A catheter assembly comprising a catheter body defining an arterial lumen 2 and a venous lumen 3, wherein at least the arterial lumen 2 is movable relative to the longitudinal axis of the catheter body between an insertion position and an expanded drawing position. At least one of the arterial lumen 2 and the venous lumen 3 form a helix around the longitudinal axis of the catheter body. The lumens have apertures, wherein most or all of the apertures of the arterial lumen 2 face towards the longitudinal axis of the catheter body, and most or all of the apertures of the venous lumen 3 face away from the longitudinal axis.
