Systematic review and meta-analysis of the use of lean methods and tools in healthcare services: an alternative to improve care during the pandemic


 Background: Lean approach has become a trend due to its credibility achieved in several sectors, including Health services having target at the care and security of patients. This paper aims to map how Lean tools are being used in healthcare and what are their results, including those related to humanization. Methods: A Systematic Literature Review was performed according to the following steps: search for articles approaching the Lean Healthcare theme published in English between 2014 and 2020, selected on the databases of Web of Science, Scopus and Compendex (no other articles were introduced on the literature review), followed by discarding duplicates. The records were screening focusing in the section of articles reporting cases of lean healthcare adopting. No articles were excluded after the screening, which resulted in 48 articles that were deeper analysed through both qualitative and quantitative analyses. Results: Value Stream Mapping (VSM), 5S and Kaizen were the most used Lean tools in related study, with 24, 14 and 13 occurrences. The simulation and the “5 Whys” were Lean tools less used, with 3 and 2 occurrences. The main benefits found with the use of such tools were a reduction in the service time and an increase in patient satisfaction. The influence of teams and doctors behavior was identified as barrier to Lean implementation. Conclusions: The word "human" was discovered to be the most used word to describe Lean works in healthcare, that was not related in earlier reviews. There was also an increase in the number of Brazilian publications on subject, compared to previous period, in which the United States led on the number of publications. Throughout the study, two related cases added an annual savings of US $ 444,911, with the implementation of Lean Healthcare. The Lean approach has been applied in some health services to reduce the time of attendance and increase patient satisfaction. These results are indicative for expanding its application in the context of pandemics such as COVID-19.


Background
The Lean management system, proposed by Womack, Jones and Roos (1990) has, among other consequences, the reduction of waste, including time wasting, being steps for the continuous improvement of the e ciency and effectiveness in a healthcare system. Reducing the number of people in the waiting room, triage and attending room, will reduce waste and facilitate its management.
On the other hand, the time spent by patients at care units is a variable that must be reduced to mitigate the exposure of patients to hospital risks, especially at the moment of a pandemic, as the COVID-19 reported in the most varied newspapers, broadcasters and social media, due to its rapid spread worldwide, and with many cases, deaths, incidence and mortality rates in all regions of Brazil, as shown in table 1. This fact forces the health sector to look for new ways to manage its processes, in order to offer higher quality and faster services, and to provide better and higher numbers of patients assisted. Therefore, the search for new tools to improve seems to be an inevitable goal in the health sector. In this scenario, Brazilian Ministry of Health in partnership with the Universidade Federal Fluminense implements a project entitled "Lean nas UPAs" (i.e. Lean in the Emergency Care Units), as a successful Lean bet to humanize and improve the ow of patients cared in the UPAs. Table 1-Shows the number of cases, deaths, incidence rate and mortality in all regions of Brazil. This table was extracted from the Ministry of Health website and its information is updated every day.
Thus, the application of Lean concepts within hospitals seeks to increase the patient care quality, support employees and doctors to eliminate waste and allows them to focus on providing care, according to Graban (2012).
There are reports of Lean practices applications in hospital emergencies and among other health sectors, characterizing the term "Lean Healthcare". However, the records of these actions are dispersed in the literature, which, as described in Azevedo and Costa (2001)  The following research question was used to guide data collection: What are the main bene ts in the hospital system when taking the Lean Healthcare approach?
This paper aims to map how Lean tools are being used in healthcare and what are their results, including those that regards with humanization on the principle of respect for people. To this end, the results found in earlier research, cited in previous topic, are updated and complemented, and contribute to knowledge expansion on the topic of Lean Healthcare. In addition, the research methods used in the present study did not nd studies of systematic reviews, following PRISMA protocol, related to the years 2014 to 2020 that applied a statistical method of quantitative studies of publications, indicating research trends. Which makes it di cult to establish comparison standards.
This study also aims to contribute lling this gap, for this purpose the tool 5W1H was adopted (acronyms that represent the main questions that must be answered: What, Where, When, Who, Why and How) as a way to de ne the questions used in this work: 1) What Lean methods and tools were implemented in the health service and what results were found? 2) Where were implemented Lean methods and tools in health services? 3) When were the articles published? 4) Who dealt with the subject in the literature? 5) Why is Lean used in health services? 6) How was lean thinking implemented in health services? Therefore, these questions are the basis that this research was developed on, to report the cutting-edge of the state of the art of the Lean Healthcare in the period from 2014 to April 20, 2020. In relation to the traced objective, it is possible to relate humanization through the application of Lean methods and tools (value stream mapping, work standardized, rapid improvement events / Kaizen event and process mapping), which result in continuous improvement. They deal with patients as a priority and try to understand what creates value according to the patients. In Brazil, the Política Nacional de Humanização -PNH (i.e. National Humanization Policy -PNH) launched in 2013 that seeks to put into practice the principles of Sistema Único de Saúde -SUS (i.e. Single Health System) in the daily basis of health services, producing changes in the way of managing and caring. It can be associated with the Lean methods and tools use.
In recent years, the health sector has changed its efforts to quality initiatives, such as Lean systems, which were introduced by the manufacturing industries (SLOAN et al., 2014).
When we think about the hospital area, Lean, together with its tools, shows great e ciency, because it makes possible to reduce waiting time in patients admission process, the time spent by patients at care unit, seeking control mechanisms for rational use of resources, which can promote a better quality of life for patients and reduce costs.
Thus, as described by Costa and Godinho Filho (2016) the systematic elimination of waste is one of the main focuses of Lean philosophy, and according to Toussaint and Gerard (2010), the seven categories of waste from the Toyota Production System can be adapted from Ohno (1998) to healthcare: waiting (for an appointment), motion (searching for drugs), transport (transferring patients to new rooms), overproduction (unnecessary treatment), defect (work already done for errors), over-processing (unnecessary forms) and inventory (stock of medicines). Liker and Meier (2006) mentioned the eighth waste, not using people's creativity.
In their study, Mazzocato et al., (2010) presented four tools: Value Stream Mapping (VSM) for Lean intervention as methods to understand processes, to identify and analyse problems; Process mapping to organize more e cient and/or e cient processes; 5 whys to improve error detection, relay information to problem solvers and prevent errors from causing damage; 5S (so called due to the rst letter of 5 Japanese words Seiri -Classi cation, Seiton -Order, Seiso -cleaning, Seiketsu -standardization, Shitsuke -Discipline) to manage change and solve problems with a scienti c approach, these were the most used tools according to the studies found. This article classi ed the studies found between the years 1998 to 2008, 33 articles were reviewed in total. The main results of the Lean implementation found were the reduction of errors, patient satisfaction, reduction of mortality, reduction of costs and waiting time. It can be highlighted the preference for the applicability of Lean tools, according to the literature, in the following health sectors: emergencies, anesthesiology/intensive care, gynecology and obstetrics.
Souza (2009) in his study separated the articles selected by the research methodology (case studies and theoretical studies) and the countries cited in the literature between the years 2002 to 2008 analysing 90 articles. The case studies analysed by the author refer to the use of Lean methods and tools in some departments of a hospital, including, pharmacy, radiology, pathology and laundry. The study of the patient ow made it possible to reduce the waiting list and reduce costs, yet, it improved the quality of patient care and patient satisfaction, they realized the use and effectiveness of the application of other tools of the Lean like A3, 5S and Just in Time. They identi ed the United States, United Kingdom and Australia as the main countries in the implementation of Lean, according to the literature.
The study conducted by Costa and Godinho Filho (2016), reviewed 107 articles in the Engineering Village, Web of Knowledge, Scopus and Google Scholar databases between 2009 and 2014. In this study, the United States, United Kingdom and the Netherlands appear as the leading publishers of scienti c articles detailing the Lean implementation in health services. Authors classi ed health services into four categories: 1) auxiliary services, 2) therapeutic and clinical operations, 3) hospital and 4) general. In category 1, they identi ed hospital pharmacy, radiology, pathology, anesthesia, laboratory, hospital laundry and outpatient clinics. Standard work was the most accepted tool, but Value Stream Mapping (VSM) was the most used tool. At the outpatient clinic he found unsatisfactory results and the project was nished because of the team's discouragement. In category 2, the implementation of Lean approach in the emergency department and operating room was identi ed as relevant in numbers of cases. Some doctors report that the work standardization impairs the individualized treatment of the patient, but the standard work was the most cited tool in the literature, behind the VSM. The main results were the decrease in the patient's stay and an increase in the service capacity. In category 3, it reports on the application of the Lean approach throughout the hospital, highlighting the Value Stream Mapping and Ishikawa (or shbone) diagram and the DMAIC method (composed of the steps: De ne, Measure, Analyse, Improve and Control). Most frequent results were related to cost, time and increased service capacity. Finally, in category 4, the greatest use of the Lean tools mentioned in the literature was highlighted, the Value Stream Mapping and the Work Standardization. Other studies mentioned in this article highlighted the state of the art of Lean Healthcare.
In the study by Gomes et al., (2017), also used as the basis for this work, a systematic literature review was carried out including 175 articles from the years 2002 to 2015. The study highlighted three main Lean tools and techniques mentioned in the literature. for Value Stream Mapping, Kaizen and 5S. It was also noted the use of quantitative tools applied along with the Lean approach such as Six Sigma and Simulation. The health sector identi ed as the most used for Lean tools application are emergencies, followed by the surgery sector and the post-operative team. Decreased processing time (exams and visits) and reduced queues were the results found.
In order to understand the topic, this article is organized as follows: the methods are presented in section 2 applied to generate the core of references; in section 3, the results found are presented; section 4 the discussion; section 5 presents the conclusions and considerations about the work.

Search strategy and appraisal of studies
The review was performed in papers that approached the subject Lean tools and Healthcare which were published in journals indexed in Web of Science, Scopus and Compendex, limited to articles written in English that were published from January 2014 to April 20, 2020. The choice of these databases intends to avoid grey literature from the able of papers. This study was conducted according to the Preferred Reporting Items of Systematic Reviews and Meta-Analysis Protocols (PRISMA) checklist guideline. In addition to that, the journals were also veri ed through a search in lists of predatory journals to ensure that all used articles of this study do not belong to grey literature neither were published in predatory journals. The key terms used for the database searches were connected by Boolean operators and combined as follows: "Lean Healthcare" OR "Lean Hospital" AND "Tools".

Exclusion
Studies that had as research methodology literature review were not highlighted.
Studies that have not the full text in English or that were published until December 2013 or after April 2020 were not analysed.

Outcome measurement
Mapping of lean tools, opportunities, and barriers.
The database search results were exported Duplicate articles from the merging of Web of Sciences and Scopus results were removed from the sample using Mendeley Desktop software (version 1.19.5 / 2019; Paul Foeckler, Victor Henning, Jan Reichelt, London, England). In this article was utilized also VOS Viewer (version 1.6.14; Leiden University, Netherlands) with the focus to map keywords and authors citation found on step 3.2 (Selection of articles) and shown on step 3.4 (Statistical analysis of the selected records). Therefore, VOSviewer is a computer program that can be used to create maps based on network data. Maps are created using the VOS mapping technique and the VOS clustering technique. Any disagreement between reviewers was resolved through discussion and reaching consensus.

Statistical analysis
Information on the studies characteristics such as years of publication, study region, Lean tools, authors, countries, journals and actuation health area were extracted from each study using a Microsoft Excel. Then, data were exported to BibTex (version 0.99d; Oren Patashnik, Leslie Lamport, California, United States) for further analysis to use in VOSViewer Software.

Study design
In this study, all articles were included giving a highlight for case studies. All selected works were full-text articles written in English-language and published from January 2014 to April 20, 2020. A Systematic Literature Review (SLR) is carried out, a mapping of the literature, which is structured in the following steps ( Figure 1): 3.1) Choice of databases to be searched and de ne, test and apply the search phrase or Query to search on the selected databases; 3.2) Selection of articles to be analysed; 3.3) Reading and analysis of texts and framing of subjects of accord with the construct: health area, Lean methods and tools mentioned, country of application, main journals and authors, ways to implementation and their results, barriers and opportunities found; 3.4) Statistical analysis of the selected records and obtain from the analysis the graphic content for this article; 4) Discussion; 5) Conclusion of the work and proposition of suggestions for future research.

Results
In this section, the results obtained through the application of the steps de ned in the methods of this work are presented.

Choice of database to be searched and de nition of Query
For the selection of articles, the Web of Science and Scopus database was used because it has data processing and analysis of bibliographic mappings. To complement the study, the Compendex database (Engineering Village platform) was used. The research carried out on the Compendex database did not change the number of articles for the present study.
De nition and application of Query.

Selection of articles
In the selection criteria, the search string "Lean healthcare" OR "Lean hospital" AND "Tools" was used. This keyword choice represents most of the terms described within this literature. With this search criterion, in the database Web of Science were found eighty-six publications, fty-six publications were found in Scopus and twenty publications were found in Compendex, identifying a total of one hundred and sixty-two articles. The next step was the selection for the year of publication of the articles. Only publications made between 2014 to April 20, 2020 were considered. In this stage, the total of seventyeight publications resulted in the Web of Science, in Scopus there were forty-one documents and in Compendex there were twelve documents.
In addition, three lters were de ned as criteria for selecting documents. The rst lter selects only documents of type "Article". In this step, thirty-two records were excluded in the Web of Science database, in Scopus twenty-two records were excluded and in Compendex ten records were excluded from the selection process. With forty-six articles selected on the Web of Science, nineteen articles selected on Scopus and two articles selected on Compendex, the second selection lter was English language. In this step, two articles written in German and three articles written in Spanish on the Web of Science were excluded. Based on these criteria, forty-one articles were selected for the work by the Web of Science database. One article written in German and two articles written in Spanish were excluded from the Scopus database. Based on these criteria, seventeen articles were selected for the work of the Scopus database. In the Compendex database, articles were not excluded, because two articles selected in the previous step were written in English. Based on these criteria, two articles were selected for the work of the Compendex database. In the eligibility stage, she obtained a total of sixty records identi ed in English.
Replicated records were excluded from the selected studies in a total of twelve replicated articles. Therefore, forty-eight documents were included for the analysis, following the criteria: applied research methodology, the mentioned country, the health area covered by the document, in addition to the Lean methods and tools used and the results of each study, classifying them.
Thus, a meta-analysis was used, addressing the PRISMA method according to Moher et al., (2009) for the selection of the analysed articles. Also addressed by Lobo et al., (2018). Being illustrated in the owchart represented in gure 2.

Implementation areas
In this step, the analysis of the articles selected for the study was carried out, with the areas and departments of health that applied the methods and tools of Lean Healthcare, as shown in Figure 3. The applicability preference of the methods and tools can be highlighted in hospitals as a whole, found in fourteen documents, emergencies and the surgery department, found in six documents. Even so, it is possible to verify the success of the tools application in other health sectors such as oncology, mental health center, cardiology, radiography, pharmacy, public hospitals, health organizations, chemotherapy, urology, Intensive Care Unit -ICU and among other sectors, however, they were found in fewer documents in the literature. Table 2 compiles the results found in this section, relating the areas of health with the respective article, the number of times that each area has been addressed in the literature and the percent of each health area actuation in analysed cases.

Lean methods and tools mentioned.
The other stage of the study was to identify, among the forty-eight documents selected, the methods and tools of Lean that are being applied in health departments identi ed in the previous stage and their purposes of use. Thus, it was found out which and how these methods and tools were being implemented and the results caused by their application. Figure 4 shows the percent of times that each Lean method and tool was addressed in the selected studies through of the methods described in item 3.2. The use of Value Stream Mapping to nd problems such as bottlenecks and delays in production processes, helping to solve problems in different health sectors, is cited in twenty-four articles selected in this research, with seventeen percent of the total number of lean tools applications, appointing a preference of use.
Another tool addressed as preferential is the 5S, being used in ten percent of the studied applications and being presented in fourteen documents, and the Kaizen method with the application being cited in thirteen articles and used in nine percent of studied applications, the 5S acts, above all, in the improvement of quality, using 5 "senses", sense of use and discard, sense of order and organization, sense of cleanliness, sense of standardization and sense of self-discipline. Its importance in health can be attributed to the need for a clean and sterile environment. According to Kanamori et al., (2015) there is a reduction in the time to search for items; greater capacity of the team to move around the o ce; centrality of the patient; reduction of waiting time for patients; better guidance for patients; improved sterilization processes and others. These were the results found by applying the 5S tools and Kaizen methods.
Following by the tools Visual Management, Standardization and Kanban, in this order with ten, seven and six articles mentioning their use. It was also observed in the literature the application of Lean tools along with other methods such as DMAIC, found ve times, Analysis of variance (ANOVA), being mentioned twice, Simulation, found three times, Total Quality Management (TQM) and Total Quality Control (TQC), found twice each, Theory of constraints (TOC) and Fast-Track, each being found once in the literature. These results are best seen in gure 4.  Table 3 shows the highlighted authors and the respective number of publications, with three or more publications.

Ways to implementation and their results
Analysing the selected scienti c documents, we found the preference for the applicability of the Value Stream Mapping tool in several areas of health following the 5S tools and Kaizen method, which is one of the objectives of the article to identify what Lean tools are most used in Lean implementation through different areas of health.
Thus, it was observed the primordial ways of implementing of tools and the main results obtained. In general, as a form of implementation, there are team training workshops, project simulation, meetings with the team, information gathering, separation of activities that generate value and those that do not generate value, engagement between employees and questionnaire with patients to identify what is value to the patient and what the patient identify as waste. Thus, the fundamental results were shown: decrease in hospital waste such as out-of-date medicines, decrease in stock, patient satisfaction, decrease in lead time, stabilization of the process, increase in the number of visits, decrease in errors doctors and errors with blood collection, reduction in the average time for exams delivery, reduction in patient's stay time, cost reduction in the appointment and decrease in the number of appointment and exam cancellations. Therefore, some of the studies analysed were highlighted below, highlighting the ways to implement the Lean tools and the results obtained. The following are related thirteen cases that show the application of Lean tools in health services and its achievements.
The tools of Lean 5S and Kaizen were implemented in the sterilization of surgical materials in Brazil in the study by Fogliatto et al., (2019). For implementation, Lean principles were studied, and it was divided which surgical materials could be prioritized and which could be rationalized to reduce costs and the burden of sterilization processes, divided the teams into Kaizens groups to achieve the objective of continuous improvement. They reported the results proposing a strategy to address the rationalization of trays, prioritizing complex and frequent surgical specialties, and using group technology to agroup surgical trays, streamlining specialized analyses. Thus, they reduced the number of instruments by an average of 9.75% and the time to assemble trays by 9.68%, achieving an annual savings of US $ 285,756.00 in sterilization processing costs.
In the study by Barnabè et al., (2018) he applied the principles of Lean thinking and shared competences in collaborative processes in a hospital, devoted to educational tools for training health decision-making agents. He used the role-playing game (RPG) as a simulation measure and team training. It guaranteed the satisfaction of patient demand, patients reported improvement in the process, improvement in lead time and quality in the process according to health professionals and patients. Barnabè et al., (2017) proposed a simulation game that not only provides a suitable physical environment for the purpose (an open space within the hospital), but also stimulates and encourages the use of a large number of medical instruments (for example, a portable chest X-ray machine), administrative documents (for example, medical records and laboratory tests) and Lean tools to make the simulation as real and engaging as possible. The game challenges participants with work-related tasks, a variety of possible scenarios (for example, a growing patient demand) and a complete set of metrics to measure their performance. In particular, a dedicated business intelligence software program is used to monitor and evaluate performance. The graphs, key performance assessment, tables and panels inform the discussion and decision making during all phases of the game. As a result, participants obtained recognition of the simulated environment as realistic (58.8%) or absolutely realistic (17.6%). In total, 86.7% of the participants perceived an increase in knowledge and understanding about the speci c simulated process. 93.4% of the participants emphasized that the basis of a simulation game was more useful and effective than traditional classroom training. Speci cally, players stated that this simulation game encouraged them to re ect and use / implement various Lean tools and techniques (for example: 5S technique, visual management tools, various Lean metrics, value stream mapping) during the simulation. Overall, 94% of the participants were willing to participate more often in the simulation game. Through medical screening, patients are sent to Fast-Track using the Emergency Severity Index parameter. Fast-Track has access to those less serious patients for whom the system's crossing time is supposed to be shorter. In medical screening, the patient is separated by colors, red (patients with a critical condition), yellow (patients with a potentially critical condition), green (patients who need a medical service) and white (patients who do not have changes in vital functions). Patients are sent to a speci c emergency area according to their classi cation, the shock room receives all patients identi ed with the color red, in this environment it has a multidisciplinary team and all the necessary equipment to save lives. In the Urgency area, patients identi ed with the yellow and green code are received, the distinguishing characteristics of this area is the system's exibility in accepting additional patient ows (agglomeration). The area of minor codes is dedicated to the evaluation and treatment of patients with minor problems. Assisted waiting area for patients who need to complete treatment but are unable from accessing the hospital due overcrowding. Brief observation, for patients that it is not possible to make a decision about the result in the rst hours of arrival at the emergency room. Finally, a short intensive observation area, patients with trauma and toxicology, in which the diagnostic procedures are not exhaustible in a few hours. In this way, they improved the ow of patients, allowing them to assist almost everyone in the ward and reallocating resources in a timely manner.
In this way, the Lean approach such as VSM, 5S, Kaizen and other tools mentioned in this work, can be applied to different sectors in health. Such as clinics, hospitals, surgical center, oncology, geriatrics, gynecology and obstetrics, neurology, emergencies, cardiology, Intensive Care Unit, hospital pharmacy, SUS, mental health service, chemotherapy, radiotherapy, sterilization, maternity and primary care. The use of such methodologies is recommended for health departments that wish to achieve better results and e ciency during health procedures. It is worth mentioning two related cases, one by Flogliatto et al.,

Barriers and opportunities found
In this stage of the study, it focused on nding in the studied documents the barriers and opportunities to start the Lean journey in health services, mentioned in this work. Therefore, some of the studies analysed were highlighted below, highlighting the barriers and opportunities to implement Lean tools in health services and the results obtained. New studies can be developed regarding speci c barriers for adopting the Lean approach in health services. In addition, it is possible to study how other sectors such as urology, chemotherapy, maternity and primary health care are seldom mentioned for the applicability of Lean methods and tools in health services.

Statistical and graphic analysis of the selected records
In the identi cation stage of the articles it resulted in 48 documents with the union of the Web of Science, Scopus and Compendex databases. Figure 6 shows the graph of distribution of articles over the period from 2014 to April 20, 2020, illustrating the number of these publications per year. The last step of this SLR was to generate, through the VOS Viewer software, the co-citation and cooccurrence networks of keywords, for that it was necessary to join the bibliographic data acquired in the Web of Science and Scopus databases.
Co-citation map.
The co-citation network, shown in gure 7, is composed of 8 nodes and 28 edges. The size of the nodes indicates how many times they were mentioned by other authors. Among them they are mentioned in the same way, because the nodes have the same size.
Keywords co-occurrence maps.
In gure 8, it is about the keyword co-occurrence map made in VOSViewer software, to address the keywords used in the articles. Note that the possible Hot Topics are: "Lean healthcare", "quality improvement", "human" and "total quality management". The least used keywords are: "Hospital operations", "person-centered care" "Management" and "lean thinking". The keyword co-occurrence network, illustrated in gure 8, is composed of 238 nodes and 2406 edges. The size of the nodes indicates how many times they were used in the articles. The generated network obtained 16 clusters, that is, 16 sets of items included in the map. Therefore, it was visualized, highlighted in the keyword "human", it has been mentioned in the literature more over the years, due to the preference of humanized treatment focused on the client / patient de ned as one of the pillars of Lean (respect and transparency) which is linked to the National Humanization Policy (PNH) created in 2003 linked to the Ministry of Health in Brazil.

Publication bias
In the present study there was no publication bias because studies were equally studied within PRISMA as shown on gure 2.

Discussion
In this stage, there criteria were used for comparative analysis of the results found in previous bibliographic studies: 1) The methods and tools of Lean most applied in health services and their results; 2) Where the tools were applied; 3) The years studied by each author and the countries that gained prominence by the number of publications. Comparison under tools adoption perspective The most used Lean tools analysing the articles found from 2014 to April 20, 2020 were Value Stream Mapping, Kaizen, 5S and Visual Management. In previous studies, it also showed notoriety of these tools; however, the Visual Management tool was not equaly mentioned. The results found in previous studies obtained by implementing the Lean approach were repeated in the present study.

Comparison of actuation health area
The health areas that most appeared to start the Lean journey in health services in this study are hospital, surgery, emergency and oncology. In previous bibliographic studies, the preference for use in hospitals and emergencies is mentioned in additional to other areas that showed the application of Lean tools as a priority.

Additional aspects analysed in this work
Behind the previous comparison, this work incudes other variables to the research that were not adopted in the previous literature review, such as: authors, journals, co-citations and co-occurrence maps. It allowed to discovery that, in the period analysed, the articles were: Hot Topics: "Lean healthcare", "quality improvement", "human" and "total quality management".

Limitation
This study was limited for years of publication between January 2014 to April 20, 2020, document of type: articles and only English language written articles were synthesized. Moreover, the articles were studies following the criteria: applied research methodology, the mentioned country, the health area covered by the document, Lean methods and tools used and the results of each study, classifying them in opportunities and barriers.

Conclusions
This article discussed some issues, above all, how health organizations can bene t from the concepts and tools of Lean Thinking to start the Lean journey in health services. In addition, some examples were reported in the present study. Being discussed, the role of some basic tools such as Value Stream Mapping, 5S, Kaizen and Visual Management in the process of adopting the beginning of the Lean Journey in health services. Considering that the objectives of this current study are to update previous studies on the implementation of the Lean approach in health services, to analyse the applicability of the tools in the articles studied and to verify the areas of application. Therefore, the subjects addressed throughout this article answered the research questions de ned at the beginning of the study, which were: 1) What Lean methods and tools were implemented in health services and what results were found? 2) Where Lean methods and tools were implemented in health services? 3) When the articles were published? 4) Who discussed the subject in the literature? 5) Why is Lean used in health services? 6) How was lean thinking implemented in health services?
With the methodology applied in this work, it appears that despite the oscillations in the number of publications, there has been an advance in the acceptance and application of these tools in health services. This can be con rmed by the growing number of studies using the Lean healthcare approach in several countries in the world, with the main users of these tools are: Brazil, United States, Sweden, England and Italy. It is necessary to emphasize that Brazil has stood out in this scenario with a greater production of articles.
There is still a high degree of heterogeneity in the health areas where Lean practices have been implemented, but most of these areas are categorized as clinical operations and applied in hospitals. In addition to applications in emergencies, surgeries and public hospitals.
After the introduction described above, the SLR projected by Moher et al. (2009) was the research method selected to achieve the objectives of this research. The rst step carried out allowed the identi cation of 48 records by consulting the Web of Science, Scopus and compendex database (from 2014 to April 20, 2020) through a structured search. Number of publications, provided information to assess the applicability, results and the area of expertise in the health of Lean tools in general. We conclude that it is possible to apply the tools, even though some adaptations and considerations were made by the authors who published their results. With this research, he found that in 2017 there was a greater number of publications on the theme.
Authors, with the largest number of publications, were highlighted about the theme Lean Healthcare who brought in their studies means for the implementation of tools in the health sectors such as workshops, team training workshop, team engagement, simulation project, meetings with the team, information gathering and among other less mentioned ways.
Concomitantly, a limited number of publications were found on the use of certain tools and barriers to the adoption of tools by health services. Most articles showed acceptance and good results with the implementation of Lean Healthcare or Lean in health services.
Lean methods and tools (value stream mapping, work standardized, rapid improvement events / Kaizen events and process mapping) and results (reduced waiting time, reduced cost, reduction in patient's stay time and increased capacity) are similar to works previously found. However, in previous work it resulted in that the Lean implementation was done in a super cial way and with simple techniques. The current study showed that Lean Healthcare has been more accepted in health over the years, promoting greater training for health professionals. Furthermore, the implementation of Lean Thinking in health services has been carried out, through the implementation of several techniques of Lean Healthcare and is an alternative to improve care in health services in times of pandemic. However, techniques that require a greater degree of knowledge and maturity from the health institution are seldom used, such as Jidoka and Leveling Production (Heijunka). Thus, we can analyse that there has been an evolution in the research and applicability of Lean Healthcare in the world.