Apparatus for extracorporeal fluid treatment comprising: a filtration unit (2) having a primary chamber (3) and a secondary chamber (4) separated by a semipermeable membrane (5)； a blood collection line (6) connected to an input of the primary chamber (3) and a blood return line (7) connected to an output of the primary chamber (3), said bloodlines being configured to its connection to a patient's cardiovascular system； a blood pump (11) configured to control the blood flow through the blood lines (6, 7)； a line (13) of effluent fluid connected, at one end thereof, to an outlet of the secondary chamber (4) and at its other end to a waste container (14)； at least two other fluid lines selected from among the members of the fluid line group consisting of: a predilution infusion fluid line (15) connected at one end thereof to the blood collection line (6) and at its other end to a first container (16) of unused fluid, a line (25) of post-dilution infusion fluid connected at one end thereof to the blood return line (7) and at its other end to a second container (26) of unused fluid, a line (19) of dialysis fluid connected at one end thereof to the inlet of the secondary chamber (4) and at its other end to a third container (20) of unused fluid, a line (21) of pre-pump blood infusion fluid connected at one end thereof to a fourth container (23) of unused fluid and at its other end to the blood collection line in a area of the latter that is positioned in use upstream of the blood pump, one or more lines (50) of syringe (s) connected at one end of the same (s) either to the blood collection line (6) or to the blood return line (7) or directly to the patient, and at its other end to a syringe container (S), means (17, 18, 21, 22, 27, P) to regulate the flow of fluid through one or more of said fluid lines ( 13, 15, 21, 25, 19)； and a control unit (10) connected to the regulation means, the control unit being configured to: calculate the established values (Qiset) of two or
