To recap the advice from UA members so far:

While officially the rule is to call and let UA know you are planning on using your CPAP on the flight so that they can make sure that the device is FAA cleared, this can cause problems if/when there is a cancellation or aircraft swap or otherwise changed itinerary. I would add this would probably be especially problematic on a complex ticket or with an international partner airline. In my own experience, with all airlines when I would arrange CPAP usage, is there is a section in the record for "special assistance" that gets ticked and I would always be asked if I needed any help to gate and I would get a visit from the purser asking if I needed any assistance after landing. Perhaps it is that special assistance designation that prevents the record from being flexible.

I would still like anyone's experience using CPAPs on UA partner airlines like Lufthansa on long haul. I'm wondering if the information is passed along through the record when purchased on UA, say LAX-EWR-FRA-LIS. I know that's roundabout but for example's sake. If the long hop EWR-FRA is on Lufthansa would they get the CPAP request automatically if it were called in properly to UA? Sorry if this is too nerdy but I'm not a UA expert.