Abstract

Paper aims

The demand for quality health services is increasing and the efficiency in hospitals is related to the continued improvement in their processes and services. Faced with this problem, this study aimed to perform a literature review of the application of lean health care to hospital services.

Originality

Link between theory and practice, helping health professionals in their routine.

Research method

The concepts of bibliometrics were used. The databases that make up the sample are ISI Web of Science, Scopus, Lilacs, PubMed, and Cinahl; all the articles were in the ISI Web of Science database.

Main findings

The analyses suggest that the continuous improvement in processes and in the quality of the services offered are factors that influence the development of teams concerned with patient safety.

Implications for theory and practice

Shows the results and difficulties encountered by hospitals with the implementation of lean methodologies.

Keywords
Bibliometric; Lean health care; Planning lean health care management; Hospital services

1. Introduction

Process reengineering methodologies have become an international management phenomenon ( Waring & Bishop, 2010 Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... ), as there have been a growing pressure on health services to increase their efficiency. To achieve this goal, health services have sought alternatives to traditional models, adopting methodologies for improving processes commonly used in the manufacturing sector, including lean manufacturing ( Radnor et al., 2012 Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... ).

The lean methodology, originated at Toyota, and also known as the Toyota Production System (TPS), is considered a radical alternative to the traditional mass-production model. Lean is defined as a methodology that adopts the elimination of waste, as well as the aggregation of value to all processes, whose goal is to improve the final product ( Brackett et al., 2013 Brackett, T., Comer, L., & Whichello, R. (2013). Do lean practices lead to more time at the bedside? Journal for Healthcare Quality, 35(2), 7-14. http://dx.doi.org/10.1111/j.1945-1474.2011.00169.x. PMid:22093157.
http://dx.doi.org/10.1111/j.1945-1474.2... ) and to maximize operational efficiency, quality, speed and cost of operations ( Holweg, 2007 Holweg, M. (2007). The genealogy of lean production. Journal of Operations Management , 25(2), 420-437. http://dx.doi.org/10.1016/j.jom.2006.04.001.
http://dx.doi.org/10.1016/j.jom.2006.04... ).

The lean approach finds popular appeal in health care as it seeks to redesign clinical practices and resources around simplified, efficient and value-added care ( Waring & Bishop, 2010 Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... ).

The approach adopted in health systems is different from that adopted in manufacturing systems, since the processes are different, particularly for working with human lives. Thus, the definition of lean for health systems has different interpretations and practices, and is commonly called lean health care.

Nelson-Peterson & Leppa (2007) Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... state that lean health care is neither an adapted manufacturing tactic nor a cost reduction program; it is a management strategy based on process improvement in a system. Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... claim that it is a management practice based on the philosophy of continuously improving processes, reducing activities of little or no value added to the patient, variation in processes and precarious working conditions.

Lean promotes a structured approach to problem solving and improvement efforts linked to hospital strategy ( Mazzocato et al., 2012 Mazzocato, P., Holden, R. J., Brommels, M., Aronsson, H., Bäckman, U., Elg, M., & Thor, J. (2012). How does lean work in emergency care? A case study of a lean-inspired intervention at the Astrid Lindgren Children’s hospital, Stockholm, Sweden. BMC Health Services Research, 12(1), 28. http://dx.doi.org/10.1186/1472-6963-12-28. PMid:22296919.
http://dx.doi.org/10.1186/1472-6963-12-... ). It illustrates the desire of policy makers to reorder clinical work by introducing managerial philosophies and techniques, involving the systematic evaluation of the existing work process to determine the evidence of its waste and inefficiencies, increasing productivity and efficiency according to the new evidence ( Waring & Bishop, 2010 Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... ).

The lean methodology for hospitals focuses on key processes, and aims to improve and standardize processes, increase patient efficiency and satisfaction, and decrease unnecessary resources ( Vats et al., 2012 Vats, A., Goin, K. H., Villarreal, M. C., Yilmaz, T., Fortenberry, J. D., & Keskinocak, P. (2012). The impact of a lean rounding process in a pediatric intensive care unit*. Critical Care Medicine, 40(2), 608-617. http://dx.doi.org/10.1097/CCM.0b013e318232e2fc. PMid:21983366.
http://dx.doi.org/10.1097/CCM.0b013e318... ). This places lean principles at the heart of patient-oriented strategies ( MacFarlane, 2014 MacFarlane, M. A. (2014). Sustainable competitive advantage for accountable care organizations. Journal of Healthcare Management, 59(4), 263-271. http://dx.doi.org/10.1097/00115514-201407000-00006. PMid:25154124.
http://dx.doi.org/10.1097/00115514-2014... ).

Health professionals need to be aware that lean helps in process improvement and value stream mapping, offering many opportunities for health organizations and their ongoing improvement initiatives ( Vats et al., 2012 Vats, A., Goin, K. H., Villarreal, M. C., Yilmaz, T., Fortenberry, J. D., & Keskinocak, P. (2012). The impact of a lean rounding process in a pediatric intensive care unit*. Critical Care Medicine, 40(2), 608-617. http://dx.doi.org/10.1097/CCM.0b013e318232e2fc. PMid:21983366.
http://dx.doi.org/10.1097/CCM.0b013e318... ). When applied correctly, they help assess the value of each step in the process, as well as measure and identify the variation of a process for conducting positive and repeatable results ( Vats et al., 2011 Vats, A., Goin, K. H., & Fortenberry, J. D. (2011). Lean analysis of a pediatric intensive care unit physician group rounding process to identify inefficiencies and opportunities for improvement. Pediatric Critical Care Medicine, 12(4), 415-421. http://dx.doi.org/10.1097/PCC.0b013e3181fe2e3c. PMid:20975612.
http://dx.doi.org/10.1097/PCC.0b013e318... ).

Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... identify three key aspects for the lean methodology to be introduced in a hospital: the evaluation of existing processes, the adoption of improvements in processes and the monitoring of performance of the improvements implemented. Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... add to the need and willingness to improve organizational performance, creating alternative solutions and increased team communication.

Waring & Bishop (2010) Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... say that management should emphasize creating value streams and reducing waste, leading to the reconfiguration of clinical practices to produce more productive and value-added processes.

Eliminating unnecessary steps in a process improves patient productivity, quality, and flow. To eliminate waste, process changes are required ( Toussaint, 2009 Toussaint, J. (2009). Writing the new playbook for U.S. health care: lessons from Wisconsin. Health Affairs, 28(5), 1343-1350. http://dx.doi.org/10.1377/hlthaff.28.5.1343. PMid:19738250.
http://dx.doi.org/10.1377/hlthaff.28.5.... ). The application of lean principles has created conditions that enable health professionals to perform their functions without wasting or, in a minimized way, increasing patient satisfaction ( Nelson-Peterson & Leppa, 2007 Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... ).

To materialize the potential benefits of lean, organizations need to minimize the impact of barriers and make specific conditions available to the local context ( Mazzocato et al., 2012 Mazzocato, P., Holden, R. J., Brommels, M., Aronsson, H., Bäckman, U., Elg, M., & Thor, J. (2012). How does lean work in emergency care? A case study of a lean-inspired intervention at the Astrid Lindgren Children’s hospital, Stockholm, Sweden. BMC Health Services Research, 12(1), 28. http://dx.doi.org/10.1186/1472-6963-12-28. PMid:22296919.
http://dx.doi.org/10.1186/1472-6963-12-... ). In a hospital, the work of multidisciplinary teams is also important for the methodology to be well accepted.

The resources available, the involvement of doctors and managers indicate and affect the strategic importance and, therefore, the opportunity to change ( Andersen et al., 2014 Andersen, H., Røvik, K. A., & Ingebrigtsen, T. (2014). Lean thinking in hospitals: is there a cure for the absence of evidence? A systematic review of reviews. BMJ Open , 4(1), e003873. http://dx.doi.org/10.1136/bmjopen-2013-003873. PMid:24435890.
http://dx.doi.org/10.1136/bmjopen-2013-... ).

The transformation of the quality system must be part of a comprehensive management system, within an institutional culture of support and with committed leadership. Quality improvement specialists do not work in isolation, but in collaboration with operational leaders ( Kaplan et al., 2014 Kaplan, G. S., Patterson, S. H., Ching, J. M., & Blackmore, C. C. (2014). Why Lean doesn’t work for everyone. BMJ Quality & Safety, 23(12), 970-973. http://dx.doi.org/10.1136/bmjqs-2014-003248. PMid:25056985.
http://dx.doi.org/10.1136/bmjqs-2014-00... ).

Many clinical leaders motivate teams to develop timely improvements rather than a unified improvement program with other departments or organizational units ( Radnor et al., 2012 Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... ), limiting themselves to adopting specific lean techniques to solve a specific problem within a specific unit or department ( Mazzocato et al., 2010 Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... ). This makes the professionals resist to the changes, reluctant to adopt new working procedures ( Nelson-Peterson & Leppa, 2007 Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... ).

The way lean methodology is adapted to health care is not fully recognized in the literature ( Papadopoulos et al., 2011 Papadopoulos, T., Radnor, Z., & Merali, Y. (2011). The role of actor associations in understanding the implementation of Lean thinking in healthcare. International Journal of Operations & Production Management, 31(2), 167-191. http://dx.doi.org/10.1108/01443571111104755.
http://dx.doi.org/10.1108/0144357111110... ); it cannot be said that lean works for everyone.

The use of lean in isolated niches of quality improvement is not enough. Transformation requires the use of lean as part of a comprehensive management system together with changing institutional culture and new leadership approaches to all aspects of health care delivery ( Kaplan et al., 2014 Kaplan, G. S., Patterson, S. H., Ching, J. M., & Blackmore, C. C. (2014). Why Lean doesn’t work for everyone. BMJ Quality & Safety, 23(12), 970-973. http://dx.doi.org/10.1136/bmjqs-2014-003248. PMid:25056985.
http://dx.doi.org/10.1136/bmjqs-2014-00... ). For implementing the lean methodology, it is essential to know how to identify clients and processes, using clear and appropriate terminology ( Proudlove et al., 2008 Proudlove, N., Moxham, C., & Boaden, R. (2008). Lessons for lean in healthcare from using six sigma in the NHS. Public Money & Management, 28(1), 27-34. http://dx.doi.org/10.1111/j.1467-9302.2008.00615.x.
http://dx.doi.org/10.1111/j.1467-9302.2... ).

Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... state that there are two main reasons for the lack of implementation of lean: lack of training - lean is not understood by system actors; lack of incentive of the organization's leadership to conduct lean in a structured way. Few studies are found about lean basics to improve the operations of hospital services ( Laganga, 2011 Laganga, L. R. (2011). Lean service operations: reflections and new directions for capacity expansion in outpatient clinics. Journal of Operations Management, 29(5), 422-433. http://dx.doi.org/10.1016/j.jom.2010.12.005.
http://dx.doi.org/10.1016/j.jom.2010.12... ).

In this scenario, the implementation of lean methodology in health services has a great impact on the efficiency of hospital processes, acting as a facilitator and / or an inhibitor in the implementation of projects of continuous improvement.

The purpose of this paper is to analyze the literature on the application of lean to hospital services; based on this analysis, to identify the research trends and gaps, the theoretical pillars and the most relevant topics commonly addressed by authors within this area. The study on the development of the theme over time was based on a literature review, with the help of bibliometric, which shows the academic evolution of lean health care, from its initial approaches.

2. Methods

The methodological approach was the review of the literature, supported by bibliometric and the analysis of networks of relationship between publications. It was thus possible to analyze the development of the theme over the years, identifying the main authors and subjects discussed, as well as contributing to the content evolution.

For Haunschild et al. (2016) Haunschild, R., Bornmann, L., & Marx, W.. (2016). Climate change research in view of bibliometrics. PLoS One, 11(7), e0160393. http://dx.doi.org/10.1371/journal.pone.0160393. PMid:27472663.
http://dx.doi.org/10.1371/journal.pone.... , bibliometric aims to quantify the result and interconnection of scientific activity, with the number of publications being the measure of production, while the number of citations is the impact indicator, the “measurable” aspect of quality. In addition, it is possible to measure the content by searching keywords, showing the connection between the authors and the subjects studied.

The keywords of the search were: 'lean health care', 'lean health care management' and 'planning lean health care management', all searched with the 'AND' connector. The research was conducted in five different databases: ISI Web of Science, Scopus, Cinahl, Lilacs and PubMed, because of their relevance to the health area. The ISI Web of Science and Scopus databases have filters by 'document type', 'categories' and 'source titles'. The Cinahl database does not have the division by 'categories' and the PubMed and Lilacs databases do not have the division by 'source titles'.

During the filtering process, no filters were used for the criteria ‘journals’ and ‘period of publication’; the objective was to select all articles published by the database until the date of the search.

In 2007, the theme lean health care became relevant to researchers, with a growing number of research. For this reason, this study includes articles in the period that varies between 2007 and 2017.

The initial survey of the sample, considering all articles, resulted in 2788 titles. After analyzing the filters considered, according to the areas of interest and the relevant and impact journals for the research, this number lowered to 853 articles. Of this total, duplicate titles were discarded, only one article per theme being considered. The final base resulted in 670 articles; they had their summaries evaluated, allowing to fit the really relevant articles to the theme, which resulted in 98 articles. Note that the metadata was extracted from the ISI Web of Science database, since this database has the largest number of articles available. Figure 1 shows the process for selecting the articles.

From the selected articles, according to the process shown in Figure 1 and considering the period from 2007 to 2017, the studies that involved process improvements (8 articles), efficiency (5 articles) and patient safety (4 articles) had the largest amount of publications. In contrast, articles discussing lean and six sigma have little relevance in the period. Table 1 shows the topics covered in the articles throughout in this period.

Table 2 shows a summary of the search: the filters used in each database, the results achieved from each search and the final result, including articles with repeated themes.

From the complete database, the Bradford Dispersion Law was applied, which shows the relationship between the set of journals used in the database and its productivity, in descending order ( Araújo, 2006 Araújo, C. A. (2006). Bibliometria: evolução história e questões atuais. Questão, 12(1), 11-32. http://dx.doi.org/10.19132/1808-5245121.
http://dx.doi.org/10.19132/1808-5245121... ). In this group, the articles with the highest number of citations were considered, which established the minimum cut in 20 citations per article. This resulted in 13 publications, which accounted for 74% of the total citations. Table 3 shows a summary of the 13 most important publications and their number of citations.

Haunschild et al. (2016) Haunschild, R., Bornmann, L., & Marx, W.. (2016). Climate change research in view of bibliometrics. PLoS One, 11(7), e0160393. http://dx.doi.org/10.1371/journal.pone.0160393. PMid:27472663.
http://dx.doi.org/10.1371/journal.pone.... hold the number of citations is a good indicator of impact. Thus, the 13 most cited articles shown in Table 3 were predominantly considered in the literature. When the sample was selected, the article metadata was imported by the VOSviewer software, version 1.6.4, and the networks were analyzed by the Netdraw software, version 2.161.

3. Results

The characterization of the sample of the publications sought to map the orientation of the articles over the period considered. It is noteworthy that the theme gained significant importance as of 2007, when a greater number of publications began to occur. Thence, the analysis period is from 2007 until the year of the survey, 2017. Figure 2 shows this evolution.

Figure 2 shows that the peak of publications occurred in 2016, with 22 publications, which corresponds to 22.45% of the total number of publications in the sample. Note that in 2017, there were 10 publications; however, the sample was collected in July, which does not allow concluding whether there was a greater or lesser number of publications in 2017 as compared to 2016. From 2007 to 2010, an evolution occurred in this line of research; between 2011 and 2013, the evolution of publications occurred intermittently and from 2014 onwards, a new growth of publications, with an upward trend over the years.

Concerning the issues addressed by the authors in the articles, Table 1 shows that 30.6% of the articles (30 articles in the sample) discuss process improvement, 16.3% (16 articles) deal with process efficiency, 12% (12 articles) deal with quality in services and 16.3% (16 articles) deal with adding value to services. Considering the point of view of processes and services, 46.9% of the articles (46 articles) discuss processes and 28.5% (28 articles) discuss services, totaling 75.4% of the sample (74 articles) that discuss processes or services. It is noteworthy that only 4.1% of the sample (4 articles) represents studies in the lean and six sigma, a very small portion for such an important subject.

Among the articles selected, the sample highlights there is a great increase in publications in different journals. Totaling 98 publications, 53 articles were published in 11 different journals, corresponding to 54% of the publications, emphasizing that the subject attracts great interest by journals, although there are few publications; this justifies the study of lean in health care is a very important. Table 4 shows a summary of journals with more publications.

The qualitative analysis of the publications occurred under the scenario of iterations between the publications, the main authors, the keywords used and the countries with the largest number of publications. We tried to understand the patterns of relationship between the database articles and the main theme, lean health care.

This analysis shows three main theoretical lens influencing lean healthcare and the main authors: Management and Operation, which highlight articles focused on process management, health professionals' management and how lean healthcare influences its activities ( Drotz & Poksinska, 2014 Drotz, E., & Poksinska, B. (2014). Lean in healthcare from employees’ perspectives. Journal of Health Organization and Management, 28(2), 177. http://dx.doi.org/10.1108/JHOM-03-2013-0066. PMid:25065109.
http://dx.doi.org/10.1108/JHOM-03-2013-... ; Mazzocato et al., 2014 Mazzocato, P., Thor, J., Bäckman, U., Brommels, M., Carlsson, J., Jonsson, F., Hagmar, M., & Savage, C. (2014). Complexity complicates lean: lessons from seven emergency services. Journal of Health Organization and Management, 28(2), 266-288. http://dx.doi.org/10.1108/JHOM-03-2013-0060. PMid:25065114.
http://dx.doi.org/10.1108/JHOM-03-2013-... ; Morrow et al., 2014 Morrow, E., Robert, G., & Maben, J. (2014). Exploring the nature and impact of leadership on the local implementation of the Productive Ward Releasing Time to Care. Journal of Health Organization and Management, 28(2), 154-176. http://dx.doi.org/10.1108/JHOM-01-2013-0001. PMid:25065108.
http://dx.doi.org/10.1108/JHOM-01-2013-... ; Nelson-Peterson & Leppa, 2007 Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... ; Papadopoulos et al., 2011 Papadopoulos, T., Radnor, Z., & Merali, Y. (2011). The role of actor associations in understanding the implementation of Lean thinking in healthcare. International Journal of Operations & Production Management, 31(2), 167-191. http://dx.doi.org/10.1108/01443571111104755.
http://dx.doi.org/10.1108/0144357111110... ; Seidl & Newhouse, 2012 Seidl, K. L., & Newhouse, R. P. (2012). The intersection of evidence-based practice with 5 quality improvement methodologies. Journal of Nursing Administration , 42(6), 299-304. http://dx.doi.org/10.1097/NNA.0b013e31824ccdc9. PMid:22617691.
http://dx.doi.org/10.1097/NNA.0b013e318... ; Van Lent et al., 2012 Van Lent, W. A. M., Sanders, E. M., & Van Harten, W. H. (2012). Exploring improvements in patient logistics in Dutch hospitals with a survey. BMC Health Services Research , 12(1), 232. http://dx.doi.org/10.1186/1472-6963-12-232. PMid:22852880.
http://dx.doi.org/10.1186/1472-6963-12-... ); Quality, where the articles analyze the quality management and the quality in processes and services stand out ( Farrokhi et al., 2015 Farrokhi, F. R., Gunther, M., Williams, B., & Blackmore, C. C. (2015). Application of lean methodology for improved quality and efficiency in operating room instrument availability. Journal for Healthcare Quality, 37(5), 277-286. http://dx.doi.org/10.1111/jhq.12053. PMid:24112283.
http://dx.doi.org/10.1111/jhq.12053 ... ; Grove et al., 2010 Grove, A. L., Meredith, J. O., Macintyre, M., Angelis, J., & Neailey, K. (2010). Lean implementation in primary care health visiting services in National Health Service UK. Qual Saf Health Care, 19(5), 1-5. PMid:20511600. ; Hydes et al., 2012 Hydes, T., Hansi, N., & Trebble, T. M. (2012). Lean thinking transformation of the unsedated upper gastrointestinal endoscopy pathway improves efficiency and is associated with high levels of patient satisfaction. BMJ Quality & Safety, 21(1), 63-69. http://dx.doi.org/10.1136/bmjqs-2011-000173. PMid:21917646.
http://dx.doi.org/10.1136/bmjqs-2011-00... ; Kaplan et al., 2014 Kaplan, G. S., Patterson, S. H., Ching, J. M., & Blackmore, C. C. (2014). Why Lean doesn’t work for everyone. BMJ Quality & Safety, 23(12), 970-973. http://dx.doi.org/10.1136/bmjqs-2014-003248. PMid:25056985.
http://dx.doi.org/10.1136/bmjqs-2014-00... ; Mazzocato et al., 2010 Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... ; Naik et al., 2012 Naik, T., Duroseau, Y., Zehtabchi, S., Rinnert, S., Payne, R., McKenzie, M., & Legome, E. (2012). A structured approach to transforming a large public hospital emergency department via lean methodologies. Journal for Healthcare Quality, 34(2), 86-97. http://dx.doi.org/10.1111/j.1945-1474.2011.00181.x. PMid:22188582.
http://dx.doi.org/10.1111/j.1945-1474.2... ; Young & McClean, 2008 Young, T. P., & McClean, S. I. (2008). A critical look at Lean Thinking in healthcare. Quality & Safety in Health Care, 17(5), 382-386. http://dx.doi.org/10.1136/qshc.2006.020131. PMid:18842980.
http://dx.doi.org/10.1136/qshc.2006.020... ) and Services, which identifies articles targeted to the services offered by hospitals ( Andersen et al., 2014 Andersen, H., Røvik, K. A., & Ingebrigtsen, T. (2014). Lean thinking in hospitals: is there a cure for the absence of evidence? A systematic review of reviews. BMJ Open , 4(1), e003873. http://dx.doi.org/10.1136/bmjopen-2013-003873. PMid:24435890.
http://dx.doi.org/10.1136/bmjopen-2013-... ; Mazzocato et al., 2012 Mazzocato, P., Holden, R. J., Brommels, M., Aronsson, H., Bäckman, U., Elg, M., & Thor, J. (2012). How does lean work in emergency care? A case study of a lean-inspired intervention at the Astrid Lindgren Children’s hospital, Stockholm, Sweden. BMC Health Services Research, 12(1), 28. http://dx.doi.org/10.1186/1472-6963-12-28. PMid:22296919.
http://dx.doi.org/10.1186/1472-6963-12-... ; Van Lent et al., 2012 Van Lent, W. A. M., Sanders, E. M., & Van Harten, W. H. (2012). Exploring improvements in patient logistics in Dutch hospitals with a survey. BMC Health Services Research , 12(1), 232. http://dx.doi.org/10.1186/1472-6963-12-232. PMid:22852880.
http://dx.doi.org/10.1186/1472-6963-12-... ).

The place where the studies were published highlights the regions where quality in healthcare systems is at a developed stage and they apply different methodologies.

The approach to determining this network was based on a minimum number of publications per country, 5. England distinctly has a large network of connections. One possible explanation for this is due to the National Health Services (NHS), one of the largest and best-known health systems in the world. Consequently, countries such as Northern Ireland, Wales Scotland and Australia, all of which belong to the United Kingdom, also play a prominent role.

The United States also stands out as the precursor to hospital quality seals in the world through the Joint Commission International (JCI), and has a long tradition of quality health systems. Figure 3 shows the countries with the highest incidence of lean-related publications.

Considering the 13 most cited articles of the sample, the network of relationships between the articles and their references was constructed in order to identify the behavior between the authors and their relationship patterns.

Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... , despite being one of the most cited articles, with 112 citations, is not in a prominent position, unlike Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... , with the same number of citations (112). One possible explanation for this may lie in the fact that Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... is a literature review. In this article, the authors show that lean thinking successfully applied to a wide variety of health settings; although lean emphasizes a holistic view, most reported cases show restricted technical applications with limited organizational reach.

Waring & Bishop (2010) Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... approach lean health care as a difficult subject to be deployed in hospitals; Young & McClean (2008) Young, T. P., & McClean, S. I. (2008). A critical look at Lean Thinking in healthcare. Quality & Safety in Health Care, 17(5), 382-386. http://dx.doi.org/10.1136/qshc.2006.020131. PMid:18842980.
http://dx.doi.org/10.1136/qshc.2006.020... show a critical look at lean health care and its association with other quality methodologies; Nelson-Peterson & Leppa (2007) Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... refer to a practical application of lean health care.

Figure 4 shows the behavior among the most cited authors, presented in Table 2 . It highlights articles with over 50 citations in the database. The authors marked with a rectangle refer to the most cited articles (112 citations each) and those marked with an ellipse refer to the authors who stood out during the search.

The network of the most cited authors and their relations, the degrees of centrality and betweenness stand out. Bordin et al. (2014) Bordin, A. S., Gonçalves, A. L., & Todesco, J. L. (2014). Análise da colaboração científica departamental através de redes de coautoria. Perspectivas em Ciência da Informação, 19(2), 37-52. http://dx.doi.org/10.1590/1981-5344/1796.
http://dx.doi.org/10.1590/1981-5344/179... state that the degree of centrality shows how much an author relates to other authors, that is, shows the direct and indirect relationship between the published works. The higher this value, the more influential the work of a particular author is.

The degree of intermediation corresponds to how much an article acts as a facilitator of integration with other articles ( Lopes & Carvalho, 2012 Lopes, A. P. V. B. V., & Carvalho, M. M. (2012). Evolução da literatura de inovação em relações de cooperação: um estudo bibliométrico num período de vinte anos. Gestão & Produção, 19(1), 203-217. http://dx.doi.org/10.1590/S0104-530X2012000100014.
http://dx.doi.org/10.1590/S0104-530X201... ), it shows how an author is connected with other authors in the network, attributing the importance that this author has in a specific flow of information, characterizing the shortest path possible between the authors ( Bordin et al., 2014 Bordin, A. S., Gonçalves, A. L., & Todesco, J. L. (2014). Análise da colaboração científica departamental através de redes de coautoria. Perspectivas em Ciência da Informação, 19(2), 37-52. http://dx.doi.org/10.1590/1981-5344/1796.
http://dx.doi.org/10.1590/1981-5344/179... ). This means that the greater degree of betweenness, the more works cited by the related authors, making the cited work become a reference among references. Figure 4 shows that Mazzocato et al. (2012) Mazzocato, P., Holden, R. J., Brommels, M., Aronsson, H., Bäckman, U., Elg, M., & Thor, J. (2012). How does lean work in emergency care? A case study of a lean-inspired intervention at the Astrid Lindgren Children’s hospital, Stockholm, Sweden. BMC Health Services Research, 12(1), 28. http://dx.doi.org/10.1186/1472-6963-12-28. PMid:22296919.
http://dx.doi.org/10.1186/1472-6963-12-... and Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... present a large number of connections, making them references in the network of citations. Table 5 shows a summary of these relationships.

The last analysis of the networks deals with the occurrence of keywords, shown Figure 5 , where stand out five clusters:

• Lean: addresses the different lines regarding the application of the methodology;

• Six Sigma: addresses the use of the Six Sigma methodology associated with other methodologies;

• Operations: addresses the implementation of proposed methodologies, reengineering and results expected;

• Quality: addresses quality management as a means to achieve the objectives proposed in continuous improvement;

• Institutions: addresses the main actions that institutions adopt to achieve the best results with quality processes.

The criterion proposed for cutting was at least five keyword citations within the set of keywords used in all articles. Keywords without meaning, or with generic sense, were discarded, as well as those not recognized, indicated by 'error'. Keywords also have not been considered: lean health care, lean health care management, planning lean health care management.

The application of lean as a methodology for improving quality in health services is essential, since the methodology is approached from different perspectives, according to the need of each institution. Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... affirm that a wide variety of specialized management domains are introduced to transform established organizational and professional work practices, considered wasteful, evidencing an increasing impact on quality, cost, time, and satisfaction of both staff and patients.

The keyword 'Six Sigma' has strong association with quality processes, management and operations. This methodology addresses procedures for eliminating or reducing errors in processes and procedures. Although difficult to implement in the service sector, its use has been increasing, especially when associated with other methodologies and quality tools. Here, it appears as an alternative to associate lean tools and procedures.

The words 'lean', 'health care' and 'management' are centralized in the keyword network. All of them connect with the other clusters and very intensively. The word 'lean' stands out for its connections with the words 'patient safety' and 'employee involvement'. The first is to emphasize the importance of patient safety and the second to validate the importance of patient safety, highlighting the involvement of employees in achieving satisfactory levels of safety.

The word 'health care' emphasizes that operations are paramount to achieve consistent quality health service objectives. The relationship between health care, reengineering, impact, and performance shows that processes influence institution structures; when applied correctly, they produce good performance in quality management.

The word 'management' is the one that has the greatest relationship among all the other words in the network. It is very strongly related to three clusters of the network of keywords: operations, quality and institutions. This word shows that quality management, when associated with the best operations guidelines, is fundamental for health institutions.

4. Discussion

According to Table 1 , subjects related to processes and services dominate the discussion about lean health care, corresponding to 75.4% of the articles considered in the study. This is the foundation of kaizen, which aims to continuously improve the culture of the institution, impact on service improvement, reducing waiting times and improving patient care, with more organized spaces and better use and with changes in the flow of processes for workers and patients ( Radnor et al., 2012 Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... ). This shows that the use of lean tools has great insertion capacity, mainly for the continuous improvement of processes.

Figure 2 shows that 2016 was the year with the highest number of publications related to the lean health care subject. Table 4 shows that there is an increase in publications, with a low concentration of journals; 54% of the publications are in 11 different journals, showing the scope of the subject and the diversity of areas related to the subject.

The two most cited journals, Herd Health Environments Research Design Journal and Journal of Health Organization and Management, have only 7 publications each, resulting in 14.3% of all the publications. However, of the 856 citations, 634 correspond to the 13 most cited articles, resulting in 74% of the citations, which shows that few authors dominate the subject, making them the 'gurus' of the theme. This implies that 26% of the citations are divided among the other 85 articles, many of them with no citations.

Relationship networks play an important role between authors and their works. They show the major influencers in the theme, the countries with the largest number of publications, which encourage carrying out related studies and the connection between the keywords used by the authors.

The social network of countries shows the place where there is a greater concentration of published articles. England stands out for its robust and comprehensive health system, which results in many experiments and, consequently, many articles related to this system. In addition, Figure 3 shows that England has connections with practically all countries, with the exception of Japan, Switzerland, and Senegal. Northern Ireland, which integrates the United Kingdom and has a health care system similar to that of England, also stands out for the number of articles referenced.

In relation to the database, it is important to map the theme in relation to the 13 most cited articles that composed the guiding axis of this work.

The first article relevant to the theme was written by Nelson-Peterson & Leppa (2007) Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... ; the authors define lean health care in the Journal of Nursing Administration. In this article, the authors state that the health sector, as occurs with the manufacturing sector, is composed of a series of processes or actions aimed at creating value to patients and that, although there are differences between patients and products, health organizations are complex, with thousands of processes interacting.

This causes hospitals to work towards a good understanding of the patient's needs, requirements or how he interprets a service with high added value, so that there is ambiguity and uncertainty in what should be implemented with Lean ( Radnor et al., 2012 Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... ).

Moraros et al. (2016) Moraros, J., Lemstra, M., & Nwankwo, C. (2016). Lean interventions in healthcare: do they actually work? A systematic literature review. International Journal for Quality in Health Care, 28(2), 150-165. http://dx.doi.org/10.1093/intqhc/mzv123. PMid:26811118.
http://dx.doi.org/10.1093/intqhc/mzv123... corroborate this thinking, stating that lean has expanded to the health sector. The application of specific lean tools, such as kaizen and continuous improvement, tend to produce small and localized productivity gains ( Radnor et al., 2012 Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... ). Their goal was to show that although manufacturing works with different objectives, lean can also be applied to other areas, including health care.

The lean methodology adopts as a precept the importance of value, the search for eliminating waste and adding value to all processes ( Brackett et al., 2013 Brackett, T., Comer, L., & Whichello, R. (2013). Do lean practices lead to more time at the bedside? Journal for Healthcare Quality, 35(2), 7-14. http://dx.doi.org/10.1111/j.1945-1474.2011.00169.x. PMid:22093157.
http://dx.doi.org/10.1111/j.1945-1474.2... ). Different tools and methods are used together in a variety of settings, generating concepts that create value for patients and healthcare professionals ( Mazzocato et al., 2010 Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... ). Lean simplifies the standardization of tasks, processes, and the reduction of bureaucracy.

Grove et al. (2010) Grove, A. L., Meredith, J. O., Macintyre, M., Angelis, J., & Neailey, K. (2010). Lean implementation in primary care health visiting services in National Health Service UK. Qual Saf Health Care, 19(5), 1-5. PMid:20511600. state that the successful deployment of these improvements liberates organization resources, which are redirected to provide direct patient care. Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... , Seidl & Newhouse (2012) Seidl, K. L., & Newhouse, R. P. (2012). The intersection of evidence-based practice with 5 quality improvement methodologies. Journal of Nursing Administration , 42(6), 299-304. http://dx.doi.org/10.1097/NNA.0b013e31824ccdc9. PMid:22617691.
http://dx.doi.org/10.1097/NNA.0b013e318... , Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... , Waring & Bishop (2010) Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... and Nelson-Peterson & Leppa (2007) Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... corroborate this analysis, as they believe that this generates value to the patient.

Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... and Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... are the articles most cited in the database. Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... address the issue in the context of a review of the literature, highlighting interventions used in health care, methods for understanding and organizing processes, improving error detection, relaying information to problem solvers, and preventing errors from causing damage and to manage change and solve problems with a scientific approach. In turn, Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... highlight the difficulties encountered in the implementation of this methodology in the health sector, as an element of resistance on the part of the professionals involved, reinforcing the results shown by Moraros et al. (2016) Moraros, J., Lemstra, M., & Nwankwo, C. (2016). Lean interventions in healthcare: do they actually work? A systematic literature review. International Journal for Quality in Health Care, 28(2), 150-165. http://dx.doi.org/10.1093/intqhc/mzv123. PMid:26811118.
http://dx.doi.org/10.1093/intqhc/mzv123... , Kaplan et al. (2014) Kaplan, G. S., Patterson, S. H., Ching, J. M., & Blackmore, C. C. (2014). Why Lean doesn’t work for everyone. BMJ Quality & Safety, 23(12), 970-973. http://dx.doi.org/10.1136/bmjqs-2014-003248. PMid:25056985.
http://dx.doi.org/10.1136/bmjqs-2014-00... , Mazzocato et al. (2012) Mazzocato, P., Holden, R. J., Brommels, M., Aronsson, H., Bäckman, U., Elg, M., & Thor, J. (2012). How does lean work in emergency care? A case study of a lean-inspired intervention at the Astrid Lindgren Children’s hospital, Stockholm, Sweden. BMC Health Services Research, 12(1), 28. http://dx.doi.org/10.1186/1472-6963-12-28. PMid:22296919.
http://dx.doi.org/10.1186/1472-6963-12-... and Waring & Bishop (2010) Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... .

Andersen et al. (2014) Andersen, H., Røvik, K. A., & Ingebrigtsen, T. (2014). Lean thinking in hospitals: is there a cure for the absence of evidence? A systematic review of reviews. BMJ Open , 4(1), e003873. http://dx.doi.org/10.1136/bmjopen-2013-003873. PMid:24435890.
http://dx.doi.org/10.1136/bmjopen-2013-... emphasize that lean methodology, if not applied properly, does not generate significant results, since this methodology consists of multiple elements that interact with each other. To realize the potential benefits, health organizations need to directly engage top management and seek value creation for patients, nurturing a long-term vision of continuous improvement ( Mazzocato et al., 2010 Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... ).

According to Figure 4 , Andersen et al. (2014) Andersen, H., Røvik, K. A., & Ingebrigtsen, T. (2014). Lean thinking in hospitals: is there a cure for the absence of evidence? A systematic review of reviews. BMJ Open , 4(1), e003873. http://dx.doi.org/10.1136/bmjopen-2013-003873. PMid:24435890.
http://dx.doi.org/10.1136/bmjopen-2013-... have strong connections with Mazzocato et al. (2012) Mazzocato, P., Holden, R. J., Brommels, M., Aronsson, H., Bäckman, U., Elg, M., & Thor, J. (2012). How does lean work in emergency care? A case study of a lean-inspired intervention at the Astrid Lindgren Children’s hospital, Stockholm, Sweden. BMC Health Services Research, 12(1), 28. http://dx.doi.org/10.1186/1472-6963-12-28. PMid:22296919.
http://dx.doi.org/10.1186/1472-6963-12-... , which deal with the problems presented by lean, if not implemented with the necessary resources.

Radnor et al. (2012) Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... emphasize the difficulty in having different working groups interacting in favor of lean implementation. Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... , despite showing lean with a holistic view, in most cases report more restricted technical applications with limited organizational reach. Waring & Bishop (2010) Waring, J. J., & Bishop, S. (2010). Lean healthcare: rhetoric, ritual and resistance. Social Science & Medicine, 71(7), 1332-1340. http://dx.doi.org/10.1016/j.socscimed.2010.06.028. PMid:20702013.
http://dx.doi.org/10.1016/j.socscimed.2... , highlight the difficulties in implementing lean in the health sector and Young & McClean (2008) Young, T. P., & McClean, S. I. (2008). A critical look at Lean Thinking in healthcare. Quality & Safety in Health Care, 17(5), 382-386. http://dx.doi.org/10.1136/qshc.2006.020131. PMid:18842980.
http://dx.doi.org/10.1136/qshc.2006.020... emphasize that lean, when applied in isolation, produces little or no significant results. Many approaches are reported as having a punctual impact on quality, cost, time, and patient satisfaction as a single process ( Papadopoulos et al., 2011 Papadopoulos, T., Radnor, Z., & Merali, Y. (2011). The role of actor associations in understanding the implementation of Lean thinking in healthcare. International Journal of Operations & Production Management, 31(2), 167-191. http://dx.doi.org/10.1108/01443571111104755.
http://dx.doi.org/10.1108/0144357111110... ).

The social network of keywords, Figure 5 , has density large number of connections between the terms 'lean', 'health care' and 'management' with lean clusters, quality, institutions, operations and six sigma. Essentially, lean health care is a subject matter based on subjectivity between different terms, elements and a certain difficulty in quantitatively measuring the real benefits the methodology can bring to health systems.

However, the occurrence of cluster ‘institution’ shows that the central terms 'lean', 'health care' and 'management' have strong connection with the words patient safety, hospitals, environment and perspective. This helps to understand the importance of lean health care to institutions, since clusters of ‘quality’ and ‘operations’ have strong links to the central terms, forming a tripod that encourages the dissemination of lean methodology in hospital institutions, supported by quality and the way of operations are performed, highlighting improvements to clinical operations that can have a significant effect on patient care, especially in the development of health systems without high-level management of actions ( Carter et al., 2012 Carter, P. M., Desmond, J. S., Akanbobnaab, C., Oteng, R. A., Rominski, S. D., Barsan, W. G., & Cunningham, R. M. (2012). Optimizing clinical operations as part of a global emergency medicine initiative in Kumasi, Ghana: Application of lean manufacturing principals to low-resource health systems. Academic Emergency Medicine, 19(3), 338-347. http://dx.doi.org/10.1111/j.1553-2712.2012.01311.x. PMid:22435868.
http://dx.doi.org/10.1111/j.1553-2712.2... ).

The six sigma cluster is related, with greater intensity, to the outcomes of cluster operations, efficiency and quality improvement of cluster quality and transformation of cluster institutions. This indicates that the six sigma methodology is part of the process of continuous improvement, since it directs its efforts to achieve satisfactory results, seeking the efficiency in the quality processes and the transformation in the hospital routines associated to the new established processes. Lean Six Sigma methodology assists hospitals to serve patients better and faster, which in turn will lead to a reduction in treatment delay and faster patient recovery ( Gijo & Antony, 2014 Gijo, E. V., & Antony, J. (2014). Reducing patient waiting time in outpatient department using lean six sigmamethodology. Quality and Reliability Engineering International , 30(8), 1481-1491. http://dx.doi.org/10.1002/qre.1552.
http://dx.doi.org/10.1002/qre.1552 ... ).

De Mast et al. (2011) De Mast, J., Kemper, B., Does, R. J. M. M., Mandjes, M., & Van Der Bijl, Y. (2011). Process improvement in healthcare: overall resource efficiency. Quality and Reliability Engineering International, 27(8), 1095-1106. http://dx.doi.org/10.1002/qre.1198.
http://dx.doi.org/10.1002/qre.1198 ... state that the six sigma, lean, and total quality management approaches provide the opportunities needed to identify process improvements from a more accurate diagnosis. For improvement efforts to be successful, promising approaches such as benchmarking and operational research are needed for the selection and application of lean and six sigma factors ( Van Lent et al., 2012 Van Lent, W. A. M., Sanders, E. M., & Van Harten, W. H. (2012). Exploring improvements in patient logistics in Dutch hospitals with a survey. BMC Health Services Research , 12(1), 232. http://dx.doi.org/10.1186/1472-6963-12-232. PMid:22852880.
http://dx.doi.org/10.1186/1472-6963-12-... ). Gijo & Antony (2014) Gijo, E. V., & Antony, J. (2014). Reducing patient waiting time in outpatient department using lean six sigmamethodology. Quality and Reliability Engineering International , 30(8), 1481-1491. http://dx.doi.org/10.1002/qre.1552.
http://dx.doi.org/10.1002/qre.1552 ... and Van Lent et al. (2012) Van Lent, W. A. M., Sanders, E. M., & Van Harten, W. H. (2012). Exploring improvements in patient logistics in Dutch hospitals with a survey. BMC Health Services Research , 12(1), 232. http://dx.doi.org/10.1186/1472-6963-12-232. PMid:22852880.
http://dx.doi.org/10.1186/1472-6963-12-... show the relationship between lean and six sigma increase the patient satisfaction.

The connection between lean clusters and institutions shows that hospitals are targeting the improvement of their processes, products and services from the perspective of patient safety. Wilson (2009) Wilson, G. (2009). Implementation of releasing time to care: the productive ward. Journal of Nursing Management, 17(5), 647-654. http://dx.doi.org/10.1111/j.1365-2834.2009.01026.x. PMid:19575723.
http://dx.doi.org/10.1111/j.1365-2834.2... says that the lean methodology can improve patient satisfaction and safety-oriented clinical outcomes.

Crema & Verbano (2015) Crema, M., & Verbano, C. (2015). How to combine lean and safety management in health care processes: a case from Spain. Safety Science, 79, 63-71. http://dx.doi.org/10.1016/j.ssci.2015.05.007.
http://dx.doi.org/10.1016/j.ssci.2015.0... point out that improvements in patient safety and efficiency associated with lean & safety projects can be deployed together to improve efficiency and patient safety levels. Contradicting Wilson (2009) Wilson, G. (2009). Implementation of releasing time to care: the productive ward. Journal of Nursing Management, 17(5), 647-654. http://dx.doi.org/10.1111/j.1365-2834.2009.01026.x. PMid:19575723.
http://dx.doi.org/10.1111/j.1365-2834.2... and Crema & Verbano (2015) Crema, M., & Verbano, C. (2015). How to combine lean and safety management in health care processes: a case from Spain. Safety Science, 79, 63-71. http://dx.doi.org/10.1016/j.ssci.2015.05.007.
http://dx.doi.org/10.1016/j.ssci.2015.0... , Moraros et al. (2016) Moraros, J., Lemstra, M., & Nwankwo, C. (2016). Lean interventions in healthcare: do they actually work? A systematic literature review. International Journal for Quality in Health Care, 28(2), 150-165. http://dx.doi.org/10.1093/intqhc/mzv123. PMid:26811118.
http://dx.doi.org/10.1093/intqhc/mzv123... state that lean does not generate the potential benefits in the processes established for patient safety.

The operations cluster stands out for its connections with the word health care, showing the importance of operations management for health care systems. Drotz & Poksinska (2014) Drotz, E., & Poksinska, B. (2014). Lean in healthcare from employees’ perspectives. Journal of Health Organization and Management, 28(2), 177. http://dx.doi.org/10.1108/JHOM-03-2013-0066. PMid:25065109.
http://dx.doi.org/10.1108/JHOM-03-2013-... highlight the importance of teamwork in the organizational environment and personal development, influencing organizational performance. De Mast et al. (2011) De Mast, J., Kemper, B., Does, R. J. M. M., Mandjes, M., & Van Der Bijl, Y. (2011). Process improvement in healthcare: overall resource efficiency. Quality and Reliability Engineering International, 27(8), 1095-1106. http://dx.doi.org/10.1002/qre.1198.
http://dx.doi.org/10.1002/qre.1198 ... maintain that the division of labor into micro processes, tasks, and resources yields a system of metrics for process flow and resource efficiency.

The application of lean health care in hospital services, within a process of interaction with health professionals, shows the relevant difficulties in applying continuous improvement methodologies focused on quality.

5. Conclusion

The present study aimed to analyze the literature on lean health care in hospital services, using bibliometric resources. It sought to identify the main elements and aspects related to the proposed theme, as well as research gaps. The descriptive analysis showed an overview of lean health care and the social network analyses showed the main countries that publish on the topic, the relationships between the authors and the main keywords used in the articles of the database.

Within the lean health care research, the term 'management' serves as the central point of connection between three major areas: operations, quality and institutions. Programs that adopt lean health care as a methodology for continuous improvement in products and services need the support of management to implement the methodologies, as they often overcome internal obstacles, both regarding infrastructure and human resources. Mazzocato et al. (2010) Mazzocato, P., Savage, C., Brommels, M., Aronsson, H., & Thor, J. (2010). Lean thinking in healthcare: a realist review of the literature. Quality & Safety in Health Care, 19(5), 376-382. http://dx.doi.org/10.1136/qshc.2009.037986. PMid:20724397.
http://dx.doi.org/10.1136/qshc.2009.037... state that to improve lean efficacy in health care, it is necessary to involve management in the continued resolution of problems.

For hospital institutions, safety and patient care, coupled with lean perspectives, are critical to its application. However, this perspective can vary, since hospitals have different human resources, which are influenced by different organizational forms.

The team plays a key role in the implementation of lean methodologies. Morrow et al. (2014) Morrow, E., Robert, G., & Maben, J. (2014). Exploring the nature and impact of leadership on the local implementation of the Productive Ward Releasing Time to Care. Journal of Health Organization and Management, 28(2), 154-176. http://dx.doi.org/10.1108/JHOM-01-2013-0001. PMid:25065108.
http://dx.doi.org/10.1108/JHOM-01-2013-... reaffirm that the empowerment of the team allows leaderships to continuously disseminate the learning and the sustainability of the improvements. However, Drotz & Poksinska (2014) Drotz, E., & Poksinska, B. (2014). Lean in healthcare from employees’ perspectives. Journal of Health Organization and Management, 28(2), 177. http://dx.doi.org/10.1108/JHOM-03-2013-0066. PMid:25065109.
http://dx.doi.org/10.1108/JHOM-03-2013-... warn that lean can change the roles, responsibilities and characteristics of the work of the health team.

In most cases, lean applications emphasize the reduction of waste, since lean is a managerial concept ( Radnor et al., 2012 Radnor, Z. J., Holweg, M., & Waring, J. (2012). Lean in healthcare: The unfilled promise? Social Science & Medicine, 74(3), 364-371. http://dx.doi.org/10.1016/j.socscimed.2011.02.011. PMid:21414703.
http://dx.doi.org/10.1016/j.socscimed.2... ; Nelson-Peterson & Leppa, 2007 Nelson-Peterson, D. L., & Leppa, C. J. (2007). Creating an environment for caring using lean principles of the Virginia Mason Production System. The Journal of Nursing Administration, 37(6), 287-294. http://dx.doi.org/10.1097/01.NNA.0000277717.34134.a9. PMid:17563521.
http://dx.doi.org/10.1097/01.NNA.000027... ). However, Table 1 shows that patient safety has increased its influence on the subjects studied, since it directs the focus to the final client.

Future studies may direct their efforts toward the contradiction between the use of lean for managerial factors - which encompasses large multidisciplinary teams, or punctual factors - which comprises specific points of the processes involved. An approach in this line maybe will be interesting.

Acceptance of projects that aim to modify a work structure usually finds strong resistance, where critical success factors in lean projects are determinant for their performance, even if the impact is not significant in all dimensions ( Berssaneti & Carvalho, 2015 Berssaneti, F. T., & Carvalho, M. M. (2015). Identification of variables that impact project success in Brazil companies. International Journal of Project Management , 33(3), 638-649. http://dx.doi.org/10.1016/j.ijproman.2014.07.002.
http://dx.doi.org/10.1016/j.ijproman.20... ). Future studies may address the relationship between worker qualification and the use of lean methodologies when evaluating productivity in the health care environment, as well as the relationship with customers and suppliers and the development of systems capable of encouraging process innovation in search for continuous improvement.

The increasing use and dissemination of the internet, relating process data associated with the productivity of health care professionals and the need to manage different types of information, in a short period of time is increasingly present in this universe. In this direction, to study the possible connections between lean methodology and its application in internet of things (IoT).

The relationship between quality, costs and time need to be better equated, surpassing the purely qualitative approach. A more careful analysis of these factors would provide greater applicability to lean methodology.

The application of the lean methodology still remains rooted in the improvement of productive processes, associated with products. Future research could go deeper into lean studies, directing it to the service sector, specifically in health care.

The work has some limitations. It cannot be generalized, since the final database included only the articles that were in the ISI Web of Science database; this limitation is a reflection of the software used, VOSviewer, which only accepts files generated by a database.

The identification of the articles pertinent to the theme was made from reading the abstracts of each article; therefore, it cannot be said that the abstracts faithfully expresses the content of the article.

Some articles may not have been listed in the database because of the difficulty in relating as many keywords as possible. This gives a degree of lack of assertiveness to the full analysis of the topic.

The articles studied do not represent the universality of the theme but only those that were captured by the search for keywords adopted.

References

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