The goal of this clinical trial is to compare two different types of perioperative mechanical ventilation (MV), specifically Protective Mechanical Ventilation (PMV) and MV with the lowest possible Driving Pressure (ΔP), in relation to the appearance of postoperative pulmonary complications (PPCs) in adult patients who are operated and have higher risk of PPCs.

The main questions it aims to answer are:

• Is MV with lower ΔP better than conventional PMV in preventing PPCs in patients with higher risk for PPCs?
• Does MV with lower ΔP decrease hospital stay, Intensive Care Unit (ICU) need and mortality?
• Does MV with lower ΔP suit better than PMV to lung characteristics and needs intraoperatively?

Researchers will compare MV with the lowest possible Driving Pressure (ΔP) to Protective Mechanical Ventilation (PMV) to see if any of this is more protective than the other concerning PPCs.

All participants will receive perioperative MV.

Half of them will receive conventional Protective Mechanical Ventilation (PMV). This will include well known generally protective settings for mechanical ventilation of patients, concerning volumes, pressures, respiratory rate, inspiratory gases and ventilation maneuvers.

The rest of participants will be ventilated with the lowest possible Driving Pressure (ΔP). This will be similar to PMV in the chosen volumes, respiratory rate, inspiratory gases and ventilation maneuvers. However, the pressure inside lung at the end of expiration, eg Positive End Expiratory Pressure (PEEP), will be not be preset for every patient. Initially, the investigators will perform a maneuver that will quantify each individual's lung characteristics and mechanics. According to this, the investigators will find the exact PEEP that seems to suit each patients lungs most, and use this perioperatively, trying to provide lungs the best conditions every time.

After the completion of the operation, all the patients will be screened for PPCs, via arterial blood testing and chest X ray, and the results will be statistically analyzed trying to find if any of the forementioned strategies of mechanical ventilation surpasses the other concerning PPCs appearance. PPCs include atelectasis, respiratory failure, bronchospasm, pleural effusion, pneumonia, aspiration and pneumothorax.

Furthermore hospital stay, ICU need and mortality will be noted. Finally, measurements of perioperative lung pressures, volumes and derived variables will be noted and compared statistically as well.

Inclusion Criteria

• >17 years old
• Surgery with general anesthesia & invasive mechanical ventilation
• Preoperative ARISCAT score estimation >25

Exclusion Criteria:

• <18 years old
• Preoperative ARISCAT score estimation <26
• Women during pregnancy or just given birth
• Other type of anesthesia (Not general)
• Contraindication of administration of neuromuscular blockade agents.
• Contraindication of cease of spontaneous ventilation.
• Mechanical ventilation without endotracheal intubation.
• Severe heart failure / Severe cardiac arrhythmia.
• Severe emphysematous lung disease.
• Patient denial of participation in the trial.

Excel file per patient containing all the collected data Preoperatively; Patient demographics, ARISCAT score Perioperatively; Mechanical ventilation settings and measurements. Type and duration of operation. Anesthetic methods. Aerial blood gases results. Data from haemodynamic monitoring. Quantity of crystalloids , vasoperessors and inotropes.

Postoperatively; Arterial blood gases results in PACU, Potential presence of other postoperative pulmonary complications.

Statistic analysis of the collected data

Beginning at the end of data collection, possibly August 2027. Ending 3 years after publication of results.

Reviewers. Researchers of relevant subjects. Anesthesiologists with interest in optimum mechanical ventilation.

A request via email will be initially needed. A data sharing agreement will be needed to be signed.