Top 100 Cited Articles on Peritoneal Dialysis: A Bibliometric Analysis

There are 21 journals in which the top-100 cited articles were published. The names of the journals, in the order in which the articles are cited, are as follows: Kidney International (25 articles), Nephrology Dialysis Transplantation (13 articles), and Journal of the American Society of Nephrology (12 articles). The top 100-cited articles were published in 15 countries. The country with the greatest number of publications was the United States of America (19 articles). The institution with the greatest number of articles (7 articles) was the University Health Network of Toronto. The author who wrote the most number of articles (5 articles) was Davies SJ.


INTRODUCTION
End-stage renal growth (ESRD) is a condition in which the renal function is terminated, and dialysis is required. Since the prescription of dialysis to patients with chronic kidney disease is subjective, ESRD is defined as an advanced stage of chronic kidney disease with a glomerular filtration rate of less than 15 mL/min/1.73 m2 or as symptomatic uremia that requires dialysis [1]. ESRD is recognized as a major global health problem. The prevalence of ESRD is increasing, both globally and in Korea [2,3]. Patients with ESRD may often suffer from various complications due to multi-organ dysfunction. In ESRD, two forms of renal replacement therapy may be used: peritoneal dialysis (PD) and hemodialysis (HD). As PD and HD, both have advantages and disadvantages over the other, the selection of the appropriate modality can be determined by the patient's preference, age, or other co-morbidities. Due to the technological innovation of peritoneal dialysis, treatmentrelated complications have been reduced. This has resulted in the increased use of PD as the long-term treatment of ESRD [4].
The Science Citation Index (SCI) was used to select journals with high academic contributions. The SCI was introduced in 1964 by the Institute for Scientific Information (ISI). It was also necessary for building indexes and collecting citation information for database screening of scientific journals. The SCI has become one of the most frequently and widely used databases for evaluating research performances and retrieving literature. In the field of science, as the number of articles increased, there was a corresponding increase in the limitation of providing these articles in the form of books and compact discs. This led to the development of a larger Web version known as the Science Citation Index Expanded in the Web of Science. The number of citations reflects the interest of the academic community. Reviewing frequently-cited articles can provide information on key areas and the areas of substantial growth in the specific field.
As the high number of citations is an indicator of high impact in the academic community, most-cited articles are especially important. The most-cited articles provide interesting insights on how topics, authors, and articles affect the field of study over time. Several studies have previously conducted analyses on highly-cited papers in various fields. These fields include anesthesiology, general surgery, plastic surgery, orthopedic surgery, dermatology, emergency medicine, obstetrics and gynecology, headache disorders, and critical-care medicine [5 -13]. However, no previous study has analyzed the top-100 cited articles on PD.
The purpose of this study is to broaden the understanding of peritoneal dialysis by presenting the most-cited articles pertaining to it.

MATERIALS AND METHODS
We performed a citation analysis of PD. The study was conducted in the following manner.
First, we searched for articles only related to peritoneal dialysis by excluding those that involved HD. We searched on the Web of Science (https://apps.webofknowledge.com) by limiting the document type to journal articles and reviews. The publication time was set from 1969 to 2019, a total of 50 years. Articles that fit these criteria were sorted based on the citation count.
Second, we selected 100 articles related to PD according to citation frequency. Then, we reviewed the contents of each article and organized these according to the number of citations, article title, publishing journal, topic categories, year of publication, and authorship. The topic categories were subtyped as mortality and survival, peritoneal membrane characteristics, presence of peritonitis, epidemiology, and pathophysiology. When there was more than one author, the first author was used as the criterion. Recommendations were excluded. No statistical technique was used. The data were presented using descriptive statistics.

RESULTS
A total of 10,803 PD-related articles were reviewed. We selected 100 articles and ranked them from the highest to the lowest number of citations ( Table 1). The most-cited article was cited 565 times. The top 20 articles were cited over 230 times. There are 21 journals in which the top-100 cited articles were published. The names of the journals, in the order in which the articles are cited, are as follows: Kidney International (26 articles), Nephrology Dialysis Transplantation (13 articles), and Journal of the American Society of Nephrology (12 articles). Nearly half of the articles have been published in these three journals (51 articles) ( Table 2).
The top-100 cited articles have been published in 15 countries. The country with the greatest number of publications was the United States of America (19 articles). The other countries were the United Kingdom (18 articles), Canada (13 articles), Sweden (9 articles), and the Netherlands (8 articles) ( Table 3).   Eight institutions provided more than three of the top-100 cited articles (Table 4). Counting was based on the first author's name for articles with multiple authors. The institution that published the greatest number of articles was the University Health Network of Toronto (7 articles), followed by The Chinese University of Hong Kong (6 articles) and the University of Amsterdam (6 articles).  1969-1979 1980-1989 1990-1999 2000-2009 2000-2009 Number of articles 3 21 31 38 7  Table 5 lists the top-ranked authors who had three or more published PD articles. The author who wrote the most number of articles was Davies, SJ (5 articles).

DISCUSSION
This study identified the top-100 cited articles for PD. These articles provided interesting insights into scientific advances and perspectives in the field of PD using the ISI database.
The most-cited article was published in 2010 by the Journal of the American Society of Nephrology and was authored by Bargman JM [14]. Previous CANUSA data showed that clearance of small solutes like creatinine and urea was associated with patient survival. The solute clearances could be divided into either peritoneal or renal clearance. This article analyzed the peritoneal and renal clearances separately in terms of the CANUSA date. The results showed that the contribution of residual renal function is more important than peritoneal clearance.
The second most frequently-cited article was titled "Peritoneal dialysis and epithelial-to-mesenchymal transition of mesothelial cells" [15]. This article was cited 518 times. It was authored by Yáñez-Mó, M in 2005 and published in the New England Journal of Medicine. The article stated that mesothelial cells undergoing epithelial-to-mesenchymal transition may change the pathophysiology of ultrafiltration failure. For patients undergoing PD, markers related to mesothelial cells such as snail, E-cadherin, and α2 integrin may be useful markers for follow-up.
The earliest paper on PD is "A simple and safe technique for continuous ambulatory peritoneal dialysis(CAPD)" [16]. This article was published in April 1978 in the Transactions American Society for Artificial Internal Organs. It reports the experience of performing CAPD using plastic dialysis bags instead of intermittent peritoneal dialysis using glass dialysate containers in 28 patients. This technique is safer because peritonitis was reduced. It was more suitable for chronic dialysis by making dialysis available at home. Since this paper, a large number of articles related to the benefits of CAPD have been published, and CAPD patients have increased.
The most interesting topic was under the umbrella of pathophysiology (28 articles). The articles under this topic covered laboratory changes during PD, changes in metabolism, and changes in residual renal function. The second most interesting topic was about the PD membrane (20 articles). The article with the greatest number of citations related to PD patient physiology was authored by Michael, J in 1981 and published in Kidney International [17]. The article discussed protein losses during PD. It stated that there was no significant difference in the patient's weekly protein loss on intermittent maintenance PD and continuous ambulatory PD. Rather, protein loss was increased in patients who developed peritonitis. According to the results of this study, the dialysate protein losses did not limit the usefulness of PD.
We found some interesting trends among the article topics as these have changed over time. First, the most frequent subject was pathophysiology. This was consistent with the results of the analyses in other fields [5,6,8,13]. Other topics often mentioned in many articles were basic research, treatment, and pathophysiology. Second, more articles were being published as time passed from the 1980s, 1990s, to the 2000s. Throughout the 1990s to 2000s, sixty-nine of the top-100 cited articles were published. Physiology articles were evenly published in each decade, but these articles were most common during the 2000s. This is probably due to the increase in the number of patients undergoing PD [18] and the possibility of increased large-scale researches launched. The second most interesting topic, the PD membrane, was published mainly in the 1980s. This trend is presumed to be due to the high initial interest in the role of membranes in PD. The differences among patients were revealed after the initiation of peritoneal dialysis.
Nineteen articles originated from the United States, while eighteen articles were published from the United Kingdom. Other fields also have the largest number of articles that came from the United States [5 -8, 10 -13]. There are a total of 9 top 100 cited articles published in Asia. Today, Asia is facing a strategic test to catch up with the West in several fields of research. As the access to data improves and large-scale research becomes possible in Asia, it is expected that many papers with a high level of evidence will be published. Accordingly, the number of citations and contributions will increase. We found that none of the top-100 cited articles came from South America or Africa. This could be related to the difficulties in access to information, research, publishing, and language barriers in these areas.
Kidney International was the most frequently cited journal (25 articles), followed by Nephrology Dialysis Transplantation (13 articles). More articles have been published in General Nephrology Journals, not specific PD journals such as Peritoneal Dialysis International. The reason can be estimated as follows. First, Peritoneal Dialysis International began publishing in June 1980. Second, because it deals with a variety of aspects of nephrology and urology, the accessibility to the journal itself is high and it has a high preference for authors. Institutions in the United States have made significant contributions to the research of PD. This can be explained by the enormous financial resources and the large-scaled American scientific community. Moreover, United States authors prefer to publish at accessible American journals and usually cite from American papers written in English [19]. However, the institution with the greatest number of citations on PD was the University Health Network of Toronto. It is a group comprising the Toronto General Hospitals, the Princess Margaret Cancer Centre, the Toronto Rehabilitation Institute, Toronto Western Hospitals, and The Michener Institute of Education. As a large, hospital-based research center in Canada, it has conducted research on transplantation, oncology, cardiology, infectious diseases, neurosciences, rehabilitation medicine, surgical innovation, and genomic medicine. It is among Canada's Top 40 Research Hospitals in 2018.
There are some inherent limitations to our study. Because of a debate about the value of citations, we attempted to analyze these citations. The citation count does not reflect whether it is a positive or negative reference [20]. The more frequently cited paper might not necessarily be the most meaningful and important one [21]. Certain types of articles, such as guidelines, systematic reviews, and meta-analyses tend to be cited more than other study designs [22]. It is also likely that older articles and journals have been cited more. However, identifying citation numbers is widely recognized as a good way to judge the merits of an article. The analysis of the citation rate would be able to identify the advanced field of expertise and provide a historical perspective on its scientific progress.

CONCLUSION
This study is the first in the field of nephrology to provide a list of the top-100 cited articles dedicated to peritoneal dialysis. Through this study, the research trends and major academic interests pertaining to peritoneal dialysis would be identified.

ETHICS APPROVAL AND CONSENT TO PARTI-CIPATE
Not applicable.

HUMAN AND ANIMAL RIGHTS
No human and animal were used for studies that are the basis of this research.

CONSENT FOR PUBLICATION
Not applicable.

AVAILABILITY OF DATA AND MATERIALS
Not applicable.

FUNDING
None.