Good luck with the surgery! I just had nf done last month and use cpap (AHI of 90). I let the respitory guy know and gave it to the assistant before surgery. Woke up with it on in recovery. No problems. Surgen said it would put some extra air in my stomach and it does. He said many of his patients with cpap are far more flatulant (sp) after surgery and I have found that to be true. Although I cannot burp the air does find a way out.
The air pressure did not affect the surgery at all and visit with surgen showed everything going well.