We have presented a visual analysis of the research literature into the treatment of ARDS, which revealed the following epistemological characteristics. The body of literature has grown over time, with Critical Care Medicine and Intensive Care Medicine publishing multiple papers on the topic. Many of the researchers publishing on the topic were affiliated with the University of Toronto, St. Michael’s Hospital, the University of Washington, and the University of California, San Francisco. Co-citation analysis grouped the references into eight major co-citation clusters indicating research interests within the field of ARDS therapy. The 15 keywords thus identified may be helpful in formulating future research.
The growth in the number of publications indicates that an increasing number of researchers were studying ARDS treatments, frequently in collaboration with researchers in other institutions. Nearly one-third of the literature was published in just 10 journals, indicating that ARDS treatment was within the scope of research published by these journals.
Reference co-citation analysis was used to assess the co-citation relevance between papers, and to categorize the data into major clusters representing research interests. In our study, the reference network was grouped into eight clearly defined co-citation clusters. Active research in this field appears to be dominated currently by extracorporeal membrane oxygenation and acute lung injury. Extracorporeal membrane oxygenation, as an approach to cardiopulmonary support, has been shown to improve the survival of patients with severe respiratory failure [20], and was used in influenza A (H1N1)-associated ARDS [21]. Related topics of research discussion were criteria for extracorporeal membrane oxygenation, extracorporeal carbon dioxide removal and long-term outcomes of this approach [22, 23]. However, the most recent study (EOLIA trial) in patients with severe ARDS showed no benefit, in terms of 60-day mortality, with extracorporeal membrane oxygenation [24]. The ventilatory strategies cluster, which contained the most articles, including comprehensive topics involving the open lung [25], PEEP level setting [26] and fluid-management strategy [27], short-term prone positioning, and the burden of ARDS [28], has been inactive since 2010. The clusters marked with long-term outcome and acute lung injury have developed and remain active. In particular, the former was in an inherent relationship with the cluster of ventilatory strategies, and we found some overlapping topics in their core literature, such as PEEP [29] and prone positioning [30]. Treatment outcome has always been the focus of attention in research into ARDS and, perhaps for this reason, the long-term outcome cluster kept in close contact with the acute lung injury cluster and extracorporeal membrane oxygenation, which served as a bridge among the clusters. The core articles targeting prognosis of ARDS were contained in the aforementioned clusters. From the timeline view, “acute lung injury” was the recent cluster, and is still active. The themes of core articles contained ventilator-induced lung injury [31], the exploration on sub-phenotypes of ARDS [32], driving pressure [33], the effect of high-flow oxygen on acute hypoxemic respiratory failure [34], and the reassessment of ARDS burden [1]. These topics seemed to be unfocused but involved basic data, issues of wide concern, and exploration of new direction, which were often co-cited in the papers to provide basic support and guide the elaboration, and probably developed over time.
A heavily cited keyword is considered an indicator of a topic of research interest, or an emerging trend. Extracorporeal membrane oxygenation and its abbreviation (ECMO) take the top two spots in the ranking of citation burst strength in recent years, indicating that this topic will continue to be studied. Meta-analysis can comprehensively analyze the results of previous randomized controlled trials on ARDS, to come to more-objective conclusions, and it is still expected to be the popular research methodology based on the strength value obtained. In the field of basic research, oxidative stress has become a popular topic of investigation in ARDS therapy. Table 5 shows the progress in ARDS research through the evolution of burst keywords over the past decade. Factors that can precipitate ARDS, which appeared in the literature we analyzed, were pneumonia, infection and severe sepsis, in chronological order. A similar evolution was reflected in the therapeutic methods, from lung recruitment and protective ventilation, to noninvasive ventilation, to extracorporeal membrane oxygenation.
To perform the co-citation clustering analysis, we selected the Web of Science as our final literature source, which may have excluded some studies. Valuable articles can also be found in evidence-based medicine databases such as the Cochrane Library and citation databases such as Scopus. When constructing the retrieval strategy, we listed a large number of technical terms related to ARDS treatment, and limited the scope to treatment, possibly ignoring the literature related to diagnosis, prevention and control of ARDS, which may influence treatment. We selected as many search terms as possible, to cover as much of the relevant literature as we could. Research topics that are deemed exciting are often pursued intensively during a given period and result in multiple publications, but the findings may not be clinically valuable with the passage of time and further investigation, weakening the value of the research topic. Finally, we did not include conference abstracts in our search, which may have influenced the weighting of results.