Intraoperative protective ventilation with low tidal volumes (TV), positive end-expiratory pressure (PEEP) and possibly lung recruitment maneuvers (RMs) reduces postoperative pulmonary complications. In thoracic surgery, in one-lung ventilation (OLV), the evidence is lacking. However, in this context protective ventilation with PEEP titration is related to better intraoperative oxygenation and respiratory mechanics. It is not clear whether this strategy is associated also with better postoperative oxygenation and less postoperative pulmonary complications.

In this randomized controlled trial the investigators will enroll 42 patients scheduled for elective thoracic surgery (minithoracotomic or video-assisted thoracoscopic segmentectomies and lobectomies). Patients will be randomized in two groups: BEST PEEP and STANDARD PEEP. In OLV the investigator will set a TV = 5ml/kg IBW in volume control ventilation (VCV) and an adequate respiratory rate (RR) to keep PaCO2 < 60 mmHg. With the patient in lateral decubitus and open chest, a cycling step RM (in pressure control ventilation, RR =10/min, I:E=1:1, up to Paw = 40 cmH20 with a PEEP = 20 cmH2O, lasting 2.5 minutes) and a PEEP decremental titration trial (in VCV, from 16 to 4 cmH2O) will be performed to all patients. Then, after another RM, in STANDARD PEEP group a PEEP of 5 cmH2O will be set, and in BEST PEEP group an individualized PEEP (the one corresponding to the lower driving pressure, +2 cmH2O) will be applied till the end of surgery. A blood gas analysis will be performed before surgery, with the patient in supine position breathing room air (T1). The respiratory mechanics (Ppeak, Pplateau, PEEP, driving pressure) and blood gas (PaO2, PaCO2, pH, HCO3, lactates) parameters will be then collected at the following time points: T2 - 5 minutes after induction, patient supine, two lung ventilation; T3 - lateral decubitus, chest open, OLV, before RM; T4 - 10 minutes after second RM; T5, 6, 7 - every hour after T4; T8 - at the end of OLV, before lung re-expansion; T9 - patient supine, two lung ventilation, before neuromuscular block reversal. Postoperatively all patients will spend at least one hour in a Recovery Room, in oxygen-therapy through a Venturi mask with FiO2 = 60%. A blood gas analysis and data about pain (NRS scale 0-10) and sedation (Ramsey score) will be collected at 1 hour postoperatively (T10). The primary outcome of the study is intra- and postoperative oxygenation and secondary outcomes are intraoperative respiratory mechanics parameters.

Inclusion criteria:

• Patient's consent to the trial
• Candidate to elective lung lobectomy or segmentectomy (minimally invasive thoracotomy or video-assisted thoracoscopy)
• ASA class 1-3
• BMI < 30 kg/m2

Exclusion criteria:

• Pregnancy
• Previous pneumothorax,
• Emphysematous bullae
• Severe COPD
• METs < 4 due to cardiac disease