Increase or decrease in patient satisfaction
The purpose of this systematic review was to evaluate the impacts of lean implementation on patient satisfaction in the healthcare services. In this study, we found that most of the reviewed studies reported increased patient satisfaction after lean implementation, and the view is consistent with those mentioned earlier in Weinstock .But our study also found that satisfaction remains  and satisfaction declines after intervention [6, 47]. The reason may be that if the satisfaction baseline is already very high, there will be relatively little room for improvement of patient satisfaction brought by the implementation of lean medicine. In addition, another reason may be that it takes more time to improve patient satisfaction .
Two studies conducted in primary care organizations found that patient satisfaction decreased after lean implementation. The study points out that the patient doctor meeting is the most important occasion to jointly create patient value and to evaluate the quality of nursing function. Lean implementation improves the operation efficiency of medical institutions, and the most immediate effect is an increase in patient throughput. Then the doctor spends less time on every patient, the patient noticed this change [6, 47]. While in primary care, patients seem to be more likely to notice this change, and therefore show dissatisfaction, which is consistent with our previous point of view that "patient-doctor interaction time" will affect patient satisfaction .
Thus, the impact of the lean on patient satisfaction cannot be precisely determined with certainly, which is consistent with the views of Suzan Hammoudeh et al . In addition, there is a potentially important reason that most studies use researcher-defined parameters to measure patient satisfaction. The effectiveness of this research tool is questioned because the focus of patient satisfaction should be on the patient, using predetermined parameters instead of exploring the potential value held by the patient .
Factors affecting patient satisfaction
In terms of factors affecting patient satisfaction, our study found that external factors such as the environment were not significantly associated with patient satisfaction, which is consistent with the research of Larkins et al  and McEntire, et al . In the department regarding patient complaints, 95% of the complaints are non-medical aspects, such as communication, cleanliness, food, parking, staff attitude, waiting time, wrong bills, et al . This reminds us that first, improving patient satisfaction requires more starting from internal hospital activities, and secondly, the survey of satisfaction should involve weight issues. Otherwise, although the logical relationship between the patient's personal characteristics and satisfaction has not been demonstrated, it is certain that there is a certain connection between them .
In terms of satisfaction measurement, although most of the included literature use some tools to draw quantitative or qualitative conclusions that patient satisfaction is improved, there is no unified evaluation standard. Most of the evaluation tools are designed by the project implementers or rely on the national satisfaction survey. Among them, the reliability and validity self-designed questionnaire in some studies still need to be tested, and it is difficult to determine the extent to which the improvement in satisfaction is due to the lean implementation in the satisfaction measurement that relies on the national survey, so the value of the research results is limited.
In the dimension of satisfaction, patient expectations are less considered in measurements of patient satisfaction. Since lean production was originally designed to improve the efficiency of the production system. While in the medical field, it is generally believed that value is created by healthcare providers, and the contribution from patients’ perspective is limited. Therefore, healthcare institutions only focus on internal activities within the organization without thinking too much about the role of patients in the value creation process. However, patients have their own preferences and experience requirements (functional quality). In order to achieve more timely and efficient care and more patient-centered care, the patients’ perspective needs to be better integrated into current lean applications .
Regarding the follow-up issues, only four studies have adopted follow-up. In fact, a change in patient satisfaction can be appreciated only after a while and not immediately after the launch of Lean initiatives . Secondly, follow-up time (accountability and continuous estimation of the effectiveness of changes in implementation [52, 53]) is short, which makes it difficult to confirm the sustainability of the improvement. In fact, through continuous follow-up research on patient satisfaction, the changes in patient satisfaction can be dynamically revealed, so as to evaluate the effect of lean implementation on satisfaction and formulate the most effective action strategy.
Purpose of lean implementation
Analysis the problems of lean implementation and improvement in the searched studies, most of them are concentrated in the medical service process, and uses the time comparison before and after the application of the lean method to evaluate the improvement degree of this method. Non-medical activities concern little in the selection of departments, for example with only one direction of literature research in improving the patients’ diet. This may be because of the hospital nature. The main function of the hospital to treat diseases and save people, which determines that these departments become the main department of the hospital. With the increasing number of patients, the hospital is more urgent to improve these departments, but in fact, the hospital is a comprehensive organization that encompasses many different types of departments, and there must be varying degrees of waste in the operation of these departments and opportunities to improve, but did not give full attention.
Regarding the continued improvement of the results, our study found that most of the current studies are one-off studies, and the satisfaction evaluation is limited to twice before and after implementation. Only two studies mentioned that the lean improvement and patient satisfaction assessment continued after the completion of the project, and maintained the results of the improvement. Lean methods are iterative . Lean is never a one-time solution, it is based on continuous improvement . But apparently, maintaining these results is challenging .
The essence of lean healthcare
Lean management creates value by focusing on patients and meeting patients' needs for the essence of medical services, which includes creating value for patients in service process and medical results. This study found that in lean practice, the core factor to solve the medical needs of patients has been ignored. For medical institutions, the application of lean can provide maximum services at the least cost. Reducing costs through the implementation of lean is the initial purpose of many medical institutions to implement lean. Therefore, it is not surprising that efficiency priority has become the primary choice of medical institutions. In this study, 51 cases, most of the original intention of implementing lean is to improve efficiency to improve satisfaction, and only cases propose to improve quality to improve patient satisfaction.
Lean medical emphasizes creating value for patients, and the definition of value is also from the perspective of patients. In the whole medical service process, eliminate waste in all links, realize value flow and achieve zero harm. However, in lean practice, we often focus on the service process, and the essential needs of patients for medical services, that is, the treatment effect and results, are lack of sufficient research.
For patients, coming to the hospital is to solve their own diseases. This process includes service process and service results. Both are very important to patients, but the latter is the most fundamental. No patient is expected to be hurt when he comes to the hospital. Therefore, lean emphasizes zero harm more from the perspective of hospital managers. The perception of patients' satisfaction with medical services should not be just efficiency factors such as process, service attitude and waiting time compression. The treatment effect, that is, effectiveness, should be the core value of medical services.
Suggestions on the future study of patient satisfaction
Therefore, through the literature review, we suggest future research can seek inspiration from the following aspects to better explore the impact of lean implementation on patient satisfaction. First of all, before the lean improvement, set up the experimental group and the control group to control the relevant variables.
Second, the evaluation dimension of patient satisfaction should be patient-centered and fully consider the needs of patients. To this end, the concept of "patient expectations" can be introduced, that is, what kind of services and treatment patients expect before entering a hospital or a certain department for treatment. The degree of satisfaction of the patient’s relevant expectations by the time the treatment is completed and leaving the hospital or department; at the same time, the evaluation of satisfaction should be evaluated in different dimensions, and should not be limited to an overall and general evaluation.
Third, the survey methods should be a combination of qualitative and quantitative. Quantitative research mostly uses questionnaires. In order to obtain a more accurate relationship between lean intervention and patient satisfaction, a questionnaire that match this item should be set up, and the questionnaires should be tested for reliability and validity; qualitative interviews should be used as a supplement to quantitative research. Sometimes you receive unexpected answers, and you can more accurately get the patient’s true thoughts through non-verbal information. At the same time, all the above surveys are best conducted by third-party agencies or personnel to avoid the influence of participants, and it can also exclude patients from making tendentious choices due to concerns about the effect of treatment and the authority of doctors. Finally, after the project is over, follow-up should be conducted to continuously track the effect of impact on patient satisfaction, follow-up changes in real time, and pay attention to the long-term impact of lean implementation on patient satisfaction.