Key words : Blood flow sensing technology, Graft survival, Renal vein thrombosis, Surveillance device

Introduction
About 10% of the world's population has chronic kidney disease (CKD).¹ The prevalence of CKD in the United Kingdom is 7.2 million people, with about 20 individuals per day diagnosed with CKD.² Among patients with CKD, about 30,000 depend on dialysis to stay alive.² The CKD-associated annual mortality in the United Kingdom is 45,000 people; this is equivalent to 5.1 individuals every hour.²

In Europe, the overall 5-year mortality rate for CKD patients on hemodialysis is 50%.³ In the United Kingdom, the annual mortality rate for CKD patients on hemodialysis aged 60 to 65 years is 15%, and the rate increases sharply in older age groups.⁴ Apart from lung and pancreas cancers, most cancers have a better prognosis than CKD patients on hemodialysis.⁴ The mortality rate in CKD patients is 17-fold higher compared with age-matched controls in the general population.⁵ Moreover, 30% to 45% of the CKD patients on hemodialysis have mental impediments, like depression and neurosis.²

A successful kidney transplant is the best treatment for dialysis-dependent CKD patients because a kidney transplant improves long-term survival, generalized health, mental well-being, and quality of life of patients.⁶ However, a discrepancy exists between the number of kidney grafts available for donation and the number of dialysis-dependent patients with CKD on transplant wait lists.⁷ The high organ demand is due to the rising global prevalence of CKD.⁷ In the United Kingdom, over 10 patients per day are added to the national transplant waiting list.² Despite 3895 kidney transplant surgeries taking place in 2023-2024, there are still 6250 CKD patients on the national transplant waiting list.⁷ Consequently, the average wait time for a kidney transplant in the United Kingdom is 900 days.⁷

Every day, 2 patients with CKD on the national transplant waiting list die before having a transplant and only 20% ultimately receive a suitable graft.² The COVID-19 pandemic only aggravated the situation because of a reduction in transplant activity.⁸

Early graft loss adds to this disparity.⁹ About 3.5% to 5.7% of total kidney transplants are lost due to renal vascular complications in the first month posttransplant. Among kidney transplants, rates of renal arterial complications have been reported as 0.2% to 7.5%, whereas rates of renal venous complications have been reported as 0.1% to 8.2%.¹⁰ Early graft loss is a devasting complication, with 1-month, 3-month, and 12-month mortality rates of 5.2%, 11.1%, and 12.28%, respectively.¹¹ The high rate of mortality is precipitated by cardiovascular complications, infections, depression, and the physiological stress of reverting to hemodialysis.¹¹

Early detection of vascular complications is crucial to reduce early graft loss posttransplant.¹² Only rapid recognition allows for an immediate surgical correction necessary to salvage the compromised graft.¹³ Currently, kidney transplant patients are monitored postoperatively by traditional clinical care and color duplex ultrasonography as the standard diagnostic test.¹⁴ The detection of an ischemic graft can be challenging in the initial phase as patients are clinically asymptomatic.¹⁵ Other indicators of graft dysfunction like urine output and serum creatinine are also inconsistent.¹⁶ A delayed diagnosis almost always leads to a thrombosed nonsalvageable graft.¹⁷ The role of blood flow sensing technology in kidney transplant patients can be valuable in the timely diagnosis of diminished blood flow toward the graft, thereby allowing a window of opportunity to reduce graft loss.¹⁷ However, no such technology has been formally tested in clinical practice.⁹

The implantable Doppler probe (Cook-Swartz Doppler Probe, Cook Medical) utilizes blood flow sensing technology to monitor the patency of vascular anastomosis to which it is applied.¹⁰ The probe comprises a 1-mm² piezoelectric crystal and a 20-MHz transducer attached to a silicon cuff¹⁰ (Figure 1). The cuff is linked to the external monitor through a thin connecting wire.¹⁰ The cuff is placed around the vessels supplying the graft.¹⁰ The implantable Doppler probe produces audible Doppler signals from blood flow in the vessels by using flow sensing technology.¹¹ These audible signals indicate blood flowing toward the grafted tissues and are used to monitor real-time perfusion.¹¹ Because of the simplicity of its function, the implantable Doppler probe has been used successfully in plastic surgery and breast reconstructive surgery.¹⁵ With the same principle of blood flow monitoring, this device might be useful in kidney transplant surgery.¹⁵

During a kidney transplant, the implantable Doppler probe is attached to the renal artery (ie, the blood vessel supplying the graft).¹² The kinetic energy of the blood flowing toward the graft is converted into electric energy and translated into audible Doppler signals.¹² These signals are produced continuously in real-time, indicating blood flow in the renal artery.¹² Cessation of audible signals implies vascular occlusion due to any complication impeding blood flow toward the graft.¹³ To rule out the suspicion of graft hypoperfusion, the patient requires immediate surgical exploration if still in the theatre or urgent radiological investigations (ie, color duplex ultrasonography) if returned to the ward.¹³ If the role of an implantable Doppler probe is established, clinicians may confidently bypass the need for color duplex ultrasonography, thereby avoiding delay before surgical exploration.¹⁴

There is a clinical requirement for a continuous and reliable blood flow monitoring device that can be conveniently used at the bedside in kidney transplant patients.^12,13 A color duplex ultrasonography is the gold standard radiological investigation that detects vascular complications with a sensitivity of 97%.⁹ However, its limitations include operator dependency, high body mass index patients with postoperative pain, financial constraints, and administrative challenges encountered when serial scans are required for continuous monitoring in high-risk cases.¹⁴

Presently, there is a clinical equipoise regarding the role of implantable Doppler probes in the postoperative management of kidney transplant patients.¹⁵ The main reason is the lack of information and clinical evidence in the literature regarding the effectiveness of the implantable Doppler probe as a blood flow monitoring device.¹⁷

To date, no systematic review has been conducted on the effectiveness of blood flow sensing technology in kidney transplant patients. This systematic review aimed to evaluate the effectiveness of blood flow sensing technology compared with standard clinical care in reducing thrombosis-related graft loss and the requirement for color duplex ultrasonography in the first 24 hours postoperatively in kidney transplant patients. Our objective was to critically appraise, synthesize, and present the best available evidence in medical literature regarding the application of blood flow sensing technology in kidney transplants.

Materials and Methods
Inclusion criteria and study groups: The review considered studies that reported on transplant recipients with end-stage renal disease who had deceased or living kidney donor transplants and had or did not have implantable Doppler probe monitoring. Studies were included if participants were aged ?18 years. Studies were excluded if kidney transplant recipients had 2 or more arteries (evident at the time of surgery) or were aged <18 years. The intervention group included studies in which patients had kidney transplant surgery with implantable Doppler probe monitoring. The comparator group included studies in which the patients had kidney transplant surgery with standard clinical care.

Outcomes of interest: We aimed to understand whether blood flow sensing technology was effective in postoperative graft surveillance. The primary outcome evaluated was the number of early graft losses due to vascular complications in the first 30 days. The secondary outcome was the requirement of color duplex ultrasonography in the first 24 hours postoperatively.

Types of studies: The quantitative component of this review considered all retrospective observational studies and prospective nonrandomized and randomized controlled trials published in English with no limits (until January 15, 2024). Studies in other languages were excluded.

Search strategy: We followed the Joanna Briggs Institute (JBI) methodology for systematic reviews of effectiveness.¹⁸ It was performed using a priori protocol, and the study was registered with PROSPERO (CRD4202345 5444).¹⁹ According to the JBI methodology for systematic reviews, we used a 3-step search strategy.¹⁸ In the first step, we undertook an initial limited search of MEDLINE (Ovid) and PubMed to identify articles. We used words contained in the titles and abstracts of potentially relevant articles for further search. We conducted a second search of all included databases and specialized journals using the identified key words and index terms related to the application of blood flow sensing technology in kidney transplant patients. As a third step, we searched reference lists of all retrieved articles for additional studies. Two researchers independently conducted a comprehensive search aimed at locating both published and unpublished studies in the English language with no limits (until January 15, 2024). The search strategy comprised key words like implantable Doppler probe, kidney transplant, early graft loss, and vascular monitoring device. These terms were combined using Boolean phrases (Table 1) and searched in information sources.

Information sources: For searches, we used the following databases on the Ovid platform: MEDLINE, Embase, PubMed, Cochrane Database of Systematic Reviews, JBI Database of Systematic Reviews, and Implementation Reports. We searched reference lists of studies in Google Scholar. We also searched trial registries, including ClinicalTrials.gov, WHO’s International Clinical Trials Registry Platform (ICTRP) Search Portal (http://apps.who.int/trialsearch/), European Union Clinical Trials Register, and International Standard Randomized Controlled Trial. We also searched unpublished studies through Google Scholar, Dissertation Abstracts International, ProQuest Dissertations and Theses, and Mednar. We searched grey literature with the Grey Literature Report, conference papers in Partners in Information Access for the Public Health Workforce, COS conference papers index via ProQuest, and dissertations using Trove.

Study selection: After searches, we collated the identified citations, uploaded these citations into EndNote X9 (Clarivate Analytics), and then removed duplicates. Titles and abstracts were screened by 2 independent reviewers for assessment against the review inclusion criteria. Potentially relevant studies were retrieved in full, and citation details were imported into the JBI System for the Unified Management, Assessment, and Review of Information.²⁰ The full text of selected citations was assessed in detail against the inclusion criteria by 2 independent reviewers. Reasons for exclusion of full-text studies that did not meet the inclusion criteria were recorded and reported in the systematic review. Any disagreements that arose between the reviewers at each stage of the study selection process were resolved through discussion or with a third reviewer. Search results are shown in a Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) flow diagram^21,22 (Figure 2).

Assessment of methodological quality: Two independent reviewers critically appraised eligible studies for methodological quality using standardized critical appraisal tools for experimental (randomized controlled trials) and nonexperimental (observational) studies from the JBI System.²⁰ Authors of papers were contacted to request missing or additional data for clarification if needed. Any disagreements between reviewers at each stage of the study selection process were resolved through discussion or with a third reviewer. Studies that did not meet a certain quality threshold were excluded. For a study to be included in the review, it was required to get a score of 7 or more in a predetermined scoring system based on appropriate research questions, internal validity, review outcomes being measured, accuracy, reliability, appropriate statistical analysis, and generalizability. Scores of 0 to 3 were considered very low quality, scores of 4 to 6 were considered low quality, scores of 7 to 9 were considered moderate quality, and scores of 10 to 11 were considered high quality. Table 2 and Table 3 show critical appraisal results of the included experimental and nonexperimental studies, respectively. Table 4 lists the characteristics of the included studies in narrative form.

Data extraction: We used an extraction tool from JBI SUMARI to extract quantitative data.²⁰ Data extracted included specific details on review questions, study objectives, study settings, sample sizes, population demographic characteristics, interventions, control, study methods, and surgical outcomes necessary to evaluate the effectiveness of implantable Doppler probes in clinical contexts. The extracted data also informed the generalizability of findings. Data extractors received training on the JBI SUMARI²⁰ data extraction tool before commencement to ensure data consistency. Results were cross-checked to minimize errors. Disagreements between reviewers were resolved through discussion or with a third reviewer. Authors of the included papers were contacted to request missing or additional data if needed.

Data synthesis: We pooled, where possible, quantitative data in a statistical meta-analysis using JBI SUMARI.²⁰ All results were subject to double data entry. Effect sizes with 95% CIs were expressed as either odds ratios (for dichotomous data) or standard mean differences (for continuous data). Heterogeneity was assessed statistically using the standard chi-square and I² tests. We performed statistical analyses using the random effects model to calculate overall estimates of the surgical outcomes.²³ We used forest plots to show individual study effect sizes and the overall pooled effect estimate.²⁴ If the Cochran Q test showed statistical significance (P < .05), it implied statistical heterogeneity. Similarly, an I² value of ?50% indicated heterogeneity between studies. It is not appropriate to synthesize heterogeneous studies by meta-analysis. In cases where statistical pooling was not possible, the findings were presented in narrative and tabular forms.²⁴

Assessing certainty in findings: The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach was used to assess the certainty in the quality of evidence.^25,26 A well-designed summary of findings table can improve understanding and retrieval of information from a systematic review.²⁰ We presented the results of this assessment in a summary of findings table, created using GRADEpro software (McMaster University).²⁷ The summary of findings table describes absolute risks for the intervention and control, estimates of relative risk, and a ranking of the quality of the evidence. The quality of evidence for the review results was based on the risk of confounding factors, directness, heterogeneity, precision, and the risk of publication bias. The 4-point rating scale (ie, high, moderate, low, and very low) was used to assess the quality of evidence. The surgical outcomes in the summary of findings table included early graft loss due to vascular complications and the number of color duplex ultrasonography scans required in the first 24 hours postoperatively (Table 5).

Results
Study inclusion: The search strategy identified 43 studies. Five studies were added to make a total of 48 studies by hand searching the references. Among them, 29 duplicates were identified and excluded. The remaining 19 studies were screened for relevance based on the title and abstract. Two studies were excluded as full-text studies could not be retrieved. The full-text versions of the remaining 17 studies were assessed against the inclusion criteria. Of these, 10 studies did not meet the inclusion criteria as they were unrelated to the review question (ie, did not involve the application of an implantable Doppler probe in kidney transplant patients or were qualitative studies). Seven studies that reported the application of implantable Doppler probes in clinical settings proceeded to the next step in the review (ie, assessment of methodological quality). The PRISMA flowchart illustrates the study selection and inclusion process^21,22 (Figure 2).

Methodological quality: Seven studies (1 randomized controlled trial [RCT], 6 observational) were included to appraise their methodological quality. All had affirmative reporting of at least 50% of questions in the JBI critical appraisal tool.^20,28 These studies were determined to be of adequate quality and included in the review. The overall quality of the included studies demonstrated a low to moderate risk of bias.^29,30 The RCT³¹ received a 10 of 13 (76% of total criteria) in the JBI Critical Appraisal Checklist for RCTs.²⁰ Questions related to blinding of the participants (Q4), those delivering the intervention (Q5), and those assessing the outcomes (Q6) were marked as not applicable. This was due to the nature of the intervention (ie, implantable Doppler probe monitoring device), which is impossible to blind (Table 2). There were no losses to follow-up as the intervention was well received by the patients and its delivery was completed within the admission period without any hindrance.³² Therefore, Q8, Q9, and Q10 were marked as “yes.”

The 4 observational studies^12,13,14,16 scored 6 of 11 (55% of the total criteria) in the JBI Critical Appraisal Checklist for observational studies.²⁰ These preliminary studies reported the benefits of using the intervention in kidney transplant patients without drawing a comparison with a control group. No confounding factors or strategies to mitigate them were identified. These descriptive studies did not elaborate on results using statistical analysis. Hence, Q1, Q2, Q5, Q6, and Q7 were marked as “no.”

The remaining 2 observational studies^9,10 scored 10 of 11 (90% of the total criteria) in the JBI Critical Appraisal Checklist for observational studies.²⁰ Because there were no losses to follow-up, no strategies to ensure compliance were required. Thus, Q10 was indicated as “not applicable.” Table 2 and Table 3 outline the critical appraisal results of the included experimental and nonexperimental studies. Using the GRADEpro software, the summary of findings table determined the certainty of evidence level of the review findings was moderate (Table 5).

Characteristics of included studies: The 7 studies reviewed included 1 RCT and 6 observational studies. These single-center studies recruited participants from London and Plymouth Transplant centers in the National Health Services, United Kingdom. The total sample size was 874 participants. The sample population had characteristics similar to those of the target population (adult kidney transplant recipients in the United Kingdom). Surgical outcomes measured in all participants were thrombosis-related graft loss and the requirement for color duplex ultrasonography in the first 24 hours postoperatively. Table 4 provides detailed information about the characteristics of the included studies. The review did not comprise the minimum number (?10 studies) needed to justify a funnel plot to investigate publication bias in the included studies.²⁴

Meta-analysis: Clinical and methodological homogeneity was warranted as the review studies were sufficiently similar from clinical (ie, population, intervention, comparator, and outcome) and methodological (ie, study design and risk of bias) perspectives. Statistical homogeneity in the review studies was described with the standard chi-squared test (Cochran Q test) and I² statistic. The review studies demonstrated clinical, methodological, and statistical homogeneity. Therefore, it was considered appropriate to synthesize the respective studies with meta-analysis. The meta-analysis was performed using JBI SUMARI.²⁰ The random effects model was used to calculate combined effect size standard errors by accounting for variability within and between studies.²³ All surgical outcomes were dichotomous and measured in relative risk (RR) or odds ratio (OR).³³ A forest plot represented the graphical display for meta-analysis. The outcome measures were expressed as summary statistics of each study and the overall pooled effect estimate with confidence intervals.³⁴

Thrombosis-related graft loss: The meta-analysis revealed a relative risk of 0.44 (95% CI, 0.21-0.94). The test for the overall effect showed P = .033, indicating that the results were statistically significant. This means that the use of blood flow sensing technology resulted in a 66% reduction in the risk of thrombosis-related graft loss in kidney transplant recipients included in the studies. The Cochran Q test was not significant (P < .818) and I² = 0. These results meant homogeneity in the included studies and therefore minimal inconsistency in the meta-analysis. Any variability identified among the effect sizes would likely be because of sampling errors within studies. The forest plot also displayed point estimates of individual studies (Figure 3). The combined effect size favored the use of implantable Doppler probes in kidney transplant patients to prevent thrombosis-related graft loss. Table 4 lists the findings of individual studies in narrative form.

Requirement for color duplex ultrasonography in the first 24 hours postoperatively: The meta-analysis revealed an odds ratio of 0.39 (95% CI, 0.28-0.55). The test for overall effect showed P < .001, indicating significance. This means that there was a 61% less probability of requiring color duplex ultrasonography in the first 24 hours postoperatively in kidney transplant recipients with blood flow sensing technology than in standard clinical care. The Cochran Q test was not significant (P < .74) and I² = 0. These results meant homogeneity in the included studies and minimal inconsistency in the meta-analysis. Any variability among the effect sizes would likely be because of sampling error within studies. The forest plot also displayed point estimates of individual studies (Figure 4). The combined effect size favored the use implantable Doppler probes in kidney transplant patients to reduce the requirement for color duplex ultrasonography postoperatively. Table 4 lists the findings of individual studies in narrative form.

Discussion
Clinical practice increasingly demands improvements in patient outcomes and reductions in graft loss. Researchers grapple with the complex challenges of investigating new technologies in public health practice. The UK Medical Research Council published influential guidance on developing and evaluating complex interventions, presenting a framework of 4 phases: development, feasibility, evaluation, and implementation (Figure 4).³⁵ The UK Medical Research Council framework guided researchers with actions to evaluate and develop novel blood flow sensing technology in kidney transplant recipients at the NHS United Kingdom.³² This systematic review critically appraises, synthesizes, and presents the best available evidence in the medical literature relating to the application of blood flow sensing technology in kidney transplantation.

Identifying the intervention’s evidence base is essential before an investigation process is initiated.³⁶ Malik and colleagues conducted a comprehensive descriptive synthesis of a significant knowledge base of 79 experimental and clinical studies in 9 different surgical disciplines in their literature review. The authors narrated the benefits and limitations of blood flow sensing technology in 9 surgical disciplines.¹⁵ Understanding the intervention’s theoretical basis is crucial for evaluation and implementation.³⁷ Crane and Hakim, in their observational study, described the effective monitoring of 15 kidney transplant recipients with blood flow sensing technology without any complications.¹² Hakim and colleagues reported the successful rescue of a compromised kidney transplant following a vascular complication. The graft loss was prevented because of monitoring by blood flow sensing technology.¹³

Analyses of key uncertainties, technical limitations, and clinical benefits provide valuable insight into the theoretical basis of an intervention.³⁶ Malik and colleagues¹⁴ reported false-negative results in a kidney transplant recipient with blood flow sensing technology monitoring. Despite a thrombosed graft, persistent reassuring signals were produced by the monitoring device. The authors identified this limitation and emphasized the importance of interpreting the signals alongside the traditional clinical assessment techniques.¹⁴ Malik and colleagues¹⁶ advocated the benefits of blood flow sensing technology in a kidney transplant implanted on an iliofemoral polytetrafluoroethylene (PTFE) graft. The patency of renal artery-PTFE graft anastomosis was successfully monitored without requiring any Departmental ultrasound scans for three days.¹⁶

The UK Medical Research Council's framework advocates identifying and developing the research evidence that informs the intervention's context.³⁷ Malik and colleagues, in their retrospective cohort study, recruited 324 kidney transplant recipients with and without blood flow sensing technology and compared the surgical outcomes between the intervention and control groups by using descriptive statistics.⁹ The results showed lower graft loss (1.5% vs 3.1%; RR = 0.4%; 1.6% reduction) and fewer first 24-hour ultrasonography scans (71.1% vs 83.7%; RR = 0.8%; 12.6% reduction) in the intervention group compared with the control group.⁹ Likewise, Malik and colleagues conducted a cross-sectional analytical study comprising 472 kidney transplant recipients and explored risk factors and preventable measures for thrombosis-related early graft loss using inferential statistics.¹⁰ The blood flow sensing technology group displayed lower graft loss (1.5% vs 3.8%; RR = 0.39%; 2.3% reduction) and fewer first 24-hour ultrasound scans (67.8% vs 84.6%; RR = 0.8%; 16.8% reduction) compared with the control group.¹⁰ These studies contain the largest reported series of kidney transplant recipients using blood flow sensing technology and advocate the utility of intervention.^9,10

Intervention development is a dynamic iterative process involving an increasing number of key groups, including those who will deliver, use, and benefit from the intervention.³⁶ The NHS recommends the inclusion of local voices in the design and improvement of health care interventions to create a truly patient-led health service.^38,39 In a patient-public involvement consultation, Malik and colleagues conducted qualitative interviews of 12 participants (ie, kidney transplant recipients and health care professionals) to understand perceptions of key groups regarding the intervention, identify potential confounding factors, and highlight challenges in clinical practice.¹⁷ The results revealed that blood flow sensing technology was well received by the patients; however, there was a clinical equipoise among the health care professionals. Furthermore, the participants proposed useful strategies for the smooth conduct of future research and educational sessions for staff training.¹⁷

The Medical Research Council framework endorses feasibility/piloting studies as a vital step for testing procedures and estimating recruitment and sample sizes.⁴⁰ In clinical research, feasibility studies are increasingly being conducted to investigate potential areas of uncertainty and support the development of future pragmatic trials.⁴¹ In a 2-arm feasibility RCT, surgical outcomes of kidney transplant recipients with blood flow sensing technology (n = 30) were compared with recipients who had standard clinical care (n = 30).³¹ The intervention group showed lower graft loss (0% vs 6.6%; 6.6% reduction) and fewer first 24-hour ultrasonography scans (71.1% vs 83.7%; risk ratio: 0.8%; 12.6% reduction) compared with the control group.³¹ All probes were removed safely after 72 hours, and no complication related to the device was reported. The concluded preliminary evidence addressed the uncertainties around the feasibility study’s objectives needed to inform future research.³¹

Posttrial qualitative interviews can be used to assess the acceptability, values, and priorities of those delivering and receiving the intervention.³⁶ In a qualitative study embedded in a feasibility trial aimed at testing blood flow sensing technology’s clinical acceptability and gathering suggestions from key groups for the development of the intervention,³² interviews demonstrated a wide acknowledgement of the clinical value of blood flow sensing technology in kidney transplantation. However, the technical limitations and lack of research were identified as the main challenges to its acceptance in clinical practice.³² Innovative ideas comprised integrating intervention with an advanced signal-displaying LED screen to facilitate interpretation, an alarm system that is activated by signal loss, small-sized disposable units to reduce overall cost, and a wireless networking connection to reduce signal errors, increase patient safety, and allow monitoring remotely.³²

This systematic review represents an important effort to expand our understanding of the potential benefits of blood flow sensing technology in kidney transplantation. The best available evidence in the medical literature relating to the intervention’s effectiveness is presented in narrative and tabular forms (Table 4 and Table 5).

An essential action in intervention development is connecting, including, and engaging developers and wider stakeholders.³⁶ The research findings were shared with the intervention manufacturer Cook Medical Europe Limited.⁴² They highly appreciated the stakeholder feedback (Figure 5).

Limitations
The literature search identified 7 studies (1 RCT and 6 observational) addressing the research question. Irrespective of the study design, all were included in the review. Apart from the RCT, the other preliminary observational studies described local kidney transplant units’ experience with blood flow sensing technology. The nonexperimental study design was not considered high on the hierarchy of evidence, and conclusions drawn from this review must be interpreted with caution.⁴³ However, it was possible to generate overall estimated effect sizes due to the homogeneity of interventions and surgical outcomes measured in the included studies.²³

The participants in the included studies were kidney transplant recipients in the UK NHS. Study samples should be representative of the target population for the accuracy and reliability of the research results.⁴⁴ The external validity of this review favors further evaluation in conventional medical setups because the study participants are similar to kidney transplant recipients in a standard healthcare system. This review was based on an a priori protocol that reduced the chances of reviewer bias.¹⁹

Recommendations for practice
Inadequate evidence presently exists on the effectiveness of blood flow sensing technology for postoperative monitoring in kidney transplant recipients. Based on the review findings, there is complete consensus among all key groups for continuing research and investigating the role of blood flow sensing technology in improving graft outcomes.

According to the UK Medical Research Council’s framework for evaluating and developing complex interventions, this review summarized the research to address the first 2 steps (Figure 4). Moving forward (ie, step 3: evaluation), a pragmatic large-scale controlled study is recommended to evaluate the effectiveness of blood flow sensing technology in clinical settings.

Furthermore, the literature search did not identify any study on the long-term implications of blood flow sensing technology. Future studies must consider including long-term follow-up assessments in the research design. Also, it would be appropriate to incorporate the cost-effectiveness evaluation of using blood flow sensing technology in kidney transplant practice in future clinical trials.

Conclusions
Blood flow sensing technology can be used as a helpful adjunct in the postoperative monitoring of kidney transplant recipients. However, given the technical limitations, it is emphasized that the signals should be interpreted alongside the traditional clinical assessment techniques. The stakeholders have contributed to the intervention development research by putting forward innovative ideas. The technology manufacturers have duly acknowledged the valuable suggestions and design modifications to enhance monitoring and circumvent shortcomings, which are underway.

The review results achieved suitable feasibility-level progression criteria and transferability to other transplant centers across the United Kingdom. A pragmatic large-scale RCT is warranted to evaluate the effectiveness of blood flow sensing technology in clinical practice.

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