Residual AHI is the apnea-hypopnea index your machine records while you are on therapy.
Does it matter? The trend matters more than a single night, and a low AHI with poor sleep is a reason to look at the full data, not to stop asking.
What is a good AHI on CPAP?
A residual AHI under 5 is a common reference point on CPAP, borrowed from the sleep-lab titration benchmark, and your clinician decides what is right for you. The number is a machine estimate and it leaves out flow limitation and RERAs, so a good AHI does not always mean good sleep.
Source: Kushida CA et al., Clinical guidelines for the manual titration of positive airway pressure in patients with obstructive sleep apnea, J Clin Sleep Med 2008;4(2):157-171 [S1]. Checked 21 October 2026.
Medical disclaimer: AirwayLab is a data-visualization tool, not a medical device. Nothing in this article constitutes medical advice, diagnosis, or treatment. Always discuss your therapy data and any concerns with your sleep physician or qualified clinician.
What is AHI?
AHI stands for Apnea-Hypopnea Index: the count of apneas (complete breathing pauses) and hypopneas (partial obstructions) per hour of sleep.
Your AHI before treatment, recorded in your diagnostic sleep study, is what led to your CPAP prescription. Your residual AHI, sometimes called treatment AHI, is the figure recorded by your CPAP machine while you're on therapy. It reflects how many qualifying events occur per hour even with the machine running.
Most CPAP and APAP devices record this automatically. With data from your SD card, tools like AirwayLab give you a night-by-night residual AHI view so you can review trends over weeks and months.
What AHI is considered "normal" on CPAP therapy?
There is no single universally mandated target. Your clinician sets the goal appropriate to your situation. That said, the sleep medicine field uses established thresholds:
| AHI (events/hour) | Common classification |
|---|---|
| < 5 | Within normal range |
| 5–14 | Mild |
| 15–29 | Moderate |
| ≥ 30 | Severe |
These classifications come from American Academy of Sleep Medicine (AASM) guidance and are most commonly applied in diagnostic contexts. For therapy monitoring, a residual AHI below 5 is a figure many sleep specialists reference in clinical discussions with patients. Some clinicians aim for below 2, particularly where certain conditions are present, but your sleep physician is best placed to establish a specific target for you.
On therapy, residual AHI is generally expected to be substantially lower than the AHI recorded during your diagnostic sleep study. What constitutes adequate reduction depends on individual clinical context.
AirwayLab shows you your residual AHI data as recorded by your device. What that number means for your specific health situation is a question for your sleep physician.
Why might residual AHI still be high on CPAP?
A residual AHI above the typical threshold doesn't always mean nothing can be done. Several common factors can contribute, and all are worth raising with your clinician.
Mask fit and seal
A mask that leaks air can reduce the effectiveness of delivered pressure. Most CPAP machines log total leak rate alongside AHI. If your leak data shows elevated or variable leak on the same nights your AHI is high, that's a useful data point to bring to your next appointment.
Pressure delivery
Fixed-pressure CPAP delivers the same pressure all night. Auto-titrating CPAP (APAP) adjusts within a clinician-set range. If the pressure range isn't matched to your nightly needs (which can vary with sleep position, nasal congestion, alcohol, or weight changes), some events may not be prevented.
Whether any pressure adjustment is appropriate is a clinical decision. Your sleep physician or respiratory therapist can review your full therapy data and advise accordingly. AirwayLab does not recommend or suggest pressure changes.
Sleep position
Back-sleeping (supine position) is associated with increased airway narrowing in many people. If you notice higher AHI on specific nights, and your machine records positional data, this is worth discussing with your clinician.
Mask interface type
Different mask styles (nasal pillow, nasal, full-face) interact differently with airway mechanics and leak patterns. If your data shows a consistent pattern across nights, a different mask type may be something to discuss with your provider.
Central versus obstructive events
Not all events counted in your AHI have the same origin. Some residual events may be central in nature, originating in the respiratory control system rather than upper airway obstruction, and respond differently to CPAP therapy. Identifying the nature of events requires clinical assessment.
Alcohol, sedatives, and congestion
These factors can temporarily increase airway collapsibility. If your data shows isolated spikes, lifestyle context may be relevant to note when you discuss the data with your clinician.
AHI doesn't tell the whole story: flow limitations and RERAs
AHI counts complete apneas and hypopneas, but it doesn't capture everything that can affect sleep quality. Flow limitations (partial reductions in airflow that don't meet the threshold for a hypopnea) and RERAs (Respiratory Effort-Related Arousals) can disrupt sleep continuity even when AHI appears low.
Some CPAP devices, particularly certain ResMed models, record detailed flow waveform data. AirwayLab can visualise flow limitation patterns alongside AHI where your device supports it, giving you additional data to bring to clinical appointments.
A night with an AHI of 2 and frequent flow limitation events may warrant a different conversation than a night with an AHI of 2 and clean waveforms. Your sleep physician can help you interpret what these patterns mean in your case.
When to contact your sleep physician
Bring your therapy data to your clinician if any of the following apply:
- Your residual AHI consistently reads above 5 across multiple weeks of data
- You're still experiencing symptoms (fatigue, unrefreshing sleep, morning headaches) despite apparently normal AHI readings
- Your data shows high leak on most nights
- You notice a sudden change in your AHI trend without an obvious explanation
- Your AHI was previously stable and has risen over recent weeks or months
This list isn't exhaustive. If something in your data concerns you, that's reason enough to raise it. Your sleep physician or respiratory therapist is the right person to review your therapy in full clinical context.
How AirwayLab helps you track AHI over time
A single night's AHI is a data point. Tracked across weeks and months, it becomes a pattern, and patterns are what help you and your clinician have informed conversations. Open your SD card in AirwayLab to see this pattern for your nights.
AirwayLab reads your CPAP machine's SD card data directly in your browser. Your data never leaves your device. It renders your AHI, leak rate, pressure, and flow waveforms as an interactive timeline so you can:
Night-by-night AHI trends
Review AHI with trend lines across any date range. Patterns across weeks are easier to spot in a chart than in your device's rolling 7-day average.
Leak and AHI correlation
See which nights had elevated leak alongside elevated AHI, a useful data point when discussing mask fit with your provider.
Pressure data for APAP users
Review session-level pressure ranges and percentile data across your nights.
Flow limitation visualisation
Where your device supports it, AirwayLab visualises flow limitation patterns alongside AHI, providing additional data to bring to clinical appointments.
This is the data your clinician may ask you to bring to appointments. Having it organised in one place, without uploading it to a cloud server, makes those conversations easier.
AirwayLab is free and always will be. The analysis engine's source code is GPL-3.0 licensed and publicly auditable. If you're also using OSCAR, AirwayLab works alongside it. The two tools serve different viewing needs and neither replaces the other.
Check your own nights
AirwayLab tracks your nightly AHI automatically from your CPAP SD card. See your trends over weeks and months. Free, browser-based, and your data never leaves your device.
Summary
- Many sleep specialists reference a residual AHI below 5 in clinical discussions with patients, but your clinician determines what's appropriate for your situation
- Factors that can contribute to elevated residual AHI include mask fit, pressure delivery, sleep position, and event type, all worth discussing with your provider
- AHI alone doesn't capture flow limitations and RERAs, which are also relevant to overall sleep quality
- If your AHI stays consistently elevated or you remain symptomatic, contact your sleep physician
- AirwayLab lets you track your nightly AHI trends privately from your SD card, with no cloud upload required
Frequently Asked Questions
What is a good AHI on CPAP?
A residual AHI under 5 is a common reference point on CPAP, borrowed from the sleep-lab titration benchmark, and your clinician decides what is right for you. The number is a machine estimate and it leaves out flow limitation and RERAs, so a good AHI does not always mean good sleep.
What is residual AHI?
The AHI your CPAP records during use, after treatment is applied.
Is an AHI under 5 always good?
It is a common reference point, but AHI does not count flow limitation or RERAs, so check how you feel and the full data.
What if my AHI is still high on CPAP?
Talk to your provider and bring your data, causes range from leak to settings to central events.
Related reading
What Does My CPAP AHI Number Mean? , a plain-language guide to the metric at the centre of your report.
Low AHI but Still Tired? , covering why flow limitations and RERAs can matter even when AHI looks normal.
What Are RERAs? , the breathing events your compliance report doesn't count.
AHI vs RDI: What's the Difference? , covering how the two indices are calculated and what each captures.
AHI glossary entry , the short definition of apnea-hypopnea index.
AHI Normal but Still Tired? , what to check next when the number looks fine but sleep does not feel that way.
CPAP Leak Rate Explained , why leak can make a night's AHI less trustworthy.
Sources
- [S1] Kushida CA et al., Clinical guidelines for the manual titration of positive airway pressure in patients with obstructive sleep apnea, J Clin Sleep Med 2008;4(2):157-171. Defines an optimal in-lab PAP titration as a respiratory disturbance index under 5. That is a sleep-lab benchmark, not a rule for the number your machine reports. Grade: AASM clinical guideline, consensus-based.
AirwayLab is a data-visualization tool, not a medical device. The metrics described in this article are data recorded by your CPAP device. Nothing on this page constitutes medical advice, diagnosis, or treatment. Always discuss your therapy data and any concerns with your sleep physician or qualified clinician.