Postoperative respiratory failure, particularly after surgery under general anesthesia, adds to the morbidity and mortality of surgical patients. Anesthesiologists inconsistently use positive end-expiratory pressure (PEEP) and recruitment maneuvers in the hope that this may improve oxygenation and protect against postoperative pulmonary complications (PPCs), especially in obese patients. While anesthesiologists tend to use PEEP higher than in non-obese patients. While it is uncertain whether a strategy that uses higher levels of PEEP with recruitment maneuvers truly prevents PPCs in these patients, use of higher levels of PEEP with recruitment maneuvers could compromise intra-operative hemodynamics.

The investigators aim to compare a ventilation strategy using higher levels of PEEP with recruitment maneuvers with one using lower levels of PEEP without recruitment maneuvers in obese patients at an intermediate-to-high risk for PPCs.

We hypothesize that an intra-operative ventilation strategy using higher levels of PEEP and recruitment maneuvers, as compared to ventilation with lower levels of PEEP without recruitment maneuvers, prevents PPCs in obese patients at an intermediate-to-high risk for PPC.

Inclusion Criteria:

• Patient scheduled for open or laparoscopic surgery under general anesthesia
• Intermediate-to-high risk for PPCs following surgery, according to the ARISCAT risk score (≥ 26)
• BMI ≥ 35 kg/m2
• Expected duration of surgery ≥ 2 h

Exclusion Criteria:

• Age < 18 years
• Previous lung surgery (any)
• Persistent hemodynamic instability, intractable shock (considered hemodynamically unsuitable for the study by the patient's managing physician)
• History of previous severe chronic obstructive pulmonary disease (COPD) (non-invasive ventilation and/or oxygen therapy at home, repeated systemic corticosteroid therapy for acute exacerbations of COPD)
• Recent immunosuppressive medication (patients receiving chemotherapy or radiation therapy up to two months prior to surgery)
• Severe cardiac disease (New York Heart Association class III or IV, acute coronary syndrome or persistent ventricular tachyarrhythmias)
• Invasive mechanical ventilation longer than 30 minutes (e.g., general anesthesia for surgery) within last 30 days
• Pregnancy (excluded by anamneses and/or laboratory analysis)
• Prevalent acute respiratory distress syndrome expected to require prolonged postoperative mechanical ventilation
• Severe pulmonary arterial hypertension, defined as systolic pulmonary artery pressure > 40 mmHg
• Intracranial injury or tumor
• Neuromuscular disease (any)
• Need for intraoperative prone or lateral decubitus position
• Need for one-lung ventilation
• Cardiac surgery
• Neurosurgery
• Planned reintubation following surgery
• Enrolled in other interventional study or refusal of informed consent