An international team of experts is working on a project called PrECiSIOn to develop a clear, consistent definition of PPCs. The goals of this study are to:

• Define postoperative pulmonary complications in a way that makes sense for patients, families, and healthcare providers.
• Rank complications by severity so doctors can focus on the most serious ones first.
• Decide how and when to monitor patients after surgery to catch problems early.

Postoperative pulmonary complications (PPCs) are associated with prolonged hospital stays, increased mortality, and significant clinical and economic burdens. Despite their importance, the definition of PPCs varies across studies, leading to inconsistencies in reported incidence rates and research outcomes. Existing definitions, such as the EPCO criteria, have been developed based on expert opinion but lack systematic consensus-building methods.

To address these limitations, the StEP collaboration conducted a systematic review and Delphi process to refine PPC classifications. However, challenges remain, including the lack of universal definitions, hierarchical ranking of complications, and representation from diverse healthcare settings. Composite outcome measures improve statistical power but may obscure differences in severity and clinical significance among PPC subtypes.

The PrECiSIOn Delphi initiative aims to develop an expert consensus on defining PPCs, grading their severity, and determining standardized monitoring methods. The goal is to create a valid, reliable, and universally accepted patient-centered definition of PPCs that enhances comparability across studies and informs clinical decision-making.

Inclusion Criteria: Panellists will be identified based on either of the following criteria

• At least 10 years of clinical experience as a staff member in Anesthesiology, Surgery or Intensive Care Medicine with involvement in care of patients with postoperative complications
• Author of at least three publications (observational studies or randomised controlled trials) using postoperative pulmonary complications as a primary or secondary outcome For patients and public involvement Individuals who have either personally experienced PPCs following surgery within the last 5 years or, primary caregivers of such patients will be recruited as patient care representatives. Proficiency in English is required. To mitigate potential bias, patient care representatives mustn't maintain a professional or advisory relationship with the steering committee or panellists.

Exclusion Criteria

- None

To encourage the continued engagement of the panellists and help prevent them from dropping out before completing the full process, at least three personalised email reminders will be sent during each Delphi round, in addition to an effort to establish personal contact. Furthermore, all panellists will be recognised as collaborative authors in the final publication in appreciation of their professional expertise. Should the attrition rate of panellists exceed 20%, a sensitivity analysis will be conducted, considering the plausible worst-case and best-case scenarios, and taking into account the opinions of non-responders.

The IPD is available to investigators and can be shared with appropriate requests.