Seeing your AHI (Apnea-Hypopnea Index) suddenly jump on your CPAP data — after weeks or months of stable, low numbers — can be alarming. It’s a genuinely common experience among CPAP users, and it usually has an identifiable cause rather than signaling that therapy has stopped working altogether.
What AHI actually measures
AHI is the average number of apneas (complete breathing pauses) and hypopneas (partial breathing reductions) per hour of sleep, and it’s one of the main numbers CPAP machines report each night. According to the American Academy of Sleep Medicine, an AHI under 5 while on therapy is generally considered well-controlled, though target ranges can vary by individual and by prescribing clinician.
Common reasons for a sudden spike
- Mask leak or fit changes. A shifted mask, worn-out cushion, or new facial hair can all cause air leaks that some machines misread as respiratory events, or that genuinely reduce effective pressure delivery (Sleep Foundation).
- Sleeping position. Back-sleeping (supine position) is well documented to worsen obstructive sleep apnea for many people compared to side-sleeping, since gravity allows the tongue and soft tissue to collapse more easily into the airway (National Institutes of Health / PMC).
- Alcohol or sedative use before bed. Both relax the muscles of the upper airway and can meaningfully worsen apnea events even with CPAP running, per the Mayo Clinic.
- Weight changes. Even modest weight gain can increase soft-tissue mass around the airway and raise AHI; this is one of the more common longer-term drivers of a rising trend rather than a single-night spike.
- Nasal congestion or illness. A cold, allergies, or sinus congestion can increase upper-airway resistance and disrupt normal airflow, and often causes short-term spikes that resolve once the illness clears.
- Central or complex apnea emerging. Less commonly, a rise in AHI reflects an increase in central apneas (where the brain briefly stops signaling the breathing muscles) rather than the original obstructive pattern — this is a different mechanism that CPAP alone doesn’t always fully address, and it’s worth flagging to a sleep physician if it’s suspected (AASM).
What’s worth doing
Most single-night or short-term spikes are traceable to something identifiable — a leaky mask seal, a rough night with alcohol, more time spent on your back, or a cold. Checking your machine’s detailed data (leak rate, not just AHI) for the nights in question can often point to the cause. If leak rate is elevated, refitting or replacing the mask cushion is usually the first, simplest fix.
A spike that’s persistent over multiple nights or weeks, especially without an obvious explanation, is different — that’s a pattern worth bringing to your sleep medicine provider, since it may call for a pressure adjustment, a mask refit, or in some cases a repeat sleep study.
This article is for general educational purposes only and isn’t a substitute for individualized medical advice. Don’t adjust your prescribed CPAP pressure settings on your own — if your AHI trend is concerning you, your sleep medicine team can review your detailed data and determine the right next step.
