What Is the Goal AHI for CPAP Treatment of Sleep Apnea?

The apnea-hypopnea index (AHI) is a test used to determine the severity of sleep apnea based on the number of breathing interruptions you have per hour of sleep. An AHI of less than five is considered normal (meaning you have sleep apnea), while an AHI of five or more is considered abnormal.

The AHI is measured during a sleep study and can help determine which treatments are best suited for you. These include oral appliances to prevent airway collapse, a breathing apparatus called a continuous positive airway pressure (CPAP) machine, or surgery.

This article explains how AHI is performed, what the scores mean, and how they are used to select the correct treatment for sleep apnea.

woman with sleep apnea mask

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What Is the Apnea-Hypopnea Index (AHI)?

The apnea-hypopnea index (AHI) is a diagnostic test used in adults and children that measures the number of times your breathing stops during sleep (apnea) and the number of times you have slowed, shallow, restricted breathing for 10 seconds or more (hypopnea).

Apnea is the complete absence of airflow through your nose and mouth, while hypopnea is a partial collapse of the airways that restricts normal breathing. When these happen, your blood oxygen will drop, leading to hypoxia.

The AHI score is calculated by dividing the number of times your body has an apnea or a hypopnea event by the number of hours of sleep.

What Is an AHI Used For?

The AHI score is used to select the best treatment for you if you have been diagnosed with sleep apnea. Treatment options include:

  • CPAP: This is a machine that uses mild air pressure to keep airways open while you sleep. CPAP may be appropriate for people with mild, moderate, or severe sleep apnea.
  • Oral appliance: This is a type of mouth guard that holds your tongue down to keep it from blocking your airways. This may be a better choice for mild or moderate sleep apnea.
  • Positional therapy: This may involve pillows, alarms, and other tools that keep you sleeping on your side rather than on your back (which makes sleep apnea worse).
  • Surgery: This is typically reserved for severe cases. Options include tonsillectomy (removal of the tonsils), uvulopalatopharyngoplasty (used to open the throat), thyrohyoidopexy (used to reposition the tongue), and maxillomandibular expansion (used to widen the upper airways).

AHI can also be used to determine how effective a treatment is based on a comparison of your baseline results.

How AHI Is Performed

The AHI is performed during a sleep study, also known as a polysomnogram, in a specialized sleep facility. Home sleep apnea testing is possible, but it may not be as accurate.

For AHI testing, the sleep study will involve sensors such as:

  • Nasal cannula: A narrow tube that rests under your nose to measure airflow
  • Respiratory effort belt: A device stretched across the chest and/or stomach to measure the extent and number of inhalations and exhalations
  • Pulse oximeter: A device clipped to your finger that continuously measures your blood oxygen and pulse rate

These sensors show how many times you stop breathing or breathe shallowly during the night. They also can detect changes in the blood oxygen levels and when hypoxia occurs.

The test begins the moment you fall asleep until the time you wake up the next morning.

Associated Tests

A test similar to the AHI is the respiratory-disturbance index (RDI). This measures not only apnea and hypopnea but also the number of times a breathing event awakens you at night (called respiratory effort-related arousal, or RERAs).

Another test called the oxygen-desaturation index (ODI) only counts the number of apnea or hypopnea events that cause your blood oxygen to drop at least 3%.

These tests together can not only establish how severe your sleep apnea is but also characterize the impact of sleep apnea on your cardiovascular health.

How to Make Sleep Apnea Worse

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What's a Good Goal for AHI?

The AHI score indicates the average number of apnea and hypopnea events per hour. Lower scores are better than higher scores. With that said, the goals and interpretations can differ for adults and children.

The AHI values for adults are categorized as follows:

  • Normal (no sleep apnea): Under 5 per hours
  • Mild sleep apnea: From 5 to 14 per hour
  • Moderate sleep apnea: From 15 to 29 per hour
  • Severe sleep apnea: Over 30 per hour

Because of their smaller size and physiology, an AHI over 1 is considered abnormal for children. Kids with an AHI of 2 or greater are typically referred for treatment.

Target AHI Goals

An ideal AHI for adults is fewer than five events per hour. Some sleep specialists aim for one or two events per hour as the "safe zone."

Children’s sleep is analyzed with stricter criteria. More than one event per hour of sleep is considered abnormal.

Can You Have Sleep Apnea When Using CPAP?

The AHI is most commonly used to determine if CPAP is needed and how effectively it is working. If needed, a CPAP machine can improve your sleep quality and quality of life, and even protect your long-term cardiovascular health.

However, a CPAP machine may not prevent sleep apnea entirely. It depends, in part, on the pressure set by your sleep specialist.

Modern CPAP machines are designed to track the number of breathing events you have each night. This information can then be automatically translated into an AHI score (either on the machine or via an app or website). Some can even be set up to share the results with your healthcare provider. 

If your AHI reading is rising or fluctuating, you can speak with your provider to see if a change in pressure might help. If it doesn't, you may need to schedule a visit with your provider to see if other factors are involved or if there is a problem with your machine.

Factors That Affect AHI Scores

Your AHI score can change from one night to the next and be influenced by any number of factors, including:

  • Sleeping more on your back
  • Having more rapid eye movement (REM) sleep
  • Using muscle relaxants
  • Drinking more alcohol near bedtime
  • Having nasal congestion or a stuffy nose due to a cold or allergies

Because of this, it often helps to keep track of your AHI scores, particularly if the numbers are fluctuating. Make note of anything that may have happened or anything you may have taken the night before. Over time, a pattern may emerge that reveals the underlying cause.

Simply changing the CPAP pressure without investigation can hurt more than it helps. If you turn the pressure up too high, for example, central sleep apnea can occur. This happens when your brain doesn't tell you to breathe during sleep.

By tracking your AHI results, you and your healthcare provider can better pinpoint the cause of the fluctuations, whether it be the machine, a medical concern, or a lifestyle issue.

Summary

An AHI is a measurement of the average number of apnea or hypopnea events you have per hour each night. During your initial sleep study, you'll receive a baseline AHI score. That score will be used along with other tests to find the best treatment options for you.

Modern CPAP machines are able to calculate your AHI on a nightly basis. This can inform you if sleep apnea is still occurring. If it is, your healthcare provider can determine if there is a medical cause for this or if there is a problem with the machine or pressure settings.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
Brandon Peters, M.D.

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.