Point‐of‐care ultrasound use for vascular access assessment and cannulation in hemodialysis: A scoping review

Abstract Point‐of‐care ultrasound (POCUS) for access assessment and guided cannulation has become more common in hemodialysis units. The aims of this scoping review were to determine: circumstances in which renal nurses and technicians use POCUS; the barriers and facilitators; and evidence of the effects of POCUS in guiding assessment and cannulation. A search was conducted of CINAHL, Medline, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, and ProQuest, Trove and Google Scholar as grey literature sources. Of 1904 publications, 21 studies met inclusion criteria (11 full text and 10 abstracts). These included primary research publications (n = 5), clinical observational cohort studies (n = 5), case studies (n = 3), published guidelines (n = 2), and published position papers (n = 6). POCUS was used for: assessing arteriovenous fistula (AVF) maturation; identifying landmarks and abnormalities; assessing alternate cannulation sites; performing new AVF cannulation; performing difficult cannulation; increasing cannulation accuracy; performing cannulation through stents; and patient self‐cannulation training. There were scant data on the barriers to, and facilitators of the use of POCUS, and a distinct lack of empirical evidence to support its use. These knowledge gaps highlight the need for further clinical studies, particularly randomized clinical trials, to test the effectiveness of POCUS in hemodialysis for assessment and guided cannulation.

Ultrasound for assessment and guidance is a useful adjunct to other vascular access clinical assessments, particularly for vessels that are new, small, mobile, or tortuous. 5,6 Currently, the use of ultrasound for assessment and cannulation guidance is recommended in only one hemodialysis guideline worldwide; however, this recommendation is not supported by empirical evidence. 19 Furthermore, it is not clear what evidence currently exists in relation to ultrasound use for vascular access assessment and cannulation guidance.
Scoping reviews are generally conducted when there is a distinct lack of randomized controlled trials in a particular clinical research area that precludes synthesis of findings from homogenous data sets to undertake a systematic review and meta-analyses. 20 A scoping review allows for the inclusion of published and non-published material, and includes any heterogeneous data to provide an overview of the breadth (or lack) of information available on a particular topic of interest. [21][22][23] The purpose of this scoping review was to investigate current available literature and gaps in evidence related to point-ofcare ultrasound (POCUS) for hemodialysis vascular access, and particularly POCUS-guided cannulation in hemodialysis vascular access.
Information gathered from this review will inform requirements for clinical practice and further clinical research.

| AIM
The aim of this scoping review was to answer the following questions: 1. In what circumstances do renal nurses and technicians in hemodialysis units use POCUS for cannulation guidance of vascular access?
2. What are the reported barriers and facilitators related to the experience of renal nurses and technicians using POCUS for cannulation guidance in hemodialysis? 3. What is the empirical evidence to support the use of POCUSguided cannulation of vascular access in hemodialysis?

| ME THODS
The scoping review was guided by a predefined protocol informed by contemporary methodologies for scoping reviews, specifically following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses-Extension for Scoping Reviews reporting guidelines. 20,[22][23][24]

| Eligibility criteria
The lack of evidence for use of POCUS-guided cannulation in hemodialysis informed the decision to include grey literature such as conference abstracts, literature reviews, opinion pieces, position papers, letters, and theses, along with the published peer-reviewed primary research studies. The date range for retrieval was 1980 onwards because ultrasound was not used in hemodialysis prior to the 1980s. Inclusion criteria were literature reporting: adult (18+ years) hemodialysis patients; hemodialysis patients with AVF; hemodialysis patients with AVG; use of POCUS for cannulation by nurses and renal technicians; use of POCUS for assessment by nurses and renal technicians; use of POCUS for AVF monitoring; and studies based in any hemodialysis setting (in-center, satellite, home).
Publications were excluded if they: were not published in English; investigated POCUS-guided peripheral cannula insertion or POCUS use in general vascular access; included iatrogenic AVF; were animal studies; referred to guided ultrasound being undertaken by a sonographer, radiographer, physician or surgeon; investigated CVAD insertion; investigated ultrasound dilutional access flow monitoring; or examined cannulation techniques but did not mention use of ultrasound. While there are frequently cited abstracts, 25,26 letters 27,28 and other published works related to the use of POCUS in hemodialysis by nephrologists, 17,29 surgeons, 30 or sonographers, 31 these did not meet agreed inclusion criteria, so were excluded from this review.

| Database search
A bibliographic database search of CINAHL complete, Medline complete and EMBASE was conducted. Restricted to the years 1980-2019, MeSH (Medical Subject Heading) and CINAHL terms were searched for in both title and abstract. Search terms included: "hemodialysis," "vascular access," "AVF," "AVG," "ultrasound," "sonography," "cannulation," "miscannulation," and "nurse". Search terms were combined Publication titles and abstracts were independently reviewed by two reviewers (MS, PB, or MS, AH) using the Rayyan QCRI system. 32 Reviewers resolved all conflicts without the requirement of a third reviewer.

| Data extraction
Data extraction was undertaken by one researcher (MS) using a tool based on the inclusion criteria and checked by a second researcher (AH) with consensus reached on relevant data. Data extraction tables were devised by the authors to collate and present information according to the scoping review questions (see Tables 1 and 2). United States of America n = 6, Australia n = 3, and one each from United Kingdom, Spain, Brazil, and Japan) (see Figure 1).

| Characteristics of included publications
Characteristics of included publications are detailed in Tables

| Assessing new AVF maturation
Three publications reported use of POCUS to assess new AVF maturation. 36

| Identifying landmarks and abnormalities
Point-of-care ultrasound can be used to view the vessel if abnormalities are detected on physical assessment 38 and allows for the creation of a visual map of the AVF to identify straight and curved sections. 5 Schoch et al 11 argues that POCUS can also be used as an adjunct to physical assessment, complementing the skillset of the cannulator. Additionally, POCUS can be useful in identifying valves, 11 pseudoaneurysms, 11,45 aneurysms, 11 adjacent artery or nerves 5,6 or hematomas, 5,11 in order to improve cannulation. 5 Anecdotal reports suggest that cannulation-induced intraluminal thrombus does not require diagnostic imaging by a sonographer, and if the area is left for a period of weeks the clot will dissipate allowing for recannulation of that area without incident. 11 An example of identifying abnormalities with POCUS was detailed in an Australian case study of a 77-year-old hemodialysis patient who had a radial artery pseudoaneurysm identified when POCUS was used for guided cannulation of the overlying AVF. The pseudoaneurysm resulted from cannulation infiltration through the AVF during blind cannulation. 45 Therefore, POCUS shows promise as a tool, not only to assist in identifying abnormalities within the vessels, but also to prevent harm to patients from blind cannulation extravasation. 45

| Assessing for alternate cannulation sites
The use of POCUS to assess for alternate cannulation sites was reported in two publications. 33

| New AVF cannulation
One randomized prospective pilot study was undertaken specifically to investigate new AVFs requiring cannulation due to the higher needle infiltration risk in this cohort. 34 This small cohort study (POCUS n = 5, blind cannulation n = 4) did not show a difference between infiltrations in the POCUS group versus the blind cannulation group. However, Kumbar et al 34 did report patient satisfaction was higher in the POCUS group, but the time taken to assess vessels using POCUS and time taken to cannulate using POCUS were longer. 34 Authors of a retrospective audit reported that when POCUS was used to guide cannula-

| Difficult access cannulation
The increasing prevalence of co-morbidities and an ageing population has resulted in increasingly complex access cannulation. 5,6 Definitions of "difficult access" vary and include: the inability to achieve three successful dialysis sessions (two needles in each), with resulting CVAD use 43 or the requirement of more than two needles in a session more than once per week. 41 Others have referred to difficult access in terms of length, diameter, location, depth or tortuosity. 5 35 Similarly, a decrease in the requirement for more than two cannulations, from four episodes per patient year to 1.78 episodes per patient year has been reported. 38 Adams et al 43  Authors of a Canadian prospective cohort study reported implementing an access procedure station with POCUS in an attempt to decrease adverse cannulation events. 41

| Increasing cannulation accuracy
Increasing cannulation accuracy is vital to ensure correct needle posi-

| Successful cannulation through stents
Blind cannulation through stents surgically inserted into the useable segment of AVFs is rare and can challenge clinicians. Adverse outcomes reported by Jian et al 44 in a case study of three patients (reported as an abstract) were: stent separation from the vessel wall, stent fracture or distortion, infection or pseudoaneurysm.
Arising from this study was a recommendation for POCUS assessment and guided cannulation to be used to prevent stent separation and damage by visualizing the needle tip insertion into stents in the useable segment of the AVF. 44 POCUS may prevent issues with the needle sliding between the stent and the lumen causing stent separation. 44 Jian et al 44 suggest POCUS has the potential to decrease vessel damage and stent damage from misdirections and miscannulations.

| Barriers and facilitators to renal nurses' and technicians' POCUS use
There In an online survey exploring renal healthcare worker perceptions of cannulation outcomes, only 13.6% (n = 34) of 252 respondents reported they used POCUS for guided cannulation. 37  Anecdotal reports indicated appropriate training and competency testing increased nurses' abilities with using POCUS for assessment and guidance. 16,39 According to Wilson et al, 37 more in-depth understanding of the perceptions of nursing and technical staff, and patients, regarding the possible barriers to and facilitators of POCUS use is required. 37 Overall, the authors concluded that POCUS could be a factor in improving cannulation outcomes and recommended further research into nurses' perceptions about the use of POCUS in hemodialysis. 37

| Procedural Requirements for POCUS
Two hemodialysis vascular access guidelines from Canada recommended POCUS for assessment and/or cannulation. 19,46 Recommendations from the Canadian Association of Nephrology Nurses and Technologists (CANNT) 19  The integration of POCUS into local cannulation guidelines, 47 and the facilitation of training, written tests and certification after six successful cannulations using ultrasound were described in two position paper abstracts. 48 As these abstracts were descriptive and not research-based with methods and results reported, there is scant detail about how the education program was operationalized.
General steps required to achieve successful POCUS-guided cannulation were outlined in two publications, 5,6 with one taking a step further by scaffolding competencies into basic, intermediate and advanced levels. 16 The authors of two position papers specified from their experience that the preferred ultrasound probe direction is transverse as the first preference, and longitudinal the second. 5  low response rates to surveys; and poorly operationalized concepts or omitted methodological definitions of terms like "expert."

| D ISCUSS I ON
None of the included publications outlined costs associated with the use of POCUS in hemodialysis units.

| Limitations of the scoping review
This scoping review has several limitations. First, any studies that were not published in English were excluded, thus possibly omitting relevant information from non-English publications. We also excluded studies relating to use of POCUS by allied health professionals, this may have also excluded information that, whilst not directly related, could be applied by renal nurses and technicians in practice.

| Empirical evidence
There is a lack of published evidence related to the use of POCUS in hemodialysis vascular access, particularly related to POCUS guidance during cannulation, 35 and there is a dearth of empirical evidence to advise on POCUS use. 5 Adequately powered randomized controlled studies are required to determine whether POCUS may lead to improvements in vascular access outcomes. 34 Prospective clinical trials are required with a specific focus on the indications for use of POCUS, comparison with the standard practice of blind cannulation, and measurement of outcomes related to the dependence on CVAD and optimal POCUS techniques. 5 New guidelines call for "rigorous study of use of ultrasound-guided cannulation-its safety, efficacy, and impact in busy dialysis units." 49

| Implications for clinical practice
The small number of clinical cohort publications and position papers and conference proceedings suggest positive outcomes are associated with the use of POCUS for hemodialysis access for clinical use.
The findings of the included research show promise, particularly in relation to identifying possible access abnormalities 40,45 (such as pseudoaneurysms, presence of clot, tortuosity, and stenoses), facilitating routine and difficult cannulations 40,42 (which may decrease area puncture and aneurysm formation) and decreasing miscannulations and needle manipulation, thus minimizing access damage 6,11,35,38,39,43 (such as back wall damage and hematoma formation from infiltrations). However, these findings need to be treated with caution given the limitations in the existing evidence base.

| Implications for further research
There is a need for further clinical studies into the use of POCUS for assessment and guided cannulation. In particular, randomized clinical studies to test the effectiveness of this intervention on key patient outcomes are recommended, with recognition that recruiting large sample sizes will be required to adequately power such studies. To assist with future meta-analyses, common sets of variables and standardized measures are recommended. Inclusion of the following variables and design characteristics is suggested. Variable

| CON CLUS IONS
This scoping review has highlighted that whilst there are positive reports on the use of POCUS assessment and guided cannulation in hemodialysis, there is a distinct lack of robust studies evaluating POCUS in this context. In addition, gaps in our knowledge regarding staff perceptions and perceived barriers to, and facilitators of, POCUS use exist. Recommendations based on expert opinion suggest that use of POCUS for assessment and cannulation guidance has the potential to provide improved outcomes for patients' AVF. Further research into these possible outcomes is required in order to substantiate or refute the published opinions of experts and provide higher quality evidence and more precise guidance for practice.