Before induction of anesthesia, an epidural catheter and an arterial canula for invasive blood pressure monitoring will be inserted. Immediately after induction of anesthesia and orotracheal intubation, all patients will be submitted to an alveolar recruitment maneuver (ARM) using the sustained airway pressure by the CPAP method, applying 30 cmH2O PEEP for 30 seconds. After ARM PEEP will be set to 6 cmH2O in the control group ("standard PEEP") and LPV will be performed. In the study group ("optimal PEEP") PEEP will be set to 14 cmH2O and a Cstat directed decremental PEEP titration procedure will be performed (every 4 minutes PEEP will be decreased by 2 cmH2O, until a final PEEP of 6 cmH2O) to determine the best individual PEEP. During surgery ARM will be repeated and arterial and central vein blood gas samples (ABGs, CVBGs) will be evaluated every 60 minutes. PCT levels will be measured 2, 6, 12, 24, 48 and 72 hours after surgical incision.