My mother was the vent after being in a car wreck to allow time for healing. She had a fracture of her breastbone, got pneumonia, etc. It was really scarey for me, seeing her on that thing. But it did its job and she was slowly weaned off. It is better for your Dad if they go slow getting him off than to do it too quickly and have to put him back on it. I hope his recovery will go well and that he doesn't have any more problems. God Bless.
Pat