Obstructive sleep apnea (OSA) is a syndrome characterized by intermittent dynamic obstruction of the upper airways that causes a fall in oxygen saturation, reflex sympathetic activation and sleep micro-arousals. In surgical patients, OSA is a well-known risk factor for perioperative complications. At Institut Universitaire de cardiologie et de Pneumologie de Quebec (IUCPQ), the investigators perform more than 450 bariatric surgeries per year. Consequently, the identification and management of OSA in this high-risk surgical population is an essential part of practice. Actual guidelines recommend that treatment for OSA be initiated before the surgical procedure. Presently, the first line treatment for OSA is continuous positive airway pressure (CPAP) therapy delivering a fixed pressure continuously to maintain the patency of the upper airways. However the compliance to this therapy is poor. An available alternative is automatic positive airway pressure (APAP) which delivers a variable amount of pressure to prevent reduction in airflow that accompanies upper airway obstruction. The APAP delivers the lowest pressure needed to prevent upper airways collapse. APAP significantly reduces the mean level of pressure delivered in comparison to conventional treatment. Theoretically, it seems logical that applying the lowest pressure necessary would allow a better device-patient synchrony and therefore improve patient's comfort.Recent trials comparing APAP and CPAP have shown that APAP is non-inferior to CPAP in controlling obstructive events. APAP would be a valuable alternative if it was not for its excess cost. However, APAP improves compliance to treatment in two types of population: poor compliant subjects and those needing high pressure levels. The investigators know that compliance to positive pressure is poor in patients without excessive daytime sleepiness, which represents the majority of patient waiting bariatric surgery. Moreover, in patients needing levels of pressure ≥ 10 water cm (cmH20), APAP improves treatment compliance, minimises side effects and improves quality of life. The review of 180 files of OSA patients treated by CPAP who had bariatric surgery in our center in 2012 demonstrated that the majority of patients needed high level pressure. These values suggest that APAP could improve treatment compliance in apneic patients waiting for bariatric surgery because they are usually poorly symptomatic and they generally require high positive pressure level.

Inclusion Criteria:

• Obese patients with a BMI ≥ 40 kg/m2 or ≥ 35 kg/m2 with additional risk factors for cardiovascular disease and eligible for bariatric surgery;
• Laparoscopic bariatric surgery planned in 2-6 months. Procedures include biliopancreatic diversion with duodenal switch and sleeve gastrectomy;
• Recent diagnosis of obstructive sleep apnea made by a sleep study. The sleep study must be a overnight pulse oximetry showing a 3% desaturation index ≥ 25/hour or a polysomnography with a apnea + hypopnea index (AHI) ≥ 25/hour* ;
• No previous use of positive airway pressure device;
• ≥18 year old.

Exclusion Criteria:

• Severe comorbidities (respiratory, cardiac, neurologic or metabolic unstable disease);
• Central sleep apnea;
• Obesity hypoventilation syndrome;
• Planned bariatric surgery by laparotomy;
• Contraindications to positive airway pressure therapy: pneumothorax within the preceding 6 months, cerebrospinal fluid leak, cranial surgery or trauma within the last year.