Oral unintentional leak is a common side effect of continuous positive airway pressure (CPAP) for obstructive sleep apnea (OSA) treatment. Management of oral unintentional leakage has not been standardized and the effectiveness of potential approaches have not been studied in controlled studies. Higher levels of CPAP are associated with higher leak. In the present study, a sequential approach to control excessive unintentional leak will be tested. In study A, the reduction of therapeutic CPAP level will be tested. In study B, oronasal CPAP will be compared to nasal CPAP with a chinstrap.

Study A will consist of a cross-over controlled randomized trial to compare unintentional leak during auto-CPAP and during fixed CPAP after the progressive reduction of fixed CPAP, starting at the 90 th percentile obtained during a period of auto-CPAP. The order of interventions will be randomized. Auto-CPAP with a nasal mask will be used for 7 days. In the fixed CPAP arm, CPAP will be progressively reduced over a period of up to 21 days until leak is controlled or residual apnea-hypopnea index increases over 10 events/h. Subjects that persisted with excessive leak at the end of the Study A will be invited to Study B.

Inclusion Criteria:

• Diagnosis of moderate and severe obstructive sleep apnea;
• Use of CPAP with a nasal mask;
• 95th percentile of unintentional leak from the last 7 days above 24 l/min or at least 4 sudden leak line drop events

Exclusion Criteria:

• Patients who experience unintentional leakage from the mask/accessories.
• Diagnostic polysomnography examination with a predominance of central apnea;
• Patients with unstable heart disease, bedridden, neurodegenerative diseases, severe psychiatric disorders and COPD;
• Previous surgery for obstructive sleep apnea;
• Severe nasal obstruction (NOSE questionnaire score equal or greater then 55 points).

CPAP device screen is taped to hide CPAP level and mode