I think you may observe for the next few nights to see whether this just happens once. It is sometimes due to machine error or others that would yield an inaccurate AHI. If the AHI continues to be higher than normal, the following should be considered.
Mask leak: If air is escaping your CPAP mask, you’re not getting all the air pressure you need to keep your airway open. The three most common causes of mask leak are a poorly fitting mask, inadequate cleaning or mouth leak. Mouth leak is most common if you use a bilevel PAP machine or you tend to breathe through your mouth and are using nasal pillows or a nasal mask. Here are some common fixes to each of these causes.
Mask off events: It’s common for some people to remove their mask during the night, either consciously or unconsciously, due to the initial foreign feeling or discomfort of wearing a mask. If your CPAP machine is reporting this happening or you suspect that it is, don’t worry, it’s normal. But do talk to your doctor about ways to reduce these events so you can get the full benefit of your therapy.
Alcohol, medicine and other drugs: The periodic use of certain medication, alcohol or narcotics may cause your AHI to go up. Ask your doctor if anything you’re taking could be causing your fluctuation, and how you can compensate for it.
Central or complex sleep apnea: A rising AHI could also be a sign that while CPAP is treating your obstructive apneas, your brain might not always be telling your body to breathe. This can cause central sleep apneas, “central” because your apneas are caused by a dysfunction in the central nervous system, not a physical obstruction. Most newer CPAP machines will report if you’re experiencing central apneas, but it takes a specific type of machine to treat them. If your machine is reporting central apneas or you can’t identify what is causing your rising apnea-hypopnea index, talk to your doctor or equipment provider as soon as possible.