CPAP vs. BiPAP: What Is the Difference?

CPAP and BiPAP are both positive airway pressure (PAP) machines that treat sleep apnea by blowing air through a mask to keep your airway open. CPAP uses one steady pressure all night. BiPAP uses two: a higher pressure when you breathe in and a lower one when you breathe out. Most people with obstructive sleep apnea start on CPAP or auto CPAP, and BiPAP is used when a person needs it for a specific reason.^[1]

What each machine does

All three machines pull in room air, pass it through a filter, and push it through a hose to your mask. The gentle pressure acts like an air splint, so the soft tissue in your throat cannot collapse while you sleep. The difference is how the machine sets that pressure.

• CPAP (continuous positive airway pressure) — one fixed pressure, the same when you breathe in and out. Your sleep doctor sets it from a sleep study.
• APAP (auto CPAP) — still one pressure at a time, but the machine raises or lowers it through the night within a range your doctor sets.
• BiPAP (bilevel positive airway pressure) — two pressures that switch with every breath: higher to breathe in, lower to breathe out. BiPAP started as a brand name and became the everyday word. Doctors and insurance forms often say BPAP or bilevel.

Pressure is measured in centimeters of water (cm H₂O). In a sleep lab, CPAP usually starts at 4 cm H₂O and is raised step by step, up to 20 cm H₂O if needed for people 12 and older.^[2]

How BiPAP settings work

A BiPAP prescription has more parts than a CPAP prescription:

• IPAP (inspiratory pressure) — the higher pressure you get while breathing in. It helps keep the airway open and can help move more air into the lungs.
• EPAP (expiratory pressure) — the lower pressure while breathing out. It still holds the airway open, but breathing out feels easier.
• Pressure support — the gap between IPAP and EPAP. In sleep lab titration, the gap is usually kept between 4 and 10 cm H₂O, and IPAP goes up to 30 cm H₂O if needed for people 12 and older.^[2] A bigger gap gives more help with each breath.
• Spontaneous (S) mode — the machine waits for you to breathe and follows your rhythm.
• Spontaneous-timed (ST) mode, or backup rate — the machine follows your breaths, but if you pause too long, it gives a breath on its own. This backup rate matters for some kinds of central sleep apnea, where the brain briefly stops sending the signal to breathe.^[3]

Fixed CPAP vs auto CPAP (APAP)

The American Academy of Sleep Medicine (AASM) recommends either fixed CPAP or auto CPAP for ongoing treatment of obstructive sleep apnea in adults. Both work well. For routine sleep apnea, it suggests CPAP or APAP over BiPAP.^[1]

• Fixed CPAP — simple and steady. A good fit when a sleep study has found one pressure that works in every sleep position and stage.
• Auto CPAP — senses when the airway starts to narrow (for example, on your back or in dream sleep) and turns the pressure up, then eases it down. Many people start treatment on auto CPAP at home.
• Not for everyone — the AASM supports starting auto CPAP at home for adults with sleep apnea and no significant other health problems.^[1] People with heart failure, serious lung disease or breathing that is too shallow during sleep are often better served by a sleep lab study first.

Who usually needs BiPAP instead of CPAP

BiPAP is not a stronger CPAP. It is a different tool for specific problems, such as:

• Very high pressure needs — if breathing pauses keep happening at 15 cm H₂O of CPAP during a titration study, the AASM titration guideline allows a switch to BiPAP.^[2]
• Trouble breathing out against CPAP — some people find high CPAP pressure uncomfortable and feel they are fighting the air to breathe out. The titration guideline allows trying BiPAP for them.^[2]
• Obesity hypoventilation syndrome — breathing that is too shallow, so carbon dioxide builds up. The American Thoracic Society (ATS) suggests PAP for stable patients, with CPAP as the first try for those who also have severe obstructive sleep apnea. People leaving the hospital after breathing failure are usually sent home on bilevel ventilation until they are retested.^[4]
• COPD with high carbon dioxide — the ATS suggests nightly bilevel ventilation for people with stable COPD and long-term high carbon dioxide, and screening for sleep apnea first.^[5]
• Some nerve and muscle diseases — conditions that weaken the breathing muscles, such as ALS, can call for bilevel support. Medicare lists neuromuscular disease among the conditions that can qualify.^[6]
• Some central sleep apnea — the AASM suggests BiPAP with a backup rate for several types of central sleep apnea, and suggests against BiPAP without a backup rate for them.^[3]

ASV is a separate machine. Adaptive servo-ventilation (ASV) adjusts its support breath by breath and is used for some central sleep apnea.^[3] It carries a warning: in the SERVE-HF trial, people with heart failure with reduced pumping (ejection fraction of 45% or less) and mainly central sleep apnea had a higher risk of death on ASV.^[7] Anyone with heart failure needs a heart and sleep evaluation before ASV is considered.

How the switch is decided: the titration study

You cannot simply change machines on your own. The decision is based on testing and your symptoms.

• Fix the common problems first — mask fit, leaks, a dry mouth and comfort settings cause many CPAP struggles. See common CPAP problems and fixes.
• Check the machine's data — your sleep team can review leak, usage and breathing events from your machine.
• Titration study — an overnight sleep lab study where a technologist adjusts the pressure while you sleep. If CPAP is not tolerated or not controlling your apnea, they can switch to BiPAP and find the IPAP and EPAP that work.^[2] Learn what to expect in CPAP titration study.
• New prescription and follow-up — your doctor writes the new settings, and your sleep team checks how you are doing on them.

What the equipment looks like

From across the room, CPAP and BiPAP machines look almost the same: a small bedside box with a screen, a water tank for the humidifier, a hose and a mask. The difference is inside, in the software and the prescription.

The masks are the same. Nasal pillows, nasal masks and full face masks all work with both machines, so if you switch, you can usually keep a mask that already fits. See CPAP mask types for help choosing one.

Comfort features to try before switching

Many CPAP and auto CPAP machines have comfort settings that may solve the problem without BiPAP:

• Ramp — starts at a low pressure and slowly rises while you fall asleep.
• Exhale relief — briefly lowers the pressure as you start to breathe out. Makers give it different names. It is milder than BiPAP, but for some people it is enough.
• Heated humidifier and heated hose — warm, moist air can ease a dry nose, a dry mouth and congestion.
• Mask refit — a mask that leaks or presses too hard can feel like a pressure problem.

Ask your sleep team before changing settings. For more ideas, see tips for using CPAP every night.

CPAP vs BiPAP side by side

Insurance and Medicare basics for BiPAP

Insurance treats BiPAP as a step beyond CPAP, so it asks for proof that you need it. Medicare's rules are a common model:

• For obstructive sleep apnea — a BiPAP without a backup rate (billing code E0470) is covered only after CPAP (E0601) has been tried and proven ineffective, meaning it did not meet treatment goals despite a proper mask fit and appropriate pressure settings.^[8]
• Backup-rate machines — a BiPAP with a backup rate (E0471) is not covered when obstructive sleep apnea is the main diagnosis.^[8]
• Other conditions — central or complex sleep apnea, hypoventilation, neuromuscular disease and COPD fall under Medicare's separate respiratory assist device rules, which require specific tests such as a sleep lab study or a blood gas.^[6]
• Use it to keep it — for obstructive sleep apnea, Medicare requires use of at least 4 hours a night on 70% of nights during a consecutive 30-day period, within the first 3 months.^[8]

Private plans and Medicaid set their own rules. The practice does not sell equipment; your machine comes from a medical equipment supplier, who can check your coverage.

When to talk to a sleep specialist

• CPAP feels like too much air — or you cannot breathe out comfortably, even after comfort settings.
• Snoring, gasping or sleepiness came back — your settings may need to change.
• You have COPD, a nerve-muscle disease or heart failure — and sleep apnea or poor sleep.
• You have stopped using CPAP — there may be another machine setting or another treatment that fits. See alternatives to CPAP.

CPAP and BiPAP care in Cedar Park

Teddy Bear Pediatrics & Sleep Medicine is at 14300 Ronald W. Reagan Blvd, Unit 405, Cedar Park, TX 78641. Dr. Minal Patel is board-certified in pediatrics and sleep medicine. The practice offers in-lab and home sleep studies and CPAP and BiPAP titration and therapy for children and adults. New patients are welcome. Office hours are Monday through Friday, 8:30 to 5:00, by appointment. Medicaid and CHIP are accepted for sleep patients. Call (512) 931-1575 to schedule.