Table 1 Inclusion/exclusion criteria

Inclusion criteria

• Age ≥18 years

• Ability to provide informed consent

• Elective cardiac surgery

• Surgical intervention performed with CPB, aortic cross-clamping and cardioplegic arrest

• Valvular surgery, coronary surgery, surgery on the ascending aorta, combined cardiac surgery

• Median sternotomy and bi-pulmonary ventilation

Exclusion criteria

• Patient’s refusal

• Nonelective cardiac surgery

• Previous cardiac surgery

• Anticipated circulatory arrest, aortic endoprothesis, TAVI, Mitraclip

• Thoracotomic approach, with one lung ventilation

• Patients with BMI >30 [24]

• Patients with end-stage chronic kidney disease (defined as need for dialysis)

• Patients with known respiratory diseases (ongoing respiratory infections, asthma, COPD, OSAS)

• Patients already intubated before arrival in operating theatre

• Pneumonia in the previous 30 days

• Previous pulmonary resection

• Patients with a preoperative oxygen saturation <90%, or P_aO₂ < 60 mmHg without supplemental oxygen, or a PaO₂/FiO₂ ratio <300, or P_aCO₂ > 45 mmHg

• Patients with hepatic disease, defined as elevated liver enzymes (higher than two reference intervals)

• Patients with pulmonary hypertension (defined as preoperative estimated systolic pulmonary artery pressure >45 mmHg)