An intravenous catheter assembly, comprising: a catheter adapter having an inner lumen, the inner lumen having an inner surface, a proximal end, a distal end and a middle portion; a septum (50, 356) disposed within a portion of the inner lumen, said septum having a slit (56, 66, 366); an introducer needle positioned within the inner lumen, a portion of the needle extending through the inner lumen, such that a tip portion of the introducer needle extends beyond the catheter adapter, a portion of the introducer needle being inserted through the septum; a septum activator (80, 180, 380, 344) positioned within the proximal end of the inner lumen, the septum activator having a pathway through which the introducer needle is inserted, the septum activator further having a first end for biasing open a slit of the septum, and a second end having a contact surface; and an opening forming a proximal end of the catheter adapter, wherein an external device is inserted through the opening to contact the contact surface of the septum activator thereby advancing the first end of the septum activator through the slit of the septum, characterized by a recessed portion of the inner surface 24 forming the middle portion of the inner lumen, the recessed portion being configured to receive a septum (50, 356), the septum forming a defeatable barrier between the proximal end and the distal end of the inner lumen; and a ventilation channel constructed by removing portions of the recessed portion, thereby being interposed between the septum and the inner surface of the inner lumen of the catheter adapter, the ventilation channel having a surface area and a perimeter selected to permit passage of at least one of air and blood between the proximal end and the distal end of the inner lumen, at a desired rate of flow. a catheter adapter having an inner lumen, the inner lumen having an inner surface, a proximal end, a distal end and a middle portion; a septum (50, 356) disposed within a portion of the inner lumen, said septum having a slit (56, 66, 366); an introducer needle positioned within the inner lumen, a portion of the needle extending through the inner lumen, such that a tip portion of the introducer needle extends beyond the catheter adapter, a portion of the introducer needle being inserted through the septum; a septum activator (80, 180, 380, 344) positioned within the proximal end of the inner lumen, the septum activator having a pathway through which the introducer needle is inserted, the septum activator further having a first end for biasing open a slit of the septum, and a second end having a contact surface; and an opening forming a proximal end of the catheter adapter, wherein an external device is inserted through the opening to contact the contact surface of the septum activator thereby advancing the first end of the septum activator through the slit of the septum, characterized by a recessed portion of the inner surface 24 forming the middle portion of the inner lumen, the recessed portion being configured to receive a septum (50, 356), the septum forming a defeatable barrier between the proximal end and the distal end of the inner lumen; and a ventilation channel constructed by removing portions of the recessed portion, thereby being interposed between the septum and the inner surface of the inner lumen of the catheter adapter, the ventilation channel having a surface area and a perimeter selected to permit passage of at least one of air and blood between the proximal end and the distal end of the inner lumen, at a desired rate of flow.