An intravenous catheter assembly (101), comprising: a catheter adapter (14) having an inner lumen (16), wherein the inner lumen has an inner surface (24), a proximal end, a distal end and a middle part； a partition (50, 356) disposed inside a part of the inner lumen, wherein said partition has a slit (56, 66, 366)； an introducer needle (350) positioned within the inner lumen, in which a part of the needle extends through the inner lumen, such that a pointed part of the introducer needle extends beyond the catheter adapter, in the that an introducer needle part is inserted through the septum； a partition activator (80, 180, 380, 344) positioned within the proximal end of the inner lumen, in which the partition activator has a path through which the introducer needle is inserted, into which the partition activator it also has a first end for opening a partition groove, and a second end having a contact surface； and an opening (26) forming a proximal end of the catheter adapter, into which an outer device is inserted through the opening to contact the contact surface of the partition activator thereby advancing the first end of the activator in this manner. of partition through the partition of the partition characterized by a recessed part of the inner surface 24 that forms the middle part of the inner lumen, in which the recessed portion is configured to receive a partition (50, 356), in which the septum forms an unlockable barrier between the proximal end and the distal end of the inner lumen； and a ventilation channel (70) constructed by eliminating parts of the recessed portion, thereby interposing between the partition wall and the interior surface of the inner lumen of the catheter adapter, in which the ventilation channel has a selected surface area and perimeter to allow the passage of at least one of air and blood between the proximal end and the distal end of the inner lumen, at a desired flow rate.Un conjunto (101) de catéter intravenoso, que comprende: un
