A Continuous Positive Airway Pressure (CPAP) machine is a common medical device used to treat sleep-related breathing disorders. Many people new to this therapy often wonder if the machine is supplying them with oxygen, similar to a tank or concentrator. The primary function of a CPAP machine is not to deliver concentrated oxygen. Instead, it uses mechanical pressure to ensure the patient can breathe normally and without interruption. Understanding the physical mechanics of the device clarifies the distinction between pressure therapy and oxygen therapy.
What CPAP Machines Actually Deliver
CPAP machines operate by drawing in ambient air from the room. This air is passed through a filter to remove impurities before a motor pressurizes it. The pressurized air is then delivered to the patient through a hose and a mask worn over the nose or mouth. The machine functions as a pump that moves and pressurizes existing air, rather than a generator that creates or concentrates a specific gas.
It is a common misconception that CPAP machines are the same as oxygen concentrators. Oxygen concentrators separate nitrogen and other gases from ambient air, delivering a highly concentrated stream of oxygen, typically ranging from 85% to 95% purity. In contrast, the air composition delivered by a standard CPAP machine remains the same as the room air it pulls in. This means the air stream contains approximately 21% oxygen, which is the natural concentration of the atmosphere.
The core difference is that CPAP focuses on maintaining a clear airway. The benefit seen in blood oxygen levels is a result of uninterrupted breathing, not from an increase in oxygen concentration. By ensuring stable airflow, the machine prevents drops in blood oxygen that occur when breathing repeatedly pauses. CPAP simply facilitates the body’s natural ability to take in the oxygen that is already available in the room.
How Pressurized Air Keeps Airways Open
The purpose of CPAP therapy is to provide continuous positive airway pressure, a constant level of air pressure maintained throughout the entire breathing cycle. This pressure is measured in units like centimeters of water (cmH2O). The CPAP motor creates an airflow slightly greater than the surrounding atmospheric pressure. This increased pressure acts as a mechanical support system for the upper airway.
The positive pressure functions as an “air splint,” preventing the collapse of soft tissues in the back of the throat. During sleep, muscles relax, and structures such as the soft palate and tongue base can sag, causing an obstruction that characterizes obstructive sleep apnea (OSA). By gently nudging these tissues aside, the pressurized air keeps the pharynx open. This ensures an uninterrupted pathway for the flow of air into the lungs.
The pressure setting is determined by a physician or sleep specialist to meet the patient’s specific needs. Some CPAP devices deliver a fixed pressure level, while auto-adjusting models (APAP) automatically vary the pressure in response to changes in breathing. The mechanism of action remains the physical force of the air, not the gas content, that treats the underlying condition. By stabilizing the airway, CPAP eliminates the breathing pauses, or apneas, that lead to sleep fragmentation.
When Supplemental Oxygen Is Used
While a standard CPAP machine does not enrich the air with oxygen, supplemental oxygen is required in specific circumstances. Physicians may prescribe oxygen therapy in addition to CPAP for patients who have co-existing medical conditions that cause low blood oxygen levels, a state known as hypoxemia. These conditions include chronic obstructive pulmonary disease (COPD), central sleep apnea, or severe cardiovascular diseases.
In combination therapy scenarios, the oxygen is delivered from a separate source, such as a concentrator or tank, and integrated into the CPAP system. This integration is typically achieved using a “bleed-in” adaptor, a small connector that fits between the CPAP hose and the machine. This adapter has a port where the oxygen tubing attaches, allowing the pure oxygen to blend with the pressurized room air before it reaches the mask.
Some modern CPAP masks and heated hoses feature a built-in oxygen port, which simplifies the connection process. The combined approach ensures the patient receives both the pressurized air needed to maintain an open airway and the increased concentration of oxygen required to elevate blood oxygen saturation. Oxygen delivery is a separate, physician-prescribed treatment, and the flow rate must be set precisely to address the patient’s specific respiratory requirements.