What are the numbers on my CPAP machine, and what do they mean?

ResMed AirSense 10 with CPAP humidifier

Last updated on February 19th, 2024 at 03:49 pm

CPAP Numbers: Understanding Sleep Apnoea Indicators

A CPAP machine (Continuous Positive Airway Pressure) can help provide you with a restful night of sleep, as it will provide a continuous flow of oxygen. However, these units can sometimes be slightly confusing to understand, particularly if you are becoming acclimated to their functions. Let’s take the confusion out of this scenario by examining what specific readings signify. You can, therefore, make the most out of these modern marvels.

Our advice: If you have symptoms of Obstructive Sleep Apnoea (OSA) and you are concerned that you may have OSA – an In-Home Sleep Test done by us or a sleep study conducted through the NHS will help you find out.

If your result confirms Sleep Apnoea, you will probably benefit from (and be eligible for) CPAP therapy.

Apnoea-Hypopnea Index (AHI)

One of the critical indicators that our expert sleep technicians use in our sleep test report is the AHI.

There are other indicators, but to illustrate a simple idea of your potential issue, I’m going to explain the AHI, which stands for the Apnoea-Hypopnea Index.

Hypopnoeas occur when your airway significantly narrows or partially collapses. Apnoeas are events where the airway completely collapses. In other words, Apnoea is more severe. To be classified as an apnoea or hypopnoea, the obstruction needs to last at least 10 seconds.

The AHI signifies the number of times every hour that your airway either partially or fully closes. The main goal of the AHI is to determine the severity of your OSA – positional, mild, moderate or severe. To find out what Sleep Apnoea treatment is beneficial to you.

Let’s see how this index is broken down into different categories:

  • Fewer than five instances: Normal range
  • Between five and 14.9: Mild OSA
  • Between 15 to 29.9: Moderate OSA
  • Higher than 30: Severe OSA
AHI Scale on sleep test

How do I reduce my AHI?

  • Change your mask to one that fits better and suits the way you breathe.
  • Change your sleeping position.
  • Replace your mask parts when necessary
  • Clean your equipment daily.

Pressure numbers

As you might have already realised, this reading signifies the amount of pressure that the CPAP machine is delivering to your airways. However, keep in mind that most CPAP machines offer a fixed pressure setting (as opposed to an APAP or a BiPAP).

The main point here is that you will need to find the optimum level of pressure so that your breathing will not become impeded during the overnight hours. While some individuals may wish to set this pressure to a lower reading to enjoy greater comfort levels. This might not always be the best option for everyone.

It is, therefore, wise to consult with a sleep specialist. He or she will be able to determine the correct pressure settings within a clinical environment. These can then be applied at home. If you instead require a variable level of pressure, an APAP machine might represent a valuable alternative.

Several variables can impact your pressure setting, and these may include:

  • A deviated septum.
  • If your soft palate tends to collapse while sleeping.
  • Allergies or a cold.
  • If your tongue relaxes to the point where it partially or fully blocks your airway.

Those who are overweight with OSA could also require a higher pressure setting. This is why it is essential to obtain professional advice and not manually manipulate your CPAP device’s pressure.

Mask Leaks

Although this may appear to be a self-explanatory reading, there is slightly more than meets the eye. Your unit normally measures the flow of air in terms of litres per minute. A slight amount of air escaping from the unit is actually quite normal. This is primarily due to the presence of an exhalation port that is built directly into the mask.

Leak values are considered during the manufacture of your machine, and values that fall within normal ranges are commonly referred to as ‘intentional leaks’. These types of leaks are partially engineered to prevent you from breathing in unhealthy levels of carbon dioxide during therapy.

However, there can be other times when you notice that the “leak” icon is frequently activated. This is relatively common if the CPAP mask is more than six months old. It may be time to purchase a replacement or new mask parts. Mask leaks can also cause you to wake up with a dry mouth or nose as the air escapes, creating dryness. Other circumstances can cause the leak indicator to display, including:

  • The mask may be too big.
  • Facial hair beneath your nose could cause a poor seal.
  • The style of the CPAP mask might not be appropriate for your face and mouth.

Leaks may also inadvertently occur during the overnight hours if you happen to change positions while sleeping suddenly. If you suspect that this is the case, it could be wise to purchase a specifically designed CPAP pillow to accommodate the presence of a mask. Speak with your doctor or sleep therapist to learn more about this option.

Cleaning your CPAP equipment regularly will also impact the lifespan of your equipment and create leaks.

Usage hours

Another number you may observe on your machine is usage hours. This number indicates how many hours you have used your machine; if the number is too low, it means you are not gaining enough use from your therapy equipment.

CPAP applications

More recent CPAP devices have been designed to connect to an app via a smart device – allowing you to monitor your therapy. The remote monitoring systems make it easier to understand your CPAP numbers and settings and gain helpful insights. The applications often feature various guidance videos, tips and tricks.

An example of this is within the ResMed AirSense 10 and the AirMini, providing users with the ability to access ResMed myAir. myAir lets you know how secure your mask seal is and how many leaks occur during the night.

Ramp settings

Depending upon the style of your machine, this next feature may or may not be present within the display. The ramp function is designed to gradually increase the pressure when the machine is activated. The main intention behind this option is to allow you to become more comfortable and make it easier to fall asleep (as opposed to being immediately exposed to full pressure levels). The airflow slowly increases during the start of your sleep (or “ramps up”) until it reaches a satisfactory level.

When this setting is switched on, you will notice the ramp icon is activated. It may also display a numerical figure on your device – This represents the duration of the ramp stage measured in minutes (for example, 20 or 30). In the majority of cases, you will likely fall asleep well before the cycle itself completes. If you observe a much higher initial pressure or if the ramp icon suddenly disappears, it is best to consult with the manufacturer to diagnose any potential issues with the CPAP machine.

EPR settings

The EPR number on your machine stands for Exhalation Pressure Relief. This function is a comfort setting that decreases the airflow pressure when you exhale, making it easier to breathe. The customisable setting can be set from 1 to 3, depending on your chosen comfort level. Please be aware this is not always turned on by default therefore you may need to turn on the EPR and adjust it yourself.

When might my readings indicate a problem?

It can be argued that the AHI is the most crucial reading to monitor. However, certain situations can cause this figure to fluctuate, such as:

  • If you are ill.
  • If you are prone to sleeping on your back.
  • If you have recently been prescribed muscle relaxants.
  • If you consumed alcohol or caffeine before bed.

It is, therefore, better to take longitudinal readings over 30 or 60 days. These will provide you with a much more insightful overview of how your machine is affecting your condition. Having said this, readings that suddenly spike within the high range (more than 30 instances each hour) for no apparent reason should be reported to a sleep specialist as soon as possible. This could indicate an issue with the machine or that the treatment needs to be modified. 

Of course, other indicators, such as a leak or pressure fluctuations, should also be monitored closely. There can be times when a unit may need to be upgraded to address your unique condition.

Putting it all together

Getting the most out of your CPAP machine will involve knowing how to interpret its diagnostic display.

While units will naturally vary between different manufacturers, this article should serve as a basic guide. If you have additional questions or should you suspect that there may be an issue with the unit, always make it a point to speak with your doctor as soon as possible.

If you need any further help, please contact us.