Getting started
CPAP vs APAP vs BiPAP: What Is the Difference?
CPAP blows one fixed pressure all night, APAP (auto CPAP) adjusts pressure within a range your clinician sets, and BiPAP uses a higher pressure when you breathe in and a lower one when you breathe out. The American Academy of Sleep Medicine (AASM) recommends CPAP or APAP for routine adult obstructive sleep apnea, with BiPAP kept for people who need something those machines cannot deliver.
CPAP: one steady pressure
A CPAP (continuous positive airway pressure) machine pushes room air through a hose and mask at a single pressure your clinician prescribes. That steady air acts like a splint that holds your throat open so it does not collapse while you sleep.
Fixed CPAP is simple and predictable. The tradeoff is that the pressure you need can change with sleep position, sleep stage, alcohol, congestion or weight, and a fixed machine cannot follow those changes on its own.
APAP: pressure that adjusts
An APAP (automatic positive airway pressure, also called auto CPAP or AutoSet on ResMed machines) watches your breathing breath by breath and raises or lowers pressure inside a minimum and maximum range set by your prescriber. ResMed describes its AutoSet mode as adjusting pressure to keep it as low as possible while still treating events.
Most machines sold today can run in either fixed CPAP or auto mode. Which mode you use, and the pressure range, is part of your prescription. Changing the mode or range is a decision for your sleep clinician, not something to do from the clinical menu yourself.
BiPAP: two pressures
BiPAP or bilevel PAP (ResMed calls its machines VPAP or AirCurve) uses a higher inhale pressure (IPAP) and a lower exhale pressure (EPAP). People who need high pressures sometimes find it easier to breathe out against a lower pressure.
The 2019 AASM guideline suggests CPAP or APAP over bilevel for routine treatment of obstructive sleep apnea, and notes bilevel may be needed when someone requires pressures above what CPAP or APAP can comfortably deliver. Medicare covers a bilevel device without a backup rate (code E0470) for obstructive sleep apnea only after a CPAP has been tried and proven ineffective, per the CMS coverage policy L33718.
Comfort features are not the same as BiPAP
Many CPAP and APAP machines have exhale relief, such as ResMed EPR or Philips Flex, which lowers pressure slightly as you breathe out. ResMed notes that with EPR on, delivered pressure does not drop below 4 cm H2O. This can feel similar to bilevel, but it is a small comfort adjustment, not a second prescribed pressure.
Exhale relief is usually in the patient comfort menu, so you can try it yourself. If you still feel like you are fighting the air after trying comfort settings, tell your clinician; that is a reason to review your settings, not to change them yourself.
Other modes you may hear about
ASV (adaptive servo ventilation) and bilevel with a backup rate are used for central sleep apnea and other breathing disorders, not routine obstructive sleep apnea. They are set up and monitored closely by a sleep specialist.
If your doctor mentions one of these, ask why, what your sleep study showed, and how your follow-up will work. These machines are not interchangeable with a standard CPAP.
Frequently asked questions
Is APAP better than CPAP?
Neither is better for everyone. The AASM 2019 guideline rates CPAP and APAP as equally appropriate for ongoing treatment of adult obstructive sleep apnea. APAP can be more comfortable if your pressure needs vary, while fixed CPAP is predictable once your pressure is known.
Can I switch my CPAP to BiPAP myself?
No. A CPAP machine cannot become a bilevel machine, and bilevel is a separate prescription and device. If CPAP pressure feels hard to exhale against, ask your clinician about exhale relief or a pressure review.
Why did insurance deny my BiPAP?
Medicare and many private plans follow the rule that bilevel is covered for obstructive sleep apnea only after CPAP was tried and failed. Your clinician has to document that failure, so ask them what your plan requires.
Does APAP mean I do not need a prescription?
No. Every CPAP, APAP and BiPAP sold in the US is a prescription device, and the auto pressure range itself is part of the order your clinician writes.
Sources
Last reviewed October 11, 2026. How we research · Report an error