoid subclavian vein access when possible due to thrombosis and stenosis risk, which can compromise catheter function and filter life 2, 7