Patients submitted to general anesthesia and artificial ventilation almost always develop pulmonary atelectasis, which can determine adverse consequences both intraoperatively and postoperatively. It is recommended to use physiological tidal volume (6 - 8 mL / kg of ideal body weight) during the intraoperative period in order to minimize the risk of lung injury. To prevent the formation of atelectasis, minimizing the risk of complications, the use of PEEP has been recommended. At present, there is no way to make an optimal adjustment of PEEP to the needs of each patient, seeking a value that keeps the alveoli open without forming atelectasis and also without areas of hyperdistension.