SBE is an embedded component of undergraduate, postgraduate and continuing professional education and training in healthcare professions curricula and workplaces worldwide [9]. The widespread adoption of simulation is underpinned by a growing body of published evidence affirming its benefits, supporting preparedness for practice, and improvements in patient safety and patient care [10]. However, the hegemony of SBE has emerged from hospital-based specialities, and bespoke simulation centres in academic or clinical locations [11]. Typically, SBE is adopted in strategic locations with geographic concentrations of simulation personnel, facilities and resources, which benefits convenience and cost for many and consolidates simulation faculty expertise and capacity [12]. However, many healthcare communities continue to face challenges connecting with and sustaining SBE initiatives [13,14]. This research explored an innovative programme aimed at addressing this challenge by implementing a mobile simulation facility, funded as part of a National Clinical Skills and Simulation Strategy by NHS Education for Scotland [15]. A key objective of this strategy was to provide high-quality SBE across geographical and professional boundaries. The Mobile Skills Unit (MSU) (Figure 1) was one element of the strategy and provides a peripatetic, versatile space for clinical and surgical skills education and simulation faculty development [7] and aims to promote accessible, inclusive and sustainable SBE for healthcare communities in RR Scotland [16].

Health and social care staff living in RR Scotland report feeling professionally and physically isolated from clinical colleagues and specialities and some services [17]. These challenges impact upon the retention and recruitment of staff across the diverse RR healthcare contexts and workforces of NHS Scotland [18,19]. These issues are not unique but echo a global challenge for health professions education in complex healthcare systems [20]. Initiatives to promote new ways of providing health and social care and improve access to continuing education include UK national strategies [21,22] and international Global Policy recommendations for RR workforce development [23].

In RR communities such as in Scotland there is an acceptance of healthcare role and skill diversity and resilience [19] to address the tyranny of distance, the challenge of delivering healthcare in remote communities by heterogeneous healthcare teams [24,25]. This includes providing services for acute and chronic healthcare conditions, and the infrequent but urgent need to assess, stabilize and manage a critically ill or injured patient with limited resource, knowledge or skills until transfer to a tertiary care centre is possible. Training for these high acuity and low occurrence (HALO) events [26–28] typically means RR staff have to travel long distances. The time and cost of being away from home and work is inconvenient, but moreover may be prohibitive [25,29]. Recognizing these challenges, the National Clinical Skills and Simulation Strategy and the MSU were seen as proposed solutions to the ‘inequity of provision of high-quality clinical skills education using simulation’ affecting RR Scotland [7] (p.221).

However, Greenhalgh and Papoutsi argue that creative innovations which are designed to offer solutions and opportunities are complex to implement, with respect to their spread (replication) and scale-up (building infrastructure) [30]. This is particularly true in diverse social contexts such as in RR Scotland and other global contexts in which communities are harder to reach [2,31,32]. Therefore, this realist review was conducted as part of a longitudinal study and realist evaluation [33] and sought to explore the evidence base for SBE interventions targeting RR communities.

Booth et al. [48] assert that an explicit and transparent reporting of the search logic counters the tensions between the creative realist and rigid systematic review protocols and demonstrates rigour consistent with realist inquiry. The six steps of a realist search and synthesis proposed by Booth et al. [48] guided the search logic adopted in this review (Figure 3).

The guiding search question (step 1) was formulated in consultation with stakeholders and in accordance with the RAMESES Quality Standards [41] who advocate stakeholders are key informants in decision-making about the focus of the research, we asked: What does the published evidence say about the phenomena of mobile SBE in RR healthcare? Step 2, a background search and scope of published literature was followed by a review of stakeholder documentation (step 3) to identify initial programme theories and captured tacit and historical insights from these key informants [49]. Next, an iterative search for empirical evidence (step 4) explored a wider conceptual framework of simulation literature and innovative programmes targeting harder-to-reach communities. Step 5, the testing and refining of initial programme theories, was conducted as part of a realist evaluation with empirical data collection [33]. This step is not reported in this publication; instead, this realist review documents and reports the realist search and synthesis (step 6) of the published literature identified.

Ethical approval was requested since this realist review involved stakeholder consultation and documentary analysis [38,41]. Ethical approval was granted by the University of Dundee Research Ethics Committee (UREC 16037).

The initial search of databases included the NHS Knowledge Network, Medline (via the OVID interface) and Google Scholar, adopting recommendations to use a restricted range of generic sources at this stage [39,50]. Medical Subject Headings (MeSH) controlled language terms and Boolean operators were adopted, minimal restrictions were applied and the search looked at a 10-year period (2005–2015), the time during which the MSU was proposed, designed and launched. In consultation with a librarian colleague [51], the following search terms were adopted:

Literature selection and appraisal were based on relevance (contribution to theory building) and rigour (data are credible and trustworthy), the key criteria by which literature is appraised in realist reviews [39,52,53]. Selection, appraisal and exclusion criteria were also guided by a Realist Review Appraisal Form from a publication by Jagosh et al. [54] to guide the identification of papers of relevance. Endnote reference management software was used for data extraction of published literature to organize citations, explore and analyse pdfs.

After screening and appraisal nine resources describing approaches to address the SBE needs of RR communities were identified. Three pertained to the MSU of this study [55–57]; however, one was excluded as this conference abstract proposed a qualitative research study which was not conducted. The remaining publications included an in-depth critique of an in situ intervention in the USA [58]; a descriptive report of a rural surgical bus in New Zealand providing education and mentorship to nursing and surgical staff remotely [59]; and a discussion of a UK-based clinical skills bus for undergraduate students [60]. A report for the World Organization of Family Doctors (WONCA) discussed case studies of clinical skills and SBE for RR practitioners, although it did not describe a mobile facility exclusively [25], and two papers reported surgical skills training specifically using mobile vehicles for simulation interventions [61,62].

Empirical research on mobile vehicles for simulation is lacking, and only one original research paper was identified amongst the eight reviewed, which were published between 2006 and 2014. The common focus of these mobile SBE publications was procedural skills acquisition, particularly HALO, acute and emergency skills and drills, and laparoscopic and minor surgical procedures. Learning opportunities were vaguely and varyingly described as facilitator-led and self-directed. The most frequently reported outcomes were learner satisfaction, and skills acquisition, which is typical of, but also a criticism of the quality and value of SBE publications [63–65]. What these papers shared were largely positive descriptions of SBE interventions, based on the reflections of participants and authors. They discussed creative and innovative solutions for engaging with SBE on-site rather than in a fixed simulation centre, thus making simulation more accessible and inclusive for RR communities in respect of the physical and/or human resources which facilitate SBE. However, none of the papers added to the literature on the sustainability of these interventions.

The nine papers analysed varied in their richness of descriptions of contexts and mechanisms, supporting the outcomes of the SBE programmes they advocated. Longer term outcomes of the interventions in respect of enablers and barriers were difficult to discern as none of the papers took a longitudinal view of the innovations they described. Common motives were driven by needs assessments underpinning the training for HALO events. Expressions of forging social connections, collaborative partnerships and informal networks within and across healthcare organizations, created opportunities to facilitate and capitalize on shared educational and physical SBE resources.

The search for programme theories (step 3) expanded on the background search to include programme documents via stakeholder consultation. These stakeholders were employees of NHS Education for Scotland, including the original architects of the MSU and staff responsible for its design, operationalization and facilitation of SBE. A large volume of programme documents included historic business plans, steering group meeting minutes, training needs analysis, annual reports, training records, course programmes and timetables, course feedback and evaluations from facilitators and participants and were shared in digital and paper formats.

During consultations, the social connections that were identified as causative mechanisms in the literature were also discussed and echoed by stakeholders who proposed that the MSU – works at the level of informal networks – and that supplying a mobile simulation vehicle alone was – a recipe for failure [66]. Seminal SBE publications have similarly asserted the fundamental need for simulation faculty development for specific educational and professional contexts [3,67,68] and argue that the inherent value of SBE is ‘unrealisable without skilled educators and technicians… and professional networks for simulation specialists’ [6] (p.5). The key mechanisms for implementing SBE interventions advocated by stakeholders are nurturing social connections alongside longitudinal faculty development to avoid a mere ‘train and hope’ [69] (p.6) approach to implementing SBE.

Stakeholder consultation and documentary analysis is recommended in realist reviews as a participatory way to identify authentic, contextually situated evidence [48]. Capturing the tacit knowledge and experiences of stakeholders narrowed and prioritized the focus of the study to three initial programme theories. These programme theories (Figure 4) are constructed as an if–then–because hypothesis, a realist research heuristic [49]. The reader may interpret this as – if we deliver a programme in this way (context) then this will bring about an improved outcome, because… (mechanism).

Iterative strategies were employed to search for empirical evidence to test the programme theories proposed. This included additional database searches for published literature in Scopus, Web of Science and PubMed using the search terms above. In addition, search strategies included CLUSTER searching [70] (Citations; Lead author; Unpublished materials; Scholar searches; Theories; Early examples; Related projects), and ‘berry picking; the foraging and browsing for information which is proximate to items of interest’ [48] (p.157). These complementary search strategies included exploring simulation journals for conference abstracts, library repositories for doctoral theses, ResearchGate for unpublished manuscripts, podcasts, webinars and Google for training courses or promotional materials. The rationale for this unconventional searching approach is advocated by the RAMESES Standards [39]. The purposive iterations of searching pursued titles and abstracts if they implied aspects of mobile or distance simulation, but not exclusively describing a mobile vehicle. Date restrictions were not applied during iterative searching; the oldest paper identified was from 2004 and the last was in 2020 when the search concluded.

After screening and appraisal of publications and grey literature, three mobile simulation typologies and five simulation programmes were considered of relevance. The iterative searching identified publications which have in common the concepts of hub and spokes [71] and outreach [72], programmes seeking to make simulation accessible and inclusive to harder-to-reach communities. Whilst the initial focus of this research was an exploration of the MSU, a physical unit, this is an example of ‘a family of programmes’ [73] (p.25) of mobile and distance approaches to simulation. It is a fundamental aspect of a realist review to seek relevant literature which identifies programmes in diverse contexts, with variable outcomes so as to explore the reasons (the causative mechanisms) for what, how and why they work (or not). The iterative searching strategies and metaphorical zooming out and in [74] of the literature created the opportunity to illuminate and magnify [75] a body of evidence of contrasting simulation interventions, identifying key features, variables and relationships between heterogeneous simulation phenomena [67].

Realist research asserts that interventions or programme theories are not implemented into a social vacuum and encourages researchers to explore the social architecture in other words – the structure and agency of a context to explain the mechanisms of how, why and for whom intended outcomes are achieved, or not [73]. Implementing programmes of mobile and distance simulation manifests in the tangible form of equipment, personnel and combinations of these and other resources into heterogeneous social contexts. These are the visible, observable and measurable outcomes of any SBE interventions which are compared here with the image of the tip of an iceberg (Figure 5). Explaining how and why these observable outcomes emerge requires a deeper exploration of social contexts, to explore the causative mechanisms. In other words, what motivates and triggers support, or conversely which barriers inhibit intended outcomes? These findings may be hidden below the metaphorical waterline.

Social contexts are the complex, dynamic backdrop for the adoption of any intervention, which in turn becomes the product of its context [49], and so simulation stakeholders may assume that a proposed intervention (programme theory) offers innovative solutions to perceived challenges, generating learning and improvement. However, while observable outcomes may be highly visible and easy to make an early judgement about, they may also be transient and maladaptive in different contexts and may not support sustainable intentions.

The literature described in this realist review reveals a heterogeneity of interventions and contexts, and the intended outcomes are attributed to the strength of relationship building, social networks and connections which are the causative mechanisms resulting from insightful implementation approaches within the co-located communities of practice. This realist review proposes that the scale-up (infrastructure building) of SBE interventions is more socially and contextually contingent than dependent on the spread (replication) of its physical resources and environments [29].

The strengths of this realist review are that it showcases to the simulation community a methodological approach for researching SBE using realist theory-driven approaches. It seeks to acknowledge, explore and advance our understanding of complexity in relation to the implementation of simulation interventions. This publication responds to calls for research which adopts theory, innovative methodologies and methods to study simulation for health and social care [65] and therefore contributes valuable knowledge to the Healthcare Distance Simulation Collaborative [122]. However, a limitation is that this realist review was conducted prior to the characterization of the Healthcare Distance Simulation Collaborative, and hence this concept was not identified as a search term during the review. This Collaborative has since generated much needed new evidence [122], and guidelines [123] as well as creating a nascent research and practice community [124] for the advancement of SBE for harder-to-reach communities. New evidence published subsequent to this review [125] also provides this community with rich and varied insights into mobile and distance simulation programmes. This realist review may now be a valued contribution to integrate with developing evidence-base of the Healthcare Distance Simulation Collaborative.