The invention relates to a system, and the associated method for using said system, for treating haemorrhagic fluid previously taken from a patient for the purpose of autotransfusion, comprising a unit for treating (100) haemorrhagic fluid, said treatment unit (100) comprising: a filtration device (110) for tangential filtration comprising a filtration membrane (113) arranged in a housing (114) so as to separate an intake chamber (111) from a discharge chamber (112), the intake chamber (111) and the discharge chamber (112) each having an inlet (111a; 112a) and an outlet (111b; 112b) for fluids; a treatment pouch (140) having an inlet (140a) and an outlet (140b) fluidically connected by a recirculation line (150) to the outlet (111b) and to the inlet (111a) of the intake chamber (111) of the filtration device (110), respectively, allowing haemorrhagic fluid to circulate in the recirculation line (150) in a direction going from the outlet (140b) of the treatment pouch (140) to the inlet (140a) of the treatment pouch (140) through the intake chamber (111) of the filtration device (110), a cleaning line (180) fluidically connected to the inlet (112a) of the discharge chamber (112) of the filtration device (110) to convey cleaning fluid into said discharge chamber (112); and a first flow regulation member (181) arranged to regulate the flow in the cleaning line (180) and a second flow regulation member (131) arranged to regulate the flow in a discharge line (130) fluidically connected to the outlet (112b) of the discharge chamber (112) of the filtration device (110), so as to be able to control the pressure of cleaning fluid in the discharge chamber (112).