CPAP vs APAP vs BiPAP: What's the Difference?

Written and medically reviewed by Kwaku Osafo-Mensah, MD
Pulmonary Medicine | Sleep Medicine | Diplomate, American Board of Sleep Medicine (ABSM)
Medically reviewed: September 2026.

CPAP vs. APAP vs. BiPAP: What’s the Difference?

CPAP, APAP, and BiPAP are all forms of positive airway pressure (PAP) therapy, but they do not deliver pressure in exactly the same way.

That distinction matters.

A person may hear:

“CPAP didn’t work, so I need BiPAP.”

Or:

“APAP is automatic, so it must be better than CPAP.”

Neither conclusion is automatically correct.

The appropriate PAP approach depends on the breathing disorder being treated, pressure requirements, treatment response, comfort, respiratory physiology, and other clinical factors.

CPAP, APAP, and bilevel PAP are not simply three levels of increasingly powerful treatment. They are different ways of delivering positive airway pressure.

Quick Answer: CPAP vs. APAP vs. BiPAP

The simplest distinction is

CPAP

Continuous positive airway pressure (CPAP) generally provides a single therapeutic pressure during treatment.

APAP

Auto-adjusting positive airway pressure (APAP) changes pressure automatically within a prescribed range in response to breathing patterns detected by the device.

BiPAP / Bilevel PAP

Bilevel positive airway pressure provides different pressures during inspiration and expiration.

These are commonly called the following:

IPAP — inspiratory positive airway pressure

and

EPAP — expiratory positive airway pressure.

The difference between IPAP and EPAP is called pressure support.

However, bilevel PAP includes different modes, and they do not all serve the same purpose.

Is BiPAP the Same as Bilevel PAP?

The terms are commonly used interchangeably in everyday conversation, but there is a terminology distinction.

BiPAP® is a trademark associated with Philips Respironics.

The generic treatment category is:

bi-level positive airway pressure

or:

bilevel PAP.

Because “BiPAP” is a familiar search term and patients commonly use it when referring to bilevel therapy, you will encounter both terms.

For the remainder of this article, bilevel PAP generally refers to the treatment category.

How Does CPAP Work?

CPAP maintains positive pressure in the upper airway during sleep.

In obstructive sleep apnea, the upper airway becomes narrowed or collapses despite continued respiratory effort.

Positive airway pressure acts as a pneumatic splint, helping keep the airway open.

For example, a fixed CPAP prescription might be

CPAP: 10 cm H₂O

The device provides the prescribed therapeutic pressure during treatment, subject to device-specific features such as ramp or expiratory pressure relief when enabled.

CPAP remains a standard and highly effective treatment for obstructive sleep apnea.

Learn more in CPAP & PAP Therapy.

How Does APAP Work?

APAP stands for auto-adjusting positive airway pressure.

Instead of remaining at one fixed therapeutic pressure throughout treatment, APAP operates within a prescribed pressure range.

For example:

APAP: 6–14 cm H₂O

The device analyzes breathing and adjusts pressure according to its algorithm.

Depending on the manufacturer and device, the algorithm may respond to patterns such as the following:

Flow limitation
Snoring
Obstructive apneas
Hypopneas
Other airflow characteristics

The goal is to provide additional pressure when needed while allowing lower pressure during portions of the night when higher pressure may not be necessary.

Is APAP Better Than CPAP?

Not automatically.

APAP can accommodate changing pressure requirements during the night in appropriately selected patients.

Pressure requirements may vary with factors such as:

Body position
REM sleep
Nasal congestion
Alcohol exposure
Weight changes
Night-to-night variability

However, appropriately selected fixed-pressure CPAP can also provide excellent treatment.

The better question is not

“Which machine is more advanced?”

It is:

“Which pressure-delivery strategy effectively treats the sleep-disordered breathing and can be used comfortably and consistently?”

Can APAP Use Lower Pressure Than CPAP?

During portions of the night, yes.

Suppose a patient requires:

12 cm H₂O

during supine REM sleep but substantially less pressure during other portions of the night.

An APAP device operating within an appropriate prescribed range may deliver lower pressure when less is needed and increase pressure when obstructive breathing patterns appear.

This feature can improve comfort for some users.

But the APAP range still needs to be appropriate.

A range that is too restrictive may fail to provide sufficient pressure when needed.

A poorly selected range may also create treatment or comfort problems.

Automatic pressure adjustment does not eliminate the need for appropriate prescription, monitoring, and clinical interpretation.

What Does Bilevel PAP Do Differently?

Bilevel PAP provides separate inspiratory and expiratory pressures.

For example:

IPAP: 14 cm H₂O
EPAP: 9 cm H₂O

During inspiration, the device provides the higher IPAP.

During expiration, pressure decreases to the lower EPAP.

The difference between IPAP and EPAP is called pressure support.

In this example:

Pressure support = 14 − 9 = 5 cm H₂O

That pressure difference can influence respiratory effort, ventilation, comfort, and treatment depending on the clinical situation and bilevel mode.

What Is EPAP?

EPAP stands for expiratory positive airway pressure.

In obstructive sleep apnea, adequate expiratory pressure helps maintain upper-airway patency and prevent obstructive events.

If EPAP is insufficient for a particular patient’s airway, obstructive events may persist.

But EPAP is only one component of bilevel therapy.

What Is IPAP?

IPAP stands for inspiratory positive airway pressure.

It is the pressure delivered during inspiration.

The difference between IPAP and EPAP creates pressure support.

Depending on the clinical situation, pressure support may

Reduce inspiratory work
Improve comfort
Support ventilation
Increase tidal volume in selected circumstances

Its purpose depends on the underlying respiratory disorder and the specific bilevel mode.

What Is Pressure Support?

Pressure support can be expressed simply as:

Pressure Support = IPAP − EPAP

For example:

IPAP: 15 cm H₂O
EPAP: 10 cm H₂O

gives:

Pressure Support: 5 cm H₂O

But more pressure support is not automatically better.

The appropriate amount depends on the treatment goal and respiratory physiology.

Pressure support for comfort is not the same as pressure support for ventilatory assistance.

This distinction becomes particularly important when discussing hypoventilation, neuromuscular disease, central breathing disorders, and specialized bilevel modes.

Is Bilevel PAP Just Stronger CPAP?

No.

This is one of the most important misconceptions to correct.

A bilevel device can deliver relatively high pressures, but it is not higher pressure that defines bilevel therapy.

Its defining feature is the use of different inspiratory and expiratory pressures.

Therefore:

Bilevel PAP should not simply be thought of as “CPAP for severe sleep apnea.”

A patient with severe obstructive sleep apnea may respond extremely well to conventional CPAP or APAP.

Another patient with a lower AHI may require bilevel or another specialized PAP approach because of different respiratory physiology or treatment needs.

OSA severity and PAP mode are not interchangeable concepts.

When Might Bilevel PAP Be Considered?

Bilevel PAP may be considered in selected clinical circumstances.

Examples may include patients with:

Difficulty tolerating required PAP pressures
Particular pressure requirements
Need for greater separation between inspiratory and expiratory pressure
Certain hypoventilation disorders
Some neuromuscular or respiratory conditions
Need for ventilatory support
Other indications requiring specialized bilevel modes

The precise indication matters because different bilevel modes behave differently.

A bilevel device prescribed primarily to improve pressure tolerance in obstructive sleep apnea is not necessarily being used for the same purpose as a bilevel device providing ventilatory support.

Does Severe Sleep Apnea Automatically Require BiPAP?

No.

A patient with severe obstructive sleep apnea may respond extremely well to CPAP or APAP.

Conversely, someone with a lower diagnostic AHI may have respiratory physiology or treatment circumstances that require a different PAP approach.

AHI describes the frequency of scored respiratory events.

It does not independently determine the appropriate PAP mode.

For more about treatment AHI and PAP data, see CPAP AHI: What Should Your AHI Be on Treatment?

Can Bilevel PAP Make Exhaling Easier?

For some patients, yes.

Because EPAP is lower than IPAP, bilevel therapy may feel more comfortable to some people who have difficulty exhaling against higher continuous pressure.

However, many CPAP and APAP devices also offer manufacturer-specific expiratory pressure-relief features.

These features may reduce pressure to some degree during expiration and improve comfort.

But expiratory pressure relief on a CPAP or APAP device is not the same thing as full bilevel PAP therapy.

A patient who finds exhalation uncomfortable should therefore not automatically conclude that a bilevel device is required.

Is CPAP Expiratory Pressure Relief the Same as Bilevel PAP?

No.

CPAP and APAP comfort features may temporarily reduce pressure during expiration.

That can create a modest difference between inspiratory and expiratory pressure.

Bilevel PAP, however, is specifically configured around separate inspiratory and expiratory pressures.

Depending on the bilevel mode, additional parameters may also control the following:

Pressure support
Respiratory timing
Backup respiratory rate
Inspiratory time
Other ventilatory characteristics

The physiologic capabilities can therefore be substantially different.

What If CPAP Pressure Is Very High?

Higher therapeutic pressures can sometimes create comfort challenges.

Potential problems may include:

Mask leak
Difficulty exhaling
Aerophagia
Dryness
Mask displacement
Treatment intolerance

But the appropriate response depends on why the higher pressure is required.

Useful questions include:

Is residual upper-airway obstruction still present?
Is a significant leak affecting the data?
Is APAP repeatedly reaching its upper pressure limit?
Do pressure requirements vary substantially during the night?
Is the interface appropriate?
Is the patient actually using PAP throughout sleep?
Would another pressure-delivery strategy be clinically appropriate?

Simply reducing pressure enough to improve comfort may allow obstructive sleep apnea to recur.

Can Bilevel PAP Help CPAP Aerophagia?

It may help selected patients in appropriate circumstances, but bilevel PAP is not a universal treatment for swallowed air.

Aerophagia may relate to:

Pressure exposure
Pressure variability
Swallowing
Mask or mouth leak
Interface issues
Sleeping position
Gastrointestinal factors

When aerophagia substantially limits PAP use, the clinician may reconsider pressure requirements, pressure-delivery strategy, comfort settings, leak, and other contributors.

But:

“CPAP aerophagia = switch to BiPAP” is not an appropriate general rule.

For a detailed discussion, see CPAP Aerophagia: Why PAP Causes Gas and Bloating—and What Can Help.

Does Mask Type Matter With CPAP, APAP, or Bilevel PAP?

Yes.

The interface is an important part of the PAP system.

Common categories include:

Nasal pillows
Nasal masks
Full-face or oronasal masks

Mask selection can influence the following:

Leak
Comfort
Mouth breathing
Pressure tolerance
Sleeping position
Treatment adherence

However, there is no universally best mask for CPAP, APAP, or bilevel PAP.

The appropriate interface depends on the individual patient’s anatomy, breathing pattern, pressure requirements, sleeping position, comfort, and treatment response.

Our next guide will compare nasal pillows vs. nasal masks vs. full-face masks in detail.

Can APAP Treat Central Sleep Apnea?

APAP is primarily designed to adjust pressure in response to obstructive breathing patterns.

Central sleep apnea involves reduced or absent respiratory effort rather than upper-airway collapse as the primary mechanism.

Therefore, simply increasing airway pressure is not automatically the appropriate response to a central respiratory event.

Persistent central events require appropriate classification and clinical interpretation.

For more detail, see Central vs. Obstructive Sleep Apnea: What’s the Difference?

Does Bilevel PAP Treat Central Sleep Apnea?

This question requires an important qualification.

Some bilevel modes can provide backup respiratory support. Others do not.

Ordinary spontaneous bilevel PAP generally depends on the patient initiating each breath.

A bilevel mode with a backup rate can provide timed respiratory support when spontaneous breathing is absent or inadequate.

Therefore:

“Central sleep apnea = BiPAP” is not an appropriate general rule.

The appropriate treatment depends on factors such as

Type of central sleep apnea
Respiratory physiology
Cardiac status
Medication exposure
Ventilation
Oxygenation
Other medical conditions

The exact bilevel mode matters.

What Is Spontaneous Bilevel PAP?

In a spontaneous bilevel mode, the patient initiates breaths.

The device responds by transitioning between the prescribed inspiratory and expiratory pressures.

Conceptually:

Patient initiates inspiration → device delivers IPAP

Patient transitions to expiration → device returns to EPAP

This approach can improve pressure tolerance or provide pressure support in selected circumstances.

However, spontaneous bilevel PAP does not provide the same type of backup respiratory support as a timed mode.

What Is Bilevel ST?

Bilevel ST refers to a mode incorporating both spontaneous and timed operation.

The device can support patient-triggered breaths but can also provide timed breaths according to configured parameters when spontaneous breathing is absent or insufficient.

This makes bilevel ST fundamentally different from ordinary spontaneous bilevel PAP.

Depending on the clinical indication, settings may involve parameters such as

IPAP
EPAP
Pressure support
Backup respiratory rate
Inspiratory timing

Bilevel ST may be used for selected ventilatory disorders under appropriate clinical supervision.

It should not be viewed simply as a comfort upgrade from CPAP.

What Is ASV?

Adaptive servo-ventilation (ASV) is a specific type of positive airway pressure therapy for certain kinds of unstable or central breathing.

ASV dynamically adjusts ventilatory support in response to the patient’s breathing pattern.

It is:

not conventional CPAP

not simply APAP

and

not interchangeable with ordinary bilevel PAP.

ASV may be considered for selected patients with certain central sleep apnea syndromes or treatment-emergent central sleep apnea.

However, patient selection matters.

Cardiac status, the underlying cause of central apnea, respiratory physiology, and other clinical factors should be considered before ASV is prescribed.

ASV should not be selected simply because a PAP machine reports several “central” or “clear-airway” events.

What About Heart Failure and ASV?

This area requires particular care.

Evidence regarding ASV in patients with heart failure has evolved, and recommendations depend on the clinical setting, cardiac function, underlying central sleep apnea syndrome, and treatment strategy.

The important practical point for patients is the following:

ASV is not a device that should be selected independently from an evaluation of cardiac and respiratory status.

When heart failure is present or suspected, the treatment decision should incorporate appropriate cardiovascular assessment and current clinical guidance.

What Is Hypoventilation?

Hypoventilation means that ventilation is insufficient to adequately eliminate carbon dioxide.

It is different from simply having repeated obstructive apneas.

A patient may have elevated carbon dioxide due to conditions affecting:

Respiratory drive
Respiratory muscles
Chest-wall mechanics
Obesity-related respiratory physiology
Pulmonary function
Neuromuscular function
Other aspects of ventilation

Certain hypoventilation disorders may require ventilatory-support strategies that differ substantially from ordinary OSA treatment.

Does Hypoventilation Automatically Mean BiPAP?

No.

The word “bilevel” describes a pressure-delivery framework, not one universal treatment.

Depending on the disorder, clinicians may need to consider the following:

IPAP
EPAP
Pressure support
Backup respiratory rate
Tidal-volume or ventilation targets in selected modes
Oxygenation
Carbon dioxide
Respiratory muscle function
Underlying disease

Different forms of noninvasive ventilatory support may therefore be appropriate for different patients.

This is another reason purchasing a “BiPAP machine” does not by itself solve the clinical problem.

What Is Treatment-Emergent Central Sleep Apnea?

Some patients treated for obstructive sleep apnea develop or continue to demonstrate central respiratory events after PAP therapy begins.

This is called treatment-emergent central sleep apnea (TECSA).

In simplified terms:

The patient initially has predominantly obstructive sleep apnea.
PAP improves the upper-airway obstruction.
Central respiratory events emerge or persist.
The subsequent course varies among patients.

In some people, these central events decrease with continued appropriate treatment.

In others, persistent events may require further evaluation.

Simply changing from CPAP to an arbitrary bilevel mode is not automatically the correct response.

Event type and respiratory physiology are important.

What If My PAP Machine Reports Central Apneas?

PAP devices may estimate that certain events appear central or “clear airway.”

These classifications can provide useful treatment information.

But a PAP device does not directly measure chest and abdominal respiratory effort in the same way as laboratory polysomnography.

Machine-reported central events can occur in circumstances such as:

True central sleep apnea
Treatment-emergent central sleep apnea
Sleep-wake transitions
Irregular awake breathing
Medication effects
Altitude
Device-classification limitations
Other physiologic circumstances

Persistent or substantial central-event estimates deserve clinical interpretation rather than an automatic pressure or mode change.

How Do CPAP, APAP, and Bilevel Affect Machine-Reported AHI?

All three types of PAP devices may provide treatment data, although available parameters and algorithms vary.

Depending on the device, information may include the following:

Usage hours
Residual AHI
Estimated event type
Mask leak
Delivered pressure
Flow limitation
Periodic breathing
Other device-specific measurements

These data can be extremely useful.

But machine-reported AHI remains a treatment-monitoring estimate, not a complete polysomnogram.

A residual AHI should therefore be interpreted together with:

usage + leak + pressure + event type + symptoms + sleep duration + clinical context.

Can the “Right” PAP Mode Still Produce a High Residual AHI?

Yes.

An appropriate PAP mode does not guarantee that every setting is optimal or that every treatment problem has been solved.

Persistent residual events may relate to:

Inadequate pressure
Significant leak
Positional obstruction
REM-related obstruction
Central events
Incomplete PAP use
Device-detection limitations
Other clinical factors

The type of residual event matters.

Later we’ll link this section to CPAP AHI: What Should Your AHI Be on Treatment?

Can You Still Be Tired With the Right PAP Mode?

Yes.

Even when PAP effectively controls obstructive sleep apnea, persistent sleepiness or fatigue may have another explanation.

Potential contributors include:

Incomplete PAP use
Residual respiratory events
Mask leak
Insufficient sleep
Insomnia
Circadian misalignment
Medication effects
Other sleep disorders
Medical or psychiatric conditions

Choosing CPAP, APAP, or bilevel PAP correctly does not eliminate every possible cause of daytime symptoms.

For a systematic approach to persistent symptoms, see Why Am I Still Tired After Using CPAP?

CPAP vs. APAP vs. Bilevel PAP: Side-by-Side

Feature	CPAP	APAP	Bilevel PAP
Pressure delivery	Generally one therapeutic pressure	Automatically varies within a prescribed range	Different inspiratory and expiratory pressures
Inspiratory pressure	CPAP pressure	Variable PAP pressure	IPAP
Expiratory pressure	CPAP pressure, with possible comfort relief	Variable pressure, with possible comfort relief	EPAP
Pressure support	Not conventional bilevel pressure support	Not conventional bilevel pressure support	Difference between IPAP and EPAP
Common OSA role	Standard effective treatment	Standard effective treatment in appropriately selected patients	Selected circumstances
Automatically responds to obstruction	No automatic pressure adjustment with fixed CPAP	Yes, within prescribed range	Depends on mode/device
Backup respiratory rate	No	No	Only in certain bilevel modes
Ventilatory support	Limited	Limited	Can be substantial depending on mode
Best choice for everyone?	No	No	No

The appropriate PAP mode depends on the disorder being treated, pressure requirements, respiratory physiology, treatment response, comfort, and relevant medical conditions—not simply on which device appears most advanced.

Which Is Better: CPAP or APAP?

For many adults with uncomplicated obstructive sleep apnea, either fixed-pressure CPAP or APAP may provide effective treatment when appropriately selected and used.

The choice may depend on factors such as

Pressure variability
Treatment response
Comfort
Clinical circumstances
Device data
Patient preference
Prescriber strategy

APAP’s ability to vary pressure can be useful when pressure requirements change during the night.

Fixed CPAP, however, may provide excellent control with a stable therapeutic pressure.

“Automatic” does not automatically mean “better.”

Which Is Better: CPAP or Bilevel PAP?

Neither is universally better.

For routine obstructive sleep apnea, CPAP may provide excellent treatment.

Bilevel PAP becomes relevant when the patient’s pressure requirements, treatment tolerance, ventilatory needs, or respiratory physiology justify separate inspiratory and expiratory pressures or a specialized bilevel mode.

Using a more complex device without a clinical reason does not necessarily improve treatment.

The goal is not to use the most sophisticated machine.

The goal is to use the appropriate therapy for the respiratory problem.

Which Is Better: APAP or Bilevel PAP?

Again, they solve different problems.

APAP automatically changes airway pressure within a prescribed range primarily in response to detected obstructive breathing patterns.

Bilevel PAP provides separate inspiratory and expiratory pressures.

Specialized bilevel modes may additionally provide timed or ventilatory support.

Therefore, APAP and bilevel PAP should not simply be viewed as competing versions of the same technology.

Is APAP Always More Comfortable Than CPAP?

No.

Some patients prefer the lower average pressure that APAP may provide during portions of the night.

Others prefer the stability of fixed-pressure CPAP.

Some people may notice pressure changes from APAP and find them disruptive.

Comfort can also depend on:

Mask fit
Leak
Humidification
Nasal symptoms
Pressure-relief settings
Sleeping position
Individual sensitivity to pressure changes

Comfort should therefore be assessed in the context of treatment effectiveness, not separately from it.

Does Bilevel PAP Always Feel More Comfortable?

No.

Some patients find the lower expiratory pressure easier to tolerate.

Others may notice the transition between IPAP and EPAP or require time to adapt to bilevel breathing patterns.

Comfort also depends on:

Pressure settings
Pressure support
Triggering and cycling behavior
Mask interface
Leak
Respiratory pattern
The specific bilevel mode

A device that is more complex is not automatically more comfortable.

Does APAP Prevent the Need for a Sleep Study?

Not necessarily.

APAP can automatically adjust treatment pressure, but it does not independently determine the cause of every sleep-related breathing problem.

Diagnostic evaluation remains important when determining whether the patient has:

Obstructive sleep apnea
Central sleep apnea
Hypoventilation
Another sleep disorder
A more complex respiratory condition

A PAP device treats according to its design and settings.

It does not replace an appropriate diagnosis.

Can you change from CPAP to APAP on your own?

PAP mode and pressure settings should be managed according to the treatment plan and relevant clinical circumstances.

Changing from fixed CPAP to a broad APAP range without understanding the diagnostic disorder and existing treatment data can lead to complications.

The diagnostic disorder
Existing treatment data
Pressure requirements
Central-event patterns
Leak
Oxygenation
Other medical conditions

may create an apparently convenient solution without addressing the underlying problem.

The same principle applies to changing from APAP back to fixed CPAP.

Can You Choose Your Own Bilevel Settings?

Bilevel therapy involves more than choosing two comfortable pressures.

Depending on the mode, settings may affect the following:

Upper-airway patency
Ventilation
Carbon dioxide
Respiratory effort
Breath timing
Tidal volume
Patient-device synchrony

For specialized bilevel modes, additional parameters may substantially influence respiratory support.

This factor is particularly important in patients with:

Hypoventilation
Neuromuscular disease
Central sleep apnea
Significant pulmonary disease
Other ventilatory disorders

Bilevel settings should therefore be matched to the clinical indication.

Does the PAP Machine Brand Change the Basic Difference?

The fundamental distinctions remain:

CPAP → generally fixed therapeutic pressure

APAP → automatically varying pressure within a prescribed range

Bilevel PAP → separate inspiratory and expiratory pressures

However, manufacturers may differ in:

Algorithms
Comfort features
Event detection
Pressure-response behavior
Data reporting
Humidification
User interface
Connectivity
Available specialized modes

These differences may affect usability and treatment experience.

They do not change the underlying physiologic distinction among CPAP, APAP, and bilevel PAP.

What About Travel CPAP Machines?

Travel PAP devices are designed to reduce size and weight for portability.

Depending on the model, they may offer fixed CPAP, APAP, or other features.

However, a travel device should not automatically be assumed to provide every mode or feature available on a full-size home PAP system.

Considerations may include:

Prescribed PAP mode
Pressure capability
Humidification
Noise
Battery options
Data capability
Mask compatibility
Travel requirements

A patient who requires specialized bilevel or ventilatory support should not assume that a standard travel CPAP can substitute for the prescribed device.

Does Mask Choice Change With Higher PAP Pressures?

It can.

As pressure increases, maintaining a comfortable mask seal may become more challenging for some users.

Potential issues include the following:

Mask displacement
Air leak
Eye irritation
Dry mouth
Mouth leak
Skin pressure
Noise

However, a larger mask is not automatically better at higher pressures.

Some patients tolerate nasal interfaces very well even at substantial pressures, while others require a different interface because of anatomy, mouth leak, comfort, or other factors.

Mask choice should be individualized.

What If My Mask Leaks More When Pressure Increases?

That is a common troubleshooting issue.

A mask may appear to seal well at a low ramp pressure but begin leaking when therapeutic pressure increases later in the night.

Useful considerations include:

Mask size
Cushion condition
Headgear adjustment
Sleeping position
Hose pull
Facial anatomy
Mouth leak
Pressure pattern

For detailed troubleshooting, see CPAP Mask Leak: What’s Normal and How Do You Fix It?

What If PAP Gives Me a Dry Mouth?

Dry mouth may result from the following:

Mouth leak
Mouth breathing
Nasal obstruction
Humidification issues
Medications
Reduced saliva production
Other causes

The appropriate response depends on the cause rather than simply increasing humidity or changing PAP mode. For a step-by-step approach, see CPAP Dry Mouth: Causes, Solutions, and When to Worry.

What If I Feel Bloated on PAP?

Gas and bloating may represent PAP-associated aerophagia in some patients.

Pressure can contribute, but aerophagia does not automatically mean that the PAP mode or pressure is inappropriate.

Treatment effectiveness, pressure requirements, leak, interface, sleep position, and gastrointestinal factors should be considered together. For more information, see CPAP Aerophagia: Why PAP Causes Gas and Bloating—and What Can Help.

What If My AHI Is Still High?

A persistently elevated machine-reported residual AHI deserves context.

Questions include:

Is PAP being used throughout sleep?
Is a significant leak present?
Are the events obstructive or central?
Is APAP reaching the upper pressure limit?
Are events clustered?
Has something changed clinically?
Does the patient remain symptomatic?

For a detailed explanation of residual treatment AHI, see CPAP AHI: What Should Your AHI Be on Treatment?

What If I Am Still Tired Despite Good PAP Data?

A low residual AHI does not explain every cause of persistent sleepiness or fatigue.

Potential contributors may include:

Insufficient sleep
Incomplete PAP use
Insomnia
Circadian problems
Medications
Other sleep disorders
Medical conditions
Mental health conditions
Residual excessive daytime sleepiness

Changing from CPAP to APAP or bilevel PAP will not necessarily resolve a problem unrelated to PAP mode.

Later, link this section to Why Am I Still Tired After Using CPAP?

Questions to Ask About Your PAP Prescription

If you are unsure why a particular PAP mode was selected, useful questions include:

What sleep-related breathing disorder is being treated?
Why was CPAP, APAP, or bilevel PAP selected?
What pressure or pressure range is prescribed?
If bilevel PAP is used, what are my IPAP and EPAP?
What is my pressure support?
Does my device have a backup respiratory rate?
What residual events are being reported?
Are those events obstructive, central, or uncertain?
Is a significant leak present?
Am I using PAP throughout the entire sleep period?
Are oxygenation or ventilation concerns present?
What symptoms or data changes should prompt reassessment

These questions provide more useful information than simply asking:

“Is BiPAP better than CPAP?”

Can You Still Be Tired With the Right PAP Mode?

For a systematic approach to persistent symptoms, see Why Am I Still Tired After Using CPAP?

When Should PAP Therapy Be Reassessed?

Professional review may be appropriate when:

PAP remains difficult to tolerate
Required pressures are uncomfortable
Significant aerophagia persists
Large mask leak continues
Severe dry mouth interferes with treatment
Residual AHI remains consistently elevated
Central events are repeatedly reported
APAP repeatedly reaches its prescribed pressure limits
Snoring or witnessed breathing abnormalities continue during PAP
Significant oxygen or ventilation concerns remain
PAP is regularly removed during sleep
Symptoms persist despite apparently effective treatment
A major weight or medical-status change occurs

The goal of reassessment is not automatically to move to a “stronger” device.

It is to determine why treatment is not producing the expected result.

A Practical Way to Think About CPAP, APAP, and Bilevel PAP

Think of the three approaches according to the problem they are designed to address.

CPAP

Can one appropriate therapeutic pressure effectively maintain the airway throughout treatment?

APAP

Would automatically adjusting pressure within an appropriate prescribed range help accommodate changing obstructive pressure requirements?

Bilevel PAP

Is there a clinical reason to use separate inspiratory and expiratory pressures or a specialized form of respiratory support?

This framework is more useful than ranking the devices from basic to advanced.

The Bottom Line

CPAP, APAP, and bilevel PAP are all forms of positive airway pressure therapy, but they deliver pressure differently.

CPAP generally provides one therapeutic pressure.

APAP automatically adjusts pressure within a prescribed range in response to detected breathing patterns.

Bilevel PAP provides separate inspiratory and expiratory pressures and, depending on the mode, may offer capabilities that go well beyond routine treatment of obstructive sleep apnea.

Bilevel PAP is not simply stronger CPAP.

APAP is not automatically better than fixed CPAP.

And a more complex PAP device is not automatically more effective.

The most useful question is not

“Which PAP machine is best?”

It is:

“Which PAP mode appropriately treats my breathing disorder, provides effective control throughout sleep, and can be used comfortably and consistently?”

That is the treatment decision that matters.

References & Further Reading

Patil SP, Ayappa IA, Caples SM, et al. Treatment of adult obstructive sleep apnea with positive airway pressure: an American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine. 2019;15(2):335–343.
https://doi.org/10.5664/jcsm.7640
Patil SP, Ayappa IA, Caples SM, et al. Treatment of adult obstructive sleep apnea with positive airway pressure: an American Academy of Sleep Medicine systematic review, meta-analysis, and GRADE assessment. Journal of Clinical Sleep Medicine. 2019;15(2):301–334.
https://doi.org/10.5664/jcsm.7638
Badr MS, Khayat RN, Allam JS, et al. Treatment of central sleep apnea in adults: an American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine. 2025;21(12):2181–2191.
https://doi.org/10.5664/jcsm.12150
Berry RB, Chediak A, Brown LK, et al. Best clinical practices for the sleep center adjustment of noninvasive positive pressure ventilation in stable chronic alveolar hypoventilation syndromes. Journal of Clinical Sleep Medicine. 2010;6(5):491–509.
American Academy of Sleep Medicine. Sleep Education — CPAP.
https://sleepeducation.org/patients/cpap/

Medical Author & Reviewer
Kwaku Osafo-Mensah, MD
Pulmonary Medicine | Sleep Medicine
Diplomate, American Board of Sleep Medicine (ABSM)
More than 20 years of experience in sleep medicine

Medically reviewed: September 2026.
About the medical reviewer · Editorial Policy

Medical Disclaimer: This information is provided for general educational purposes and is not a substitute for individualized medical evaluation, diagnosis, or treatment. PAP mode, pressure settings, pressure support, backup rate, and other ventilatory settings should be selected according to the diagnosed breathing disorder and individual clinical circumstances. Discuss PAP intolerance, persistent respiratory events, central apnea, hypoventilation, oxygen or ventilation concerns, and treatment changes with a qualified healthcare professional. Do not substantially change prescribed PAP settings or switch PAP modes solely on the basis of generalized internet information.