Heparin Administration in CRRT: Prefilter vs. Postfilter
Heparin is administered prefilter (before the blood enters the filter) in Continuous Renal Replacement Therapy (CRRT) to maximize anticoagulation effect and prevent filter clotting. 1
Anticoagulation Principles in CRRT
- Systemic anticoagulation with heparin (standard unfractionated, low-molecular-weight, or synthetic heparinoids) is commonly used in CRRT when patients do not have increased bleeding risk 1
- Prefilter administration of heparin allows the anticoagulant to immediately mix with the blood before it enters the filter, optimizing the anticoagulant effect throughout the entire extracorporeal circuit 1
- The choice of anticoagulant should be determined by patient characteristics, local expertise, ease of monitoring, and pharmacy considerations 1
Monitoring Heparin Anticoagulation
- When using prefilter heparin, safety monitoring is recommended through measurement of activated clotting times (ACT) or systemic partial thromboplastin time (PTT) 1
- ACT values greater than 218 seconds measured 10 minutes after the initial heparin bolus have been shown to predict 48-hour filter survival 2
- Routine measurement of platelets should be performed to monitor for heparin-induced thrombocytopenia 1
Alternative Anticoagulation Approaches
- For patients with high bleeding risk, regional citrate anticoagulation is preferred over heparin when there are no contraindications for citrate 1, 3
- Regional citrate anticoagulation requires frequent measurements of post-filter and serum-ionized calcium to appropriately titrate the dose of citrate and calcium replacement solutions 1, 4
- In patients who are auto-anticoagulated or at high risk of bleeding, CRRT can be performed without anticoagulation, although circuit life may be less than 24 hours 1, 5
Clinical Considerations
- Venovenous therapies are preferred to arteriovenous therapies due to the ability to provide higher rates of solute clearance and reduced risk of complications 1
- In patients with heparin-induced thrombocytopenia (HIT), all heparin must be stopped, and direct thrombin inhibitors (such as argatroban) or Factor Xa inhibitors should be used instead 1, 3
- Saline flushes can be an effective alternative to maintain extracorporeal circuit patency in patients with already elevated aPTT (>55 seconds), resulting in significantly fewer bleeding episodes 5
Practical Implementation
- Prefilter D5W administration can enhance the achievable ultrafiltration rate, which is especially important in high-volume CVVH and can be useful in patients with frequent filter clotting 6
- When using regional citrate anticoagulation, monitoring of systemic acid-base balance is advisable, particularly in patients at high risk for citrate accumulation 1, 4
- Standardized anticoagulation administration and monitoring protocols are essential for safe implementation of any anticoagulation strategy in CRRT 3, 4
Remember that the primary goal of anticoagulation in CRRT is to maintain filter patency while minimizing the risk of bleeding complications, and prefilter administration of heparin helps achieve this balance.