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Auto CPAP Machines (APAP)

Auto CPAP machines deliver automated continuous positive airway pressure. Alternative terms for these types of sleep apnea machines are AutoPAP or APAP (automatic positive airway pressure).

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Auto CPAP Machines (APAP) Overview

Auto CPAP delivers continuous pressure to stent the upper airways open during sleep. The amount of pressure is automatically adjusted up and down on a breath-to-breath basis based on the level of obstruction present. Home sleep tests are also performed with auto CPAP machines. During a home sleep study, the auto CPAP machine records the frequency of airflow obstructions or apneas and then titrates pressures up and down as needed to reduce or eliminate the frequency of obstructions.

The degree of obstructive sleep apnea may change during the night due to different sleeping positions or phases of sleep. Auto CPAP may benefit people who move a lot at night. Some people have increased obstruction during REM sleep and benefit from more pressure. Losing or gaining weight or alcohol consumption may also alter the degree of sleep apnea. The auto CPAP machine monitors for airway obstruction by sensing airflow from the patient. When it senses an obstruction, it auto-adjusts the pressure setting until it detects that the obstruction has vanished. Flow rates are increased to achieve higher air pressures and reduced to return to lower pressures. Pressure is measured in centimeters of water pressure (cmH20). The typical auto CPAP machine can deliver pressure settings between 4 cmH20 and 20 cmH20.

Although many people find auto CPAP easier to adjust to and more comfortable than fixed pressure CPAP, some people find that the machine is a bit slow to adjust at times. This gap may result in a brief wake-up due to apnea. The change in pressure may also wake the patient up. In general, though, auto CPAP is well tolerated.

The American Academy of Sleep Medicine (AASM) equally recommends auto CPAP and fixed pressure CPAP as first-line therapy for obstructive sleep apnea. The AASM concluded that neither mode is any better than the other at delivering effective therapy for obstructive sleep apnea. The AASM noted that individual patient preferences are vital contributors to therapy adherence and many patients state that they feel more comfortable with auto CPAP. All auto CPAP machines can provide both automatic positive airway pressure and fixed pressure CPAP therapy. In other words, if a patient’s needs change and if the provider determines that a manual CPAP (fixed pressure) mode is preferable, the auto CPAP machine is entirely capable of filling that role.

Dryness in the mouth and nose, difficulty falling asleep, and trouble tolerating the forced air flow is the most common complaints from CPAP users. Auto CPAP machines have features to eliminate or reduce these side effects of CPAP therapy for sleep disorders.

Auto CPAP machines differ in size, range of noise output, and the types of features they have for reducing potential complications and barriers to consistent, effective CPAP use. Machines also differ in what data they capture and how that data is stored and retrieved for use by you and by you and your physician.

Auto CPAP Options


A ramp setting creates a deliberate lag between the time when the machine is turned on and when the full prescribed pressure is delivered. The ramp gives the patient time to get in bed, read, watch TV, or do a crossword puzzle before the full flow starts. The intentional lag may make it easier to get to sleep.

A ramp feature is commonplace on auto CPAP machines but how it works varies by model. Some machines have a preset ramp time while other models let the patient set the timer. On some devices, the ramp phase may be gradual: the pressure initializes at a very low setting and rises incrementally over the preset period. On other machines, the pressure stays dormant until the device detects an airway obstruction. The machine uses the detected obstruction as the signal to ramp up to the ordered pressure level.

Expiratory Pressure Adjustments

Some models of auto CPAP machines include an option to reduce the pressure toward the end of an exhalation, just before an inspiration. This drop in pressure may make it more comfortable for the patient to take the next inward breath. Although auto CPAP does not push air in during inspiration, some people find it uncomfortable to breathe in when there is a constant flow of air. This sensation can be particularly troubling when the amount of needed pressure is in the higher ranges as higher pressure settings require higher flow rates.

By monitoring the patient's expiratory flow rate, these smart machines taper the pressure down just before inspiration to make it easier to breathe in. As soon as it senses the patient is about to exhale, it flexes back up to the ordered CPAP level. For example, if the ordered CPAP level is 12 cm H20, the machine may drop the pressure to 10 cm H20 at the end of exhalation.

Each company calls this feature something different so you will want to look for it. The ResMed AirSense 10 AutoSet calls this feature EPR for Expiratory Pressure Relief while the Philips Respironics DreamStation Auto CPAP calls this feature C-Flex. The Fisher & Paykel SleepStyle Auto CPAP refers to is as Expiratory Relief.


Oral and nasal dryness, hoarseness, and nose bleeds are potential CPAP complications. Humidification can prevent or remedy these concerns. Heated humidifiers may be built into an auto CPAP machine or available for purchase separately. Without humidification, the flow from the auto CPAP machine tends to be cool and dry. Humidifiers warm up the air and saturate it with water vapor.

Some machines maintain the humidity rate and air temperature at a fixed point, while others provide ambient monitoring and adjust the humidity and temperature level up or down to best meet the need at the moment. The dynamic adjustment helps to reduce an effect known as “rain out”, which occurs as warm, humidified gas cools when it travels through the tubing to the patient. Some machines offer a heated tubing option to help minimize condensation accumulation.

Humidifiers require distilled water which is readily available in the grocery store. Be sure to fill your water chamber away from your CPAP machine as water damage will void your warranty.

Leak monitoring

Most brands of face masks and nasal pillows function well with any brand of auto CPAP machine. Some machines, however, have software that takes input regarding the mask in use. The machine then automatically compensates flow delivery using information about that mask's design and leak profile. This feature may make it easier to get a good fit with a mask. Generally, this type of leak compensation requires that the patient chooses a mask that is compatible with the software.

Auto CPAP machines all have alarms that emit audible alerts if the device is having difficulty maintaining the set pressure. These alarms are most often related to the mask leaking too much. These alarms may also go off if the patient has pulled off the mask or blocked the exhalation ports on the mask. Machines differ in how wide a variance they allow or how long the delay is before the alert sounds.

Some machines include a leak test option that allows the patient to run a test with the mask on to see if the leaks around the face and mask are sufficiently sealed.

Information tracking

All auto CPAP equipment tracks some data regarding usage, but there is considerable variation in what information is recorded and tracked and how it is retrieved. Increasingly, machines use a wireless connection to upload data to the internet. Machines that do not have a wireless connection may have data retrieval via an SD card or USB port. The captured data may include things like how often the CPAP was in use, whether the patient had obstructive or apneic events despite wearing the CPAP, and the range of pressures required to resolve obstructions. You or your physician can look at the data to determine if the ordered sleep therapy parameters are working for you. Some machines integrate with smartphone applications both for data capture and sharing as well as for troubleshooting and adjusting machine settings.

Care and Maintenance

Auto CPAP machines need a stable location near the bed with easy access to a power supply. The machine should be flat and not easily jostled. The auto CPAP user must make sure the tubing reaches their bed space without difficulty. Longer hoses are usually available for purchase if needed.

Auto CPAP machines pull in air from the room through a filter that removes dust and other particles. The reusable filter needs to be replaced monthly to prevent device obstructions and failures. The hose or tubing requires daily cleaning. The humidifier also requires cleaning and distilled water replenished.

Follow the manufacturer's recommendations for cleaning and part replacements. Adhering to the recommendations keeps the user healthy and prolongs the life of the machine.

* Patil SP, Ayappa IA, Caples SM, Kimoff RJ, Patel SR, Harrod CG. Treatment of adult obstructive sleep apnea with positive airway pressure: an American Academy of Sleep Medicine clinical practice guideline. J Clin Sleep Med. 2019;15(2):335–343.

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