CPAP stands for continuous positive airway pressure. It is the most popular treatment for obstructive sleep apnea (OSA). It uses air pressure generated by a machine, delivered through a tube into a mask that fits over the nose or mouth.
BiPAP refers to Bilevel or two-level positive airway pressure. Like CPAP, air is sent through a tube into a mask that fits over the nose. While CPAP generally delivers a single pressure, BiPAP delivers an inhale pressure and an exhale pressure. BiPAP is a trademark of Respironics.
Each is used for a special purpose. Historically, BiPAP was more expensive than CPAP. BiPAP is often used when CPAP is not tolerated by the user. There are new technologies that increase comfort with CPAP.
BiPAP is sometimes used in patients who have pulmonary (lung) issues, like COPD. The difference in pressures helps to eliminate extra CO2 carbon dioxide gas from the body.
CPAP and BiPAP machines look similar. The attachments are the same.