The goal of this interventional study is to learn about the effects of different positions on the occurrence, regional distribution and reversibility of atelectasis by using a PulmoVista 500 monitor (Dräger. 23542 Lübeck), during general anesthesia with mechanical ventilation.

The main questions it aims to answer are:

• The increase in atelectasis after induction of general anesthesia in supine and Trendelenburg position compared with baseline (spontaneous breathing)
• The eventual possibility of reversal of atelectasis caused by general anesthesia and Trendelenburg position by reverse Trendelenburg position and recruitment manœuvre.

Participants will be adult, autonomous and able to express their will, undergoing elective gynecological or urological surgery in the extended Trendelenburg position.

Inclusion Criteria:

• Adult subjects over eighteen years old;
• Requiring laparoscopic gynecological, urological or digestive surgery;
• Surgery requiring Trendelenburg position and tracheal intubation.

Exclusion Criteria:

• Emergency operation;
• Thoracic surgery;
• Pulmonary, cardiac pathology;
• Pregnant woman;
• BMI > 30;
• Comorbidities defined as an American Society of Anesthesiologists physical condition greater than 2;
• Language barrier;
• Refusal of consent.