What is AHI? Navigating Sleep Apnea & CPAP Therapy

It can be daunting to be diagnosed with obstructive sleep apnea syndrome. However, the process of diagnosing and the subsequent treatment is relatively simple.

If you are just beginning your CPAP therapy journey, all of the new jargon and medical terms can take a while to understand. Learning about the uses and necessities of CPAP machines and devices using these terms can become quite a challenge for those new to CPAP treatment.

This guide will take you through the basics of the Apnea-Hypopnea Index (AHI) and explain the importance of measuring your AHI for your CPAP treatment.

What Does AHI Mean? 

AHI stands for Apnea-Hypopnea Index. AHI measures the amount of apneas or hypopneas a person has within an hour. This score indicates the level of sleep apnea that an individual has and will indicate the type of CPAP treatment needed.

An alternative index, the respiratory disturbance index (RDI) is sometimes used. However, this score includes not only apneas and hypopneas but also other breathing irregularities, which may make it hard to diagnose the severity of your obstructive sleep apnea (OSA).

What Do the Numbers Mean in AHI?

The numbers in your AHI score indicate how many apneas and hypopneas an individual has within one hour of sleeping. An apnea is when you stop breathing for more than 10 seconds while sleeping. The numbers or AHI score shows how many times a person stops breathing for the duration of an hour. This score can then determine how your breathing patterns should be monitored and regulated through CPAP therapy.

What Are the Different Levels of Sleep Apnea?

There are several levels of obstructive sleep apnea that are classified by severity from severe sleep apnea to mild sleep apnea. The level of severity is based on the AHI score you receive during your initial sleep study. The different AHI scores for sleep apnea are as follows:

What is a Normal AHI? 

If you have a normal AHI, it means you do not have any form of obstructive sleep apnea. This means that you have less than five (<5) apnea episodes within the duration of an hour of sleeping.

When participating in an overnight sleep study, your sleep specialist will determine whether you have a normal AHI and where to go from there. If you are normal, some sleep specialists will even aim for only 1- 2 events per hour so that you're getting the best sleep possible.

On the other hand, if you have an extremely severe sleep apnea-hypopnea index (AHI) then reducing it even by a small amount will improve your sleep immensely. For example, if you have an AHI score of 75, reducing that to 50 will improve your sleep and keep your breathing patterns much more regular.

How Do You Measure AHI?

Your AHI is the average number of sleep apnea events you have while you sleep. Sleep specialists calculate your average AHI score by dividing the total number of apneic and hypopneic events by the total number of hours you were asleep. An apnea event must be at least 10 seconds or longer to be properly registered.

Doctors will diagnose you with sleep apnea and calculate your AHI score during a sleep study.

What is a Sleep Study?

A sleep study or polysomnogram is where a doctor or sleep specialist will monitor your sleep habits and any breathing problems noticed while you are sleeping. Your brain waves, blood oxygen levels and heart rate are also supervised to determine if you have any sleeping conditions or illnesses.

Polysomnography will usually take place at a sleep laboratory at a hospital or research centre, however, there are some instances where a simplified version may be performed in the home.

While the AHI is the primary measurement for diagnosing obstructive sleep apnea or OSA, your doctor may review other metrics to better understand your sleep apnea severity. 

This can include:

• your oxygen desaturation index (ODI) which measures the fluctuation of blood oxygen levels
• the level of carbon dioxide in the blood
• your sleeping position

Treatment After a Mild to Severe AHI Score

Whether you have been diagnosed with mild or severe obstructive sleep apnea, there are a couple of different treatment options available.

If you have a mild sleep apnea-hypopnea index, your doctor may recommend small lifestyle changes such as giving up smoking or losing weight to improve your symptoms. For those that have a higher AHI score, then there are a number of treatments available that can keep your airway open, regulate breathing and improve sleep.

Continuous positive airway pressure or CPAP therapy is the most popular and most effective treatment available. Your apnea-hypopnea index score can also be improved through other air pressure devices such as a BiPAP (bilevel positive airway pressure) machine or an oral appliance that is designed to keep your airway open while sleeping.

Other treatments can include:

• surgery (tissue removal, jaw repositioning or even a tracheostomy)
• treating associated medical problems such as allergies
• medicine changes
• supplemental oxygen
• Adaptive servo-ventilation (ASV)- an airflow device

How Do You Reduce Your AHI Score?

All the treatment options available for sleep apnea are designed to reduce your AHI, however, they cannot necessarily eliminate all sleep apnea symptoms. Your AHI score may actually vary each night, and because a 'normal' AHI is under 5 apnea events per hour, your AHI may never be eliminated.

Treating AHI With a CPAP Machine

Moderate to severe OSA is most commonly treated with a continuous positive air pressure machine or CPAP machine.

A CPAP machine treats patients by holding their collapsing airways open with positive air pressure to regulate their breathing while they are asleep.

This pressure is produced by a pump that then goes through a tube and connects to your airway via a face mask. Whilst we often refer to each device as a CPAP machine, there are two main types of sleep apnea machines. The traditional CPAP machine produces fixed air pressure and the APAP or automatic machine that can consistently adjust treatment pressure to hold the airway open.  

Your AHI score for the night will be monitored by your CPAP machine and you can refer to it after sleeping if need be.

Why Does My Apnea–Hypopnea Index (AHI) Change?

Your AHI can actually change or vary each night, and sometimes throughout the night. This is because the frequency and severity of your apnea events can be affected by many factors, including:

• sleeping position
• CPAP mask fit
• alcohol use
• lifestyle changes such as weight loss or gain

That is why participating in a sleep study is so important for determining how your sleep apnea is affected by external factors.

Your AHI score should stay relatively stable, and should only fluctuate slightly. If you notice a sudden increase in your AHI score, then you should consult your sleep specialist or equipment provider.

Causes for an AHI Reading Increase

There are a few causes for a sudden increase in your AHI reading or score, including:

• Mask leak: this means there is air escaping your CPAP mask, and you are not getting the air pressure you need.
• Mask-off events: this is the removal of your mask, whether consciously or unconsciously, due to the discomfort of the CPAP mask.
• External factors: this includes ingesting alcohol, taking drugs such as sleep medicine or taking certain medication.
• Central sleep apnea: although your CPAP device is treating your obstructive apneas, your brain might not always be telling your body to breathe. This can cause central sleep apnea, which means your apnea episodes are caused by a dysfunction in the central nervous system, not a physical obstruction.

For more information, please contact our CPAP Direct Support Team on 1300 800 985 or support@cpap.com.au