The invention relates to a system, and its associated method of use, for treatment of a hemorrhagic liquid previously taken from a patient with a view to autotransfusion, including a treatment unit (100) for treating the hemorrhagic liquid, said treatment unit (100) comprising: - a filtration device (110) for tangential filtration comprising a filtration membrane (113) arranged in a casing (114) in such a way as to separate an admission chamber (111) from a discharge chamber (112), the admission chamber (111) and the discharge chamber (112) each having an inlet (111a； 112a) and an outlet (111b； 112b) for fluids； - a treatment bag (140) having an inlet (140a) and an outlet (140b) which are fluidically connected by a recirculation line (150) to the outlet (111b) and the inlet (111a) of the admission chamber (111) of the filtration device (110) respectively, permitting circulation of the hemorrhagic liquid in the recirculation line (150) in a direction from the outlet (140b) of the treatment bag (140) to the inlet (140a) of the treatment bag (140) by way of the admission chamber (111) of the filtration device (110)； - a cleaning line (180) connected fluidically to the inlet (112a) of the discharge chamber (112) of the filtration device (110) in order to feed a cleaning liquid into said discharge chamber (112)； and - a first flow regulator (181) arranged to regulate flow in the cleaning line (180), and a second flow regulator (131) arranged to regulate flow in a discharge line (130) connected fluidically to the outlet (112b) of the discharge chamber (112) of the filtration device (110), in such a way as to be able to control the pressure of cleaning liquid in the discharge chamber (112).
