Detailed Description:

Adult obese (body mass index ≥ 30 kg/m2) patients undergoing invasive mechanical ventilation for laparoscopic or robotic surgery with pneumoperitoneum will be enrolled, upon the acquisition of informed consent. Will be excluded all the patients with the following conditions: American society of anesthesiologists (ASA) score ≥ 4; severe cardiopathy, intracranial hypertension, tracheostomy, previous cardio-thoracic surgery, pulmonary hypertension, broncho-pleural fistula, pulmonary emphysema, pneumothorax, chronic respiratory failure, chronic obstructive pulmonary disease, pregnancy. Thereafter, general anesthesia will be induced, according to current clinical practice and mechanical ventilation will be commenced according to current recommendations. Following the application of definitive pneumoeritoneum and body position, the recruitment/inflation procedure will be carried out to identify PEEP. PEEP-induced recruitment will be computed with high PEEP set at 15 cmh2o (or higher) and low PEEP set at 5 cmh2o. In case of an airway opening pressure > 5 cmh2o, the airway opening pressure (AOP) will be set as low PEEP and the high PEEP will be set at the value corresponding to AOP+ 10 cmh20. During the procedure, tidal volume will be maintained between 6-8 ml/kg of predicted body weight. On the basis of the recruitment-to-inflation ratio (R/I), PEEP will be set as follows: low PEEP, in presence of R/I < 0,5; high PEEP with R/I ≥ 1.5; PEEP set within low and high PEEP range on clinical decision, if R/I ≥ 0.5 and <1.5. After 20 min from the onset of mechanical ventilation and 1 hour from PEEP application following pneumoperitoneum and definitive body position, mechanics of the respiratory system for compliance and driving pressure will be assessed. As an optional evaluation, a lung ultrasound examination will be performed before general anesthesia induction and 1 hour after extubation, before discharging the patient from recovery room. During anesthesia vital signs will be continuously monitored. On the clinically judgement, arterial blood gases will be carried out across the study stages.}}