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.