A diagnosis of obstructive sleep apnea (OSA) can introduce a lot of new terminology, equipment, and treatment options.
CPAP, APAP, BiPAP—what do they all mean, and how are they different?
Positive Airway Pressure (PAP) therapy is an established treatment for obstructive sleep apnea. While different PAP devices deliver pressure in different ways, they share a common goal: helping maintain an open airway during sleep.
This guide explains the basic differences between CPAP, APAP, and bilevel PAP so you can better understand the options and have an informed conversation with your healthcare provider.
What Is Obstructive Sleep Apnea?
Obstructive sleep apnea occurs when the upper airway repeatedly becomes narrowed or blocked during sleep, temporarily reducing or stopping airflow.
These breathing disruptions can interfere with normal sleep and may cause changes in blood oxygen levels.
OSA has been associated with several health conditions, including:
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High blood pressure
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Cardiovascular disease
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Stroke
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Type 2 diabetes
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Excessive daytime sleepiness
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Difficulty concentrating
Untreated OSA has also been associated with an increased risk of motor vehicle accidents related to daytime sleepiness.
Having OSA does not mean that you will develop these conditions. Individual risk depends on many factors, including age, overall health, OSA severity, and other medical conditions.
If you have been diagnosed with sleep apnea, following the treatment plan prescribed by your healthcare provider is an important part of managing the condition.
How Does PAP Therapy Work?
PAP therapy uses a device to deliver pressurized air through tubing and a mask while you sleep.
The airflow helps maintain an open airway and reduce obstructive breathing events.
The appropriate type of PAP therapy and pressure settings depend on your diagnosis and individual clinical needs. Your healthcare provider will determine which type of therapy is appropriate for you.
The three commonly discussed types of PAP therapy are:
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CPAP
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APAP
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Bilevel PAP
1. CPAP: Continuous Positive Airway Pressure
CPAP stands for Continuous Positive Airway Pressure.
A traditional CPAP machine delivers a fixed level of positive airway pressure during therapy. That pressure is prescribed based on the patient's clinical needs.
How CPAP Works
The device maintains the prescribed pressure while you sleep to help prevent the upper airway from collapsing.
The appropriate pressure may be established through methods such as:
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Laboratory PAP titration
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Home APAP data
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Clinical evaluation
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Other methods determined appropriate by the healthcare provider
When CPAP May Be Prescribed
CPAP may be prescribed for adults with obstructive sleep apnea when fixed-pressure PAP therapy is appropriate.
CPAP can be used for different levels of OSA severity; it is not limited to mild or moderate disease.
Potential Advantages
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Straightforward fixed-pressure therapy
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Widely used for OSA treatment
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Available in many device configurations
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May be appropriate for patients who respond well to a consistent prescribed pressure
Things to Consider
Some people may find a fixed pressure uncomfortable, particularly when higher pressure is prescribed.
If therapy becomes uncomfortable or your treatment needs appear to change, contact your healthcare provider. Your provider may review symptoms, therapy data, prescribed settings, or additional testing to determine whether any changes are appropriate.
Do not adjust prescribed pressure settings on your own unless instructed to do so by a qualified healthcare professional.
2. APAP: Auto-Adjusting Positive Airway Pressure
APAP stands for Auto-Adjusting Positive Airway Pressure and is sometimes called Auto-CPAP.
Instead of delivering one fixed pressure throughout the night, an APAP device operates within a prescribed minimum and maximum pressure range.
How APAP Works
The device monitors breathing patterns during therapy and automatically adjusts pressure within the prescribed range in response to detected breathing changes and obstructive events.
Pressure requirements may vary throughout the night because of factors such as:
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Sleeping position
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Sleep stage
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Individual breathing patterns
When APAP May Be Prescribed
APAP may be appropriate for adults with OSA when an auto-adjusting pressure range is clinically appropriate.
Current treatment guidelines support both CPAP and APAP as options for ongoing PAP treatment in appropriate adults with obstructive sleep apnea.
Potential Advantages
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Automatically adjusts pressure within a prescribed range
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May provide lower pressure during periods when higher pressure is not needed
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Can accommodate changing pressure needs during the night
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May be initiated at home in certain patients under appropriate clinical guidance
Things to Consider
Some people prefer auto-adjusting therapy, while others are more comfortable with a fixed-pressure CPAP.
Neither option is universally more comfortable or more effective for every person. Your healthcare provider can help determine which approach fits your treatment needs.
3. Bilevel PAP
Bilevel Positive Airway Pressure therapy delivers two prescribed pressure levels:
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IPAP: A higher pressure during inhalation
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EPAP: A lower pressure during exhalation
This differs from standard CPAP and APAP because inhalation and exhalation pressures are controlled separately.
When Bilevel PAP May Be Prescribed
Bilevel therapy may be considered for selected patients who:
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Require specific bilevel pressure support
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Have difficulty tolerating certain CPAP or APAP pressures
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Require higher therapeutic pressures
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Have specific respiratory or sleep-related breathing conditions
Different bilevel devices and modes are designed for different clinical circumstances.
For example, treatment of central sleep apnea can involve specialized PAP modes, and not every bilevel device or mode is appropriate for every form of sleep-disordered breathing.
The appropriate device and settings must be determined by a qualified healthcare provider.
Potential Advantages
For some patients, having a lower pressure during exhalation may improve comfort, particularly when higher treatment pressures are required.
Things to Consider
Bilevel therapy is more specialized than standard CPAP or APAP therapy.
The appropriate pressure settings and mode depend on the patient's diagnosis and clinical needs and should be prescribed and managed by a qualified healthcare professional.
CPAP vs. APAP vs. Bilevel PAP at a Glance
| Feature | CPAP | APAP | Bilevel PAP |
|---|---|---|---|
| Pressure Delivery | Fixed prescribed pressure | Automatically adjusts within a prescribed range | Separate prescribed pressures for inhalation and exhalation |
| Common Use | OSA when fixed-pressure therapy is appropriate | OSA when auto-adjusting therapy is appropriate | Selected patients requiring bilevel pressure support |
| Pressure Changes During Therapy | No automatic adjustment | Adjusts automatically within prescribed limits | Changes between inspiratory and expiratory pressure |
| Comfort | Varies by individual | Varies by individual | Lower expiratory pressure may improve comfort for some patients |
| Clinical Setup | Determined by healthcare provider | Prescribed pressure range determined by healthcare provider | Requires individualized clinical settings |
| Prescription Required | Yes | Yes | Yes |
There is no single PAP type that is best for everyone.
The appropriate choice depends on factors such as your diagnosis, pressure needs, medical history, therapy response, and healthcare provider's recommendations.
Do You Always Need an In-Lab PAP Titration?
No.
The appropriate diagnostic and titration process depends on the patient and clinical circumstances.
For appropriate adults with OSA and without certain significant comorbidities, PAP therapy may be initiated using an APAP device at home or through an in-laboratory PAP titration.
Your healthcare provider will determine which approach is appropriate based on your individual situation.
Portable PAP Technology: More Options Away From Home
PAP devices have become increasingly compact.
Some portable devices now include features such as:
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Auto-adjusting pressure
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Therapy-data reporting
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Ramp settings
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Exhalation-relief features
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Waterless humidification options
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Portable battery compatibility
Depending on the patient's prescribed therapy and individual needs, some compact PAP devices may be suitable for both everyday use and travel.
A healthcare provider can help determine whether a particular portable device is appropriate for your prescribed treatment.
What to Look for in a Portable PAP Device
Portability is about more than physical size.
If you are comparing PAP devices, consider factors such as:
Prescribed Therapy
The device must provide the type of PAP therapy and pressure range prescribed for you.
Size and Weight
A compact device may be easier to pack, transport, and fit on a small nightstand.
Humidification
Traditional PAP devices often use heated humidification with a water chamber.
Some compact systems offer compatible Heat and Moisture Exchanger (HME) technology, which provides a waterless humidification option by capturing heat and moisture from exhaled breath.
Power Options
If you travel, camp, or spend time away from reliable electrical power, compatible battery options may be important.
Mask Connection
Make sure the device works with the type of mask and tubing connection you plan to use.
Therapy Data
Some PAP devices provide therapy reports or app connectivity that can help users and healthcare providers review available treatment information.
Air Travel
If you fly frequently, confirm that the device meets applicable FAA requirements for onboard use and always check your airline's current policies before traveling.
Feature Spotlight: Transcend Micro Auto CPAP
The Transcend Micro™ Auto CPAP is a compact APAP device designed to provide prescribed positive airway pressure therapy in a portable form factor.
Depending on your prescribed therapy and individual needs, it may be used at home or while traveling.
Auto-Adjusting Therapy
The Transcend Micro operates within a prescribed pressure range and automatically adjusts pressure in response to detected breathing patterns during therapy.
Compact Design
Its compact, lightweight design makes it easier to pack for travel and takes up less space on a nightstand than many traditional bedside PAP systems.
Standard Mask Connection
The Transcend Micro is designed to work with CPAP masks that use a standard 22 mm connection, giving users flexibility when selecting a compatible mask.
Mask selection should still be based on proper fit, comfort, and the recommendations of your healthcare or equipment provider.
AirMist™ Waterless Humidification
Compatible Transcend Micro configurations can use the AirMist™ Heat Moisture Exchanger (HME).
The HME captures heat and moisture from exhaled breath and returns some of that moisture during inhalation, providing a waterless humidification option without a traditional heated water chamber.
GentleRise™
GentleRise™ provides an adjustable ramp feature that allows therapy pressure to increase gradually according to the selected settings.
AirRelief™
AirRelief™ is an expiratory pressure-relief feature designed to reduce pressure during exhalation according to the device's settings.
WhisperSoft™ Muffler
The optional or included WhisperSoft™ Muffler, depending on the Transcend Micro configuration, is designed to help reduce air-flow sound transmitted through the tubing.
FAA Compliant
The Transcend Micro meets applicable FAA requirements for use aboard an aircraft.
Airline policies can vary, so always confirm requirements with the airline operating your flight before departure.
Portable Power Options
Compatible battery options can provide an independent power source when standard electrical power is unavailable.
Battery runtime depends on factors including prescribed therapy settings, environmental conditions, accessories, battery condition, and other variables.
Choosing a PAP Device That Fits Your Therapy and Lifestyle
Selecting a PAP machine is partly a clinical decision and partly a practical one.
Your healthcare provider first determines the appropriate therapy based on your diagnosis and individual medical needs.
Once the appropriate therapy has been established, you and your healthcare or equipment provider can consider device features that fit your prescribed treatment and lifestyle.
Questions to consider may include:
Do You Travel Frequently?
If you travel for work or pleasure, size, weight, battery options, and airline compatibility may be important.
Do You Camp or Spend Time Away From Reliable Power?
A compatible portable battery or other approved power solution may make therapy easier to maintain away from standard electrical outlets.
How Much Nightstand Space Do You Have?
A smaller device may be useful if bedroom space is limited.
What Type of Humidification Do You Prefer?
Some users prefer traditional heated humidification, while others may prefer a compatible waterless HME system.
Which Mask Works Best for You?
Mask fit is highly individual.
Look for a device that works with the mask style and connection required for your therapy.
Do You Want Access to Therapy Data?
If reviewing reports or sharing therapy information with your provider is important to you, consider what reporting and connectivity features the device provides.
Frequently Asked Questions
What is the difference between APAP and bilevel PAP?
APAP and bilevel PAP deliver pressure differently.
An APAP device automatically adjusts pressure within a prescribed minimum and maximum range based on detected breathing patterns.
Bilevel PAP delivers separate prescribed inspiratory and expiratory pressures.
Bilevel therapy is typically used in selected clinical situations and must be prescribed based on the patient's individual needs.
Why might my doctor prescribe CPAP instead of APAP?
Both CPAP and APAP are established options for treating obstructive sleep apnea.
Your healthcare provider may recommend one based on your diagnosis, pressure requirements, medical history, therapy response, comfort, and other clinical considerations.
Do all PAP machines require an in-lab sleep study?
No.
The appropriate diagnostic and titration process depends on your medical situation.
In appropriate adults with OSA, PAP may sometimes be initiated with APAP at home under clinical guidance rather than through a separate laboratory titration.
Your healthcare provider will determine the appropriate process for you.
Is APAP better than CPAP?
Not necessarily.
Both CPAP and APAP can be appropriate treatments for OSA.
Some people prefer the consistency of fixed-pressure CPAP, while others may prefer an auto-adjusting pressure range.
The best choice depends on your prescribed therapy and individual response.
Is BiPAP the same as CPAP?
No.
Standard CPAP typically provides one prescribed pressure, while bilevel PAP provides separate inspiratory and expiratory pressures.
Bilevel PAP is used for selected clinical situations and should not be considered simply a more powerful or upgraded version of CPAP.
Do I need to use PAP therapy every night?
If PAP therapy has been prescribed for you, use it according to your healthcare provider's instructions whenever you sleep.
OSA-related breathing events can return when PAP therapy is not being used.
If you are having difficulty using your device consistently, contact your healthcare or equipment provider rather than stopping or changing treatment on your own.
Can a portable CPAP be my everyday machine?
Possibly.
Some portable PAP devices may be appropriate for both home and travel use, depending on the type of therapy prescribed, device capabilities, and individual treatment needs.
Discuss your device choice with your healthcare provider or equipment provider to make sure it supports your prescribed therapy.
Important Safety Information
The Transcend Micro provides positive airway pressure for the treatment of obstructive sleep apnea in adults weighing more than 66 pounds (30 kg).
In the United States, federal law restricts the device to sale by, or on the order of, a physician.
The Transcend Micro may not be appropriate for every patient.
Always review your complete medical history with your healthcare provider before beginning PAP therapy. Refer to the official Transcend Micro User Manual for complete indications for use, contraindications, warnings, precautions, adverse effects, setup instructions, and operating information.
Do not change prescribed pressure settings or discontinue prescribed PAP therapy without consulting your healthcare provider.
Disclaimer
This article is provided for general informational and educational purposes only and is not intended to provide medical advice, diagnosis, or treatment or to replace the advice of a physician or other qualified healthcare professional.
The appropriate type of PAP therapy, device, pressure settings, treatment plan, and diagnostic or titration process must be determined based on individual clinical needs. Do not start, stop, or modify prescribed PAP therapy or pressure settings without consulting your healthcare provider.
In the United States, federal law restricts the Transcend Micro to sale by, or on the order of, a physician. Please refer to the official Transcend Micro User Manual for indications for use, contraindications, warnings, precautions, adverse effects, operating instructions, and other important safety information.
References
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Weaver, T.E. & Grunstein, R.R. (2008). Adherence to Continuous Positive Airway Pressure Therapy: The Challenge to Effective Treatment. Proceedings of the American Thoracic Society, 5(2), 173–178.
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Mayo Clinic. Obstructive Sleep Apnea – Symptoms and Causes.
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Somers, V.K. et al. (2021). Obstructive Sleep Apnea and Cardiovascular Disease: A Scientific Statement From the American Heart Association. Circulation, 143(16), e714–e783.
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Reutrakul, S. & Mokhlesi, B. (2017). Obstructive Sleep Apnea and Diabetes: A State of the Art Review. Chest, 152(5), 1070–1086.
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Tregear, S. et al. (2009). Obstructive Sleep Apnea and Risk of Motor Vehicle Crash: Systematic Review and Meta-analysis. Journal of Clinical Sleep Medicine, 5(6), 573–581.
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American Academy of Sleep Medicine. Clinical Practice Guideline for Treatment of Adult Obstructive Sleep Apnea With Positive Airway Pressure.
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Cleveland Clinic. BiPAP Machine: Uses, Benefits, Side Effects & Alternatives.
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American Academy of Sleep Medicine. Clinical Practice Guideline for the Treatment of Central Sleep Apnea in Adults.
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Transcend Inc. Transcend Micro User Manual. Refer to the current revision for official product specifications, indications, contraindications, warnings, precautions, and operating instructions.
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Weaver, T.E. et al. (2007). Relationship Between Hours of CPAP Use and Achieving Normal Levels of Sleepiness and Daily Functioning. Sleep, 30(6), 711–719. https://pmc.ncbi.nlm.nih.gov/articles/PMC1978355/
