How to Interpret CPAP Data

Updated April 17, 2017

Most newer CPAP machines record a great deal of data about the sleep patterns of the patients who use them. This data is often saved on a smart card that the patient can take along to the doctor or respiratory therapist's office; some machines report the data directly via wireless modem. While each CPAP model records a slightly different set of information, there are a few basic pieces of data that show up in all reports. This information helps therapists tell whether the patient is complying with treatment and whether the CPAP machine or mask needs to be adjusted.

Look at compliance data to judge whether the patient is actually following his or her treatment regimen. Most reports will show both total hours of use and total days of use for a given period. If total days of use is smaller than the prescribed period length, it indicates the patient is skipping CPAP therapy; if the total number of hours of use divided by days of use is six or fewer, it may indicate the patient is removing his mask at some point during the night.

Review apnoea/hypopnea data to judge effectiveness of treatment. The apnoea/hypopnea index, or AHI, is an hourly average of how many times the patient stops breathing or is not inhaling fully. An AHI of greater than 5 is an indication that the treatment is not being effective; either the CPAP machine is not providing adequate pressure or the mask is not properly fitted. The report may also show the average length of apnoea/hypopnea episodes.

Look at pressure data to indicate how much pressure the patient requires to prevent apnoea episodes. The most recent CPAP designs adapt the amount pressure the patient receives according to the breathing rate data it's measuring. This pressure is usually expressed both as an average pressure (in cm/H2O) and as a percentile pressure. The percentile pressure is the pressure at which you spent that per cent of time at or below. For instance, if the report shows a 90 percentile pressure of 11, it means that 90 per cent of the time you were using your CPAP, you were receiving 11cm/H2O of pressure or less. If these pressures are close to the maximum pressure at which the machine is set, it can be an indication that the patient requires a higher maximum pressure.

Examine leakage data to determine proper mask fit. A certain amount of air escaping from a CPAP mask is necessary to prevent the patient from rebreathing the same air; however, too much leakage indicates the patient may not be receiving the correct air pressure from the mask. The report typically shows the leakage data in l/min, as both an average and as a percentile. It may also show how much time was spend with excessive leakage from the mask.


Your respiratory therapist can usually print out a data report that is specifically designed for patients. It provides definitions of unfamiliar terms. If you don't understand information in your report, discuss it with your respiratory therapist. If the report shows abnormal data, the only way to determine what's happening is by discussing your sleep experience with your therapist.


While CPAP data can provide important insights therapy effectiveness and compliance, it does not provide sufficient information to change a diagnosis or prescribed pressure. The physician or therapist needs to discuss the data with the patient to be able to fully interpret it.

Things You'll Need

  • CPAP data report
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About the Author

Scott Knickelbine began writing professionally in 1977. He is the author of 34 books and his work has appeared in hundreds of publications, including "The New York Times," "The Milwaukee Sentinel," "Architecture" and "Video Times." He has written in the fields of education, health, electronics, architecture and construction. Knickelbine received a Bachelor of Arts cum laude in journalism from the University of Minnesota.