A bi-level, often called a BiPAP or BPAP, is a type of positive airway pressure machine that delivers two different air pressure settings to help you breathe: a higher pressure when you inhale and a lower pressure when you exhale. It’s primarily used to treat sleep apnea, chronic obstructive pulmonary disease (COPD), and other conditions where breathing becomes difficult during sleep or rest. The key difference from a standard CPAP machine is that a bi-level device adjusts pressure with each breath rather than pushing a single constant stream of air.
How a Bi-Level Machine Works
A bi-level device connects to a mask that covers your nose, mouth, or both. When you breathe in, the machine ramps up to a higher pressure setting (called IPAP, for inspiratory positive airway pressure) to help open your airway and pull air deep into your lungs. When you breathe out, the pressure drops to a lower setting (called EPAP, for expiratory positive airway pressure), making it easier to exhale naturally without fighting against a strong airflow.
This two-pressure design mimics the natural rhythm of breathing more closely than a CPAP, which delivers one fixed pressure regardless of whether you’re inhaling or exhaling. Some bi-level machines also include a backup respiratory rate, meaning the device will initiate a breath for you if it detects you haven’t taken one within a set time window. This feature is especially important for people with central sleep apnea, where the brain intermittently stops sending the signal to breathe.
Bi-Level vs. CPAP
CPAP (continuous positive airway pressure) is the more common and typically first-line treatment for obstructive sleep apnea. It delivers a single, steady pressure all night. For many people, that works well. But some find it uncomfortable to exhale against constant pressure, particularly when higher settings are needed. Breathing out against 15 or 20 centimeters of water pressure can feel like blowing against a wall.
A bi-level machine solves this by allowing the exhale pressure to be set several points lower than the inhale pressure. For example, your inhale pressure might be set at 16 while your exhale pressure sits at 10. That gap makes breathing feel more natural and less effortful, which often improves comfort and helps people stick with therapy longer. Bi-level machines tend to cost more than CPAPs and are typically prescribed after a CPAP trial has failed or when clinical circumstances call for the extra capability.
Who Needs a Bi-Level Machine
Bi-level therapy is commonly prescribed in several situations:
- CPAP intolerance. If you’ve tried a CPAP and can’t tolerate the pressure, especially during exhalation, a bi-level is the usual next step.
- High pressure requirements. People who need very high pressures to keep their airway open often do better with a bi-level because the lower exhale pressure reduces discomfort.
- Central sleep apnea. Because bi-level machines can include a backup breathing rate, they’re suited for conditions where the brain doesn’t consistently trigger breaths.
- COPD and other lung diseases. People with chronic lung conditions sometimes need pressure support to help move enough air in and out, particularly during sleep when respiratory drive naturally decreases.
- Obesity hypoventilation syndrome. In this condition, excess weight on the chest and abdomen makes it harder to breathe deeply enough to maintain normal oxygen and carbon dioxide levels. Bi-level therapy helps by actively assisting each breath.
Most insurance companies and Medicare require documentation that a CPAP was tried first (or a clear clinical reason it was skipped) before they’ll cover a bi-level machine. Your sleep study results and diagnosis play a major role in what gets approved.
What Using One Feels Like
The initial sensation of a bi-level machine is similar to a CPAP: you’ll feel pressurized air flowing through a mask. The difference becomes noticeable the moment you exhale. Instead of pushing against resistance, you’ll feel the pressure ease off, letting your breath flow out more naturally. Most people describe it as less claustrophobic and more comfortable than CPAP, particularly at higher pressure settings.
The transition between the two pressures happens automatically and quickly, usually within a fraction of a second. Modern bi-level machines use sensors that detect the beginning and end of each breath and adjust accordingly. Some models also include a “ramp” feature that starts at a low pressure and gradually increases over 15 to 45 minutes, giving you time to fall asleep before reaching full therapeutic pressure.
Common side effects mirror those of CPAP: dry mouth, nasal congestion, skin irritation from the mask, and aerophagia (swallowing air, which can cause bloating or gas). A heated humidifier, which comes built into most modern machines, helps with dryness. Getting the right mask fit is often the biggest factor in long-term comfort.
Types of Bi-Level Machines
Not all bi-level machines are the same. The simplest models, sometimes called bi-level S (for spontaneous), respond only to your natural breathing pattern. They raise pressure when you inhale and lower it when you exhale, but they don’t intervene if you stop breathing.
Bi-level ST (spontaneous-timed) machines add the backup breathing rate. If you don’t take a breath within a set number of seconds, the machine delivers one for you. This is the type most often prescribed for central sleep apnea and neuromuscular conditions that affect breathing.
More advanced models, sometimes called adaptive servo-ventilation (ASV) devices, continuously analyze your breathing pattern and adjust both pressure and timing breath by breath. These are reserved for complex sleep-disordered breathing and are not appropriate for everyone, particularly people with certain types of heart failure where ASV has been linked to worse outcomes.
Getting Set Up With a Bi-Level
A bi-level machine requires a prescription. Your doctor will typically order a sleep study (either in a lab or at home) to diagnose your condition and determine the pressure settings you need. In some cases, a titration study is done where a technician adjusts the machine’s pressures while you sleep to find the optimal levels.
Once prescribed, a durable medical equipment provider will set up your machine and fit you with a mask. Expect some trial and error with mask styles. Nasal pillows work well for people who breathe through their nose and prefer minimal contact. Full-face masks cover both the nose and mouth and are better if you tend to breathe through your mouth during sleep. Nasal masks sit over the nose and fall somewhere in between.
Most modern bi-level machines track your usage data, including hours of use per night, how many breathing events you’re still experiencing, and whether your mask is leaking. This data often uploads wirelessly to your provider and helps them fine-tune your settings without requiring an office visit. Insurance companies also use this data to verify compliance, typically requiring at least four hours of use per night on 70% of nights during the first few months.