3.1 Global publications and trends
A total of 1,552 eligible publications on OLV including 1,391 papers and 161 reviews with a citation number of 24,304 were collected from the WoSCC database encompassing the past 40 years. The publication output and temporal trend on OLV research was plotted in Fig.1. During the selected period, the number of articles published and annual reference frequency fluctuated, but showed an overall trend of steady growth before 2021. The highest volume of articles and citations reached 134 and 2,510 respectively in 2021.
3.2 Contribution of Countries and Regions to Publications
The United States ranked the first regarding the number of publications (299, 23.73%), followed by China (261, 20.71%), Japan (158, 12.54%), Germany (129, 10.24%), and Korea (100, 7.94%). The detailed data of the top 10 countries/regions in the terms of the number of publications were presented in Table S1.
In terms of the total association strength, the United States (110), Italy (73), and Germany (70) were the strongest and invested more efforts to OLV research (Table S1). The citation frequency of the United States (5,246 times) accounted for 24.30% of the total. Publications by Germany were cited 3,101 times, ranking second among all countries. (Table S1).
We also analyzed the cooperation between countries for each published article (Fig.2 A). And found that research cooperation was highest with the United States. It was interesting that Korea was a self-contained collection, with only the United States.
3.3 Contribution of Institutions to Global Research on OLV
As shown in Fig.2B, most of the institutions were internal contacts and lack of cooperation and communication with other institutions. The top 10 institutions in terms of literature output were shown in Table S2. Yonsei University had the most significant number of publications (23,13.61%), followed by Stanford University (20, 11.83%) and National Taiwan University Hospital (20, 11.83%).
It is worth noting that National Taiwan University Hospital had the strongest total association strength and the highest frequency of paper citations (876) in this field. This institution should have conducted extensive researches in the field of OLV.
3.4 Distribution of authors and co-cited authors
The authors of the retrieved literature were analyzed, and the top 10 authors ranked by the number of publications and frequency of co-citation were found (Table S3). Cheng YJ from National Taiwan University Hospital in Taiwan published 15 OLV-related articles, ranking first in among global scholars. Campos JH and Chen JS both produced 13 articles, ranking joint second. All the authors are working in the department of anesthesiology except Chen JS, who is a thoracic surgeon.
Fig.3 visualized the collaborative relationships between authors in literature related to OLV. Similar to the network of national and institutional relationships, the co-authors can be divided into 31 groups according to the intimacy of cooperation. As shown in the Fig.3A, each cluster was only connected internally, and there was almost no connection between each other, which indicated that cross-agency or transnational cooperative research in the field of OLV was insufficient. The different colors in the co-cited author relationship network of Fig.3B partially reflect the same characteristics among the studies of co-cited authors. The authors were divided by the co-citation frequency into 4 clusters, perhaps because their research direction was broadly similar. According to Table S3, Benumof JL (468) has the highest number of co-citations, followed by Campos JH (432) and Brodsky JB (287). They are well-known and highly respected experts in thoracic anesthesia.
3.5 Distribution of journals
The top 10 journals with articles published on OLV, which were established by the number of articles and frequency of co-citation on OLV they published during this period (Table S4). A total of 573 articles related to OLV were included in the top 10 journals with respect to the number of publications, comprising 36.9% of the overall publications. Journal of Cardiothoracic and Vascular Anesthesia (147, IF=2.894), Anesthesia and Analgesia (92, IF=6.627), and Anesthesiology (65, IF=8.986) ranked the top three, accounting for approximately one-fifth of the total number of articles.
Co-citation frequency was a decisive factor for the impact of a journal in the field. Anesthesiology (4,380) was the journal with the most co-citation, followed by Anesthesia and Analgesia (3,088), and British Journal of Anesthesia (2,205). According to the Journal Citation Reports 2021 standards, 60 percent of the top 10 co-cited journals were classified as Q1 or Q2 (Table S4), the top 5 journals in terms of number of articles also ranked the top 5 in terms of co-cited journals, indicating these journals have a high reputation in the academic field of OLV.
We also applied VOSviewer to analyze the situation of journals and co-journals to show interactions and links between journals. As shown in Fig.4A, the journals were classified into five clusters, journals within the same cluster represented strong associations in terms of citation relationships with similar topics. The larger the node, the greater number of publications. Journal of Cardiothoracic and Vascular Anesthesia and Anesthesia and Analgesiain the yellow cluster have the largest number of journals. The purple cluster has fewer nodes, possibly because it focuses on emerging topics and research frontiers in the field.
Co-cited journals were divided into two clusters in Fig.4B. The size of the node represents the number of citations. The distance between nodes in the network reflects the closeness of their subject content. In the red cluster, Anesthesiology has the highest citation frequency and tends to be co-cited with British Journal of Anaesthesia, Anesthesia and Analgesia and Annals of Thoracic Surgery, representing their close scholarly relationship. Chest and Journal of Applied Physiology are clustered in green, with more potential internal links between American Journal of Respiratory and Critical Care Medicine, Circulation and Thorax.
3.6 Highly cited reference analysis using CiteSpace
To analyze the most influential papers in this field, we listed the top 15 publications with the most citations in Table S5 in terms of the first author, title, journal, publication year, citation numbers and digital object unique identifier. Hypoxic Pulmonary Vasoconstriction (Sylvester et al) got the highest number of citations (424). The main focus of this paper was the cellular and molecular work performed to clarify these intrinsic mechanisms of HPV[23]. The second most cited article was Protective ventilation influences systemic inflammation after esophagectomy - A randomized controlled study (Michelet et al), with 270 citations. This study shows a protective ventilatory strategy influences the proinflammatory systemic response during and after a complex surgical procedure requiring a prolonged period of OLV[24]. Guidelines for Perioperative Care in Esophagectomy: Enhanced Recovery after Surgery (ERAS®) Society Recommendations by Low is the third most cited article with 210. This review summarizes the following information, volatile or intravenous anesthetics are equally effective for maintenance of anesthesia. Intermediate-acting NMBs, BIS monitoring, avoiding volume overload, and lung protective strategies facilitate early extubation and reduce postoperative complications[25].
We analyzed the top 15 articles in terms of annual citation frequency(Table S6), which could evaluate the academic productivity, predict the development trends, and reflect the research hotspots in a field. The relationship among the studies was analyzed on Cite Space, and was found to have a specific time factor of publication (Fig.5A). In this network, each node represented a referenced article, and the size of each node was proportional to the total co-referencing frequency of related articles. The clustering of the relational network of literature (Fig.5B) yielded totally 21 co-reference clusters. These major cluster labels included mechanical ventilation, non-intubated VATS, sevoflurane, COVID-19, positive end-expiratory pressure ventilation(PEEP), intraoperative transesophageal echocardiography, endobronchial, arterial PO2, lung isolation techniques, cerebral desaturation, bupivacaine, endoscopic, complications-hypoxemia, esophageal, ERAS, pediatric surgery and electrical impedance tomography.
The burst test of annual citation frequency indicated a sharp increase in citations and some critical questions in the field proposed or solved in the documents. The top 25 cited outbreaks shown in Fig.6A started 1- 4 years after publication. Among the 1,552 articles of the past four decades, the episode concentrated from 2001 to 2022 with a high outbreak since 2009. These studies have suggested that the current research focus on OLV includes preventing lung injury after OLV and hypoxemia during OLV, and optimizing the protective ventilation strategies[6,24,26].
The network of citation relationship between the top 25 cited articles was shown in Fig.6B. The articles of Benumofin1987[27] and Slinger in 1992[28] were still cited in recent years, which implied the impressive achievements of these pioneers and foremost scholars for current understanding of OLV.
3.7 Keyword analysis
In order to analyze the frontiers of results and hot topics in the field of OLV research, we performed a keyword co-occurrence analysis using VOSviewer (Fig.7A). The thicker line between the keyword points in each section, the more frequent co-occurrence. The OLV field was co-categorized into 6 clusters, reflecting the possible six research directions. These clusters, with apparent associations among the top 15 high occurrence keywords, were in general agreement. The red cluster included “VATS”, “thoracoscopy”, “hypoxemia”, “thoracotomy” and “pneumothorax”. In the green cluster, “thoracic surgery”, “double-lumen tube”, “bronchial blocker”, “intubation” and “airway management” were all involved. In the blue cluster, there are “thoracic anesthesia”, “lung cancer”, “lung injury” and “PEEP”. The yellow cluster represented “OLV”, “propofol”, “inflammation”, “sevoflurane” and “dexmedetomidine(DEX)”. The purple cluster included “anesthesia”, “oxygenation”, “pressure-controlled ventilation” and “volume-controlled ventilation”. The smallest set is light blue and contains “esophagectomy”, “esophageal cancer” and “artificial pneumothorax”.
The top 20 most frequent keywords were listed in Table S7. “One-lung ventilation” was the most frequent keyword (575 co-occurrences), “thoracic surgery” (154 co-occurrences) and “double-lumen tube” (96 co-occurrences) ranked second and third. These keywords also had high association strength in the domain (all greater than 200).
Fig.7B shows the heat network relationship diagram of keyword co-occurrence. The keywords in red represented some of the current hotspots in the field. As can be seen from the figure, the OLV research change its focus from “hypoxic pulmonary vasoconstriction”, “thoracoscopy”, “hypoxemia” and “hemodynamics” to “ dexmedetomine”, “meta-analysis”, “inflammation”, “infants” and “airway management” in the past decade.