Blood is passed through an extracorporeal circulation into a dialyser that contains a high capacity semi-permeable membrane. Plasma fluid and solutes are sucked across the membrane by a process of convection. The patient's fluid and electrolyte balance are maintained by infusing a sterile saline solution of similar composition to dialysis solution.
In arteriovenous haemofiltration, the patient's systemic arterial pressure drives blood through the extracorporeal circuit. Venovenous haemofiltration requires a pump to be connected to the dialyser to circulate the blood. Double lumen venous catheters create the extracorporeal circuit.
Haemofiltration achieves high rates of ultrafiltration, up to 30-60 litres per day.
Haemodiafiltration combines convection and diffusion by using dialysis fluid in conjunction with a highly permeable membrane. It achieves ultrafiltration rates of 6-20 litres per day.
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