I have read that your cpap does not count towards your carry-on luggage. But getting it through maybe another story.
I hate to fly and have only done so once to see my son graduate Marine boot camp in San Diego. I ended up embarrassing myself and my daughter when we hit turbulence and I stood up and announced we were going down and may God be with us!! She still hasn't let me live it down and that was in August of 2000.
I have flown constantly with my CPAP, I strap the CPAP over the handle of my 22" carry on, and my huge purse in my hand, I go right through security. I slip the unit out and hold it until I catch someones eye going through security. They are ALWAYS wonderful and careful. On my last trip, there were four of us in the waiting area, and there was a lively discussion about face masks, and how wonderful we all felt. I have never seen medical equipment counted as a carryon, and if questioned, I would ask security for a supervisor immediately. Anyone announcing the fate of the entire airplane should be able to handle a new security person that doesn't understand that medical equipment is not "optional" and can't be checked. Loved the story.
Continuous Positive Airway Pressure (CPAP) Machines
CPAP do not count as carry-ons. They are medical equipment. Here's a quote from the Department of Transportation Fact Sheet on "Steps Taken to Ensure New Safety Requirements, Preserve and Respect the Civil Rights of People with Disabilities"
The limit of one carry-on bag and one personal bag (e.g. purse or briefcase) for each traveler does not apply to medical supplies and/or assistive devices (including service animals and their equipment). Passengers with disabilities generally may carry medical equipment, medications, and assistive devices on board the aircraft.
The Transportation Security Administration (TSA) has specific guidelines for going through the security gates with your CPAP on their website
This is a tag required for the equipent stateing its medical equipment then is not counted as a carry on. The only place I have seen this tags is on ebay fairly resonable. Hope this helps