How to Determine Your CPAP Settings

If you've been prescribed continuous positive airway pressure (CPAP) therapy to treat obstructive sleep apnea, your prescribed CPAP setting is related to several factors—the severity of your sleep apnea, as well as the anatomy of your throat muscles, your sleep position, and the timing of your sleep stages throughout the night.

This article explains the key factors that your sleep physician uses to determine the correct setting, as well as how the device can automatically adjust the settings based on your needs.

Sleep Apnea Severity

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.

Determining Required CPAP Pressure

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. Levels above 15-20 CWP may require a change to bilevel therapy, (BPAP).

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 snoring and sleep apnea and hypopnea episodes, and for deep sleep, including rapid eye movement (REM) sleep, to be observed in your sleep study. This setting should also be optimized while sleeping supine (on your back) when sleep apnea often worsens. 

Self Adjusting Machines

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. Airway resistance suggests 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, which indicates that the upper airway is collapsing. If the airway stays open at the CPAP setting delivered, the setting is maintained.

People with more severe sleep apnea might need higher pressure on CPAP or BPAP, 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.

Factors That Affect the Pressure Setting

The anatomy of the upper airway and the nature of the airway obstruction play the biggest role in determining the required CPAP pressure setting. Factors that affect the pressure setting include:

• Allergies that block the nasal passages. Keep in mind that a pressure setting of 12 cmH2O or higher may itself cause inflammation of the nasal passages, and using a humidifier may help.
• A deviated septum (off-center nasal passage)
• Collapsing soft palate
• Tongue that falls back into the airway
• Alcohol use that relaxes airway muscles
• Certain medications, such as benzodiazepines
• Sleep cycles (REM sleep toward morning may relax muscles)

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.

Complications of Incorrect Settings

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.

Summary

Multiple factors are involved in determining the best CPAP 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.

Getting treated for obstructive sleep apnea can greatly improve your quality of life by increasing the amount of restful sleep you get each night. This will result in less daytime sleepiness, and also reduces the risk of health complications associated with obstructive sleep apnea. It can take some time to get a diagnosis and to find the right settings, but most people feel that the effort pays off substantially.