A Continuous Positive Airway Pressure (CPAP) machine is often confused with a device that provides supplemental oxygen, but the two are not the same. A CPAP machine delivers pressurized air drawn directly from the room. Its function is mechanical support for the airway structure, not altering the gas composition or increasing the concentration of oxygen in the air you breathe.
CPAP Delivers Air Pressure, Not Oxygen
The fundamental principle of CPAP therapy is the physical splinting of the upper airway using air pressure. The device uses a motor to draw in ambient air, which is filtered and pressurized to a physician-determined setting. This pressurized air is delivered through a mask and tube, creating an air cushion that prevents throat tissues from collapsing during sleep. This mechanism is highly effective in treating Obstructive Sleep Apnea (OSA), where breathing pauses occur due to a physical blockage.
The air moved through the CPAP system maintains the same concentration of oxygen as room air, which is approximately 21%. The continuous stream of air keeps the airway open, allowing the user’s lungs to function normally. The therapeutic action comes solely from the pressure applied, measured in centimeters of water (cmH2O).
What Supplemental Oxygen Therapy Does
Supplemental oxygen therapy is a different medical treatment focused on increasing the gas concentration inhaled by the patient. While ambient air contains about 21% oxygen, supplemental sources, such as oxygen concentrators or compressed gas tanks, deliver a much higher percentage. An oxygen concentrator filters nitrogen from room air, leaving a gas mixture that is typically 87% to 93% pure oxygen.
This therapy is prescribed to treat hypoxemia, a medical condition characterized by abnormally low blood oxygen levels. Conditions like Chronic Obstructive Pulmonary Disease (COPD) or severe heart failure impair the lungs’ ability to transfer oxygen into the bloodstream, making supplemental oxygen necessary. Unlike CPAP, which solves a mechanical problem, oxygen therapy addresses a physiological problem of gas exchange. Oxygen is delivered via a nasal cannula or a mask, and the flow is measured in liters per minute (LPM).
When Oxygen Is Added to CPAP
While CPAP and oxygen therapy are distinct, they are sometimes intentionally used together to treat complex breathing conditions. A physician may prescribe the combination for patients who have both Obstructive Sleep Apnea and an underlying chronic lung condition like COPD, a situation often referred to as Overlap Syndrome. In these cases, the patient needs the airway-opening pressure of the CPAP machine and the higher concentration of oxygen to maintain safe blood saturation levels.
To combine the two therapies, supplemental oxygen is supplied by a separate device, such as an oxygen concentrator, and is fed into the CPAP circuit. This connection is achieved using a small adaptor, known as a bleed-in connector. The connector is placed between the CPAP tubing and the machine or directly into a port on the mask, allowing the enriched oxygen to mix with the pressurized room air before reaching the patient.