Role of Lung Ultrasound Imaging for Intraoperative Monitoring of Atelectasis During Laparoscopic Surgery

General anesthesia results in the development of atelectasis in the dependent areas of the lungs exposing patients to an increased risk of hypoxemia. During laparoscopic procedures, pneumoperitoneum increases already present atelectasis. Several methods have been suggested to reduce the impact of atelectasis during surgery. However, few intraoperative modalities for the diagnosis and monitoring of atelectasis are available. Lung ultrasound imaging is a promising non-invasive, non-radiant, portable and easy to use tool that as yet to be studied in the intraoperative setting. This observational study will aim to clarify the role of lung ultrasound imaging during laparoscopic surgery for the diagnostic and monitoring of atelectasis. This study is designed to: * Demonstrate a link between the lung ultrasound aeration score, the partial pressure of oxygen in arterial blood (PaO2) / fraction of inspired oxygen (FiO2) ratio and the oxygenation index. * In the event of intraoperative desaturation, study the impact of positive end-expiratory pressure (PEEP) and/or increase of FiO2 on the aeration score. * Study the impact of pain on diaphragmatic function and the aeration score. Our hypothesis is that lung ultrasound imaging allows detection of lung aeration changes associated with induction of general anesthesia, pneumoperitoneum, emergence from anesthesia and changes occurring during the stay in the recovery room.