Junctional wounds are those wounds of the neck, axilla (armpit), and groin, where they are not amenable to tourniquet application but are frequent sources of massive hemorrhage.
There are many different ways to manage these wounds, this is one technique using a Foley Catheter (designed for urine drainage) to tamponade bleeding. It is best studied in neck wounds. This includes both an excerpt from the lecture section and skills station in the Advanced & Complete TC2 online courses.
First, a foley catheter is inserted to the point of bleeding. Next, using a syringe filled with saline, the balloon is then inflated and the inflation of the balloon within the wound puts pressure directly on the bleeding vasculature. Once the balloon is inflated and bleeding is stopped, the catheter must be tied off to avoid leakage and a lessening of the direct pressure on the wound.
You might also be interestd in Improvised Wound Packing with commonly available materials in a hotel room.