CPAP vs. BiPAP: What is the Difference?

When you are diagnosed with sleep apnea, you might be prescribed a machine to help you breathe at night. The two most common types are CPAP and BiPAP machines. The main difference between them is how they deliver air pressure: a CPAP machine provides a single, constant pressure of air to keep your airway open, while a BiPAP (bilevel) machine delivers two different pressures—a higher pressure when you breathe in and a lower pressure when you breathe out ^[1]. Understanding which machine is right for you depends on the type of sleep apnea you have and how your body responds to therapy.

The Three Types of Sleep Apnea

To understand why different machines exist, it is helpful to know that not all sleep apnea is the same ^[2]. There are three main types ^[3]:

• Obstructive Sleep Apnea (OSA): The most common type, where the physical airway collapses or becomes blocked during sleep.
• Central Sleep Apnea (CSA): The brain temporarily stops sending signals to the muscles that control your breathing. There is no physical blockage, but the breathing effort stops.
• Mixed (or Complex) Sleep Apnea: A combination of both obstructive and central sleep apnea. Sometimes, central sleep apnea can emerge after a patient starts using a CPAP machine for obstructive sleep apnea (known as treatment-emergent central sleep apnea) ^[4].

Properly diagnosing which type you have is critical, as using the wrong therapy can limit your improvement and quality of life ^[5].

What is a CPAP Machine?

CPAP stands for Continuous Positive Airway Pressure. It is the gold standard and most common first-line treatment for Obstructive Sleep Apnea ^[6].
A CPAP machine takes room air, pressurizes it, and delivers it through a mask at one steady, continuous pressure setting. This constant stream of air acts like an invisible splint, holding the tissues in your throat open so they do not collapse while you sleep.

Note on APAP and Comfort Settings: Many modern CPAP machines are actually APAP (Auto-adjusting CPAP) devices. While an APAP automatically adjusts its pressure up and down throughout the night based on your needs, it still delivers only one pressure at a time. Additionally, most standard CPAP and APAP machines include a comfort feature called Expiratory Pressure Relief (EPR) or C-Flex, which slightly lowers the pressure when you exhale. If you are struggling to breathe out against the air, asking your doctor to turn on or increase this comfort setting is often the first step before switching machines.

What is a BiPAP Machine?

BiPAP is actually a brand name that has become a generic term for Bilevel Positive Airway Pressure (BPAP). Unlike a CPAP, a BiPAP machine uses two distinct, medically prescribed pressure settings ^[1]:

• Inspiratory Positive Airway Pressure (IPAP): A higher pressure when you breathe in to keep the airway open.
• Expiratory Positive Airway Pressure (EPAP): A significantly lower pressure when you breathe out, making it easier and more comfortable to exhale.

While a CPAP’s comfort settings only offer a minor drop in pressure, a BiPAP machine is designed for a much larger, prescribed difference between inhaling and exhaling. In addition, BiPAP machines can include specialized settings, such as a “backup respiratory rate.” This feature monitors how often you breathe and can automatically force a breath if you pause your breathing for too long ^[7].

Why might my doctor prescribe BiPAP instead of CPAP?

Most people with sleep apnea will start with a CPAP machine. In fact, many health insurance companies require documentation that you “failed” or could not tolerate CPAP before they will cover a more expensive BiPAP machine.

Your care team might prescribe or switch you to a BiPAP machine for a few specific reasons:

• CPAP Intolerance: If your OSA requires a very high pressure to keep your airway open, exhaling against that continuous force can be exhausting. Switching to BiPAP lowers the pressure during exhalation enough to make therapy much easier to tolerate ^[8].
• Chronic Obstructive Pulmonary Disease (COPD): If you have a lung condition like COPD alongside sleep apnea, you may struggle to clear carbon dioxide from your lungs. BiPAP is highly effective at helping reduce carbon dioxide levels in the blood for patients with these chronic respiratory conditions ^[9][10].
• Central or Mixed Sleep Apnea: Because central sleep apnea involves a lack of breathing effort, the constant pressure of a CPAP is often not enough. A BiPAP machine, particularly one with a backup breathing rate, can ensure you take enough breaths per minute even if your brain pauses its signals ^[7].
• Hypercapnia: If you have high levels of carbon dioxide in your blood during the day (often seen in conditions like obesity hypoventilation syndrome), a BiPAP machine can offer greater efficiency in clearing out that gas compared to a CPAP ^[10][11].

If you are struggling with your current machine, do not give up. It does not mean therapy will not work for you. Reach out to your sleep doctor or equipment provider and describe exactly what you are feeling. It might simply mean you need a pressure adjustment, a comfort setting turned on, or a different type of machine entirely.