During One-lung ventilation, the use of lower tidal volumes (VT) is helpful to avoid over-distension, provide sufficient oxygenation, but can result in increased atelectasis.

Nevertheless, it is not known if, during one-lung ventilation with constant low VT, moderate levels of PEEP combined with lung recruitment maneuvers are superior to variable low tidal volume for intraoperative oxygenation and protection against PPCs.

Aim of the study is to compare a strategy using constant tidal volume with recruitment maneuvers versus variable tidal volume with recruitment maneuvers during thoracic surgery in adults.

We hypothesize that in adult, non-obese patients undergoing thoracic surgery under standardized OLV with variable tidal volumes, modearte PEEP and recruitment maneuvers as compared to constant without recruitment maneuvers prevent PPCs.

Patients will be randomly assigned to one of two groups:

FIX TIDAL VOLUME GROUP (Groupfix): mechanical ventilation with constant (6 ml/kgIBW) tidal volume and PEEP of 5 cmH2O with recruitment maneuvers

VARIABLE TIDAL VOLUME GROUP (Groupvar): mechanical ventilation with variable (6 ml/kgIBW ± 33%) tidal volume with variable respiratory rate to maintain constant minute ventilation and PEEP of 5 cmH2O with recruitment maneuvers.

Lung separation will be performed by DLT technique. Mechanical ventilation will be applied in volume-controlled mode. During two-lung ventilation, VT will be set at 8 mL/kg predicted body weight. During one-lung ventilation, in GroupFix VT will be decreased to 6 mL/kg PBW with 5 cmH2O PEEP.

In GroupVar VT will be 6 ml/kg predicted body weight ±33% with 5 cmH2O PEEP. Respiratory rate will be adjusted to maintain same minute ventilation as during two-lung ventilation.

Inclusion Criteria:

• Patient scheduled for open thoracic or video-assisted thoracoscopic surgery under general anesthesia requiring OLV (no emergency surgery)
• BMI < 35 kg/m2
• Age ≥ 18 years
• Expected duration of surgery > 60 min
• Expected duration of anesthesia > 90 min

Exclusion Criteria:

• COPD GOLD 3+4, lung fibrosis, documented bullae, severe emphysema, pneumothorax
• uncontrolled asthma
• NYHA 3+4, CCS 3+4
• previous thoracic surgery
• ARDS (Berlin definition)
• documented pulmonary arterial hypertension > 40 mmHg syst
• documented or suspected neuromuscular disease (thymoma, myasthenia)
• planned mechanical ventilation after surgery
• bilateral procedures
• lung separation with other method than DLT (eg diff. airway, tracheostomy)
• surgery in prone position
• persistent hemodynamic instability, intractable shock
• intracranial injury or tumor
• enrollment in other interventional study or refusal of informed consent
• pregnancy (excluded by anamnesis and/or laboratory analysis)