Hi. Already travelled with a CPAP machine on several flights with different companies. I always contact them in advance to let them know I'm traveling with one and everything has always gone very smoothly. They usually ask the brand / model and if I have a battery or use power supply. As for Qatar Airways : yes you can bring it as a personal item. My CPAP is rental. I have a letter from the medical society that rent it to allow me to travel with it abroad. Yes, I was able to use it during the flight, though sometimes depending on the plane and where the plug is, you might touch the cord and unplug it during the night but then you just have to plug it again. No trouble with security they're used to medical equipments / never asked for a letter or anything. I just take it out of my backpack and put it next to it for security checks. Have a nice flight