Fortunately, I’ve never had this happen when I’ve placed a central venous catheter:
See that bright line with the “J” at the end of it? That’s the guidewire over which a central venous catheter is threaded. It’s a very bad thing when you push it in so far that you lose it. Worse, is not reporting or admitting that you lost it before transferring a patient to another hospital. (You’d have to be really, really stupid not to realize that you lost it.)