Philips Respironics System One DS660 BIPAP CERTIFIED PRE OWNED Capacity 3L The mask is also available Size:Small Frame Small Cushion The mask is also available in all size kit With OPI a light on the front of the unit will turn orange and sound an alarm if oxygen levels ever deviate from acceptable purity levels Philips Respironics System One BiPAP PRO offers bi level therapy with a high pressure on inhalation and low pressure on expiration for a more natural sleep experience The result is synchronous pressure delivery and the assurance you can enjoy the full benefits of Respironics Flex comfort technologies no matter which mask is used