BACKGROUND: Extracorporeal cardiopulmonary resuscitation (ECPR), has demonstrated promise in the management of refractory out-of-hospital cardiac arrest (OHCA). However, evidence from observational studies and clinical trials are conflicting and the factors influencing outcome have not been well established. METHODS: We conducted a systematic review and meta-analysis summarizing the association between pre-ECPR prognostic factors and likelihood of good functional outcome among adult patients requiring ECPR for OHCA. We searched Medline and Embase databases from inception to February 28, 2023 and screened studies with two independent reviewers. We performed meta-analyses of unadjusted and adjusted odds ratios, adjusted hazard ratios and mean differences separately. We assessed risk of bias using the QUIPS tool and certainty of evidence using the GRADE approach. FINDINGS: We included 29 observational and randomized studies involving 7,397 patients. Factors with moderate or high certainty of association with increased survival with favourable functional outcome include pre-arrest patient factors, such as younger age (odds ratio (OR) 2.13, 95% CI 1.52 to 2.99) and female sex (OR 1.37, 95% CI 1.11 to 1.70), as well as intra-arrest factors, such as shockable rhythm (OR 2.79, 95% CI 2.04 to 3.80), witnessed arrest (OR 1.68 (95% CI 1.16 to 2.42), bystander CPR (OR 1.55, 95% CI 1.19 to 2.01), return of spontaneous circulation (OR 2.81, 95% CI 2.19 to 3.61) and shorter time to cannulation (OR 1.14, 95% CI 1.17 to 1.69 per 10 minutes). INTERPRETATION: The findings of this review confirm several clinical concepts wellestablished in the cardiac arrest literature and their applicability to the patient for whom ECPR is considered - that is, the impact of pre-existing patient factors, the benefit of timely and effective CPR, as well as the prognostic importance of minimizing low-flow time. We advocate for the thoughtful consideration of these prognostic factors as part of a risk stratification framework when evaluating a patient's potential candidacy for ECPR.

Adult Intensive Care Services and Critical Care Research Group The Prince Charles Hospital Brisbane Queensland Australia; Faculty of Medicine University of Queensland Brisbane and Bond University Gold Coast Queensland Australia

Australian and New Zealand Intensive Care Research Centre Monash University Melbourne Australia

Department of Cardiothoracic Surgery Maastricht University Medical Centre and Cardiovascular Research Institute Maastricht Maastricht the Netherlands

Department of Intensive Care Maastricht University Medical Centre Maastricht the Netherlands

Department of Medicine Department of Cardiovascular Medicine 1st Faculty of Medicine Charles University Prague and General University Hospital Prague Czech Republic; 1st Faculty of Medicine Charles University Prague Czech Republic

Department of Medicine Division of Critical Care McMaster University Hamilton ON Canada; Department of Health Research Methods Evidence and Impact McMaster University Hamilton ON Canada

Department of Medicine Division of Critical Care Medicine University of British Columbia Vancouver BC Canada

Department of Medicine Division of Pulmonary and Critical Care Medicine Johns Hopkins University School of Medicine Baltimore MD USA

Departments of Emergency Medicine and Cardiothoracic Surgery University of Utah Health Salt Lake City UT USA

Division of Cardiology and Center for Resuscitation Medicine University of Minnesota School of Medicine Minneapolis MN USA

Division of Critical Care Department of Medicine University of Ottawa Ottawa ON Canada; Clinical Epidemiology Program Ottawa Hospital Research Institute Ottawa ON Canada; Department of Critical Care Lakeridge Health Corporation Oshawa ON Canada

Division of Critical Care Department of Medicine University of Ottawa Ottawa ON Canada; Clinical Epidemiology Program Ottawa Hospital Research Institute Ottawa ON Canada; Department of Surgery University of Ottawa Ottawa ON Canada

Institute of Anesthesiology and Intensive Care Medicine Università Cattolica del Sacro Cuore Rome Italy; Department of Intensive Care Emergency Medicine and Anesthesiology Fondazione Policlinico Universitario Agostino Gemelli IRCCS Rome Italy

Interdepartmental Division of Critical Care Medicine University of Toronto Toronto ON Canada

Interdepartmental Division of Critical Care Medicine University of Toronto Toronto ON Canada; Institute of Health Policy Management and Evaluation Dalla Lana School of Public Health University of Toronto Toronto ON Canada

Interdepartmental Division of Critical Care Medicine University of Toronto Toronto ON Canada; Toronto General Hospital Research Institute University Health Network Toronto ON Canada; Institute of Health Policy Management and Evaluation Dalla Lana School of Public Health University of Toronto Toronto ON Canada

Royal Brompton and Harefield Hospitals London UK; National Heart and Lung Institute Imperial College London UK

Sorbonne Université Institute of Cardiometabolism and Nutrition Paris France; Service de Médecine Intensive Réanimation Hôpitaux Universitaires Pitié Salpêtrière Assistance Publique Hôpitaux de Paris Institut de Cardiologie Paris France

Warwick Clinical Trials Unit Warwick Medical School Warwick University Gibbet Hill Coventry UK; Department of Anaesthesia and Intensive Care Medicine Royal United Hospital Bath UK

Yong Loo Lin School of Medicine National University of Singapore Singapore Singapore

Yong Loo Lin School of Medicine National University of Singapore Singapore Singapore; Cardiothoracic Intensive Care Unit National University Heart Centre National University Hospital Singapore Singapore

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