Understanding your AHI (Apnoea Hypopnoea Index)

Understanding your AHI Reading | Intus Healthcare

Last updated on January 31st, 2023 at 10:15 am

What does the AHI reading mean on a CPAP machine?

Most people first become aware of the term AHI from a sleep test or sleep study. A sleep study can determine if someone has Obstructive Sleep Apnoea (OSA) or not. The AHI number has to reach a certain level to confirm Sleep Apnoea. Once your OSA is confirmed, you will receive a recommended treatment plan.

AHI stands for Apnoea Hypopnoea Index, which is the calculation of apnoeas and hypopnoeas that occur during sleep. This calculated number is then divided by the hours you sleep, resulting in your AHI.

Apnoea: When your airway is completely blocked, and you stop breathing for 10 seconds or more. 

Hypopnoea: A period of shallow breathing for ten 10 seconds or longer. Your breathing doesn’t entirely stop; however, your airflow is 30% lower than usual. 

Apnoeas and hypopnoeas are very similar and can cause you to wake up to catch your breath. You may do this by waking up choking, coughing and gasping.

If you are already a CPAP machine user, you may find your CPAP readings will state your AHI in the sleep data report. This is certainly the case with newer machines. Your AHI should remain low, and if it does not, this could be a sign that there is an issue with your equipment set up, e.g. your mask is leaking air. 

What AHI indicates Sleep Apnoea?

What is a normal AHI score?

An AHI score which is less than 5 is considered normal. However, some patients with severe Sleep Apnoea may be told by their sleep clinic or doctor that higher numbers are acceptable as long as they’re feeling the benefits of the therapy and are experiencing fewer symptoms and their AHI is progressively decreasing.

What AHI is considered severe?

An AHI score which is higher than 30 is considered severe.

Here’s a breakdown of the AHI numbers and the correlating severity of OSA:

  • Normal sleep – An AHI lower than five events per hour.
  • Mild Sleep Apnoea – An AHI of 5 to 14.9 events per hour.
  • Moderate Sleep Apnoea – An AHI of 15 to 29.9 events every hour.
  • Severe Sleep Apnoea – An AHI of 30 events and above per hour.

Additional results you may see in your sleep study

Respiratory Disturbance Index (RDI)

RDI is calculated in a very similar way as the AHI, but an additional type of respiratory events named RERA are also counted. RERA is the abbreviation for Respiratory Effort Related Arousal and is essentially a very short arousal of a few seconds that follows partial closure of the airways. The normal range of the RDI score is also 5 or lower. 

Oxygen Desaturation Index (ODI)?

This shows the number of Oxygen desaturations events during an hour of sleep. A desaturation event is determined as a reduction of 4% or more of the Oxygen saturation baseline level. As you can imagine, the more your oxygen drops the harder the heart must work. The normal range of the ODI is 5 or lower. 

If you need more help understanding your Sleep Apnoea test results, please free free to contact us.

Why does my AHI change?

Many CPAP users find that their AHI changes. If your AHI alternates between the safe range of 1 to 5, there’s nothing to worry about. If the number goes above the normal range, you need to address it; read our helpful advice below.

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What is a good AHI score on CPAP?

Sleep specialists believe the ideal AHI for CPAP machine users should be below 5. However, it differs from person to person, and it is normal for the number to fluctuate.

If you use an oral appliance or Mandibular Advancement Device (MAD) for treating your OSA, you may need additional tests from your doctor for sleep clinic to understand the reason for changes in your AHI.

Why is my CPAP AHI so high?

Different factors can affect the severity of someone’s OSA, including:

  • Weight & neck circumference – Research has found that men with a neck circumference above 17 inches and women with a neck circumference above 15 inches have a much higher risk of developing Sleep Apnoea. Many people with severe cases of OSA are overweight or obese, as excess weight puts pressure on the upper airway.
  • Deviated septum – This can cause OSA or intensify the severity due to the deviation blocking the airflow, making it difficult to breathe. 
  • Smoking – Smokers are at a higher risk of OSA as it causes the upper airway to inflame and causes the airway to relax, leading to blockages. 
  • Alcohol – Regularly consuming a high amount of alcohol before you sleep disrupts your REM sleep, increasing the risk of OSA by 25%.
  • Medications and sedatives – Certain medications can aggravate sleep disorders. It is worth checking with your doctor if your medication works in partnership with your Sleep Apnoea treatment.
  • Sleeping position – Depending on the individual, certain sleeping positions can cause more apnoea events throughout the night. Sleeping on your side is generally advised for those with OSA as it comfortably opens the airway. 
  • Issues with your mask – Issues with your equipment set-up can cause your therapy to be less effective. Read on for ways to lower your AHI.

How do I lower my AHI on CPAP?

If you’re wondering why your AHI number has increased, all of the above factors should be considered to reduce your AHI. If you have addressed these things, but are still experiencing high AHI there are some extra things you can do to improve its effectiveness.

  • Use the most suitable CPAP mask for your OSA to prevent air leaks and stop yourself from taking your mask off. 
  • Replace your mask parts when necessary. Wear and tear will affecting your therapy.
  • Consider a CPAP pillow to make sleeping on your side easier. Alternatively, you can use multiple pillows to elevate your head to comfortably sleep on your back and keep your airway open.
  • If you use a nasal mask and breathe through your mouth, adding a chin strap will prevent leaks and lower your AHI.
  • Clean your CPAP equipment regularly to get the most from your equipment, prevent skin irritation and get a good mask seal.
  • Make sure your pressure settings are correct; if you have gained or lost weight, you may need to contact your doctor to ensure the settings are appropriate.
  • Use sinus and nasal care products if you suffer from congestion. Blocked sinuses can prevent your therapy from working effectively.
  • Visit your doctor and ask for your CPAP data to be downloaded to create a plan to improve your treatment.
  • Utilise a CPAP app; different brands have designed apps to help you easily track and troubleshoot what’s impacting your AHI. (ResMed myAir, Sefam Access) Please be aware that most apps are only compatible with the brand’s own equipment.

About Sleep Apnoea

Obstructive Sleep Apnoea is a common sleep disorder affecting around 4 million people in the UK. If untreated, Sleep Apnoea can lead to the development of more severe health conditions. Such as heart disease, high blood pressure, type 2 diabetes and atrial fibrillation. That is why it is essential to take a sleep test if you think you have OSA.

Common symptoms of Sleep Apnoea include:

In-home sleep test and AHI

If you have symptoms of OSA, you should consider taking a Sleep Apnoea test.

When completing a sleep study or sleep test, your AHI is calculated and will confirm your risk of having Sleep Apnoea.

If you choose to take a private in-home sleep test, you will receive a detailed sleep report referencing your AHI throughout the night.

Our Sleep Test experts use this data to recommend the correct treatment for your OSA. Treatment options vary, from CPAP therapy and lifestyle changes to alternatives to CPAP therapy

To Summarise

Your AHI indicates the severity of your Sleep Apnoea and how many times your breathing pauses during sleep.

Treating your sleep disorder manages and controls your breathing disruptions.

If you need any help or advice do not hesitate to contact us.

Author Danielle Myatt