The global publication trend and research development of nerve block: A visualisation analysis between 1997 and 2021

Background: Nerve block is a clinical technique for relieving pain during surgery as well as for postoperative analgesia and chronic pain. Here, we analysed the trends in nerve block research and compared the contributions from different countries, institutions, journals, and authors. Methods: We extracted all studies concerning nerve block published between 1997 and 2021 from the Web of Science database. Microsoft Excel and VOSviewer were used to collect publication data, analyse publication trends, and visualize relevant results. Results: A total of 6,437 publications with 111,612 citations were identied between 1997 and 2021. The United States contributed the greatest number of publications (2010), whereas China ranked second (518). Regional Anesthesia & Pain Medicine had published the most papers concerning nerve block. Harvard University and Mariano ER were the most productive institution and author, respectively, in the eld. Keywords were categorized into ve clusters: the association between nerve block and anaesthesia or analgesia, local anaesthetic drugs for nerve block, nerve block techniques, nerve block for postoperative analgesia, and nerve block for oral local anaesthesia. Management-related research was a heavily researched topic in the eld. Conclusions: We concluded that the United States contributed the most studies, and developing countries, led by China, are also encouraging study in this area. The exploration of new drugs in the elds of nerve block, multi-modal analgesia after surgery, treatment of chronic pain, analgesia for thoracic and abdominal surgeries, and analgesic interventions in oral therapy are a potential focus for future research. analgesia. Nerve blocks associated with the serratus anterior block are popular research topics, demonstrating that it is widely accepted as an alternative method for postoperative analgesia after chest wall surgery. In addition, the second article focused on postoperative analgesia of the knee and hip joints, indicating that nerve block is still one of the most important methods of postoperative analgesia after limb surgery. The third most popular article was a study of analgesia and complications after orthopaedic surgery with continuous nerve block. coloured the settlements according to the chronological of keywords and research hotspots, with earlier settlements represented in blue and recent settlements represented in yellow. The rst cluster focused on the association between nerve block and anaesthesia or analgesia. The second cluster focused on local anaesthetic drugs for nerve block. The third cluster dealt with nerve block techniques, such as ultrasound guidance or nerve stimulation. The fourth cluster focused on postoperative analgesia for clinical procedures related to nerve block. The fth cluster dealt with nerve block for oral local anaesthesia.


Introduction
Nerve block refers to the temporary blocking of the nerve conduction function by injecting local anaesthesia and adjuvant drugs around the nerve trunk; it includes central and peripheral nerve blocks (PNBs). Nerve block has a history of approximately 100 years and remarkable progress has been made in the last decade (1). Previously, nerve block techniques were used for relieving pain during the surgical period and their application gradually extended to other elds, such as postoperative analgesia and chronic pain, including chronic headache and low back pain (2,3). Nerve block techniques have been developed through blind exploration operations based solely on localisation through the application of nerve stimulators (4) and ultrasound imaging technology (5). An ultrasound-guided brachial plexus block was rst reported in 1978, with a success rate as high as 98% (6). Ultrasound-guided nerve blocks no longer block the super cial nerve trunk but have gradually developed to block the deep nerve plexus, which cannot be accessed from the surface of the body. The injection pattern of nerve blocks has also improved from single injection to continuous injection (7). Because of its safety, reliability, good analgesic effect, and the reduction in the amount of general anaesthetic drugs used, nerve block has become one of the most important methods for assisting general anaesthesia and for postoperative analgesia.
Bibliometrics is an optimal approach to quantitatively and qualitatively evaluate the achievements and trends of different research activities in a speci c eld over time. Bibliometric analysis can demonstrate the cross and cooperation between different countries, authors, and hotspots in some research elds in recent decades. VOSviewer (Leiden University, Leiden, The Netherlands) constructs and visualises data, which can couple keywords, authors, units, countries, and articles in the literature through clustering and constructing views to analyse the relationships among them.
Although nerve block techniques have made great progress and the frequency of nerve block use has been increasing, there is still no systematic bibliometric analysis that provides an overview of the development of nerve blocks over the decades. Thus, the present study involved a bibliometric analysis of published literature on nerve blocks from 1997 to 2021, presenting a history of the advances in this eld and providing supporting evidence to determine the future research direction and development trend for nerve blocks. VOSviewer was used to determine which countries, organisations, and authors had published the most studies, and to identify the articles and journals with the highest international collaboration in this eld. In addition, recent hotspots and research trends in this eld were identi ed through keyword analysis. The present analysis contributes to characterising and predicting development in a speci c eld and comparing contributions among countries, institutions, journals, and authors.

Methods
We searched through the Web of Science (WOS) Core Collection database; removed irrelevant articles, such as reviews, letters, duplicates, and retractions; and assessed and veri ed the data entry and collection independently. Differences between the two researchers' veri cations were discussed to reach a consensus. Finally, the two researchers manually cleaned and analysed the data using Microsoft Excel (Redmond, Washington, USA). Publication sources were collected from 1997 to 2021. The keywords included were 'nerve block', 'nerve blocking', 'nerve blockade', 'nerve blockades', and 'nerve blocks'. All literature searches and screening began on 31 September, 2021, to prevent search bias in the database.
The following indexes were included: Science Citation Index-Expanded, Social Sciences Citation Index, Arts and Humanities Citation Index, Conference Proceedings Citation Index (CPCI)-Science, CPCI-Social Science & Humanities, Emerging Sources Citation Index, Current Chemical Reaction-Expanded, and Index Chemicus. The VOSviewer (version 1.6.13) program was used to visualise the bibliometric network. The data were extracted carefully, including titles, publication dates, countries and regions, institutions, authors, keywords, publishing journals, sums of citations, and H-indexes. Subsequently, the data were imported into Microsoft Excel 2010 and VOSviewer and quantitatively and qualitatively analysed.

Results
The total literature screened included 12,851 published items, of which 6,211 were excluded based on the type of publication (reviews, editorials, letters, case reports, bibliographies, news items, book chapters, editorial materials, notes, corrections, biographical items, book reviews, correction additions, retracted publications, and proceedings papers). The study also excluded 203 studies written in non-English languages ( Figure 1). Finally, we performed a bibliometric analysis of 6,437 published articles.
There were 111,612 citations (85,922 excluding self-citations), and the H-index of the articles was 114, with 17.34 average citations per item.

Publication by country and international cooperation
The literature included articles from 108 countries. The world map showing country-wise publications on nerve blocks is shown in Figure 2. The countries producing more than 100 articles were the United States  Table 1 details the article and citation details of the top 20 journals with the most published articles. Regional Anesthesia & Pain Medicine published the most, with 399 papers (6.19%), followed by Anesthesia & Analgesia, with 301 papers (4.68%); the British Journal of Anaesthesia, with 133 (2.06%); and Anesthesiology, with 128 (1.98%). Acta Anaesthesiologica Scandinavica had the least published papers among the journals that had published more than 100 articles, with 108 (1.67%) ( Figure  5).

Active organisations and authors
The top 20 organisations and the articles produced by these organisations are listed in Table 2 Table 3. The authors from American make the greatest contributions among the top 20.
The top 10 citations of articles analysed According to total citation numbers, the top 10 most cited articles are presented in Table 4. In the top 10 most frequently cited articles, nerve block procedures were technically guided primarily by ultrasound, with the occasional use of nerve stimulators. Most of the research content of these articles focuses on the analgesia and treatment of chronic neuralgia after limb surgery, which is a large part of multi-modal analgesia. Nerve blocks associated with the serratus anterior block are popular research topics, demonstrating that it is widely accepted as an alternative method for postoperative analgesia after chest wall surgery. In addition, the second article focused on postoperative analgesia of the knee and hip joints, indicating that nerve block is still one of the most important methods of postoperative analgesia after limb surgery. The third most popular article was a study of analgesia and complications after orthopaedic surgery with continuous nerve block.

Keywords and research trends
Keywords that appeared more than 20 times in each article were analysed using VOSviewer. This study found that by combining words with the same meaning and removing meaningless words, these keywords could be divided into ve clusters, mainly including the research elds shown in Figure 6.

Development and trends in nerve block
In 1885, American scientist Halsted presented the concept of nerve block by injecting cocaine into the region surrounding nerves in the eld of oral surgery (8). By the 1950s, Pearson (9) and Sarnoff (10) located motor nerves by electrical stimulation with an insulated needle and pioneered the use of nerve stimulators for nerve blocks. With the further development of medical science, nerve blocks guided by nerve stimulators are gradually being replaced by ultrasound-guided nerve blocks. Ultrasound guidance can enhance the e cacy of local anaesthetics and reduce associated complications (11,12).
Furthermore, there is a wide range of drugs available, from a single local anaesthetic to a combination of multiple drugs for nerve block. The most commonly used drug for nerve block has been constantly updated from lidocaine in the past to ropivacaine now (13). Nerve blocks can reduce the use of analgesics and facilitate postoperative pain management (14). In recent years, the development of anaesthesia management with nerve block surgery includes prostate puncture (15) and surgical analgesia, including head, neck, and maxillofacial surgery analgesia (16), and postoperative analgesia for total hip and total knee replacement (17). The erector spinae plane block is an emerging regional anaesthetic technique with signi cant potential for clinical use, such as analgesia in breast surgery (18). Suprascapular nerve block is combined with axillary nerve block for arthroscopic shoulder surgery (19). Peripheral nerve block is also an ideal analgesic method during ambulatory surgery (20). Recently, nerve block not only is used in daytime surgery but also in analgesia in emergency surgery, such as the fascia iliaca compartment block relieving hip fracture pain (17). Adjuvant pharmaceutics have been shown to prolong the duration of local anaesthetic for PNB. Research ndings provide evidence for the consideration of dexmedetomidine (13), dexamethasone (21), and clonidine (22) as adjuvants to prolong PNB duration. Reversible nerve block can be achieved within a non-destructive temperature range.
Currently, nerve block has become an alternative option for postoperative multi-modal analgesia and some forms of chronic pain treatment (2,3,23). Based on the current number of published nerve block articles, the overall research trend has been increasing from 1990 to the present. In 1997, there were only 73 publications worldwide, but between 2010 and 2015, the number increased from under 200 to 400. By 2020, the number of articles on nerve blocks has increased to nearly 800, and according to the prediction made using regression statistics, the number of articles on nerve block will exceed 1000 by 2023, indicating that nerve block remains an important area of anaesthesia and pain research.
The United States still has the most related publications among the developed countries, followed by The journals that published more than 100 articles are basically anaesthesiology journals, such as Regional Anesthesia & Pain Medicine, Anesthesia & Analgesia, British Journal of Anaesthesia, Anesthesiology, and Acta Anaesthesiologica Scandinavica. This indicates that nerve block is the main eld of anaesthesiology research. Notably, among the journals with more than 100 articles published, the Journal of Endodontics is also included. Therefore, from the perspective of treatment, nerve block has been increasingly used in oral therapy for assisted analgesia in recent years. In addition, a number of articles have been published in the Journal of Arthroplasty, illustrating the increasing use of nerve blocks in perioperative analgesia for extremity surgery. Among the top 10 most cited articles, the rst was the study of a new method for ultrasound-guided nerve block in the chest wall (24), and seven of the articles were related to nerve block for limb surgery or pain (three articles were related to knee or hip surgeries, two were related to lower limb nerve blocks, and three were related to brachial plexus block and ischaemic nerve block in the forearm). The other two articles were mainly about the improvement of B-ultrasound guidance technology and the exploration of abdominal plane block after cholecystectomy for postoperative analgesia. In summary, we believe that the current focus of researchers on nerve block is mainly on the postoperative analgesia for limb surgery and the treatment of pain caused by other factors. In addition, researchers are constantly attempting to apply nerve block techniques in various aspects of postoperative analgesia, and the effect has been con rmed.
As shown in Figures 6A and B, using VOSviewer settlement analysis and trend analysis of the keywords, the study of nerve block has the following ve aspects: nerve block anaesthesia, nerve block, nerve block and ultrasonic technology, nerve block analgesia (especially limb surgery), and all types of surgery with oral and maxillofacial nerve block therapy and drugs. From the perspective of increasing trends in the current research on nerve block, the injection of dexmedetomidine around the nerve has recently become the focus of many studies. In other words, dexmedetomidine (13,25,26) has become a new target drug for nerve block in recent years. In terms of postoperative pain management, adductor canal block and local in ltration analgesia may be a good method for postoperative analgesia in lower extremity surgery.
By searching bibliometric articles, we found only two similar bibliometric articles, one describing regional anaesthesia (27) and the other describing epidural anaesthesia (28). The emphases and concerns of the two articles are different from those of ours. Through the quantitative analysis of nerve block literature, our study aims to understand the emphases and hotspots of current national and institutional studies on nerve block and their correlation. In addition, this study also focused on the development trend of nerve block in the future. The following areas require further research: the use of new auxiliary drugs for nerves containing dexmedetomide and local nerve blocks in oral therapy.
Our study had some limitations. First, only the WOS database was used in our study, therefore, the data retrieval may have been incomplete. Future studies should include the PubMed and Scopus databases as well. Second, regarding the de nition of keywords, nerve block includes central nerve block and PNB. Although the literature on these two parts is included in our search results, it seems more reasonable to measure the literature of central nerve block separately in future studies.

Conclusions
This study summarized and analysed articles related to nerve block from 1997 to 2021. The United States still contributes the most studies, and developing countries led by China are also encouraging study in this area. The exploration of new drugs in the eld of nerve block, multi-modal analgesia after surgery, treatment of chronic pain, analgesia for thoracic and abdominal surgeries, and analgesic interventions in oral therapy will all become research trends in the future.

Declarations
Con icts of interest:

None
Funding sources: None Data availability: The data used and/or analysed in our study are available from the corresponding author on reasonable request.  Figure 1 Flow diagram of the inclusion process. Detailed searching and screening process.  Fitting curves of cumulative publications and growth trends. Distribution of the top 20 journals which published research in the eld. Figure 6