Have you ever wondered what the difference is between CPAP, AutoCPAP and BiLevel devices? How do you know which one is the best for your treatment? Great questions and although the answers can be complex, it’s a good place to start your patient education after the sleep apnea diagnosis. All 3 are referred to as flow generators and are FDA controlled medical devices, which requires dispensing by prescription.


This is the most basic flow generator and the device most often prescribed first. In many cases, our insurance coverage dictates CPAP first, because it costs less and most patients do well with it. If challenges arise, then AutoCPAP or BiLevel are then prescribed.

CPAP stands for Continuous Positive Airway Pressure and is just that; a constant and continuous flow of air that the patient must inhale and then exhale over. One of the biggest challenges adjusting to CPAP is the overwhelming feeling of that continuous flow of air pressure upon exhalation. Most manufactures offer a resolution to this challenge by sensing and / or reducing the machine pressure upon exhalation. Depending on the manufacturer, this feature has different names. The Philips Respironics features are known as it CFLEX, AFLEX or BiFLEX. ResMed refers to it as EPR (expiratory pressure relief) and Fisher & Paykel Healthcare offers the uniquely different SensAwake™. These comfort features have the ability to reduce or self adjust the machine pressure up to 3 cm H2o.

Example: Your CPAP pressure is 10. You have no problem inhaling that delivery of air, but when you begin to exhale while the air is still being delivered, you may feel overwhelmed, claustrophobic or even experience a choking sensation. So if your machine is set with EPR at 3, you would receive 10 at inhalation and then the machine reduces to 7 to make it easier for you to exhale.

AutoCPAP – Automatic titrating (measuring and adjusting) continuous positive airway pressure

This machine is also known as APAP. Unlike CPAP which is set to deliver one continuous pressure, APAP is set within a high and low pressure range for the purpose of varying inhalation needs. The range is predetermined by your prescribing physician. APAP has a sensitive algorithm technology that allows the machine to detect how much inhalation pressure you need with each breath.

The theory of providing a range is that one’s pressure needs may vary during any given night or hour of sleep. One example is sleeping position; most of us have more apnea episodes and of longer duration when we sleep on our backs vs. side or stomach sleeping. Think “gravity” as when we lay flat on our back, the jaw and tongue naturally relax and fall back, thus blocking the airway and causing apnea episodes. Some of us may have nasal conditions or seasonal allergies that require higher pressures during part of the night or seasonally. Even a slightly stuffy nose may cause worsening apnea episodes. We may need higher pressures on occasions when we are under the influence of alcohol too close to bed time (yes, with your doctors approval it is ok to have a glass of wine or alcoholic beverage). Some of us require sedative medication for pain causing deeper sleep and thus more apnea events. Even over the counter cold and flu medications can have a sedative effect. On those nights, APAP should provide the proper inhalation pressure we need on a breath by breath basis.

In theory, an AutoCPAP should work set at the lowest pressure of 4 and the highest of 20, however some experts believe APAP is more effective if the range is tightened a bit closer to the average known cpap pressure needed by each patient. If APAP is challenging for you, bring this to the attention of your prescribing physician.

BiLevel  indicates a flow generator that delivers 2 distinct pressures, one for inhalation and the second for exhalation.

The most complex device, it is also the most expensive and typically reserved for special needs. Most Bilevel devices offer a high setting range of 25 cm H2O vs CPAP and APAP which typically top out at 20. Since exhaling over a constant pressure is one of the most challenging aspects of adjustment for the patient, BiLevel best serves those who require mid to high range inhalation pressure needs. Since high inhalation pressures are extremely difficult to exhale over, this device is set at 2 distinct and constant pressures, one for inhalation and one for exhalation. Remember that CFLEX, EPR only have the ability to reduce pressure 3 points lower, so when a patient requires an inhalation pressure of 20 for example, lowering to 17 is still extremely challenging, so BiLevel can be set at any pressure from its minimum of 4 cm H2O. AutoBilevel are now available and have similar features as the APAP regarding the inhalation and exhalation pressure variables.

Since BiLevel works similarly to a ventilator, it is commonly used for patients with other disorders such as ALS, Parkinson’s or other diseases with patients who need assistance with breathing. It is also frequently prescribed for patients who have central sleep apnea, although many with central apnea do quite well with CPAP or APAP.

Having three options for treating your sleep apnea is useful knowledge. If you have tried and failed on CPAP, discuss APAP or BiLevel or AutoBilevel with your prescribing physician. Each flow generator has different features and benefits, so finding the one that best suits your needs is very important to your successful therapy.

The information included on this site is for educational purposes only. It is not intended nor implied to be a substitute for professional medical advice. Contact your physician or health care provider when you have health related questions. Never disregard or delay medical advice because of information you have obtained on this site.