Understanding your CPAP Report

  • By Clay Rollyson
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Modern CPAP machines provide a myriad of information that can help you and your physician determine how well your CPAP is working for you. So much of this information is abbreviated or is shown as an acronym. This can make it really difficult to understand what in the world you are looking at. That is why we have taken the time to lay out a full explanation of all the things you see on those reports.

What are the categories on the CPAP report?

The first thing that you need to understand is what all the categories mean on your CPAP Report. Then, we can take a deeper dive below on what those categories represent. So, let’s start out by defining all those abbreviations and acronyms.
  • AHI– Apnea Hypopnea Index.
  • HI– Hypopnea Index
  • AI– Apnea Index
  • CAI– Central Apnea Index
  • RERA– Respiratory Effort Related Arousal
  • Cheyne Stokes– abnormal pattern of breathing
  • Leak– Air escaping above normal thresholds
  • Pressure– Amount of pressure created by the CPAP
  • Compliance percentage– percentage of nights greater than 4 hours of usage
Now, let’s dive in a little deeper on each subject.

Apnea Hypopnea Index (AHI)

The AHI is the total number of Apnea and Hypopnea events that occur divided by the total numbers of hours that you slept on the CPAP. This metric shows you the number of times per hour that you stopped or partially stopped breathing. It is important to monitor this metric because it is the main method for determining how well the CPAP is working for you. Generally, it is considered “normal” if your AHI is under 5. Of course, that is different for everyone and only your doctor can tell you what a healthy AHI is for you. For CPAP users that are on an Auto CPAP the AHI may take time to reduce. This is because the Auto CPAP takes time to adjust to the most suitable therapeutic pressure for you.

Apnea Index (AI)

The Apnea Index is a further breakdown of the AHI. The AI is the number of times per hour that you had an apnea divided by the total hours that you were using the CPAP. The Apnea Index is typically broken down by: Obstructive Apnea, Central Apnea, and Unknown Apnea. All Apnea is defined as a stoppage of breathing for at least 10 seconds. Obviously, breathing is pretty important. Usually as you stop breathing for that length of time, your blood oxygen level falls as well. Enough Apnea events over time can cause all sorts of health concerns. Because the AI is part of your AHI score you should refer to the AHI metric for what should be determined as a “normal” score for this metric.

Hypopnea Index (HI)

A Hypopnea is very similar to the Apnea in how it is determined. The hypopnea index is the total number of hypopneas divided by the total hours of sleep. By definition a Hypopnea is when your breathing shallows to at least a 30% from your normal airflow, in addition to at least a 4% in your blood oxygen level. To boil that down, a hypopnea is when your breathing is partially blocked, and that partial blockage causes a reduction in blood oxygen. The hypopnea index is usually added to your apnea index and totals as your Apnea Hypopnea Index. That “normal’ range is cited above.

Central Apnea Index (CAI)

Central Apnea is another form of apnea that is added into the overall AI score. The Central Apnea Index is again the total number of Central Apneas divided by the total number of hours you slept. A Central Apnea is when you stop breathing, but your brain doesn’t tell you to breathe like it normally should. It is more a neurologic issue and, in most cases, requires a different therapy than standard CPAP. In many cases you may be prescribed an ASV (Auto Servo Ventilator). This total score is a part of your total AHI score, and the goal is typically to be under a total of 5 AHI. Of course, only your doctor could determine that for you. If your CAI is high even on your CPAP, you should certainly speak to your doctor about this to see if a more appropriate therapy should be prescribed.

Respiratory Effort Related Arousal (RERA)

The RERA is when your brain causes your breathing to become labored, and you are aroused from your sleep. Usually, it is represented by limitations in breathing, occurring for more than 10 seconds continuously. It is not classified as Apnea or Hypopnea but can cause some of the same symptoms if untreated. If you are seeing a significant amount of RERA on your CPAP Report, then it would be smart to consult your doctor. In most cases CPAP will resolve this issue, but if it continues on CPAP an alternative therapy may be necessary.

Cheyne Stokes Respirations

Cheyne Stokes are when you go into an abnormal breathing pattern. It is usually a progressive deeper breathing pattern than can become more rapid at first and then decreases resulting in complete stoppage of breathing (Apnea). This pattern can be repetitive for 1-2 minutes at a time in many cases. It also may repeat over and over throughout the night. In most cases your CPAP should resolve the Cheyne Stokes breathing, but in some rare cases it may not. If you have continued Cheyne Stokes on your CPAP Report, you should speak with your doctor about changing therapy or switching to a better alternative therapy.


Leak is classified in liters per minute of air escaping from your mask or tubing. It can also be from a poorly attached humidifier. On the CPAP report the leak may be shown at multiple points such as: Median Pressure leak, Maximum Pressure leak and 95th Percentile leak. This is because a leak at the maximum pressure is not nearly as concerning as a leak at your 95th percentile pressure. By most opinions the leak should not be over 24 lpm. If it is over that threshold, you should do a close inspection of all connections to make sure that everything is together correctly. If everything is tightly attached, then you should work to adjust your mask for a more secure fit. With that being said there are a couple things to keep in mind about leak
  1. There is a good chance that you will have some leak. Very rarely does anyone have a perfect mask fit throughout the entire night. Adjusting your mask to keep your leak in a proper range is good, but do not make yourself miserable over a minimal leak.
  2. Your mask will have air escaping at all times. I can’t count the times customers have come in with a mask that had tape over an exhalation port. You do not want to do that. All CPAP masks have an exhalation port that allows you to properly exhale CO2. Usually, it is in an obvious area with small holes.


Pressure is the measurement of force that the CPAP is pushing to keep your airways open. It is classified in Centimeters of water pressure, typically abbreviated as “cm”. If you are on a fixed pressure CPAP this will most likely be one pressure without much else on the CPAP Report. If you are on an Auto CPAP, then you may see a few different pressures. I will detail those below:
  • Median Pressure– This is the average pressure that your CPAP is at from start of therapy to end.
  • 95th percentile– This is the pressure that is providing the most effective therapy. In other words, this is the pressure that is working best to resolve your apnea. This may change from time to time.
  • Maximum Pressure– This is the highest amount of pressure that your CPAP is reaching during your CPAP therapy.

Compliance Percentage

For a real detailed look at compliance percentages, I would refer you to our compliance video that lays CPAP compliance out in detail. In summary, the report will typically show nights greater than 4 hours of usage as compliant nights. The number of nights with 4+ hours of usage divided by the total number of nights used will give you that percentage on your CPAP Report. For Instance: if you had 21 nights of 4+ hours usage out of a total of 30 nights, then your compliance percentage will be at 70%.