This secondary analysis aims to identify factors associated with the development of postoperative pulmonary complications (PPCs) in patients undergoing abdominal surgery, pooling and analyzing the data of two worldwide prospective studies, the 'Epidemiology, Practice of Ventilation and Outcome for Patients at Increased Risk of Postoperative Pulmonary Complications' (LAS VEGAS, NCT01601223) and the 'Assessment of Ventilatory management during general AnesThesia for Robotic surgery and its effects on postoperative pulmonary complications' (AVATaR, NCT02989415).

The primary aim is to compare the incidence of PPCs between patients undergoing non-robotic surgery versus patients undergoing robot-assisted surgery. One secondary aim is to determine which factors are associated with the occurrence of PPCs. The investigators hypothesize that differences in the occurrence of PPCs between the two surgery groups are more driven by differences in duration of anesthesia than by the intensity of ventilation.

This study involves a preplanned analysis of a merged database comprising individual patient data from two global observational studies on ventilation and postoperative pulmonary complications (PPCs). Both study protocols, the LAS VEGAS and AVATaR were approved by a central Institutional Review Board and local ethics committees, with written informed consent obtained as per local legislation. The pooled database, including modifications for patient categories, does not require additional ethical approval or informed consent. The analysis will adhere to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement.

Patients:

• The LAS VEGAS study includes patients undergoing general anesthesia with invasive ventilation for elective and non-elective surgeries.
• The AVATaR study includes patients aged over 18 undergoing robot-assisted surgery (RAS) for abdominal procedures.

Baseline Patient Characteristics:

- Key variables extracted from LAS VEGAS and AVATaR include demographic data, smoking status, comorbidities (chronic heart disease, obstructed sleep apnea syndrome, anemia, chronic kidney disease), and details about anesthesia and surgery.

Ventilation Variables:

• Ventilation-related variables extracted from the database include inspiratory pressure, plateau pressure, positive end-expiratory pressure, tidal volume, respiratory rate, fraction of inspired oxygen, peripheral oxygen saturation, end-tidal carbon dioxide.
• Mode of ventilation is classified as volume-controlled, pressure-controlled (including volume-guarantee pressure-controlled), and others.

Intensity of mechanical ventilation will be studied by three different estimators: the driving pressure, driving pressure multiplied by four plus respiratory rate and mechanical power.

For the statistical analysis medians with interquartile ranges, or as number with percentages, will be used as appropriate. Differences between the two groups of patients will be analyzes by Fisher or Wilcoxon test as appropriate. Key variables will be plotted by the cumulative distribution plots.

Numbers of available patients who meet inclusion criteria will represent our cohort of patients. The investigators estimated a 10 % of drop off for additional exclusion criteria. For this reason the enrollment of patients cannot be actual but just anticipated. The main analysis will be an univariable followed by a multivariable model including known risk factors for PPCs, intensity of ventilation and group (laparoscopic versus robotic surgery), covariates will be entered in the model. Logistic regression analysis will be performed for studying the association between PPCs and intensity of ventilation and duration of anesthesia. In case of relevant co-linearity of independent variables, separate models will be built excluding co-linear variables and the performances of the different models will be assessed using the corrected Akaike information criterion. In case of an association between RAS and PPCs: a mediation analysis to investigate the relationship between PPC and surgical approach will be conducted. In addition a matched-cohort analysis in patients with similar length of mechanical ventilation and intensity of ventilation will be performed. The mediation analysis will be reported according to the "A Guideline for Reporting Mediation Analyses" (AGReMA) statement. R Project for Statistical Computing will be used for analyzing data.

The analysis aims to compare incidences of PPCs after laparoscopic non-robotic and RAS abdominal surgeries, exploring associations with patient, surgery, and anesthesia factors.

Inclusion Criteria:

• All adult patients receiving invasive ventilation (via either an endotracheal tube or supraglottic device) during general anaesthesia for elective or non-elective surgery.

Exclusion Criteria:

• patients not undergoing laparoscopic surgery in LAS VEGAS, and not undergoing abdominal RAS in AVATaR;
• patients undergoing combined thoracic-laparoscopic surgery and patients in whom the intervention was converted from laparoscopic or RAS to open surgery are excluded;
• patients that received recent ventilation before surgery;
• patients with incomplete ventilation datasets not allowing the computation of intensity of ventilation, and patients with an incomplete follow-up for PPCs are also excluded.

Surgical patients receiving invasive mechanical ventilation for laparoscopic or robot-assisted laparoscopic surgery