Plan of investigation:

This is an observational cohort study to determine the effect of OSA, independent of other risk factors, on postoperative vascular events. The study is conceived, designed and will be conducted, and analyzed independent to any company. There is no commercial sponsorship.

The potential study subjects will be approached by study coordinator at preoperative clinic. If the patient is interested in participating the study, he/she will be screened and consented. Undetected or untreated OSA will be established by STOP-Bang questionnaire and subsequent overnight PSG by using Apnea Link Plus which is level ( 2 ) at patient's home.The following data will be recorded: including age, gender, history of coronary artery disease, prior revascularization, cerebrovascular disease, peripheral vascular disease, critical aortic valvular stenosis, congestive heart failure, atrial fibrillation, diabetes treated with insulin or an oral diabetic drug, hypertension, hypercholesterolemia treated with drug therapy, tobacco use, renal insufficiency and the type of surgery. For all study patients, the nocturnal blood oxygen saturation will be monitored by a pulse oximeter (PULSOX 300i) for first 3 nights postoperatively.During their stay in hospital, patients will be followed daily, and outcomes will be recorded, until discharge.. ECG will be measured preoperatively and repeated on day 1 to 3 after surgery. Venous blood will be collected 6-12 hours and on the first 3 days after surgery for measuring cTnT concentration.If patient's ECG is abnormal and/or patient is positive for troponin test, treating physician will be contacted for further treatment. Patient will be contacted 30 days after surgery by phone to ascertain if they have experienced any adverse out come.

Patients Inclusion & Exclusion Criteria:

Inclusion criteria:

Ethics Committee approval and informed consent will be obtained. We plan to study patients at moderate-to-high risk for postoperative vascular complications because our data from other trials suggested that the incidence of OSA in these patients is higher than the general population. We will include patients who are:

1. adult males and females, age ≥ 45 years, undergoing elective non-cardiac surgery that is expected to require a postoperative hospital stay of more than 3 nights, and
2. at increased risk for postoperative vascular events, defined as having at least one of the following risk factors (a) high-risk surgery (intra-peritoneal, intra-thoracic or supra-inguinal vascular surgery); (b) history of ischemic heart disease; (c) history of congestive heart failure; (d) history of cerebrovascular disease (d) diabetes requiring insulin therapy (e) serum creatinine > 175 µmol/L.

Exclusion criteria:

Patients will be excluded if:

1. they have a previous diagnosis of OSA or any sleep-related breathing disorder and on treatment
2. they are unwilling or physically unavailable for PSG on any night before surgery;
3. their surgery included tonsillectomy, septoplasty, uvuloplasty, pharyngoplasty, tracheostomy, or prolonged (> 48 hrs) postoperative mechanical ventilation of the lungs is anticipated. It is because these procedures/interventions are likely to cure or at least modify the severity of OSA.

Surgical patient