Obstructive sleep apnea (OSA) and Obesity-Hypoventilation Syndrome (OHS) are common conditions in obesity, which may influence the prognosis in patients undergoing surgery. There is a need for simple screening tools to identify such patients at high risk. The current multicenter observational study aims to investigate occurrence of OSA and OHS in obese individuals undergoing elective abdominal surgery and further address its impact on perioperative and postoperative complications.

Obstructive sleep apnea (OSA) and Obesity-Hypoventilation Syndrome (OHS) are common conditions in obesity, which may influence the prognosis in patients undergoing surgery. There is a need for simple screening tools to identify such patients at high risk. The current multicenter observational study aims to investigate occurrence of OSA and OHS in obese individuals undergoing elective abdominal surgery by using questionnaires (STOPBANG questionnaire, Berlin Questionnaire, and Epworth Sleepiness Scale) and arterial blood gases. Perioperative and 72-h postoperative complications will be documented.

Inclusion Criteria:

• Patients undergoing elective abdominal surgery
• Body-Mass-Index >=30 kg/m2
• Ability to read and speak
• Signed informed consent.

Exclusion Criteria:

• Use of diuretics
• Use of theophylline
• Use of respiratory depressing drugs
• Severe lung disease (FEV1/FVC<%50)
• Severe hearth failure (EF<%35)
• Central nervous system or muscle disease
• Untreated hypothyroidism
• Renal failure (GFR<50)
• Total parenteral nutrition more than 72 hours
• Hypokalemia
• Hyponatremia
• Hypomagnesemia
• Hypoalbuminemia
• Known sleep apnea or obesity hypoventilation syndrome
• Blood transfusion from blood bank within 72 hours prior to surgery

All consecutive obese patients undergoing elective abdominal surgery