CPAP is generally the initial treatment for obstructive sleep apnea, but it is not the only type of positive airway pressure (PAP) device. Other PAP devices use different methods to help keep the airway open. CPAP: CPAP therapy uses a steady, constant amount of air pressure. That pressure level does not change when inhaling and exhaling.  Bilevel positive airway pressure (BiPAP): Unlike CPAP, BiPAP utilizes two pressure levels. With a BiPAP, air pressure levels are higher when inhaling and lower when exhaling.  Autotitrating or adjustable positive airway pressure (APAP): APAP, also called auto-CPAP, machines adapt to the user's breathing patterns, adjusting pressure as needed throughout the night.  Doctors may prescribe BiPAP or APAP machines for people who find CPAP treatment uncomfortable or have other specific needs that are best met with another type of PAP