How to Determine Your CPAP Pressure Settings

If you've been prescribed continuous positive airway pressure (CPAP) therapy to treat obstructive sleep apnea, you may wonder: Does the severity of sleep apnea measured by the apnea-hypopnea index (AHI) correlate with the needed CPAP pressure for effective treatment?

Learn how the prescribed CPAP setting is related to the underlying degree of sleep apnea and what other factors might be involved to determine your optimal treatment, including anatomy, sleep position, and sleep stages.

This article discusses the sometimes inverse relationship that exists between the severity of sleep apnea and the pressure setting on a CPAP machine. It also explains the key factors that determine the correct setting. In the end, it should make sense that a board-certified sleep physician should recommend the pressure settings.

Man Wearing Cpap Mask While Suffering From Sleep Apnea By Woman On Bed At Home

Somsak Bumroongwong / EyeEm / Getty Images

Sleep Apnea Severity

It's only natural to assume that there would be a relationship between the degree of obstructive sleep apnea and the prescribed CPAP pressure setting that is being treated. Consider an analogy: If you need a medication for blood pressure, a higher dose would have a greater effect. Unfortunately, the relationship is not quite as direct when treating sleep apnea.

Obstructive sleep apnea (OSA) is diagnosed with an overnight sleep study or home sleep apnea test that assesses the number of times per hour the upper airway collapses, resulting in a drop in blood oxygen levels or awakenings from sleep.

If the airway completely collapses, it's called apnea. If it partially collapses, it's called hypopnea. The total number of these events per hour of sleep is known as the apnea-hypopnea index (AHI).

You might think that severe OSA requires a higher CPAP pressure setting to treat it. In actuality, this is not always the case as there are multiple factors involved in determining the required setting. Typically, the treatment starts at a low setting and is gradually increased to resolve all apnea and hypopnea events, as well as snoring.

The lowest setting on CPAP machines may be 4 to 5 centimeters of water pressure (abbreviated as cm of H2O or CWP). Most people require more pressure than this low setting. The maximum setting varies with the type of machine, but it could be as high as 25 or 30 CWP. The average setting often lies between these two extremes.

Learn AHI Ratings

The AHI values and corresponding ratings are:


  • Less than 5 (<5): Normal, meaning no sleep apnea
  • 5 to 15: Mild sleep apnea
  • 15 to 30: Moderate sleep apnea
  • More than 30 (>30): Severe sleep apnea

Determining Required CPAP Pressure

If the CPAP setting is determined as part of an overnight titration study in a sleep lab, a polysomnography technologist will observe your breathing patterns and adjust the setting upwards while you sleep. This is done remotely from another room so that you are not disturbed.

The goal is to eliminate the sleep apnea and snoring and observe deep sleep, including rapid eye movement (REM) sleep. This setting should also be optimized while sleeping supine (on your back), when sleep apnea often worsens. 

Some people are sent home with a self-adjusting CPAP machine, sometimes called AutoCPAP or APAP. In this scenario, the prescribing physician recommends a range of pressures. The machine will start low and adjust upwards as needed in response to measured airway resistance (suggesting persistent collapses of the soft tissues like the base of the tongue or soft palate into the throat).

The CPAP delivers intermittent pulses of extra air pressure to evaluate for resistance and, by extension, whether the upper airway is collapsing. If the airway is open at the CPAP setting delivered, the setting is maintained.

People with more severe sleep apnea often need higher pressures on CPAP or even bilevel therapy, which offers varying degrees of pressure. Children may require similar pressure levels to adults, despite their smaller overall size and the smaller dimension of their airways.

Settings Can Defy Assumptions

The required CPAP pressure does not always directly correlate with the severity of sleep apnea. Some people with mild OSA need high pressures and some people with severe OSA need relatively modest pressure.

Factors Affect the Pressure Setting

The anatomy of the upper airway and the nature of the airway obstruction plays the biggest role in determining the required CPAP pressure setting. If sleep apnea occurs because of a blocked nose due to allergies or a deviated septum (an off-center nasal passage), a collapsing soft palate, or a tongue that falls back into the airway, differing amounts of air are required to push these tissues out of the way.

In addition, being overweight or obese may influence the settings. In fact, when people lose about 10% of their body weight, it may be necessary to adjust the CPAP settings by turning them down.

Alcohol, medications that relax airway muscles (like benzodiazepines), and sleeping on your back may all transiently add to your pressure needs. Finally, REM sleep towards morning may relax muscles and exacerbate sleep apnea as well.

Anatomy Influences Settings

The biggest influences on CPAP settings? The anatomy of the upper airway and the nature of the airway obstruction.

A Physician Knows Best

Given these factors, it's not always easy to determine how much CPAP pressure you may need to treat your sleep apnea. It may also vary somewhat during the night, depending on your sleep position and sleep stage.

If the pressure is too low, you may experience five or more sleep apnea events and other symptoms, like snoring or waking up while gasping for air. If the pressure is too high, you may experience side effects like air swallowing and fitful, interrupted sleep.

So while it should help you to understand the science behind CPAP settings, the final decision should be made by an expert. In other words, it's vital that a CPAP machine be set properly by a board-certified sleep physician. A physician can ensure the best experience with the machine—and the greatest benefits.

Remember the Mask

Don't overlook the importance of the CPAP mask, which can deliver air through the nose or the mouth. The choice is up to you (are you a nose breather or a mouth breather?), but the mask must fit well. "There are no differences in efficacy among the large number of mask types. The best mask is the one you find comfortable and will wear regularly."

Summary

It makes sense to assume that severe OSA requires a higher CPAP pressure setting to treat it while mild apnea requires a lower setting. Reality can point to much different conclusion. In fact, there can be an inverse relationship between the severity of sleep apnea and the pressure setting on a CPAP machine. This is because multiple factors are involved in determining the best setting. The most important is the anatomy of the upper airway and the nature of the airway obstruction. In the end, the pressure settings should be determined by a board-certified sleep physician.

A Word From Verywell

Unlike some other conditions, sleep apnea is treatable. And eliminating it from your life promises to buoy your psychological health and happiness, the Division of Sleep Medicine at
Harvard Medical School says. If it's hard enough for you to imagine enjoying one good night's sleep, try to imagine having seven—and then another seven after that. In other words, quality sleep can be more than something you dream about. For the first time in your life, it can be a viable part of your life. Now that you've taken the first step with a CPAP machine, you have every reason to be optimistic about the outcome.

2 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.
  1. Division of Sleep Medicine at Harvard Medical School. Understanding the results.

  2.  Division of Sleep Medicine at Harvard Medical School. Understanding PAP.

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