Is my CPAP pressure well set? How to know

How to know if your CPAP pressure is well set

The pressure setting of your CPAP device is the most critical parameter of your therapy. Pressure that is too low lets apneas through. Pressure that is too high causes discomfort, leaks, and can even trigger complex central apneas. But how can you objectively tell if your setting is optimal? This guide explains the indicators to monitor.

The primary indicator: residual AHI

The residual AHI (Apnea-Hypopnea Index under treatment, also called treated AHI or AHI-T) is the number of apneas and hypopneas persisting despite CPAP therapy, per hour of sleep. It is the best single indicator of your pressure's effectiveness.

Residual AHI Interpretation Recommended action
< 5 Excellent - effective therapy No change needed
5 - 10 Acceptable for some profiles Monitor trends; consult if symptoms persist
10 - 15 Insufficient - sub-optimal treatment Consult your doctor for adjustment
> 15 Treatment not effective Urgent consultation - pressure likely too low
The recognised clinical target is a residual AHI below 5. Most modern CPAP devices display your residual AHI each morning on the screen or via their mobile app.

How to read your CPAP data

Via the myAir app (ResMed)

The myAir app from ResMed (compatible with AirSense 11 and AirSense 10) gives you a morning sleep score out of 100 and key data:

  • Treated AHI: your residual AHI for the night
  • Leaks: leak volume in L/min (ideally < 24 L/min)
  • Usage duration: hours with the mask on
  • Median and P95 pressure: on auto CPAP devices

Via the OSCAR software (open source)

OSCAR (Open Source CPAP Analysis Reporter) is a free, open-source software that analyses the full data stored on your CPAP device's SD card, offering a detailed night-by-night view: real-time pressure curve, apnea/hypopnea/RERA detection, leak curve, Cheyne-Stokes respiration, and multi-week trends.

Signs your pressure is too low

  • High residual AHI (above 5, especially regularly > 10)
  • You still snore at night (confirmed by partner or app)
  • You still wake up tired despite several hours of CPAP use
  • Sensation of suffocation or air hunger during the night
  • Data shows many residual obstructive apneas

Signs your pressure is too high

  • Difficulty exhaling - feeling of resistance when breathing out
  • Significant, frequent mask leaks (air escaping at the edges)
  • Increase in central apneas (brain not receiving the signal to inhale)
  • Morning bloating (swallowed air overnight - aerophagia)
  • General discomfort or refusal to wear the mask

Auto CPAP vs fixed CPAP: the impact on settings

An auto CPAP (APAP) automatically adapts to your moment-to-moment breathing needs, night after night. It delivers the minimum pressure needed to eliminate apneas, generally improving comfort and reducing side effects from excess pressure.

A fixed CPAP always delivers the same pressure regardless of your state. If your pressure is correctly titrated it works well, but if your needs vary (position, congestion, alcohol), the fixed pressure may be insufficient some nights and too high on others.

The doctor's role in pressure setting

  • Analyse your downloaded data to identify problems
  • Modify the minimum or maximum pressure on an auto CPAP
  • Adjust the fixed pressure of a conventional CPAP
  • Enable or adjust EPR (Expiratory Pressure Relief) for better exhalation comfort
  • Change device type (CPAP to BiPAP) if necessary
Never modify your device's clinical settings without medical advice. However, reading your data and sharing it with your doctor is strongly encouraged.

Mask leaks: a key factor

Excessive mask leaks can distort your CPAP data and reduce therapy effectiveness. The acceptable leak value is generally below 24 L/min (per ResMed) or equivalent depending on the brand. Beyond this, your device works harder, pressure may increase unnecessarily, and your residual AHI may be overestimated.

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