CPAP & Resmed's Post on Wide Variations of AHI – USA Medical Supply
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CPAP & Resmed's Post on Wide Variations of AHI

Posted by Richard Spafford on

ResMed recently posted on their website on AHI and we have reposted it here below. 


Why does my apnea–hypopnea index (AHI) change?

Recently, a CPAP patient messaged us on Facebook that over the previous week her apnea–hypopnea index (AHI) had fluctuated between 1.9 and 5. (See the definition of AHI and other sleep apnea terms.) She said she hadn’t had a “5” in 10 years, but now they were coming every other night even though her CPAP machine was reporting a good mask fit each morning. Concerned, she asked if it’s normal for AHI to go up and down from night to night.

The short answer is: Yes; it is normal for AHI to vary within reason. An AHI less than 5 is considered normal, and some patients with severe sleep apnea may be told by their doctor that they can accept even higher numbers so long as they’re feeling more rested each morning, experiencing fewer symptoms and their AHI is progressively decreasing.

If your AHI was stable, but is suddenly increasing over the past few days or weeks, you should report this to your equipment provider and/or sleep specialist.

Causes of rising AHI

In the case of our Facebook messenger, her AHIs fluctuating between 1–5 was normal and still within a safe range. If your nightly AHIs are rising above what’s considered safe, you may be experiencing:

  • 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 (often experienced by patients on bilevel machines and mouth breathers currently using a nasal pillows or 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, but do talk to your doctor about ways to reduce these events.
  • 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 they’re 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 AHI and reverse the trend, talk to your doctor or equipment provider as soon as possible.

If you’ve suddenly experienced higher AHIs, what was the cause, and how did you get them back down? (If you have concerns about your AHI, be sure to talk with your doctor before taking any action.)  

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