Our main objective is to perform an explanatory, first stage proof of concept, randomized controlled trial to determine whether a semi-upright patient position versus a supine position while asleep in the postoperative period helps decrease the worsening of AHI in patients diagnosed with OSA and compare this to usual care (i.e. supine patient positioning while asleep).

The investigators will evaluate whether a semi-upright position reduces: worsening of AHI (as measured with a portable PSG) on the second postoperative night (POD2); oxygen desaturation index (using a portable oxygen saturation monitor, oxygen desaturation defined as >4% change below baseline lasting for 10 seconds); REM sleep related change in AHI at baseline and POD2.; major and minor perioperative complications on postoperative day POD1, POD2, at discharge and POD 30.; length of hospital stay and readmission within 30 days; and patient satisfaction score on POD30

The proposed study is to determine whether patient positioning in supine or semi-sitting position can effectively control the worsening of OSA see in the postoperative period.

The study patient will be randomized to semi-sitting position (45 degrees incline) group or supine (0 degrees incline) group. Patients will undergo a portable sleep study on the first or second postoperative night. They will also be monitored with wristwatch oximeter pre and postoperatively according to the study protocol. Patients will be managed according to the routine care determined by the health care team. There will be no change in the clinical management of patients.

Inclusion Criteria:

• Adult patients (18 years and above),
• ASA physical status I to IV,
• Undergoing elective inpatient surgery with obstructive sleep apnea (as determined by initial screening using STOP-Bang questionnaire and if at high risk (>3 points),
• Confirmed by an Apnea-hypopnea index (AHI) >5 using a diagnostic home portable polysomnography)

Exclusion Criteria:

• Patients previously diagnosed as OSA and on continuous positive airway pressure (CPAP) device;
• Known cervical, shoulder, spine abnormalities, and/or chronic pain predisposing to difficulty in maintaining a sitting position; or
• Previous intervention for OSA (e.g., uvulopalatopharyngoplasty, bariatric surgery); where sitting position is contraindicated postoperatively such as hip or spine surgery, hemodynamic instability; ambulatory surgery i.e. planned discharge on the same day of surgery.