Data Point:

My aunt flew from MNL-HKG-SFO (in J) last May and just called the local CX ticketing office and she hand no problem using the CPAP both going and coming back from SFO. The CSM was even nice enough to make herself available to her in case she needs assistance with anything.

I guest it also depends on the crew how your experience will be with this device.

Adding some data to this old thread, which was actually hugely useful for me this week on my LHR-HKG-CNS-BNE in Y.

As per the advice in this thread and on the website, I notified Cathay ahead of time by phone, and had a variety of experiences during the trip:

• At nearly every stage, check-in, at the gate, boarding and onboard, the staff asked me about my 'medical device'.
• On the LHR-HKG segment, 4 staff woke me up to ask me if everything was okay with the seat power. I barely coherently said "everything is fine" and went back to sleep.
• On the HKG-CNS segment, the service manager spoke to me on boarding, asked questions about my 'medical device': they seemed to want to know if it was life-critical, or just "nice to have". I had to reassure them several times it was just to stop me snoring.
  • Same manager had me moved me to an empty row and blocked out the seats with a blanket so I would be able to sleep. Literally amazing on a Y flight. I want to figure out how to say thank you to them (I have their name).
• On the CNS-BNE 90 minute flight, I was also queried by staff after boarding, and I simply told them I wasn't going to use it. 90 minute flight!

This is a big difference between this and BA, where I've had staff joke about turning off my life support (in a friendly, well received, way).

I get the feeling that Cathay staff are extremely vigilant in making sure life-critical equipment doesn't run on the seat power, and it feels like I had to fight back their impulses here. It's good to know the history (thanks flyertalk) so i could understand their context and respond appropriately.

You may send them a commendation here on the CX website.