Objective of the study: To determine whether Perioperative Auto-CPAP treatment prevent postoperative worsening of OSA and improve nocturnal oxygen saturation in surgical patients with moderate and severe OSA.

The patients will be approached by the study coordinators at the preoperative clinic. If the patient is interested in participating the study, STOP-Bang and Epworth questionnaires will be implemented to determine the risk for OSA.If the patients are classified as high risk of having OSA, they are scheduled for an overnight sleep study at home. The patients with Apnea-Hypopnea Index (AHI)>15 from the sleep study will be randomized into two study groups: Perioperative CPAP group or control group (routine care). In the perioperative CPAP group, patients will be treated with auto-CPAP for 2-3 nights preoperatively and 5 nights postoperatively. All patients will undergo sleep study on the third postoperative night and be monitored by a pulse oximeter for 2-3 nights preoperatively and 5 nights postoperatively.

Inclusion Criteria:

the patients who meet the following criteria will be recruited

• Patients who are scheduled for inpatient surgery that required a minimum of three nights of hospital stay
• Age: >18 and <80 years old.
• Identified as high risk of having OSA or diagnosed with OSA without using CPAP.

Exclusion Criteria:

• Undergoing nasal, eye, head/neck surgery, intracranial or cardiac/thoracic surgery.
• Unwilling or unable to give informed consent.
• Currently undergoing treatment for sleep apnea including CPAP.
• Requiring prolonged postoperative ventilation.
• New York Heart Association functional class III and IV.
• Having valvular heart disease, dilated cardiomyopathy, implanted cardiac pacemaker, or unstable angina.
• Having myocardial infarction or cardiac surgery within 3 months.
• Having chronic obstructive pulmonary disease, or asthma.
• Having a presence of tracheostomy, facial, neck, or chest wall abnormalities.
• Having abdominal aortic aneurysm surgery, chemotherapy, or immunosuppressive therapy within 3 months.
• Visiting preoperative clinic less than 3 days before scheduled surgery date.
• On nasogastric tube postoperatively.