INTRODUCTION The healthcare service faces sustainability issues over time, managing ageing population and growing quality care expectation, despite heavy restrictions on budgets (Dickson et al., 2009;). With the aim of satisfying the customer demand, balancing safe, reliable and affordable care with efficiency, Lean Management (LM), a methodology derived from Toyota Production System, has been increasingly adopted in many healthcare organizations, to improve the value delivered to the patient by reducing waste and inefficiencies (Radnor et al., 2012). Emergency Department (ED) revealed to be one of the most critical area, with overcrowding, process delays, high costs and patient dissatisfaction as major concerns (Bucci et al., 2016). In this regard, lean healthcare management seeks to increase ED performances, focusing on patient flow and eliminating nonvalue-added activities, with no additional resources (Holden, 2011). Literature reports a wide evidence of LM adoption in ED (Hallam and Contreras, 2018), as the pioneer department, documenting positive effects on process capacity, reactivity and efficiency, on turnaround times and length of stay, on care quality and patient safety (Mousavi Isfahani et al., 2019). Although LM in EDs has demonstrated its potential on improving healthcare management, further studies are needed to assess its effects on performance and on patient care (Borges et al., 2019; Ramori et al., 2019). In particular, there is limited empirical research evaluating how a manufacturing methodology has been adapted to the healthcare sector (Hallam and Contreras, 2018). For this reason, this study aims to analyze how LM projects have been developed in EDs, investigating the pursued objectives, the adopted tools, the performed tasks, the systematically achieved improvements and the key factors required for a successful implementation. METHODOLOGY In order to pursue the research objective, a systematic literature review has been conducted following the PRISMA Statement (Liberati et al., 2009). A bibliographic searching in Scopus, Pubmed and Web of Science databases allowed to identify 452 articles referred to the different combinations of the following keywords: "lean management", "lean thinking", "lean healthcare", "kaizen", "patient flow", "lean methodology", "lean tools", "lean techniques", associated with the Boolean operator AND to "(emergency department OR emergency room)". According to the inclusion criteria, only papers written in English language, classified as articles or reviews and coherent with subject area filter were selected for further examinations. After the exclusion of duplications, 149 articles were submitted to a title and abstract analysis, in order to preliminarily evaluate their consistency to the investigation question, eliminating 81 documents not referring to ED as the application context or to LM as the main managerial technique adopted. Finally, the full-text articles accessed for eligibility were reviewed in relations to their relevance and to their compliance to case study methodology inclusion criteria, excluding literature reviews, theoretical papers and articles developed in less than 3 pages. The remaining publications were screened according to the following inclusion criteria: firstly, the adequacy of project setting, eliminating papers focused on specific departments or clinical pathways, without considering the global effects on ED performances; secondly, the adoption of a structured approach in implementing LM, with a developed methodology comprehensive of an adequate description of the followed tasks and a proper tools application; lastly, the objectives coherence between literature research and the case study analyzed. Finally, 28 papers have been retained for the final database. A descriptive and content analysis have been conducted on the extracted database. RESULTS The descriptive analysis highlighted the growing diffusion of LM in EDs in the last five years, especially in USA, Italy, UK and Lebanon, underlining the novelty of the phenomenon. The quality of the database was assessed through the Scimago Journal Rank (SJR), revealing that the 87% of the journal papers were published in Q1 and Q2 journals. The theme was studied in medical (79%) and in engineering (13%) journals, confirming the interest of both scientific communities in its future potential development. The content analysis was performed investigating the projects developed to implement LM in ED. It focused on the motivations underlying the adoption of LM in ED, the pursued objectives, the followed methodology (organizational and managerial aspects) to set and achieve the project objectives, the applied LM tools, the obtained quantitative results and the key success factors. The literature review showed how overcrowding, inefficiency, low quality care, unsatisfied patients and high costs represent the most critical aspects afflicting ED performances. These critical issues pull the system towards an engineering reorganization process, driven by the aim of improving patient flow, efficiency and safety, reducing waiting times and wastes, to better manage patient volume and access block. Although the experiences heterogeneity highlighted the lack of a standardized methodology to adopt LM in ED, the analyzed literature provided an evidence of the healthcare managers in developing successful LM projects. The latter should be performed adopting an improvement approach founded on employee involvement, on creation of solid processes and on introduction of small cycles of changes. Based on the guidelines developed thanks to this study, other research could be performed applying the framework for developing projects in healthcare and comparing its implementation in diverse settings. Moreover, other research should be conducted in the future, for example in order to investigate statistical correlation between LM and the obtained results, but also to diffuse a system culture oriented towards kaizen. The complexity of the ED service opens up to emerging challenges that could be managed and solved through the adoption of new organizational and managerial approaches, improving the management of healthcare and the satisfaction of internal personnel and of the community in general. ACKOWLEDGEMENT The authors gratefully acknowledge the financial support from the University of Padova (VERB_SID19_01).
