Prefilter Fluid Administration to Reduce Clotting in CRRT
Prefilter administration of replacement fluid is the recommended approach to reduce filter clotting in CRRT, especially in patients with frequent filter clotting or when high-volume hemofiltration is required. 1
Mechanisms of Reducing Filter Clotting
- Prefilter fluid administration dilutes the blood before it enters the hemofilter, enhancing the achievable ultrafiltration rate and reducing the risk of filter clotting 1
- This approach is particularly beneficial in high-volume continuous venovenous hemofiltration (CVVH) where filter clotting is more common 1
- Prefilter dilution reduces hemoconcentration within the filter, which is a major contributor to premature circuit failure 2
Clinical Application
- Prefilter fluid administration can be used in combination with post-dilution when extracorporeal clearance is limited by achievable blood flow 1
- This approach is especially useful in patients with high risk of bleeding where anticoagulation should be minimized or avoided 3
- Transmembrane pressures are significantly higher in circuits that clot (123±74 vs. 71.8±29.3 mmHg), making pressure monitoring essential when using prefilter dilution 4
Fluid Composition Considerations
- Replacement fluid used for prefilter administration should contain physiologic concentrations of electrolytes, except in patients with extreme imbalances 1
- Either lactate or bicarbonate can be used as buffer in most CRRT patients, but bicarbonate is preferred in patients with lactic acidosis, liver failure, or when using high-volume hemofiltration 1
- Avoid fluids with supra-physiologic glucose concentrations as they can lead to excessive glucose intake and hyperglycemia 1
Anticoagulation Strategies
- When prefilter dilution alone is insufficient, anticoagulation may be necessary 4
- Prefilter administration of heparin allows the anticoagulant to immediately mix with the blood before entering the filter, optimizing the anticoagulant effect throughout the circuit 5
- Regional citrate anticoagulation is emerging as a promising method for preventing circuit clotting when prefilter dilution is insufficient 2, 6
- The choice of anticoagulant should be determined by patient characteristics, local expertise, nursing comfort, ease of monitoring, and pharmacy considerations 1
Monitoring and Management
- Regular monitoring of filter pressures is essential as elevated transmembrane and filter pressures are associated with increased risk of clotting 7
- Each 1-mmHg increase in transmembrane or filter pressure is associated with a 1.5% higher risk of clotting 7
- When using prefilter heparin, safety monitoring through measurement of activated clotting times (ACT) or systemic partial thromboplastin time (PTT) is recommended 5
- Higher ACTs are associated with lower transmembrane and filter pressures, potentially decreasing the risk of circuit clotting 7
Special Considerations
- In patients with liver failure, despite abnormal laboratory coagulation tests, CRRT circuits clot frequently and may require anticoagulation in addition to prefilter dilution 4
- For patients with heparin-induced thrombocytopenia, all heparin must be stopped, and direct thrombin inhibitors or Factor Xa inhibitors should be used instead 5, 8
- In thrombocytopenic patients without contraindications to citrate, regional citrate anticoagulation is recommended over heparin 8