I believe those "pens" (actually needles) are used to drain lungs from internal fluids (blood etc) and excessive air drawn in through a chest wound.
Hey there Luke, I believe that those pens are designed to relieve a "tension pneumothorax." A pneumothorax is also known as a collapsed lung and is caused from an external trauma such as a puncture wound. A tension pneumothorax is also a collapsed lung but it happens when there is a tear in the lung on the inside of the body that results in air escaping the lung and going into the pleural cavity (the space that surrounds the lobes of the lungs). This air is then unable to exit this space and pressure begins to build which in turn causes the affected lung to collapse in addition to applying pressure to other organs of the body such as the heart; more importantly the blood vessels that return blood to the heart and vessels that feed the heart. If this pressure isn't relieved it can lead to death in an affected individual; hence the pens which in essence are probably just large-bore needles that you stab into the affected persons chest to equalize the pressure gradient.Just a thought,-Jared
P.S. I love the channel man; you're doing an excellent job. I'm also very sorry for you and your family's recent loss.