Patients will receive a standardized general anesthetic and thoracal epidural anaesthesia. Ventilatory parameters will be adjusted to maintain ETCO2 35 mmHg, Paw 25 cmH2O.Patient age, gen-der, BMI, ASA classification, the duration of surgery, anesthesia, Trendelenburg position and pneumoperitoneum. Hemodynamic parameters, blood gas analyzes, ventilation parameters and EtCO₂ values will be recorded. We determined 6 timelines to compare the difference between PaCO₂ and EtCO₂. These timelines were the times where we could collect the most data regarding blood gas analyzes. Preoperative period: to, 10th minute after the first insuflation and trendelendburg position: t₁,the first hour after the first insuflation and trendelendburg position: t₂, 10th minute after desuflation and supine position: t₃, 10th minute after the second insuflation and trendelendburg position: t₄, and 10th minute after the second desuflation and supine position:t₅. Primary outcome measure is the difference between PaCO₂ and EtCO₂ a difference greater than 5 mmHg was assumed to be important.