Auto-titrating continuous positive airway pressure, or AutoCPAP therapy, is useful for the treatment of obstructive sleep apnea. It is delivered via a face mask and tubing that attaches to a device that generates a pressurized flow of air that increases in response to measured airway resistance.
It is similar in some ways to other therapy modes, including CPAP and bilevel. There are pros and cons to using AutoCPAP therapy. Explore the potential benefits and risks and consider whether it might be the right treatment for you.
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Overview of PAP Therapy
Positive airway pressure (PAP) therapy is considered the gold standard treatment for sleep apnea. For 40 years, it has been the most effective treatment for a condition that may have meaningful effects on sleep, undesirable daytime symptoms, and serious long-term health consequences.
Over the years, this non-invasive intervention has evolved to include multiple types of devices and even different therapy modes within the same device. It is helpful to understand AutoCPAP in this context.
The simplest version of PAP therapy is continuous positive airway pressure (CPAP). This is a constant flow of air generated by what one of the major manufacturer’s engineers has described as “a box with a fan.” The pressurized airflow passes into the nose (and sometimes the mouth with a full-face mask) and creates a column of air that keeps the throat open.
The soft palate, uvula, and tongue base are suspended to keep these tissues from occluding the airway. This resolves snoring and obstructive sleep apnea.
The amount of pressure needed to keep the airway open depends on multiple factors, including:
- Anatomy of the airway
- Nasal congestion (i.e, colds or allergies)
- Body position in sleep (sleeping on the back)
- Sleep stage (especially REM sleep)
- Use of alcohol or other muscle relaxants
When the pressure need is determined during a PAP titration polysomnogram, it is generally thought to be therapeutic if someone is noted to be breathing normally on their back and in REM sleep. Unfortunately, this may not be the pressure that is needed throughout the night.
In fact, it might be too high for much of the night. Therefore, if this is selected as the therapeutic pressure setting for a CPAP machine, it may actually lead to problems with tolerance, including higher mask leak, dry mouth, and air swallowing (aerophagia), even undermining long-term use.
To remedy this, it can be helpful to use a device that is able to detect the pressure need through a surrogate measure of resistance to airflow. The proprietary algorithm is not disclosed by manufacturers, but the rationale can be theorized.
If there is a constant flow of air past the soft palate and the base of the tongue, it is possible to detect the breathing pattern (resistance rises and falls in a predictable pattern). At the point of maximal exhalation, with the diaphragm fully relaxed, the airway may become blocked in someone predisposed to sleep apnea. This increases resistance to the flow of air.
If detected, an AutoCPAP will respond by increasing the pressure of the airflow. This is meant to resolve the obstruction—as well as the associated oxygen desaturation, carbon dioxide retention, cortisol release, and arousal of the brain that occurs with sleep apnea events.
As a general rule, the pressure of the AutoCPAP will be lower at the start of the night and may gradually increase throughout the night with detected need. The algorithms seem to err on the side of increasing the pressure.
In theory, lower pressures could be attempted at later time points, but if the need still exists there may be breakthrough sleep apnea episodes. The setting of these pressure ranges is discussed further below.
Other Modes
There are still other possible settings that may be used by differing devices or in other modes of the same device. Consider these variations:
CPAP
As above, a constant flow of air set to a single pressure setting (measured in centimeters of water pressure).
AutoCPAP
Also known as APAP, auto-titrating, or by brand names such as AirSense (used by ResMed), therapy is delivered through a range of pressures as ordered by the prescribing physician and set by a respiratory therapist. The device self-adjusts based on measures of resistance.
Bilevel
Often known as BiPAP (the trademark from Philips Respironics) or VPAP (the one from ResMed), this is a two-pressure therapy. The pressure is higher as someone breathes in and lowered as they breathe out.
This can make it more comfortable to breathe out and may reduce mask leak and aerophagia. It may also reduce central sleep apnea and may improve treatment of obesity-hypoventilation syndrome and other respiratory-related neuromuscular conditions.
There are two main types: S (spontaneous) and ST (with spontaneous timed breaths, useful to treat central sleep apnea).
What Is a BiPAP Machine?
Autobilevel
This may also be called AutoBiPAP or even AutoVPAP, though ResMed’s current version is called AirCurve. Much like AutoCPAP, it is able to adjust through a range of preset pressure options.
It may include a minimum expiratory pressure called EPAP (similar to CPAP), as well as pressure support settings that increase the amount of air with inspiration (possibly with both minimum and maximum settings). There is often a maximum inspiratory pressure, called IPAP.
AVAPS (or iVAPS)
This acronym for average volume-assured pressure support is often used in pulmonary conditions that require additional support, such as chronic obstructive pulmonary disease (COPD).
ASV
The most sophisticated setting in non-invasive ventilation, ASV it allows variation in pressure support as well as the timing and volume of supported breaths. This is also known as both auto servoventilation and adaptive servoventilation, by Philips Respironics and ResMed, respectively.
These devices—and the associated masks, tubing, and other needed supplies—can look very much the same, despite differing abilities and functions.
The determination of what device or mode to use is typically made by the treating board-certified sleep physician based on underlying medical conditions, medications, and the severity and type of sleep apnea. In some cases, cost or insurance coverage may be a consideration.
Pros of AutoCPAP Therapy
There are some clear benefits to the use of AutoCPAP therapy. This dynamic adjustment may optimize response to therapy, lowering the apnea-hypopnea index (AHI) to its treatment goal. This may make AutoCPAP more effective than alternatives, including the use of an oral appliance from a dentist or surgery.
As noted above, it also may reduce some of the side effects that interfere with compliance to treatment. It may allow lower pressures to be delivered through more of the night, only increasing to the higher settings when more support is needed. This variance matches the treatment to need, leading to a better overall experience for many users.
Cons of AutoCPAP Therapy
There are some potential risks to the use of AutoCPAP therapy. If the pressure range is too broad, it may take too long for the device to adjust to get to a therapeutic setting. This may lead to additional sleep apnea events and associated symptoms.
If the range is set too high, it may cause breath-holding episodes that are labeled as central apnea events (a condition called complex sleep apnea). Therefore, the settings become more important when allowing the device to work through a range of options.
In some cases, auto-titrating devices may be a problem. For example, the use of Autobilevel devices is discouraged in obesity hypoventilation syndrome. In heart failure when the left ventricular ejection fraction is less than 45%, the use of ASV devices seem to increase the risk of mortality.
Finally, an AutoCPAP may be slightly more expensive than a standard CPAP machine, typically costing about $100 more. Fortunately, this treatment is often covered by insurance and the difference may be negligible for most people, especially in light of the more than 5-year lifespan of the device.
Pressure Settings
One might wonder: What pressure should an AutoCPAP be set at? Moreover, how might someone know if the PAP pressure needs adjusting?
The potential pressure settings for AutoCPAP range from 4 to 20 centimeters of water pressure (potentially abbreviated as CWP or cm of H20 pressure) for most modern devices.
These are the default settings from the manufacturer, and they are usually narrowed based on the prescription from a board-certified sleep physician. How is this determination made?
Some guidance may occur with the help of an in-center study called a PAP titration polysomnogram. Barring this information, a typical range may be set (often around 6 to 10 CWP or 8 to 12 CWP for most individuals).
If a person is living with severe obesity, a slightly higher range may be set. In some cases, lower or higher settings may be selected based on individual risk factors, comorbid conditions, or prior experience with therapy.
If the pressure is too low, snoring or sleep apnea may persist. The AHI should be as low as possible, and normal is less than 5 based on diagnostic testing. High pressures may exacerbate mask leak, dry mouth, aerophagia, and intolerance to treatment.
In some cases, simply turning down the pressure relieves many of these problems. This decision should be left to the treating physician who can best understand the overall clinical picture and how pressure changes may affect the therapy.
A Word From Verywell
If you are interested in learning more about AutoCPAP therapy, seek evaluation by a board-certified sleep physician. Understanding your individual risk factors will lead to the best possible outcomes of therapy.
As these technologies advance, they will become optimized to improve breathing during sleep. It is still necessary to have the guidance of a professional who can best use these tools to your benefit.
