Preventing Clotting on Dialysis Machine at 50 cc/min Blood Flow
Running blood flow at 50-100 mL/min for brief periods (15 seconds) carries a low risk of clotting the extracorporeal circuit, but requires specific technical adjustments and should only be maintained for short durations. 1, 2
Key Technical Adjustments to Prevent Clotting
Immediate Machine Settings
- Manually adjust venous pressure limits downward when reducing blood flow rate to prevent automatic pump shut-off 1, 2
- Turn off dialysate flow or decrease to minimum setting 1
- Decrease ultrafiltration rate to 50 mL/h or to the lowest transmembrane pressure setting 1
Critical Duration Limitation
- Maintain 50 mL/min flow for only 15 seconds maximum 1, 2
- This short duration is sufficient to clear dead space in arterial lines while minimizing clotting risk 2
- Prolonged periods at this low flow rate significantly increase thrombosis risk 1
Anticoagulation Strategy at Low Blood Flow
Heparin Dosing for Extracorporeal Dialysis
- Standard dose: 25-30 units/kg bolus followed by continuous infusion at 1,500-2,000 units/hour 3
- For a 4-hour session, continuous infusion of 50 IU/kg total dose provides adequate anticoagulation 4
- Target anti-Xa activity of 0.3-0.7 IU/mL is sufficient to prevent clotting 4
Heparin Administration Methods
- Continuous infusion is preferred over bolus injection for maintaining stable anticoagulation during low-flow conditions 4
- Bolus method (3000 units initially, then 2000 units at 2 hours) shows higher PTT values but may increase bleeding risk 5
- Continuous infusion maintains median anti-Xa activity of 0.55 IU/mL at peak and 0.25 IU/mL at end of session 4
Common Pitfalls and How to Avoid Them
Never Stop Blood Flow Completely
- Complete cessation of blood pump significantly increases clotting risk 1, 2
- The slow flow technique is designed to maintain continuous blood movement 1
Avoid Prolonged Low-Flow Periods
- Blood flow of 50 mL/min is only appropriate for the 15-second sampling technique 1, 2
- For actual dialysis treatment, blood flow should be ≥300 mL/min to prevent inadequate dialysis and increased clotting risk 1, 6
- Blood flow <300 mL/min during treatment extends treatment times and often results in underdialysis 1, 6
Monitor for Circuit Clotting
- Inadequate anticoagulation leads to dialyzer clotting and reduced clearance 7
- Heparin prevents clotting of the dialyzer, which would otherwise reduce effective dialyzer surface area 7
- Incidence of partial dialyzer clotting is 3-5% even with proper heparin protocols 8
Alternative Anticoagulation for High Bleeding Risk
Heparin-Free Options
- Prostacyclin infusion (423 ± 91 ng/kg total dose) can replace heparin as sole antithrombotic agent 9
- Heparin-free dialysis with high blood flow (244 mL/min) and intermittent rinsing is feasible but requires prophylactic system changes 10
- System clotting occurs in 3% of heparin-free dialyses despite preventive measures 10
Low-Dose Heparin Protocol
- Low-dose heparin (reduced total dose) has lower bleeding complications (10%) compared to regional heparin (19%) 8
- Partial dialyzer clotting incidence remains 3-5% with both low-dose and regional heparin 8
Clinical Context: When 50 mL/min Flow is Appropriate
The 50-100 mL/min blood flow rate is only recommended for the slow flow/stop pump sampling technique at the end of dialysis for accurate BUN measurement 1, 2. This technique has been successfully implemented across different dialysis care teams with minimal technical variability 1, 2.
If you need to run an entire dialysis session at low blood flow due to access limitations, this represents catheter dysfunction requiring intervention 1, 6. Blood flow <300 mL/min during treatment indicates inadequate vascular access and necessitates evaluation for stenosis, thrombosis, or malposition 1, 6.