Factors affecting circuit patency and filter 'life'.

Frequent clotting applying continuous renal replacement therapy means treatment can be inadequate and with increased costs for circuits and nursing time. Patency of the extracorporeal circuit is commonly achieved using anticoagulants such as heparin. When anticoagulants are not used, or clotting occurs within a few hours of use, with anticoagulation, blood flow failure is a likely cause. The blood pump can fail to deliver without operator awareness. Clotting within the membrane and/or venous 'air-trap' chamber is common where resistance to blood flow is high with stasis and turbulence. The design of the venous chamber allows the blood fill level to oscillate and form a clot, with a blood filter at the exit of the chamber also causing clot development. Several practices attempt to prevent clotting, however most without evidence. Adding heparin to the circuit during the preparation phase, ensuring that the access catheter is not obstructed, a blood flow setting of >or=200 ml/min, and administration of substitution fluids before the membrane (predilution) can be useful strategies for increasing circuit patency. An audit of filter life is useful and necessary feedback to nursing staff training strategies. This promotes safety and, when circuit patency is poor, may reflect poor troubleshooting ability.