CPAP delivers one constant air pressure, while BiPAP delivers two: a higher pressure when you breathe in and a lower pressure when you breathe out. That single difference shapes everything else, from which conditions each machine treats to how they feel during the night and what they cost. Most people start with CPAP for obstructive sleep apnea, and BiPAP enters the picture when CPAP isn’t enough or when a different breathing problem requires more sophisticated support.
How Each Machine Delivers Air
A CPAP (continuous positive airway pressure) machine pushes air at one fixed pressure throughout the entire breathing cycle. Whether you’re inhaling or exhaling, the pressure stays the same. This steady stream acts like a pneumatic splint, holding your airway open so it doesn’t collapse during sleep. Technically, CPAP isn’t ventilation. It doesn’t help you breathe in or out; it just keeps the passage clear so your own muscles can do the work.
A BiPAP (bilevel positive airway pressure) machine switches between two pressure levels. The inhale pressure (sometimes called IPAP) is higher, actively helping air flow into your lungs. The exhale pressure (EPAP) drops lower, making it easier to breathe out against the machine. That pressure gap between inhale and exhale is what gives BiPAP its therapeutic advantage for people who need breathing assistance, not just an open airway.
Typical Pressure Settings
CPAP machines generally operate between 4 and 20 cm Hâ‚‚O, with most people landing somewhere around 8 to 10. Your pressure is set after a sleep study or titration test and stays at that single number all night.
BiPAP settings involve two numbers. The exhale pressure typically averages 6 to 10 cm Hâ‚‚O, while the inhale pressure averages 12 to 16 cm Hâ‚‚O. Clinicians usually start with a gap of about 5 cm Hâ‚‚O between the two and adjust from there. The inhale pressure can be raised as high as 20 cm Hâ‚‚O or more to reduce the work of breathing and improve the volume of air reaching your lungs with each breath.
Who Uses CPAP
CPAP is the standard first-line treatment for obstructive sleep apnea. If your airway repeatedly collapses during sleep, the constant pressure keeps it propped open and prevents the pauses in breathing that fragment your sleep and drop your oxygen levels. For the majority of people with obstructive sleep apnea, CPAP is all they need, and it remains the most commonly prescribed positive airway pressure device by a wide margin.
Who Uses BiPAP
BiPAP covers a broader range of breathing problems because it can do something CPAP cannot: actively assist each breath. The main scenarios where BiPAP is preferred include:
- COPD flare-ups. For moderate to severe COPD exacerbations where carbon dioxide is building up in the blood, BiPAP is the first-line treatment. The pressure difference between inhale and exhale helps flush out excess COâ‚‚ that the lungs can’t clear on their own.
- Obesity hypoventilation syndrome. People whose excess weight restricts lung expansion often need the extra push on inhalation that BiPAP provides, especially during sleep when breathing naturally becomes shallower.
- Central sleep apnea. Unlike obstructive apnea, where the airway physically collapses, central apnea happens when the brain intermittently stops sending the signal to breathe. BiPAP machines with a backup breathing rate can detect these pauses and deliver a breath automatically.
- Neuromuscular conditions. Diseases that weaken the muscles involved in breathing, such as ALS or muscular dystrophy, may require the active breathing support that BiPAP offers.
- CPAP intolerance. Some people with obstructive sleep apnea who need high CPAP pressures find it difficult to exhale against the constant force. Switching to BiPAP, with its lower exhale pressure, can make therapy tolerable enough to actually use consistently.
What About CPAP Exhalation Relief?
If the exhaling-against-pressure problem sounds familiar, you may have heard of comfort features built into modern CPAP machines. ResMed calls theirs EPR (expiratory pressure relief), and Philips used the name C-Flex. These features slightly reduce pressure as you exhale, making it feel less like breathing out against a wall.
The key difference is scale. EPR can only lower the exhale pressure by about 3 cm Hâ‚‚O at most. A true BiPAP machine allows a pressure gap of 4 to 10 cm Hâ‚‚O or more. And exhalation relief on a CPAP can’t deliver backup breaths or provide the active ventilatory support that BiPAP offers. Think of it as a comfort tweak rather than a fundamentally different therapy.
Adaptive Servo-Ventilation: A Step Beyond BiPAP
For complex or treatment-resistant sleep apnea, there’s a more advanced category called ASV (adaptive servo-ventilation). Where BiPAP switches between two fixed pressures, ASV uses built-in sensors to track your breathing pattern in real time and adjust airflow breath by breath. If the machine detects a long pause or a slowing breathing rate, it ramps up air delivery. When your breathing is steady, it backs off or stops pushing air entirely. ASV is typically reserved for central sleep apnea or complex sleep apnea that doesn’t respond well to standard CPAP or BiPAP.
Cost Differences
The price gap between the two machines is significant. A CPAP typically costs between $500 and $1,000, while BiPAP machines range from $1,700 to $3,000. Auto-adjusting CPAP machines (APAP), which vary pressure within a set range but still deliver one pressure at a time, fall in between at $600 to $1,600.
Insurance coverage reflects the clinical hierarchy. Because CPAP is the standard starting point, most insurers cover it readily for diagnosed obstructive sleep apnea. Getting BiPAP covered usually requires documentation that CPAP was tried first and didn’t work, or that you have a condition like COPD or central apnea where BiPAP is the medically appropriate choice. Medicare, for example, requires specific blood gas results and overnight oxygen monitoring before approving a BiPAP for severe COPD patients, and may require at least 61 days on a simpler device before upgrading.
How They Feel to Use
Both machines use the same types of masks (nasal, nasal pillow, or full face), and the nightly routine of strapping on a mask and turning on the device is identical. The difference is in the sensation of breathing. On CPAP, the pressure never changes, so exhaling can feel like blowing against a steady wind, especially at higher settings. Some people adapt quickly; others never fully get used to it.
BiPAP feels more natural to most users because the pressure drops when you exhale, mimicking the rhythm of normal breathing more closely. People who need high inhale pressures to treat their condition often find BiPAP significantly more comfortable than CPAP set at a comparable level. That comfort advantage can translate into better adherence, which ultimately determines whether the therapy works. A machine that sits unused on the nightstand doesn’t treat anything.