The investigators propose to compare two different treatments, continuous positive airway pressure (CPAP) versus breathing of atmospheric pressure, in subjects with obstructive sleep apnea (OSA)recovering from weight loss surgery in the post anesthesia care unit (PACU). WE hypothesize that subjects with OSA will have a higher Apnea-Hypopnea Index (AHI) with desaturation and the investigators expect that post-operative CPAP treatment in the PACU will significantly improve the AHI and therefore improve patient safety in the PACU. The investigators also hypothesize that subjects with OSA have a greater decrease in oxygen saturation in response to opioid administration by patient-controlled opioid analgesia (PCA).

Patients with morbid obesity have an approximately 60-80 percent incidence of OSA depending on the criteria used for making diagnosis, and they are suggested to be at increased risk to develop serious perioperative complications, especially during the postoperative period. Weight loss might be considered as an appropriate treatment of OSA but in turn it has recently been reported that OSA is an independent risk factor for development of perioperative complications, importantly oxygen desaturation, in patients undergoing weight loss surgery. It seems logical to evaluate if these patients would benefit from post-operative CPAP treatment in the PACU. The results of this multidisciplinary study will have an impact on PACU treatment of patients with OSA and will further optimize patient care at MGH.

Inclusion Criteria:

• patients scheduled for weight loss surgery at Massachusetts General Hospital
• Male and female subjects
• age ≥ 18 years

Exclusion Criteria:

• CNS disease with impairment of cognitive function and/or muscle paresis such as stroke, or dementia
• age < 18 years
• missing or insufficient PSG data to make diagnosis OSA
• impaired decision making capacity