Postoperative Respiratory Failure

In this randomized-controlled trial the investigators will examine the effect of oxygen supplementation on the recovery of breathing for 90 minutes in the immediate post-anesthesia period starting from extubation of the trachea.

I. Study Background Postoperative respiratory failure (PRF) is a common and serious complication following major surgery, significantly increasing the rates of ICU admission and mortality. Traditional early warning methods primarily rely on blood gas analysis and vital sign monitoring, which are often delayed and may fail to identify early pathological changes in a timely manner. In recent years, ventilator waveforms, as dynamic information that directly reflects respiratory mechanics and airway conditions, have gradually attracted increasing attention in the optimization of respiratory support. International studies have suggested that analysis of ventilator waveform features may help identify patient-ventilator asynchrony, excessive spontaneous respiratory effort, ventilation-perfusion mismatch, and ventilator-related complications. In China, although a limited number of studies have explored this area, most have focused on individual parameters and lack systematic and prospective clinical validation. Therefore, this study aims to establish a large prospective cohort and integrate image feature extraction with stratified diagnostic modeling to achieve early warning and risk stratification of postoperative respiratory failure. This study is expected not only to address the current gap in this field in China but also to provide evidence-based support for precision respiratory management and improved clinical outcomes.

This prospective, non-interventional observational study will evaluate the risk of reintubation in adult postoperative patients admitted to the intensive care unit after major surgery. Reintubation after extubation is an important clinical problem because it may increase complications, prolong mechanical ventilation, and extend intensive care and hospital stay. The study will include adult patients who are extubated in the operating room and admitted to the intensive care unit with spontaneous breathing. Within the first hours after ICU admission, bedside ultrasound measurements of diaphragm thickness, parasternal intercostal muscle thickness, and lung ultrasound score will be performed. The ROX index will also be calculated using oxygen saturation, inspired oxygen concentration, and respiratory rate. Perioperative fluid balance will be recorded from anesthesia and patient files. Patients will be followed for 48 to 72 hours after ICU admission to determine whether reintubation is required. The study aims to assess whether respiratory muscle ultrasound findings, lung ultrasound score, ROX index, and perioperative fluid balance can help predict reintubation risk in postoperative ICU patients. No additional treatment or intervention will be applied as part of the study, and all clinical decisions will be made by the responsible intensive care team according to routine clinical practice.

Postoperative respiratory failure (PRF) is a dreaded complication that imposes a significant burden through unplanned admission to the ICU, post discharge disability and mortality. Despite widespread implementation of intraoperative lung-protective ventilation strategies over the past decade, results remain inconsistent. Interventions targeting individual parameters like tidal volume or positive end-expiratory pressure (PEEP) have shown equivocal results. The use of high PEEP and recruitment maneuvers raises safety concerns by possible negative hemodynamic effects. Recent studies suggest that individualizing ventilation strategies based on mechanical power-a composite parameter integrating tidal volume, plateau pressure, PEEP, and ventilator frequency-may better predict and help prevent PRF, independently of patients' baseline respiratory system compliance. These studies identified this parameter as interventional targets to reduce lung injury during mechanical ventilation. However, no multicenter randomized controlled trial has been performed in the field of ventilatory settings titration during invasive mechanical ventilation in operating room. The investigators hypothesize that a ventilation strategy aimed at decreasing mechanical power will reduce the incidence of PRF and mortality in patients undergoing abdominal surgery, compared with a standard strategy using fixed tidal volume and PEEP

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.