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What are the Numbers on My CPAP Machine and What do They Mean?

A CPAP machine 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 just 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.

What do numbers mean on the CPAP machine? What do numbers mean on the CPAP machine?

Apnoea-Hypopnea Index

AHI is an acronym for "apnoea-hypopnea index". Hypopnea occurs when your airway significantly narrows or partially collapses. Apnoea represents an event where the airway completely collapses. In other words, apnoea is a more severe condition.

The AHI simply signifies the number of times every hour that your airway either partially or completely closes. The main goal of the AHI is to determine the severity of your condition as well as to evaluate how efficiently the CPAP is working. Let's see how this index is broken down into different categories:

  • Fewer than five instances: normal.
  • Between five and 14.9: mild apnoea.
  • Between 15 to 29.9: moderate apnoea.
  • Higher than 30: severe sleep apnoea.


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

The main takeaway 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 in order to enjoy greater levels of comfort, this might not always be the best option.

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 prove to represent a useful alternative.

There are also several variables which can impact your pressure setting. These may include:

  • If you have a deviated septum.
  • If your soft palette tends to collapse while sleeping.
  • If you have allergies or a cold.
  • If your tongue relaxes to the point where it partially or fully blocks your airway.

Those who are overweight could also require a higher pressure.
This is once again why it is important to obtain professional advice as opposed to manually manipulating the pressure of your device.


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 taken into consideration during the manufacture of your machine and values which 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 the overnight hours.

However, there can be other times when you notice that the "leak" icon is frequently activated. This is rather common if the mask is more than six months old. It may be time to purchase a replacement. There are other circumstances which can cause the leak indicator to display. These include:

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

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


Depending upon the style of your machine, this next feature may or may not be present within the display. Some units have been designed to gradually increase decrease the pressure when the unit is initially activated. The main intention behind this option is to allow you to become more comfortable when falling asleep (as opposed to being immediately exposed to full pressure levels). The airflow will then slowly increase (or "ramp up") until it reaches a satisfactory level.

During this stage, you will notice the ramp icon is activated. It may also display a numerical figure. 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 in order to diagnose any potential issues with the CPAP machine.

When Might My Readings Indicate a Problem?

It is finally prudent to take a quick look at when you should seek professional advice when dealing with one of these units. It can be argued that the AHI (apnoea-hypopnea index) is the most crucial reading to monitor. However, there are certain situations which can cause this figure to fluctuate such as:

  • If you are ill.
  • If you are prone to sleep on your back.
  • If you have recently been prescribed muscle relaxants.
  • If you consumed alcohol 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 which 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 a pressure fluctuation should likewise 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 invariably involves 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.

To shop for the highest-quality selection of CPAP devices: https://www.cpap.co.uk/shop.html

Author: Jenny Hall

About author: Jenny Hall is a clinical manager at Baywater Healthcare. She has extensive specialist clinical experience from Regional Nurse Adviser through to Senior Nurse Adviser, Service Lead and Contract Manager. She has provided leadership for the Regional Nurse Advisers ensuring best practice, implementation of National Guidance and Clinical Governance. Ms. Hall has worked with Baywater Healthcare since 2013, with leadership responsibility in delivering Home Oxygen and Long-Term Conditions services. Her clinical team focuses on delivering services closer to home which offer the NHS value with optimum clinical outcomes. Previously, Ms. Hall provided leadership to Regional Nurse Advisors with Air Products, a company providing home oxygen services to Wales, East Midlands and North London. She has served as a Senior COPD National Trainer and Nurse Adviser COPD Response with Innovex, ensuring highest competencies were maintained and best practices delivered. Ms. Hall has a Ba Honours Degree as a Registered General Nurse from Oxford Brookes University and MSc Health Studies from Staffordshire University. She completed Respiratory Education and Training Courses and the Edinburgh Sleep Course. Jenny Hall’s LinkedIn profile: https://www.linkedin.com/in/jenny-hall-34331b60/

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