APAP and CPAP deliver the same therapy: pressurized air that holds your airway open to treat obstructive sleep apnea. The difference is how the pressure is set. A CPAP holds one fixed pressure your clinician prescribes; an APAP (auto-adjusting, also called AutoSet) changes the pressure breath by breath within a set range [3]. For uncomplicated obstructive sleep apnea, the American Academy of Sleep Medicine recommends either one [1], so the right choice comes down to your comorbidities, comfort, and cost, not to one being universally better [2].
This guide compares them on the dimensions that actually decide it. It does not re-explain the machine itself: for that see how a CPAP machine works, and for the full device lineup see types of CPAP machines.
APAP vs CPAP at a glance
Both are prescription devices for diagnosed obstructive sleep apnea. Here is how they compare, with the settings and evidence verified against manufacturer and AASM sources [1][3].
| Dimension | CPAP (fixed) | APAP (auto-adjusting / AutoSet) |
|---|---|---|
| Pressure delivery | One fixed pressure all night | Adjusts breath by breath within a Min to Max range |
| How the pressure is set | Clinician sets one value from a titration | Device auto-titrates on flow limitation, snore, and obstructive apnea |
| Pressure envelope | 4 to 20 cmH2O (one value) | 4 to 20 cmH2O (a Min-Max window) |
| Clinical effectiveness for OSA | Comparable; AASM recommends either, meta-analysis finds largely similar results | |
| Adherence / comfort | Reference | About 11 minutes/night more use on average (small) |
| Minimum oxygen saturation | About 1.3% higher on average | Reference |
| Best for | Stable single pressure; simple, well-established | Pressure needs that vary by night, position, or weight |
| Also used to | Ongoing therapy | Auto-titrate at home and derive a fixed pressure (95th percentile) |
| Prescription | Required | Required |
What is the difference between APAP and CPAP?
The difference is the pressure schedule, not the therapy. In CPAP mode the device delivers one fixed pressure continuously [3]. In AutoSet (APAP) mode it "analyzes the state of the patient's upper airway on a breath-by-breath basis and delivers pressure within the allowed range according to the degree of obstruction," adjusting to inspiratory flow limitation, snore, and apnea [3]. Both run inside the same 4 to 20 cmH2O envelope; CPAP holds one value, APAP moves between a clinician-set Min and Max [3].
How does each one set your pressure?
A fixed CPAP uses one pressure your clinician prescribes from a titration study. An APAP finds the pressure for you: it raises pressure only as much as needed to keep the airway open, then reports the result as the 95th-percentile pressure, the level at or below which you spent 95% of the night [3]. That is why APAP is also used as a titration tool: AASM practice parameters state that "data obtained during APAP titration can be used to provide a fixed single pressure for subsequent treatment" [4]. Your pressure starts with a sleep apnea test.
Is APAP more effective than CPAP?
No. For uncomplicated obstructive sleep apnea they are comparably effective, and the AASM gives a STRONG recommendation that "clinicians use either CPAP or APAP for ongoing treatment of OSA in adults" [1]. A systematic review of head-to-head trials concluded that "APAP and CPAP result in largely similar treatment effects for patients with OSA," with similar changes in the apnea-hypopnea index and quality of life [2]. The one measured edge for fixed CPAP was a 1.3% higher minimum overnight oxygen saturation [2]. Neither is categorically better.
Which is more comfortable, and does one improve adherence?
The comfort difference is small. In the same meta-analysis, APAP improved use by about 11 minutes per night and reduced daytime sleepiness by 0.5 points on the Epworth scale versus fixed CPAP, differences the authors themselves called small [2]. Both modes offer the same exhale-comfort feature, Expiratory Pressure Relief (EPR), which lowers pressure as you breathe out and is adjustable in three levels [3]; for how ramp and EPR ease you in, see how a CPAP machine works. The authors concluded the choice "may well depend on individual patient preferences, specific reasons for non-compliance, costs and other practical considerations" [2].
Who should choose APAP, and who should choose a fixed CPAP?
APAP tends to suit people whose pressure needs vary night to night, by sleep position, with alcohol, or as weight changes, because it adjusts automatically within its range [3]. A fixed CPAP suits people who do well on one stable, well-established pressure and prefer the simplest setup. In practice the hardware choice is often moot: most current ResMed sleep machines are AutoSet units that run both a fixed "CPAP mode" and an auto "AutoSet mode" on the same device [3], so the decision is usually a setting rather than a different-priced box. Compare current options in our best CPAP machines guide.
When is neither APAP nor plain CPAP the right machine?
Neither is right when the apnea is central, or when Cheyne-Stokes breathing or heart failure is involved: those need adaptive servo-ventilation (ASV) or BiPAP under specialist care, not APAP or CPAP [5]. The reason is mechanical: APAP treats obstructive sleep apnea only, and on a central apnea, where the airway is open but the breathing drive is absent, the device "responds appropriately by not increasing pressure" [3], so it cannot treat central events. If your apnea is central rather than obstructive, see central sleep apnea and CPAP vs BiPAP. Home APAP is also not recommended for OSA with significant comorbidities: AASM practice parameters exclude congestive heart failure, significant lung disease such as COPD, daytime hypoxemia or respiratory failure, and hypoventilation syndromes, plus non-snorers on sound-based algorithms [4].
Can APAP pressure get too high?
An APAP can only move within the Min and Max your clinician sets, so it cannot exceed the prescribed ceiling [3]. If auto pressure feels too high, the fix is usually a tighter Max, turning on ramp to start low, or adding EPR for easier exhaling, not switching machines [3]. In our experience with new APAP users, being sent a machine set to a wide-open 4 to 20 range with no coaching is a common reason auto pressure feels too high; a narrower, clinician-tuned range or a fixed pressure often feels better. See how ramp and EPR work and tips on getting used to CPAP.
Is ResMed a CPAP or an APAP?
Both. ResMed AutoSet machines are APAP devices that also run a fixed CPAP mode, so one unit covers either therapy [3]. Here is how a Sleeplay team member explains it:
"Most machines, especially this one, are commonly set on AutoSet. Being that it is an AutoSet machine, it is going to adjust to meet your needs regardless."
James Curles, CPAP specialist, Sleeplay | ResMed AirSense 11 Ultimate Guide
Does insurance or Medicare cover APAP?
Both APAP and fixed CPAP are prescription durable medical equipment for diagnosed obstructive sleep apnea, and coverage depends on your plan, your documented diagnosis, and adherence rules rather than on which mode you use. Because most machines run both modes, the auto-versus-fixed choice rarely changes coverage on its own. For paying options and financing, see our guide to CPAP financing, and confirm specifics with your provider and insurer.
Which should you choose?
For most people with uncomplicated obstructive sleep apnea, either works, and an AutoSet machine gives you both modes in one, so you and your clinician can settle on fixed or auto after a few nights of data [1][3]. Browse current CPAP machines. A few AutoSet starting points, plus a bilevel option for those who need it:
Frequently Asked Questions
Should I get an APAP or a CPAP?
For uncomplicated obstructive sleep apnea, AASM says either works, so it comes down to preference, comfort, and cost. APAP suits varying pressure needs; fixed CPAP suits a stable, proven pressure. Most modern machines run both modes, so you can decide after a few nights of data.
Is APAP more effective than CPAP?
No. Head-to-head trials show largely similar treatment effects, with comparable changes in the apnea-hypopnea index and quality of life. APAP averages about 11 minutes more use per night; fixed CPAP averages 1.3% higher minimum oxygen saturation. Neither is categorically better.
How is the pressure set on each one?
A fixed CPAP uses one pressure your clinician prescribes. An APAP auto-adjusts within a Min-Max range and reports the 95th-percentile pressure, which clinicians can also use to derive a fixed prescription. Both run inside a 4 to 20 cmH2O envelope.
Is ResMed a CPAP or an APAP?
Both. ResMed AutoSet machines are APAP devices that also run a fixed CPAP mode, so one unit covers either therapy. That is why the auto-versus-fixed decision is usually a setting rather than a different machine.
Can APAP pressure be too high?
An APAP only moves within the Min and Max your clinician sets, so it cannot exceed the prescribed ceiling. If auto pressure feels too high, a tighter Max, ramp, or Expiratory Pressure Relief usually helps more than switching machines.
Does APAP treat central sleep apnea?
No. APAP treats obstructive sleep apnea. On a central apnea it deliberately does not raise pressure, because the airway is open. Central sleep apnea and Cheyne-Stokes breathing are managed with ASV or BiPAP under specialist care.
Does an APAP machine stop snoring?
Both APAP and CPAP reduce or eliminate snoring by keeping the airway open. APAP specifically raises pressure in response to snore and flow limitation, so it targets snoring vibration as it develops, within its set range.
Does insurance or Medicare cover an APAP?
Both APAP and fixed CPAP are prescription durable medical equipment for diagnosed obstructive sleep apnea. Coverage depends on your plan, diagnosis, and adherence rules, not on the mode. Confirm specifics with your provider and insurer.
References
- Patil SP, et al. Treatment of Adult OSA With Positive Airway Pressure: AASM Clinical Practice Guideline. J Clin Sleep Med 2019 (PMC): STRONG recommendation to use either CPAP or APAP for uncomplicated OSA.
- Ip S, et al. Auto-titrating versus fixed CPAP for OSA: a systematic review with meta-analyses. Syst Rev 2012 (PMC): largely similar effects; ~11 min/night adherence for APAP; +1.3% minimum SpO2 for CPAP.
- ResMed AirSense 10 Clinical Guide: AutoSet breath-by-breath auto-titration, fixed CPAP mode, central-apnea behavior, 4 to 20 cmH2O range, 95th-percentile pressure, EPR.
- Littner M, et al. AASM Practice Parameters for the Use of Auto-Titrating CPAP (SLEEP 2002): APAP data can set a fixed pressure; comorbidity exclusions (CHF, COPD, hypoventilation, non-snorers).
- Aurora RN, et al. The Treatment of Central Sleep Apnea Syndromes in Adults, AASM 2012 (PMC): central sleep apnea is managed with ASV or bilevel therapy, not APAP.
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