What Is AHI and Why Does It Matter for Your CPAP Therapy?

AHI stands for Apnea-Hypopnea Index, and it is the single most important number on your CPAP therapy report. It measures how many times per hour your breathing is partially or completely interrupted during sleep. Understanding this number — and knowing what affects it — puts you in control of your own therapy.

What the numbers mean

Your CPAP machine records your AHI every night. Here is how to interpret it:

  • Below 5: This is the target range. Your therapy is working well and your breathing events are controlled.
  • 5 to 10: Mild range. Your therapy is partially effective but there is room for improvement. Worth investigating.
  • 10 to 15: Moderate range. Something is likely reducing your therapy effectiveness — mask leak, pressure settings, or positional issues.
  • Above 15: Your therapy is not adequately controlling your sleep apnea. Clinical review is strongly recommended.

Common reasons your AHI creeps up

An AHI that was once in the 2-3 range and slowly climbs over weeks or months usually points to equipment issues rather than a worsening condition. The most common culprits I see in BreatheSession consultations:

  • Worn mask cushion — allows air to leak, which reduces effective pressure at your airway
  • Clogged or old filters — restricts airflow and can cause the machine to underdeliver pressure
  • Positional changes — sleeping more on your back than usual can increase events
  • Weight changes — gaining weight can change your pressure needs
  • Alcohol or sedatives before bed — these relax airway muscles beyond what your current pressure can manage

How to check your AHI

Most modern CPAP machines display your AHI on the screen when you wake up. ResMed AirSense machines show it on the home screen — look for the number next to "Events/hr" or "AHI." You can also check the myAir app on your phone for a daily summary.

For a deeper look at trends over time, your clinician can access AirView — ResMed's cloud platform that stores your detailed therapy data. This is what I review during a BreatheSession: not just last night's AHI, but weeks and months of trend data that reveal patterns invisible on a single night's report.

The bottom line

Your AHI is not something to stress about night to night — it naturally fluctuates. What matters is the trend. If you see your numbers gradually climbing, start with the basics: fresh filters, a new cushion, and clean equipment. If that doesn't bring it back down, a clinical data review can identify what's going on.

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