We'll hold good hopes for the ketamine. There are people here who have it prescribed as something they take regularly. If you put the word ketamine into the search box at the top right of the page, you'll see some of those. I think that if you put the words ketamine and ricardo into the box, you'll find a report from one of the long-time members here.
Regarding O2, you can get a mask that allows him to breathe through a tube, so the nose isn't involved. Many people do it that way. It's also just a better mask system, made specifically for CH. Our very strong overall experience is that people who have found that oxygen didn't help much did a whole lot better with a higher-flow regulator and a better mask (and sometimes with better breathing technique). If you think about looking into this more, let us know.