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Understand the difference between fixed CPAP, APAP and BiPAP how each delivers therapy, who each suits, and how to know which machine matches your prescription.
Continuous Positive Airway Pressure. Delivers one prescribed pressure throughout the night. The pressure is set by your sleep specialist and does not change. The most established therapy type for obstructive sleep apnoea.
Automatic Positive Airway Pressure. Adjusts pressure during the night within a prescribed range in response to detected breathing patterns. One pressure at any moment, but that pressure can change as needs vary.
Bilevel Positive Airway Pressure. Uses a higher pressure during inhalation (IPAP) and a lower pressure during exhalation (EPAP). For specific clinical needs where separate pressure levels are required.
CPAP vs APAP vs BiPAP at a Glance
| Feature | Fixed CPAP | APAP / Auto CPAP | BiPAP / Bilevel |
|---|---|---|---|
| Pressure | One fixed pressure | Automatically changes within a set range | Two pressure levels |
| Inhalation | Same pressure | Pressure can adjust | Higher pressure (IPAP) |
| Exhalation | Same pressure | Pressure can adjust | Lower pressure (EPAP) |
| Main purpose | Consistent treatment | Responds to changing pressure needs | Greater pressure support |
| Common use | Obstructive sleep apnoea | OSA with changing pressure needs | Specific clinical needs or CPAP intolerance |
| Pressure changes during night | No | Yes | Depends on mode |
| Usually prescribed by clinician | Yes | Yes | Yes |
What Is a Fixed-Pressure CPAP?
CPAP stands for Continuous Positive Airway Pressure. A fixed-pressure CPAP machine delivers air at one prescribed pressure throughout the night. For example, if your prescribed pressure is 10 cmH₂O, the machine is set to deliver that pressure rather than automatically moving between different pressure levels. The pressure is normally determined by your sleep specialist or healthcare professional.
The machine draws in room air and sends it through the tubing to your mask. The pressurised air helps keep the upper airway open while you sleep, reducing the likelihood of obstructive breathing events.
What Is APAP or Auto CPAP?
APAP stands for Automatic Positive Airway Pressure. It works differently from fixed CPAP because it can adjust pressure during the night within a prescribed range. For example, an APAP might be prescribed with a pressure range of 6–14 cmH₂O. Instead of staying at one pressure all night, the machine can adjust its output as your breathing changes. ResMed describes APAP as a therapy that automatically changes pressure according to the user’s needs.
What Is BiPAP?
BiPAP is commonly used to describe bilevel positive airway pressure. You may also see the terms BiLevel, bilevel PAP or VPAP, depending on the manufacturer. Unlike standard CPAP, which uses one pressure, bilevel therapy uses two pressure levels: a higher pressure during inhalation (IPAP) and a lower pressure during exhalation (EPAP). This difference can make breathing out against pressure easier for some people. The exact settings are determined according to the prescribed therapy.
CPAP vs APAP vs BiPAP: The Key Differences Summarised
CPAP vs APAP: What’s the Main Difference?
CPAP = one pressure. APAP = changing pressure. Imagine your prescribed therapy requires between 6 and 14 cmH₂O. A fixed CPAP might deliver 10 cmH₂O continuously if that is your prescribed pressure. An APAP could adjust within the prescribed range as your breathing changes. The machine doesn’t simply choose a random pressure it uses its algorithm to respond to detected breathing patterns. Neither is automatically better; the right choice is the one that controls your sleep apnoea and is comfortable enough to use consistently.
APAP vs BiPAP: What’s the Difference?
APAP automatically changes the pressure according to detected breathing needs. It still operates as a single-pressure therapy at any particular moment. BiPAP uses two pressure levels the pressure during inhalation is higher, while the pressure during exhalation is lower. So the main distinction is: APAP changes the pressure according to breathing needs. BiPAP provides separate inspiratory and expiratory pressures on every single breath. ResMed describes bilevel therapy as higher pressure during inhalation and lower pressure during exhalation.
If you need a relatively high pressure, that doesn’t automatically mean you need BiPAP. Some CPAP and APAP machines can operate across a broad pressure range. If high pressure makes exhaling uncomfortable, your clinician may assess whether pressure-relief features or bilevel therapy would be more appropriate. Do not increase your pressure yourself simply because you feel that a higher setting might work better.
Important Clinical Points
Sometimes a person may move from fixed CPAP to APAP, but this should be discussed with the clinician managing their therapy. The two modes are not interchangeable for every patient. An APAP algorithm responds to detected breathing patterns, and there are situations where a fixed pressure or another therapy mode may be more appropriate. If your current CPAP treatment is uncomfortable or you’re still experiencing symptoms, speak with your provider rather than changing settings yourself.
Which Machine Should You Choose?
- You have a prescribed fixed pressure
- Your therapy is working well
- Pressure needs are relatively consistent
- You prefer a straightforward setup
- Clinician has prescribed auto adjustment
- Pressure needs vary during sleep
- You need response to changing breathing
- Auto adjustment suits your therapy type
- Clinician has prescribed bilevel therapy
- Difficulty exhaling against CPAP pressure
- You need separate IPAP and EPAP
- Respiratory condition requires bilevel support
Simple Decision Guide
Still unsure which type you’re looking at? These three questions are a way to understand the main differences between the machines not rules for self-diagnosis.
💡 Three Questions to Understand the Difference
Don’t Forget the Mask
The machine is only one part of a CPAP setup. Your mask also has a major effect on comfort and leaks. The right mask depends on factors such as your breathing style, sleep position, facial structure and comfort preferences. If you’re using higher pressures, a good mask seal becomes particularly important because leaks can affect comfort and therapy. When choosing a new machine, make sure your existing mask and tubing are compatible with the device.
- Nasal pillow masks — minimal facial contact, good for nose breathers who prefer a lightweight setup
- Nasal masks — cover the nose, a middle ground between minimal and full coverage
- Full-face masks — cover nose and mouth, suitable for mouth breathers or those with nasal obstruction
Browse CPAP Machines by Type
Final Thoughts
CPAP, APAP and BiPAP all use positive airway pressure, but they deliver it differently. Fixed CPAP delivers one consistent pressure throughout the night. APAP automatically adjusts pressure within a prescribed range as breathing changes. BiPAP or bilevel therapy provides separate pressures for inhalation and exhalation.
There isn’t one machine that is best for everyone. The right option depends on your diagnosis, prescribed therapy, pressure requirements, comfort and any other breathing conditions you may have. If your current CPAP feels uncomfortable, your pressure seems too high or your therapy isn’t working as expected, speak with your sleep clinician or CPAP provider before changing settings or switching machine types.
