A method is disclosed for operating a device that treats sleep disordered breathing (SDB) during successive treatment sessions where the device provides continuous positive airway pressure during sleep. The method comprises the steps of applying a constant treatment pressure during a first session (20) and deriving a sleep disorder index (SDI) (22) representative of the number of SDB episodes that occurred during the first session. If the treatment pressure should be increased based on the SDI, it is increase during a second, subsequent session (24).
