How to prevent clotting with low blood flow?

Preventing Clotting with Low Blood Flow of 50 cc/min

When reducing blood flow to 50-100 mL/min during hemodialysis procedures, the risk of clotting the extracorporeal circuit is low and does not require additional anticoagulation measures beyond standard heparinization protocols. 1

Evidence from Hemodialysis Guidelines

The NKF-K/DOQI guidelines specifically address this scenario in the context of the slow flow/stop pump sampling technique for hemodialysis adequacy monitoring. 1 The guidelines explicitly state:

• Decreasing blood flow to 50-100 mL/min for 15 seconds carries a low risk of clotting the extracorporeal circuit 1
• This technique is designed to stop the hemodialysis treatment without stopping blood flow completely, specifically to minimize clotting risk 1
• The procedure has been successfully implemented across different dialysis care teams in varied settings with minimal technical variability 1

Standard Heparinization Protocol

For routine hemodialysis with periods of slow flow, maintain standard anticoagulation practices:

• Use an initial loading dose of heparin followed by constant infusion rather than intermittent boluses, as this prevents periods of under-anticoagulation that increase clotting risk 2
• Monitor activated clotting times (ACT) to ensure adequate anticoagulation throughout the procedure 2
• Individual patient responses to heparin vary markedly, so doses must be determined on a patient-specific basis using pharmacodynamic modeling or empirical adjustment 2

Key Technical Considerations to Prevent Clotting

Beyond anticoagulation, several technical factors are critical:

• Minimize turbulence and foam formation in the extracorporeal circuit, as these contribute to clotting even with adequate heparinization 2
• Ensure proper delivery of the prescribed heparin dose, as failure to deliver the full dose is a common cause of circuit clotting 2
• Reduce excessive access recirculation, which can promote clotting 2
• When reducing blood flow rate, manually adjust venous pressure limits downward to prevent pump shut-off 1

Duration of Slow Flow

The slow flow period should be brief:

• Maintain 50-100 mL/min flow for only 15 seconds when using this technique for blood sampling 1
• This short duration is sufficient to clear dead space in arterial lines while minimizing clotting risk 1

Common Pitfall to Avoid

Do not stop the blood pump completely when attempting to reduce flow to 50 mL/min, as complete cessation significantly increases clotting risk. 1 The slow flow technique is specifically designed to maintain some blood movement through the circuit. 1