Table 1.

Inclusion/exclusion criteria

Eligibility 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 PaO2 < 60 mmHg without supplemental oxygen, or a PaO2/FiO2 ratio <300, or PaCO2 > 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)

BMI Body Mass Index, CPB cardiopulmonary bypass, COPD chronic obstructive pulmonary disease, FEV ₁ forced expiratory volume in 1 s, FiO ₂ fraction of inspired oxygen, HF high-frequency, OSAS obstructive sleep apnea syndrome, PaCO ₂ arterial partial carbon dioxide pressure, PaO ₂ arterial partial oxygen pressure, TAVI transcatheter aortic valve implantation