- In ultrafiltration, the effluent rate is determined by the flow of plasma into the membrane and the fraction of this which is filtered out as effluent (known as the filtration fraction)
- To maintain a constant effluent rate:
- At low blood flows a large filtration fraction is required
- At high flows, a small filtration fraction can be used
- The renal replacement circuits have inbuilt algorithms to deliver a desired effluent flow rate based upon the blood flow from the patient
