Reading Your CPAP Data: AHI, Leak, Usage and Apps Like myAir and OSCAR

Usage hours

This is how long the machine ran with the mask on. It is the number insurers look at, and it is the one you control most. Medicare's initial requirement is at least 4 hours on 70% of nights in a 30-day period within the first 3 months, but for your health, more is better. Aim to wear CPAP for your entire sleep period.

AHI (apnea-hypopnea index)

AHI is the number of times per hour your breathing stopped (apnea) or became shallow (hypopnea). Before treatment, adults are generally classified as mild (5 to under 15), moderate (15 to under 30) or severe (30 or more).

On CPAP, your machine estimates a residual AHI. Many clinicians consider a residual AHI below 5 a sign of good control. Keep in mind it is an estimate from airflow, not a full sleep study, and it can be less reliable when leaks are high. Your machine may break it down into obstructive events, central or clear airway events and hypopneas. A rise in central events is worth mentioning to your clinician.

Leak

Leak shows how much air is escaping beyond the mask's intended vents. ResMed devices report it in litres per minute, and their own software treats a leak above about 24 L/min as high. Philips devices often show time spent in large leak. Frequent high leak usually means the mask needs adjusting, replacing or changing.

Pressure

On fixed CPAP, this simply shows your set pressure. On auto machines, you will often see median and 95th percentile (or 90th percentile) pressure, showing how high the machine needed to go most of the night. If your auto machine regularly sits at the top of its range, or if pressures change after weight loss or gain, share that with your clinician. Please do not change the range yourself.

Apps and software

• Manufacturer apps (such as ResMed myAir or Philips DreamMapper) show nightly usage, leak, events and a simple score. They are good for motivation and quick checks.
• Your clinician and DME usually see more detailed data through the manufacturer's cloud portal if your machine has a modem.
• OSCAR is free, open-source software that reads the detailed data from your machine's SD card and shows breath-by-breath graphs. Many experienced users find it valuable. It is not a medical device and does not replace your clinician's interpretation.
• Remote data sharing is common. Ask your DME what is shared and with whom.

How to use your data well

Look at weekly patterns rather than single nights. Bring printouts or screenshots to appointments. Note what was different on bad nights (alcohol, a cold, a new mask, sleeping position). Good numbers and feeling unrested at the same time is important information too, so share both.