Web of Science (WoS) is a leading global citation database renowned for its coverage of natural sciences, social sciences, arts, and humanities (22). Evaluations by Gusenbauer highlight WoS’s strengths in interdisciplinary coverage, citation tracking, and deduplication, significantly enhancing the accuracy and efficiency of bibliometric analysis (23, 24). Moreover, publications in the WoS Core Collection (WoSCC) are globally recognized for their high quality and impact (25). Therefore, WoSCC was selected as the sole data source for this study.

All the data was obtained from WoSCC on March 12, 2025. The data retrieval strategy was as follows: (i) Topic 1 = (“intensive care*” OR “ICU” OR “critical care*” OR “critically ill patients” OR “critical illness”) AND Topic 2 = (“rehabilitation” OR “physiotherapy” OR “physical therap*” OR “physical medicine” OR “early mobili*” OR “early ambulation” OR “exercise” OR “occupational therap*” OR “speech therap*” OR “swallowing therap*” OR “cognitive training” OR “psychological therap*” OR “muscle * training” OR “electrical stimulation*” OR “wake promot*” OR “promot* arousal” OR “arousal promot*” OR “wakefulness promot*” OR “promot* wakefulness”) AND Topic 3 = (“mechanical ventilat*” OR “invasive ventilation” OR “non-invasive ventilation”); (ii) Document Type = article; (iii) Language = English; (iv) Publication Year = 2005–2024.

Inclusion criteria were: (1) The study population was clearly defined as ICU patients receiving MV (including invasive and non-invasive); (2) The research content must focus on the rehabilitation interventions for patients with MV, including but not limited to early mobilization, physical therapy, occupational therapy, cognitive training, and other related approaches; (3) Original articles (e.g., randomized controlled trial, cohort study); (4). Articles published from 2005 to 2024; (5) Only studies focusing on adult patients were included.

Exclusion criteria were: (1) Publications not in English; (2) Animal or in vitro experiments; (3) Not-original research (e.g., review, editorial, meeting); (4) Duplicate publication, only the latest or most complete version was retained; (5) Retracted publications.

Literature screening was conducted by at least two independent reviewers. One reviewer had a doctoral degree and rich clinical rehabilitation expertise, and another had a master’s degree and extensive experience in literature review. Discrepancies were resolved through discussion or, if necessary, by consulting a third expert. This approach ensures the objectivity and accuracy of the study selection. Finally, full records and their corresponding cited references were downloaded in plain text format, and the exported document was named “download_XXX.txt.” And then imported into the CiteSpace and Bibliometrix for visual analysis. The flowchart of literature screening is shown in Figure 1.

CiteSpace is a citation visualization analysis software under the background of scientometrics and data visualization (26). CiteSpace can visualize and analyze the literature in WoS, PubMed, CNKI, and other databases to present the structure and distribution of scientific knowledge, help researchers to quickly sort out the history of the development of a certain field, find out the key literature and keywords, and identify the research frontiers and development trends in the field (27, 28). This study utilized CiteSpace V.6.1. R6 (64-bit) to analyze relevant research. Bibliometrix is the R package for bibliometrics that integrates scientific cartographic analysis (29), which can automatically convert and analyze the bibliographic information of the selected publications, including country, institution, journal distribution, year of publication, authors, and keywords. The Bibliometrix package in R 4.4.2 was used to extract the main information, construct the global distribution network, and create a country-author-keywords three-field plot.

CiteSpace was used to analyze publications on country, institution, author, cited journal, cited reference, and keywords. The time slice ranges from January 2005 to December 2024, with an interval of 1 year. CiteSpace can generate a visual knowledge graph consisting of nodes representing different elements, such as institution or country, and links between nodes indicating cooperative or co-cited relationships. The size of the node reflects the frequency of the term, and the larger the node, the higher the frequency. The nodes are shown as circles, and the width of the circle in a given year represents how many terms appear in that year, and the wider the more terms appear. Different colors of the circle indicate different years, darker ones indicate earlier years, and lighter ones indicate more recent years. In addition, the purple outer ring represents centrality, and a thicker purple outer ring indicates greater centrality. Nodes with high centrality are generally considered to be turning points or pivotal points in the field (30). The Journal Impact Factors (IF) cited in this analysis are from the 2024 edition of the Journal Citation Reports (Clarivate Analytics).

Through our search strategy, we manually excluded irrelevant literature, and finally, a total of 375 publications were included in this study. The relevant data of retrieved publications (as shown in Figure 2A) included 167 sources, 2,479 authors, and 7,773 references. Furthermore, the document’s average age is 6.14, which indicates that critical rehabilitation is an emerging and promising research field. As can be seen from Figure 2B, the number of published articles in the field of early rehabilitation of patients with MV has shown a steady growth trend in general in the past 20 years, and the annual growth rate is 21.59%, indicating that this field is currently a hot spot of concern for researchers. According to the degree of variation, the annual number of publications can be classified into two distinct stages. The first stage is the slight growth stage: From 2005 to 2015, the total number of published papers during this period was 91, and the maximum difference in the annual number of published papers was only 23. The second stage is the significant growth stage: From 2016 to 2024, the total number of papers published during this period was 284, and the maximum of the annual publication difference was 48. It can be seen that the study of early rehabilitation of patients with MV is attracting increasing attention and may become a research hotspot and focus in the future.

To probe the connection between studies published in each country, we analyzed all articles on early rehabilitation of patients with MV from 2005 to 2024 in 1-year slices. It produced a country co-occurrence map with a merged network of 55 nodes and 202 links shown in Figure 3B. The country with the largest number of publications is the United States (99), followed by Brazil (42), Australia (39), England (28), and China (27). The top-ranked country by centrality is the United States with a centrality of 0.36, followed by Brazil (0.24) and Australia (0.14). The United States demonstrates significantly higher publication volume and centrality compared to other nations, solidifying its position as the cornerstone of this research field with unparalleled influence and academic leadership. Although China, Italy, Canada, and Japan occupy the top ten in the number of annual publications, their centrality is low. And a map of the country’s collaboration is shown in Figure 3A. Different colors represent disparate yields, with darker blue indicating that the country is publishing more articles in the field. The lines between countries represent their cooperation and connection. Research collaborations were primarily concentrated in North America, Europe, Oceania, and East Asia, with particularly strong ties between Europe and the United States but weaker connections between Asia and South America.

Setting “institution” as the node type, we generated a co-occurrence map of institutions with a network of 354 nodes and 634 links as shown in Figure 3C. The institution with the largest number of publications is Johns Hopkins University (17, the United States), then the University of Melbourne (9, Australia), the University of Toronto (8, Canada), and Austin Health (7, Australia). The leading institutions are primarily from the United States and Australia, yet low centrality scores indicate insufficient collaboration. Moreover, China, Japan, Canada, and other nations should focus on in-depth research on early rehabilitation for patients with MV while fostering closer international cooperation with other countries. The top ten most productive countries and institutions in this area of study are shown in Table 1.

Visualizing the analysis with “cited journal” as nodes, all articles on the critical rehabilitation from 2005 to 2024 were sliced with a time interval of 1 year. Then 455 nodes and 3,621 links were obtained for cited journals (Figure 4A). The most cited journal is Critical Care Medicine (292), then is Critical Care (247), Intensive Care Medicine (242), and American Journal of Respiratory and Critical Care (222). The top ten cited journals in this field and their centrality are shown in Table 2. The highest centrality of the cited journal is Anesthesia and Intensive Care (IF = 1.2) with 0.11, followed by American Journal of Critical Care (IF = 2.2) with 0.09 and Anesthesiology (IF = 9.1) with 0.09.

The dual-map overlay of the journal can intuitively represent the research dynamics of the discipline (Figure 4B). Each point on the dual-map overlay represents a journal category, which is mainly composed of two parts: the left is the citing journal, the right is the cited journal, and the curve between them is the path of citation (31, 32). We can see that most publications were published in journals related to mathematics, physics, ecology, molecular, medicine, medical, clinical, and neurology. Moreover, most publications were cited in journals related to systems, nutrition, materials physics, health, nursing, rehabilitation, and psychology education. There is one main citation path, the green curve, which indicates that journals in the field of health, nursing, and medicine are predominantly cited by journals in the field of medicine, medical, and clinical.

Selecting “author” as the node type analysis, we obtained the co-author network map with the combined network of 473 nodes and 807 links, as shown in Figure 5A. The top three active authors are Needham Dale M (9), Kho Michelle E (6), and Denehy Linda (6). Table 3 lists the top ten authors who published critical rehabilitation-related articles and their centrality. They are active and influential authors in this field. The most active academic research group came from America, followed by Australia, Canada, and Belgium.

Selecting “reference” as node types, finally generated a co-citation network map with a merged network of 638 nodes and 2,566 links, as shown in Figure 5B. The top ten most cited references in this area of study are shown in Table 4 (17, 33–41). Early physical and occupational therapy in mechanically ventilated, critically ill patients: a randomized controlled trial, written by Schweickert WD in 2009, is the most cited literature. Followed by Early intensive care unit mobility therapy in the treatment of acute respiratory failure by Morris Peter in 2008, and Safety of Patient Mobilization and Rehabilitation in the Intensive Care Unit. Systematic Review with Meta-Analysis written by Nydahl Peter in 2017. It is evident that the majority of co-citations focus on the effects of active mobilization and rehabilitation in the ICU on mortality and functional outcomes, with primary interventions including physical therapy and occupational therapy. The cited references were predominantly published in earlier years, reflecting the enduring influence of classical literature in the field. It may also be related to the time lag required for recent studies to accumulate citations and the current scarcity of high-quality evidence-based research. Therefore, future efforts should focus on exploring new research hotspots and conducting more high-level studies to advance the field.

Based on co-occurrence analysis, the log-likelihood ratio is used to cluster references, and a reference clustering network diagram was created (Figure 5C). A clustering modularity value (Q) greater than 0.3 indicates the effectiveness of the clustering, while a clustering silhouette index (S) greater than 0.7 validates the reliability of the cluster analysis results (42). The cited reference cluster exhibits a Q value of 0.7712 and an S value of 0.8904, indicating high effectiveness and reliability. A total of 8 clusters were obtained, including #0 critical care-what influence, #1 inspiratory muscle training, #2 physical therapy strategies, #3 clinical trial, #4 physical therapy, #5 daily living, #7 early mobilization program, #10 intrapulmonary percussive ventilation. Among the clusters, #1, #2, #4, #7, and #10 mainly focus on rehabilitation interventions for patients with MV in the ICU. Clusters #1 is about the outcomes and impacts of ICU patients, while clusters #3 is primarily concerned with study designs and methodological approaches. The most impactful studies in this field are predominantly centered on physical therapy and pulmonary rehabilitation. The specific information of the references cluster labels is shown in Table 5.

“Keywords” were selected as node types, and a combined network of keyword co-occurrence graphs with 399 nodes and 2,614 links was generated (Figure 6A). The top 10 high-frequency keywords are intensive care unit (163), mechanical ventilation (149), rehabilitation (80), early mobilization (56), outcome (51), physical therapy (42), therapy (41), survivor (39), acute respiratory failure (32), and exercise (26). Based on co-occurrence analysis, the keyword clustering network diagram was generated, with a Q value of 0.708 and an S value of 0.88 (Figure 6B). Ten clusters were produced including chest physiotherapy (#0), critical illness (#2), delirium (#3), mechanical ventilation (#5), quality improvement (#6), physical therapy modalities (#7), pain assessment (#8), acute respiratory failure (#9), electrical stimulation (#12), and early mobilization (#13). The specific information of keyword cluster labels is shown in Table 6.

To better understand the relationship among authors, countries, and keywords, a three-field plot was generated (Figure 6C). The width of the connecting lines between nodes is proportional to the strength of connections, and the wider the lines, the more connections there are. We can see that the United States (flow count is 17) was the most connected country, followed by Australia (flow count is 14), Germany (flow count is 6), and Canada (flow count is 5). The scholars who contributed the most keywords were Berney Sue and Denehy, Linda from Australia, and Needham Dale M from the United States. This finding further underscores the significant contributions of the United States and Australia to advancements in this field.

“Burst” means a sudden increase over a period of time. The burst word analysis can help detect the burst word with a high frequency change rate and rapid growth rate, and then analyze the frontier field and development trend of this discipline (43). The top 20 keywords with the strongest citation bursts from 2005 to 2024 are shown in Figure 6D. The blue line indicates the time intervals, and the red line indicates the time of the keyword outbreak. In the field of early rehabilitation of patients with MV research, physiotherapy, activities of daily living, respiratory failure, and airway clearance are earlier keywords (before 2010), while muscle atrophy, pulmonary rehabilitation, and muscle strength are the most recent keywords to appear (after 2020). In addition, mobility, respiratory failure, quality of life, and physiotherapy have a large strength. Pulmonary rehabilitation, cognitive training, and muscle strength training may be the future trend of early rehabilitation of patients with MV. The evolution of keywords highlights the advances in the field in optimizing patient outcomes and quality of life, reflecting the gradual maturation of early rehabilitation practices.

To further investigate research hotspots and emerging trends in rehabilitation interventions within this field, we systematically identified and extracted rehabilitation treatment-related keywords for visual analysis (Figure 7A). The main rehabilitation treatments included early mobilization, physical therapy, exercise, and mobility. Additionally, electrical stimulation, occupational therapy, and pulmonary rehabilitation are also utilized. In contrast, cardiac rehabilitation, cognitive therapy, and chest physical therapy are frequently applied. The timeline (Figure 7B) illustrates the evolution of keywords over the past two decades and forecasts their future trends. Early rehabilitation interventions primarily focus on exercise, physical therapy, and early ambulation. Between 2010 and 2015, occupational therapy, inspiratory muscle training, breathing exercises, and electrical stimulation began to gain attention. More recently, acupoint stimulation, delirium monitoring/management, and comprehensive rehabilitation therapy have started to receive increasing attention.

This bibliometric analysis probed the development of research related to early rehabilitation of patients with MV in the past 20 years via CiteSpace and Bibliometrix. Over the past few years, particularly since 2019, there has been a significant upward trend in the number of publications, which peaked in 2022. This surge is likely closely associated with the coronavirus disease 2019 (COVID-19). COVID-19 affects the respiratory system, skeletal muscles, nervous system, and nearly all bodily systems, exacerbating lung injury, muscle fatigue, and dyspnea. Furthermore, it prolongs ICU stays, significantly reduces mechanical efficiency, and extends the duration of MV (44, 45). The global COVID-19 pandemic led to a surge in critically ill patients, which directly underscored and validated the necessity and safety of early rehabilitation in the ICU, thereby driving a rapid expansion in clinical practice and research within this field. The United States, Brazil, Australia, and England are major contributing countries. North American and European countries have established the most intensive cooperation networks. Most active scholars, institutions, and journals in this field are from the United States, Canada, Australia, and England. This trend is likely attributed to the robust policy support and substantial financial investment in healthcare within these countries (46–48). Additionally, leading universities and research institutions in North America and Europe have significantly strengthened collaboration networks.

Current communication and collaboration in this field are predominantly confined to the domains of clinical medicine and related medical disciplines. However, given the complexity of providing early rehabilitation to ICU patients with MV, future studies would benefit significantly from interdisciplinary approaches. For instance, integrating materials science could advance the development of more sophisticated rehabilitation equipment, while insights from ecological research could contribute to more sustainable healthcare practices. Such interdisciplinary collaboration is not only beneficial but essential for driving pivotal advancements in this field.

According to the cited references and keyword analysis, it can be found that the focus of current research on early rehabilitation of patients with MV is the major complications and their management in the ICU, the safety and efficacy of early rehabilitation in patients with MV, and the physical therapy strategies in patients with MV. Fan E believes that further research is needed to elucidate the mechanisms leading to neuromuscular dysfunction and injury, and to better understand the relationship between ICU-acquired weakness, physical function, and quality of life in patients (49). Additionally, studies have shown that early mobilization and rehabilitation can reduce the incidence of ICU-acquired weakness, with less likelihood of adverse events, and are safe and feasible in the ICU (50). And the risk of adverse outcomes associated with early rehabilitation is minimal, with a meta-analysis reporting an overall cumulative incidence of 2.6% for potential safety events and only 0.6% for rare medical complications (34).

Although physical therapy has been widely advocated to improve dysfunction in patients with MV, clinical trials have reported different effects on the outcomes of physical therapy interventions. González-Seguel F et al. thought that this can be explained by a lack of awareness of the optimal dosage of physical therapy for a patient (e.g., frequency, intensity) or that a mismatch between the ventilatory support and exercise-induced ventilatory demand during physical therapy may overly increase the work of breathing, leading to exhaustion, which in turn limits the effectiveness of physiotherapy (51). Therefore, the setting and monitoring of physical therapy in patients with MV is a significant focus and trend in future research. Additionally, different professional groups may influence clinical decisions due to different perceptions, prejudices, and role perceptions (52). Future studies should be conducted to understand when to apply rehabilitation therapy, which treatment is more effective, and the synergistic relationship with other care measures, rather than relying on subjective biases and different perceptions.

Furthermore, our analysis found that respiratory failure emerged as a predominant keyword, inspiratory muscle training was a notably cited reference cluster, and pulmonary rehabilitation was an emerging keyword burst in this field. The results highlight the key role of respiratory management and pulmonary rehabilitation in patients with MV. As prolonged MV leads to diaphragmatic atrophy, pulmonary rehabilitation such as respiratory muscle training, deep breathing exercises, induced spirometry, postural drainage, and sputum expectoration can reduce ventilation, clear intrapulmonary inflammation, and activate the respiratory muscles (53). Neuromuscular electrical stimulation can improve patients’ functional independence and shorten MV time, but it is applied to peripheral muscles in a higher proportion and to respiratory muscles and their auxiliary muscles less (54). More studies are needed to evaluate its actual effectiveness in order to better promote this intervention. Huang et al. found that most pulmonary rehabilitation items were bundled, without explaining the individual role of each item. Intervention plans for pulmonary rehabilitation and MV should be further clarified, based on standardized treatment and long-term observation (55). In addition, future pulmonary rehabilitation can utilize new technologies such as virtual reality, brain-computer interface, and artificial intelligence to enhance the amusement and effectiveness of rehabilitation training, thereby improving patient participation and compliance. Simultaneously, it is essential to explore the unique therapeutic approaches of Traditional Chinese Medicine in pulmonary rehabilitation. By integrating Traditional Chinese Medicine pulmonary rehabilitation with modern medical rehabilitation methods, a distinctive pulmonary rehabilitation model with Chinese characteristics can be established, which will significantly enhance China’s influence in this field.

In addition to ICU-acquired weakness and pulmonary dysfunction, which are the two major challenges in early ICU rehabilitation mentioned above, delirium and disorder of consciousness (DoC) are also crucial issues requiring urgent attention. Delirium (keyword cluster #3), characterized by acute cognitive and attentional disturbances, and DoC (keyword burst: cognitive impairment), featured by arousal and awareness alterations, are highly prevalent in ICU patients with MV and linked to prolonged ventilation, extended hospital stays, functional impairment, and increased caregiver burden (56, 57). Statistical data indicate that the prevalence of delirium is generally 50 to 70% in MV patients (58). However, rehabilitation treatment-related analysis reveals a persistent focus on physical therapy and early mobilization, while cognitive therapy remains underutilized. The timeline of rehabilitation intervention-related keywords shows that delirium monitoring/management is an emerging keyword in recent years, highlighting cognitive rehabilitation as a focus and trend in future research. A meta-analysis found that multi-sensory stimulation, telling structured stories with a familiar voice, and transcranial direct current stimulation positively contribute to the recovery from DoC (59). Acupuncture has also been demonstrated to effectively improve consciousness levels, with the advantages of being well-tolerated, reversible, and having rare adverse events (60). In addition, transcutaneous vagus nerve stimulation, an important extension of acupuncture therapy, has been shown to improve DoC (61). Therefore, the application of acupuncture in the ICU to promote patient awakening holds significant potential for future research. In conclusion, cognitive rehabilitation has emerged as a burgeoning research trend, with the potential to fill a significant gap in this field. Future studies should be dedicated to devising and validating more novel cognitive interventions to improve prognoses for MV patients with delirium and DoC.

To our knowledge, this is the first bibliometric analysis on the rehabilitation of patients with MV in the ICU. This is a prospective study, the literature search terms are specific and comprehensive, and the results are clearly and intuitively presented.

This study also had some limitations. First, in this study, only studies published in the WoSCC were included, and the paper types were “article” in English, which may have neglected other high-quality literature in the field, resulting in some limitations in the literature search. Second, due to the presence of synonyms, there may be some overlap when analyzing the co-occurrence and clustering of keywords. Furthermore, bibliometric methodology cannot effectively take into account the scientific robustness or validity of a publication. Highly cited publications do not necessarily have high scientific quality and do not necessarily reflect the research hotspots comprehensively. As noted, this analysis did not systematically include pediatric studies. Early rehabilitation for mechanically ventilated children is equally crucial and safe, but must account for distinct developmental and physiological characteristics (62, 63). The link between normal baseline function and delayed rehabilitation in critically ill children highlights the necessity and urgency of early intervention (64). Unlike adult rehabilitation, pediatric care requires adjusted respiratory support and development-matched play-based strategies (65). Future research should conduct in-depth analyses of early rehabilitation for pediatric ICU patients with MV.