Optimal annual hospital volume for open surgical repairs for abdominal aortic aneurysms: a protocol of systematic review and dose-response meta-analysis

Introduction: Centralization of open surgical repairs for abdominal aortic aneurysms (AAA) has been advocated to improve patient outcomes and reduce healthcare costs. To promote centralization, it is essential to establish an evidence-based optimal threshold for annual number of procedures performed at each hospital. This review aims to conduct a dose-response meta-analysis to determine the optimal annual hospital volume for open AAA repairs. Methods and analysis: This protocol was developed in accordance with the 2015 Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines. We will include all prospective or retrospective cohort studies evaluating a volume-outcome relationship in open AAA repairs, provided they report at least two distinct hospital volumes. Studies reporting only a single hospital volume or focusing solely on surgeon-specific volumes will be excluded. Relevant studies will be searched in PubMed, EMBASE, Cochrane Library, and Web of Science from inception to 13 August 2025, without language restrictions. Three authors will independently screen and select eligible studies, extract relevant data, and assess the risk of bias. The primary outcome is short-term mortality, defined as in-hospital and/or 30-day mortality, analyzed in relation to annual hospital volume through both dose-response and pairwise meta-analyses. A dose-response meta-analysis will be performed for studies reporting three or more categories of annual hospital volume. For pairwise meta-analysis, studies with two comparison groups will be analyzed directly, whereas studies with three or more comparison groups will be converted into binary comparisons. The certainty of evidence for each outcome will be assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach and the Core GRADE approach. Ethics and dissemination: As this study will be based solely on previously published data, ethics approval is not required. The findings will be disseminated through publication in a peer-reviewed journal. PROSPERO registration number: CRD420251121357