The renal arterial resistance index and renal allograft survival

Renal arterial resistance index before and after vericiguat administration: Should it be considered the fantastic five?

BACKGROUND

Heart failure (HF) is a chronic-progressive disease. Once established, it is almost impossible to obtain a restitutio ad integrum of the cardiac function, but current strategies aim at slowing down the progression towards the terminal stages of the disease, which inevitably lead to the exitus. On the basis of these considerations, it appears clear that pharmacological interventions applied in this clinical condition should prevent first the development of the disease, by controlling the risk factors for HF thus reducing the onset of the disease, second slowing the disease evolution towards the terminal phases thus containing clinical symptoms and reducing the number of hospitalizations. In this scenario, the add-on therapy with vericiguat seems promising as reported in the VICTORIA study without affecting renal function. Several evidence indicates that renal arterial resistance index (RRI) seems to better reflect cardiovascular damage also in HF patients, thus affecting patients prognosis METHODS: In the present study we have analyzed the effect of vericiguat administration in 27 HF patients specifically evaluating RRI.

RESULTS

Vericiguat signicantly reduces RRI.

CONCLUSIONS

The findings of the present study seems to indicate that vericiguat, beyond its primary mechanism of action, might offer an additional advantage in HF patients.

Impact of Norepinephrine and Dopamine Infusion on Renal Arterial Resistive Index during Pre-Emptive Living Donor Kidney Transplantation: Propensity Score Matching Analysis

Background: Living donor kidney transplantation (LDKT) is a crucial treatment for end-stage renal disease, with pre-emptive LDKT (transplantation before dialysis initiation) offering significant benefits in graft function and patient survival. The selection of a vasopressor during LDKT, particularly between norepinephrine and dopamine, and its impact on renal arterial hemodynamics measured using the renal arterial resistive index (RARI) is poorly understood. Methods: This retrospective observational cohort study enrolled 347 eligible pre-emptive LDKT recipients from the Seoul St. Mary's Hospital between January 2019 and June 2023. Utilizing propensity score matching (PSM), the patients were categorized into dopamine and norepinephrine groups to compare the effects of these vasopressors on the intraoperative RARI, postoperative estimated glomerular filtration rate (eGFR), and hourly urine output. The RARI was measured via the Doppler ultrasonography of the renal hilum and parenchyma post-graft vascular and ureteral anastomoses. Results: The preoperative differences in the recipients' and donors' characteristics were mitigated following PSM. The dopamine group exhibited higher intraoperative RARI values at the renal hilum (0.77 ± 0.11 vs. 0.66 ± 0.13, p < 0.001) and parenchyma (0.71 ± 0.1 vs. 0.6 ± 0.1, p < 0.001) compared to those of the norepinephrine group. However, these differences were not statistically significant on postoperative day 7. The norepinephrine infusion adjusted for the propensity scores was associated with significantly lower odds of an RARI > 0.8 (hilum: OR = 0.214, 95% CI = 0.12-0.382, p < 0.001; parenchyma: OR = 0.1, 95% CI = 0.029-0.348, p < 0.001). The early postoperative outcomes showed a higher eGFR (day 1: 30.0 ± 13.3 vs. 25.1 ± 17.4 mL/min/1.73 m2, p = 0.004) and hourly urine output (day 1: 41.8 ± 16.9 vs. 36.5 ± 14.4 mL/kg/h, p = 0.002) in the norepinephrine group. Furthermore, the long-term outcomes were comparable between the groups. Conclusions: Norepinephrine infusion during pre-emptive LDKT is associated with more favorable intraoperative renal arterial hemodynamics, as evidenced by a lower RARI and improved early postoperative renal function compared to those of dopamine. These findings suggest a potential preferential role for norepinephrine in optimizing perioperative management and early graft functions in LDKT recipients. Given the retrospective nature of this study, further prospective studies are needed to confirm these observations. Additionally, the study limitations include the potential for unmeasured confounding factors and the inability to determine causality due to its observational design.

Renal Arterial and Venous Doppler in Cardiorenal Syndrome: Pathophysiological and Clinical Insights

In recent decades, there has been considerable effort in investigating the clinical utility of renal Doppler measurements in both cardiovascular and renal disorders. In particular, a measure of renal arterial resistance, the renal resistive index (RRI), has been demonstrated to predict chronic kidney disease progression and acute kidney injury in different clinical settings. Furthermore, it is linked to a poorer prognosis in individuals suffering from chronic heart failure. Examining the renal venous flow through pulsed Doppler can offer additional insights into renal congestion and cardiovascular outcomes for these patients. This review seeks to summarize the existing data concerning the clinical significance of arterial and venous renal Doppler measurements across various cardiovascular and renal disease contexts.

Significance of Arterial Spin Labeling for Reducing Biopsies in Patients With Kidney Allograft Dysfunction

BACKGROUND

Although biopsy is often entailed for managing patients with kidney allograft dysfunction, it is associated with potential complications of severe hemorrhage. Arterial spin labeling (ASL) is a non-invasive technique that assesses tissue perfusion.

PURPOSE

To assess the utility of ASL for the discrimination of patients with post-transplant allograft dysfunction who do not need biopsy from those who need.

STUDY TYPE

Prospective.

SUBJECTS

Forty-six patients (34 males/12 females, aged 38.8 ± 9.5 years) with kidney allograft dysfunction, including 31 in which biopsy directly lead to changes in management (NECESSARY group) and 15 in which clinical management did not alter after biopsy (UNNECESSARY group).

FIELD STRENGTH/SEQUENCE

3.0 T and 3D fast-spin echo sequence.

ASSESSMENT

All patients underwent both ASL scan and biopsies. The serum creatinine, proteinuria, pathologic results, and cortical ASL readings were obtained and compared between the two groups.

STATISTICAL ANALYSES

Chi-square test, independent student t-test, Mann-Whitney U test, receiver-operating characteristic curve. A two-tailed P < 0.05 denoted statistical significance.

RESULTS

The NECESSARY group presented with significantly elevated serum creatinine as compared with the UNNECESSARY group (1.87 ± 0.56 mg/dL vs. 1.31 ± 0.37 mg/dL). The acute composite score was significantly higher in the NECESSARY group than that in the UNNECESSARY group (7 [4-8] vs. 1 [0-2]). Cortical ASL in the NECESSARY group was significantly decreased as compared with the UNNECESSARY group (108.06 [69.96-134.92] mL/min/100 g vs. 153.48 [113.19-160.37] mL/min/100 g). Serum creatinine differentiated UNNCESSARY group from the NECESSARY group with an area under the curve (AUC) and specificity of 0.79 and 54.84%, respectively. By comparison, the cortical ASL yielded an AUC of 0.75 and a specificity of 70.97%. Notably, the specificity was increased to 90.30% by combined use of serum creatinine and cortical ASL.

DATA CONCLUSION

The combined use of ASL and serum creatinine yielded a high specificity for selecting patients who may not need allograft biopsy.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 3.

Investigating the role of ultrasound-based shear wave elastography in kidney transplanted patients: correlation between non-invasive fibrosis detection, kidney dysfunction and biopsy results-a systematic review and meta-analysis

INTRODUCTION

Interstitial fibrosis and tubular atrophy are leading causes of renal allograft failure. Shear wave elastography could be a promising noninvasive method for providing information on the state of the kidney, with specific regard to fibrosis but currently available data in the literature are controversial. Our study aimed to analyze the correlation between shear wave elastography and various kidney dysfunction measures.

METHODS

This review was registered on PROSPERO (CRD42021283152). We systematically searched three major databases (MEDLINE, Embase, and CENTRAL) for articles concerning renal transplant recipients, shear wave elastography, fibrosis, and kidney dysfunction. Meta-analytical calculations for pooled Pearson and Spearman correlation coefficients (r) were interpreted with 95% confidence intervals (CIs). Heterogeneity was tested with Cochran's Q test. I2 statistic and 95% CI were reported as a measurement of between-study heterogeneity. Study quality was assessed with the QUADAS2 tool.

RESULTS

In total, 16 studies were included in our meta-analysis. Results showed a moderate correlation between kidney stiffness and interstitial fibrosis and tubular atrophy, graded according to BANFF classification, on biopsy findings for pooled Pearson (r = 0.48; CI: 0.20, 0.69; I2 = 84%) and Spearman correlations (r = 0.57; CI: 0.35, 0.72; I2 = 74%). When compared to kidney dysfunction parameters, we found a moderate correlation between shear wave elastography and resistive index (r = 0.34 CI: 0.13, 0.51; I2 = 67%) and between shear wave elastography and estimated Glomerular Filtration Rate (eGFR) (r = -0.65; CI: - 0.81, - 0.40; I2 = 73%). All our outcomes had marked heterogeneity.

CONCLUSION

Our results showed a moderate correlation between kidney stiffness measured by shear wave elastography and biopsy results. While noninvasive assessment of kidney fibrosis after transplantation is an important clinical goal, there is insufficient evidence to support the use of elastography over the performance of a kidney biopsy.

Effect of Body Composition on Graft Function and Cardiovascular Outcomes in Normotensive Renal Transplant Recipients

OBJECTIVES

We evaluated the effects of body composition on graft function and cardiovascular outcomes in normotensive renal transplant recipients.

MATERIALS AND METHODS

In this cross-sectional study, we analyzed ambulatory blood pressure monitoring data from 136 renal transplant recipients with stable allograft function after living related donor transplant. We enrolled 87 normotensive recipients. We analyzed left ventricular mass index, renal resistive index, and body composition of recipients. We divided recipients into 2 groups according to mean lean body mass, defined by bioimpedance analysis, with 38 in group 1 (lean body mass <47 kg) and 49 in group 2 (lean body mass ≥47 kg).

RESULTS

Mean time posttransplant was 35.0 ± 23.3 months. Mean renal resistive index, left ventricular mass index, lean body mass, body mass index, and fat mass were 0.67 ± 0.1, 195.0 ± 118.5 g/m2, 47.3 ± 9.1 kg, 25.9 ± 5.0 kg, and 44.6±10.5 kg,respectively. Lean body mass was positively correlated to sex (r = 0.36, P = .03), body mass index (r = 0.04, P = .416),renalresistive index (r = 0.495, P = .01), and left ventricular mass index (r = 0.713, P = .02) but negatively correlated to serum albumin levels (r=-0.343, P=0.04). Lean body mass was significantly higher in males than in females (P = .03). Patients in group 2 had significantly higher left ventricular mass index (P = .01) and renal resistive index (P = .03). In multiple regression analysis, lean body mass (P = .01) and left ventricular mass index (P = .01) were predictors of renal resistive index.

CONCLUSIONS

Lean body mass significantly influences left ventricular mass index and renal resistive index. Hence, body composition analysis could be an early predictor of graft function and cardiovascular outcomes in normotensive renal transplant recipients.

Sonographic Assessment of Renal Transplantation in Adult Saudi Patients: A Cross-Sectional Retrospective Study

Kidney transplantation stands as a practical and cost-effective treatment option for end-stage renal disease patients, offering an improved quality of life with reduced morbidity when compared with hemodialysis. To evaluate the status of transplanted kidneys in Saudi patients, we conducted a retrospective single-center study at Jazan, Saudi Arabia, involving 46 adult renal recipients enrolled randomly from 2015 to December 2022. Using high-frequency ultrasound, we performed Duplex ultrasound examinations to assess renal allografts. The study revealed that the renal grafts exhibited normal length, with preserved cortical medullary differentiation (CMD) in 84.8% of cases and poor CMD in 15.2%. The echogenicity of the grafts remained normal in 69.6% of instances. Interestingly, we observed a significant rise in resistance index values as the graft duration increased (P = .04), whereas patients with abnormal creatinine levels displayed decreased peak systolic velocity and end-diastolic velocity. Notably, sonographic graft assessments unveiled complications, including perinephric fluid accumulation (8.7%), simple renal cysts (10.86%), hydronephrosis (8.7%), and one case of graft rejection. Receiver operating characteristics analysis for serum blood creatinine levels and abnormal parenchymal findings yielded fair to poor predictive accuracy, with varying sensitivity and specificity measures that lacked statistical significance. In conclusion, our study revealed that most Saudi renal transplant recipients exhibited grafts with normal echogenicity, preserved CMD, and limited perinephric fluid. This investigation provides valuable insights into sonographic changes and Doppler parameters of renal grafts, potentially aiding in the early detection of graft rejection and facilitating diagnostic and therapeutic planning.

Association of renal resistive indices with kidney disease progression and mortality

BACKGROUND

Renal resistive indices (RRI) have been shown to predict the progression of kidney disease. This study aims to evaluate the association of RRI with mortality and dialysis initiation after adjustment to therapeutic and life style interventions.

METHODS

This is a retrospective study that included all chronic kidney disease patients followed for at least two years in three nephrology clinics between 2006 and 2019 and who had a RRI level in their files. Kaplan Meier and log rank test compared the survival of patients with normal versus high RRI. Cox regression analysis evaluated the association between RRI and death or dialysis initiation after adjustment to treatments and life style modifications.

RESULTS

A total of 192 patients were analyzed: 68 had RRI < 0.7 and 124 had RRI ≥ 0.7. Their mean age was 66.5 ± 13.1 years at first visit, 78.1% were males. There was a negative correlation between baseline eGFR and RRI (p < 0.001; Spearman correlation coefficient = -0.521). The survival was significantly better in patients with RRI < 0.7 with a Log Rank test < 0.001. The univariate cox regression analysis showed a significant association between RRI and mortality (HR = 1.08; 95%CI: 1.04-1.11; p < 0.001) that remained significant after adjustment to cardiovascular risk factors and interventions such as salt reduction, blood pressure control, statins and RAAS inhibitors (HR = 1.04; 95%CI: 1.00-1.08; p = 0.036). Cox regression analysis showed a significant association between RRI and dialysis initiation (HR = 1.06; 95%CI 1.01-1.10; p = 0.011).

CONCLUSION

Our study revealed that patients with an elevated RRI ≥ 0.7 are at a higher risk of mortality after adjustment to medications and lifestyle modifications. RRI can, according to this study, be considered as an independent prognostic factor in CKD patients.

Renal hemodynamic evaluation protocol based on the pathophysiological mechanism of acute kidney injury: Critical Care UltraSound Guided-A(KI)BCDE

The multiple etiological characteristics of acute kidney injury (AKI) have brought great challenges to its clinical diagnosis and treatment. Renal injury in critically ill patients always indicates hemodynamic injury. The Critical Care UltraSound Guided (CCUSG)-A(KI)BCDE protocol developed by the Chinese Critical Ultrasound Study Group (CCUSG), respectively, includes A(KI) diagnosis and risk assessment and uses B-mode ultrasound, Color doppler ultrasound, spectral Doppler ultrasound, and contrast Enhanced ultrasound to obtain the hemodynamic characteristics of the kidney so that the pathophysiological mechanism of the occurrence and progression of AKI can be captured and the prognosis of AKI can be predicted combined with other clinical information; therefore, the corresponding intervention and treatment strategies can be formulated to achieve targeted, protocolized, and individualized therapy.

Research on the correlation between the renal resistive index, renal microvessel density, and fibrosis

BACKGROUND

This study was designed to investigate the relationship between the renal resistive index (RRI), renal microvessel density (RMD), and fibrosis in patients with chronic kidney disease (CKD).

METHODS

A total of 73 CKD patients were included in the study. Prior to kidney biopsy, we recorded the RRI of the interlobar artery and the estimated glomerular filtration rate (eGFR). Immunohistochemical analysis was performed to assess CD34 expression, and Masson staining was used to evaluate histopathological specimens for RMD and the degree of fibrosis. The percentage of the positive area (PPA) was recorded. Subsequently, we investigated the correlation between RRI, RMD, and kidney fibrosis.

RESULTS

RMD (CD34 PPA-total and CD34 PPA-peritubular capillary) showed a slight increase in early CKD stages (1-2) and gradually declined from CKD stages 2 to 5. No correlation was observed between the RRI and RMD or between the RRI and fibrosis across CKD stages 1 to 5. However, across CKD stages 2 to 5, RRI negatively correlated with CD34 PPA-glomerulus (r = -0.353, p = 0.022), but no correlation was found with CD34 PPA-total, CD34 PPA-peritubular capillary, or kidney fibrosis. eGFR showed a positive correlation with RMD (CD34 PPA-total, CD34 PPA-peritubular capillary, and CD34 PPA-glomerulus) across CKD stages 2 to 5, while no correlation was found from CKD stages 1 to 5.

CONCLUSION

There was no correlation between RRI and RMD or between RRI and fibrosis across CKD stages 1 to 5 (RRI ≤ 0.7).

Value of conventional ultrasound and contrast-enhanced ultrasound for the assessment of renal allograft dysfunction and prognosis

BACKGROUND

Ultrasound (US) is the primary imaging modality for the assessment of transplanted kidneys. This study aims to investigate the ability of conventional US and contrast-enhanced US (CEUS) in assessing renal allograft function and prognosis.

METHODS

A total of 78 consecutive renal allograft recipients were enrolled. Patients were classified as normal allograft function (n = 41) and allograft dysfunction (n = 37) groups. All patients underwent US and parameters were measured. The independent-samples t-test or Mann-Whitney U test, logistic regression analysis, Kaplan-Meier survival plots, and Cox regression analysis were used.

RESULTS

In multivariable analysis, cortical echo intensity (EI) and cortical peak intensity (PI) were determinant US parameters for renal allograft dysfunction (p = .024 and p = .003, respectively). The combination of cortical EI and PI showed an area under the receiver operating characteristic curve (AUROC) of .785 (p < .001). Of 78 patients (median follow-up: 20mo), 16 (20.5%) exhibited composite end points. Cortical PI had a general prediction accuracy with an AUROC of .691, sensitivity of 87.5%, and specificity of 46.8% at the threshold of 22.08 dB in predicting prognosis (p = .019). The combination of estimated-glomerular filtration rate (e-GFR) and PI in predicting prognosis showed an AUROC of .845 with a cut-off value of .836, sensitivity of 84.0%, and specificity of 67.3% (p < .001).

CONCLUSION

This study indicates that cortical EI and PI are useful US parameters for evaluating renal allograft function and e-GFR combined with PI may provide a more accurate predictor of survival.

Influence of arterial blood gases on the renal arterial resistive index in intensive care unit

BACKGROUND

Renal artery Doppler sonography with resistive index (RI) determination is a noninvasive, fast, and reliable diagnostic tool increasingly used in the intensive care unit (ICU) to predict and assess the reversibility of acute kidney injury (AKI). However, interpreting the RI can be challenging due to numerous influencing factors. While some studies have explored various confounding factors, arterial blood gases have received limited attention. Therefore, our study aims to evaluate the impact of arterial blood gases on the RI in the ICU setting.

METHODS

This prospective observational study enrolled ICU patients who required blood gas analysis and had not experienced significant hemodynamic changes recently. The RI was measured using standardized Doppler ultrasound within an hour of the arterial blood gases sampling and analysis.

RESULTS

A total of sixty-four patients were included in the analysis. Univariate analysis revealed a correlation between the RI and several variables, including PaCO2 (R = 0.270, p = 0.03), age (R = 0.574, p < 0.0001), diastolic arterial pressure (DAP) (R = - 0.368, p = 0.0028), and SaO2 (R = - 0.284, p = 0.0231). Multivariate analysis confirmed that age > 58 years and PaCO2 were significant factors influencing the RI, with respective odds ratios of 18.67 (p = 0.0003) and 1.132 (p = 0.0267).

CONCLUSION

The interpretation of renal arterial RI should take into account thresholds for PaCO2, age, and diastolic arterial pressure. Further studies are needed to develop a comprehensive scoring system that incorporates all these cofactors for a reliable analysis of RI levels. Trial registration This observational study, registered under number 70-0914, received approval from local Ethical Committee of Toulouse University Hospital.

Imperatives of Mathematical Model of Arterial Blood Dynamics for Interpretation of Doppler Velocimetry: A Narrative Review

Clinicians frequently study arterial Doppler velocimetric waveforms depicted by Doppler sonography of the kidneys, the heart, the brain, and the feto-maternal circulation to assess the well-being of the aforementioned vital organs. The waveform interpretation of the Doppler indices can be studied using a mathematical model. The developed models serve as teaching tools and for easy comprehension of the regulatory mechanism of the organs. It will also obtain accurate wall shear stress (WSS) and likely atherosclerotic sites can be predicted early. The aim of this review is to reveal the imperatives of mathematical models in the study of the physical interpretation of Doppler velocimetry. The models will explore sonographic Doppler velocimetry and computational fluid dynamics (CFD) in determining the segments of the arteries that are prone to the development of atheromatous plaque. It will be achieved by comparing and computing the measurement differences of the WSS. A thorough literature review was carried out between 1971 and 2021 on the mathematical modeling of blood dynamics and Doppler velocimetry of different blood vessels, across various electronic databases including NC AHEC Digital Library, PUBMED, ERIC, MEDLINE, Free Medical Journals, and EMBASE. The results of the literature search were presented using the PRISMA flow chat. The narrative review of the mathematical models of arterial blood dynamics is based on incompressible Navier-Stokes equations, the Windkessel model, and CFD. It was deduced that the blood flow velocity decreased with time across the varying frequency from 0.2Hz to 0.50Hz in the interlobar arterial channels. The review also revealed that adult humans' Doppler indices of the renal-interlobar artery agree with developed models of renal interlobar arterial blood dynamics. The mathematical model measurements of the great vessels matched the sonographic Doppler velocimetry with <15% variation. In our fast-paced world of epidemiological transition, the imperatives of mathematical modeling of arterial flow dynamics based on the Navier-Stokes equations to represent various physiologic and pathologic situations cannot be overstated. The practical consequences include the possibility of mathematical models to acquire precise WSS distribution and early detection of potential atherosclerotic sites during cardiovascular Doppler sonography.

The Resistive Index by Doppler Ultrasonography as a Predictor of the Long-Term Outcomes After Kidney Transplantation

BACKGROUND

Doppler ultrasonography (US) is a noninvasive examination for assessing graft function after kidney transplantation. Although Doppler US is routinely performed, only a few reports have investigated whether a high resistive index (RI) detected by Doppler US affects graft function and survival. We hypothesized that there is a relationship between a high RI and inferior outcomes after kidney transplantation.

METHODS

We included 164 living kidney transplant patients treated between April 2011 and July 2019. We divided the patients into 2 groups according to RI (cut-off, 0.7) 1 year after transplantation.

RESULTS

The recipient was significantly older in the high RI (≥0.7) group. Moreover, there were significant differences in the prevalence of pretransplant diabetes mellitus and the value of pretransplant hemoglobin A1c. Regarding long-term outcome, there was no significant difference in overall graft survival (5 years, 92.6% vs 91.8%; 10 years, 85.0% vs 67.9%; P = .64). On the other hand, the mortality was significantly worse in the high RI group (5 years, 99.1% vs 93.9%; 10 years, 96.4% vs 70.0%, P = .013).

CONCLUSIONS

A high RI might predict mortality after kidney transplantation.

Current Insights into the Significance of the Renal Resistive Index in Kidney and Cardiovascular Disease

Initially, the renal resistive index (RRI) was investigated with the aim of improving diagnosis in kidney diseases, but this goal was not met. Recently, many papers have highlighted the prognostic significance of the RRI in chronic kidney disease: specifically, in estimating the revascularization success of renal artery stenoses or the evolution of the graft and the recipients in renal transplantation. Moreover, the RRI has become significant in the prediction of acute kidney injury in critically ill patients. Studies in renal pathology have revealed correlations of this index with parameters of systemic circulation. The theoretical and experimental premises of this connection were then reconsidered, and studies analyzing the link between RRI and arterial stiffness, central and peripheral pressure, and left ventricular flow were conducted with this purpose. Many data currently indicate that RRI is influenced more by pulse pressure and vascular compliance than by renal vascular resistance-assuming that RRI reflects the complex interplay between systemic circulation and renal microcirculation and should be considered a marker of systemic cardiovascular risk beyond its prognostic relevance for kidney disease. In this review, we overview the clinical research that reveals the implications of RRI in renal and cardiovascular disease.

Quantitative ultrasound for non-invasive evaluation of subclinical rejection in renal transplantation

OBJECTIVES

This study aimed to investigate the predictive efficacy of shear-wave elastography, superb microvascular imaging (SMI), and CEUS for allograft rejection in kidney transplants without graft dysfunction.

METHODS

From January 2021 to November 2021, 72 consecutive patients who underwent both allograft biopsy and ultrasound were evaluated. Blood test results were obtained within a week of the ultrasound examinations, which were performed before the protocol biopsy. Resistive index (RI), tissue viscoelasticity, vascular index, and quantitative CEUS parameters were measured. Patients were divided based on biopsy results into the rejection and non-rejection groups.

RESULTS

Among the 72 patients, 21 patients had pathological characteristics of acute rejection. RI of allograft was significantly higher in the rejection group (p = 0.007), compared to the non-rejection group. There were no significant between-group differences in vascular indices of SMI, mean elasticity, and mean viscosity. Meanwhile, among the parameters obtained by the time-intensity curve on CEUS, the cortical and medullary ratios of average contrast signal intensity, peak enhancement, wash-in area AUC, wash-in perfusion index, wash-out AUC, and wash-in and wash-out AUC were significantly different between the two groups (p < 0.05). In the receiver operating characteristic curve analysis for predicting allograft rejection, the AUC was 0.853 for the combination of six CEUS parameters, RI, and blood urea nitrogen.

CONCLUSIONS

Among non-invasive quantitative ultrasound measurements, CEUS parameters are the most useful for diagnosing subclinical allograft rejection. Furthermore, the combination of CEUS parameters, RI, and blood urea nitrogen may be helpful for the early detection of renal allograft rejection.

KEY POINTS

• Among non-invasive quantitative ultrasound measurements, CEUS parameters are the most useful for the diagnosis of subclinical allograft rejection. • On CEUS, the C/M ratios of MeanLin, PE, WiAUC, WiPI, WoAUC, and WiWoAUC are significantly lower in the rejection group; the combination of these showed reliable predictive performance for rejection. • The combination of CEUS parameters, RI, and BUN has a high predictive capability for subclinical allograft rejection.

End-diastolic velocity mediates the relationship between renal resistive index and the risk of death

OBJECTIVE

Renal resistive index predicts the risk of death in many populations but the mechanism linking renal resistive index and death remains elusive. Renal resistive index is derived from end-diastolic velocity (EDV) and peak systolic velocity (PSV). However, the predictive value of EDV or PSV considered alone is unknown.

METHODS

We conducted a retrospective analysis of 2362 consecutive patients who received a kidney transplant from 1985 to 2017. EDV and PSV were measured at 3 months after transplantation, renal resistive index was calculated, and the risk of death was assessed [median follow-up: 6.25 years (0.25-29.15); total observation period: 13 201 patient-years].

RESULTS

Doppler indices were available in 1721 of 2362 (78.9%) patients (exclusions: 113 who died or returned to dialysis before, 427 with no Doppler studies, 27 with renal artery stenosis, 74 missing values). Among them, 279 (16.4%) had diabetes before transplantation. Mean age was 51.5 ± 14.7, 1097 (63.7%) were male. During follow-up, 217 of 1721 (12.6%) patients died. Renal resistive index and EDV shared many determinants (notably systolic, diastolic and pulse pressure, recipient age and diabetes) unlike renal resistive index and PSV. EDV used as a binary [lowest tertile vs. higher values: (hazard ratio: 2.57 (1.96-3.36), P  < 0.001)] and as a continuous (the lower EDV, the greater the risk of death) variable was significantly associated with the risk of death. This finding was confirmed in multivariable analyses. Prediction of similar magnitude was found for renal resistive index. No association was found between PSV used as a binary or a continuous variable and the risk of death.

CONCLUSION

Low EDV explains high renal resistive index, and the mechanism-linking renal resistive index to the risk of death is through low EDV.

Intrarenal Doppler approaches in hemodynamics: A major application in critical care

The treatment of severe cases usually requires multimodality hemodynamic monitoring approaches, particularly for tissue and organ perfusion tracking. Currently, only a few studies have investigated renal perfusion status at the bedside. Ultrasound has become increasingly utilized to guide the hemodynamic management of severe patients. Similarly, intrarenal Doppler (IRD) is widely used to assess renal perfusion from both the intrarenal artery and vein perspectives. The renal resistive index (RRI), which reflects the renal arterial blood flow profile, is often applied to predict the reversibility of renal dysfunction and to titrate hemodynamic support. Intrarenal venous flow (IRVF) patterns and the renal venous stasis index (RVSI), which reflects the intrarenal vein blood flow profile, are now being used to assess intravenous congestion. They may also be useful in predicting the risk of acute kidney injury and avoiding fluid overload. IRD can provide diverse and supplemental information on renal perfusion and may help to establish the early diagnosis in severe patients. This review focused on the specific operational methods, influencing factors, and applications of IRD in hemodynamics.

Value and limitations of sonography in kidney transplant recipients with special attention to the resistive index - An update

Kidney transplantation has become the standard treatment for end-stage renal disease. Even though the success rates are high, early and late post-transplant complications remain a major clinical problem due to the risk of graft failure. Therefore, it is of highest interest to early diagnose post-transplant complications. Ultrasound with color coded Duplex analysis plays a crucial role in imaging mechanical and vascular complications. In this article, we give an update of the visualizable complications in kidney transplant recipients and discuss the value of resistive index (RI) measurement with its limitations in allograft rejection.

Inferior mesenteric artery embolization ahead of rectal cancer surgery: AMIREMBOL pilot study

Ischaemic conditioning in rectal cancer surgery by preoperative embolization of the inferior mesenteric artery is feasible and safe. It seems to protect from ischaemic stress during the surgical procedure.

The diagnostic value of Doppler ultrasonography after pediatric kidney transplantation

Ultrasonography (US) plays a major diagnostic role in the pre- and post-transplant evaluation of recipient and donor. In most cases, US remains the only necessary imaging modality. After pediatric kidney transplantation, US can ensure immediate bedside diagnosis of vessel patency and possible postoperative non-vascular complications. Criteria for US diagnosis of kidney vessel thrombosis and stenosis in the transplant will be presented. Non-vascular complications after kidney transplantation include hydronephrosis, hematoma, lymphocele, and abscess. US can detect suggestive, but nevertheless non-specific, acute signs (sudden increase in volume and elevated resistive index), and chronic rejection, which therefore remains a histological diagnosis. US is of little or no help in detection of tubular necrosis or drug toxicity, but it can exclude other differential diagnoses. This educational review provides a practical and systematic approach to a multimodal US investigation of the kidney transplant. It includes a short overview on possible indications for contrast-enhanced ultrasonography (CEUS) in children after kidney transplantation.

The role of renal resistive index as a prognostic tool in kidney transplantation: a systematic review

Background

In kidney transplant recipients (KTRs), observational data have reported conflicting findings about the utility of renal resistive index (RRI) in determining outcomes. We aimed to synthesize the current literature and determine the prognostic role of RRI in KTRs.

Methods

We conducted a systematic review to assess the role of RRI in predicting death, graft failure, graft function, and proteinuria. Of the 934 titles/abstracts reviewed, 26 studies were included. There was significant heterogeneity in RRI measurements and thresholds as well as in analytic methods and a meta-analysis could not be performed.

Results

All included studies were observational and included 7049 KTRs. Eight studies analyzed death, of which five reported a significant association with higher RRI. In the remaining three, small sample sizes and lower/multiple RRI thresholds may have limited detection of a statistically significant difference. Three studies investigated all-cause graft failure and an association with RRI was reported but varied by time of RRI measurement. Three out of five studies that analyzed a composite of patient and graft outcomes reported an association with RRI. Evidence analyzing death-censored graft failure, graft failure (unclear if death-censored or all-cause), measures of graft function, and proteinuria were conflicting. Most studies had a moderate to high risk of bias.

Conclusions

RRI likely has a prognostic role in predicting patient outcomes, reflecting patient systemic vascular disease burden rather than graft hemodynamics. Since cardiovascular diseases are a major cause of death and graft loss, RRI may be explored as a non-invasive tool to risk stratify KTRs.

Renal Resistive Index on Intensive Care Unit Admission Correlates With Tissue Hypoperfusion Indices and Predicts Clinical Outcome

BACKGROUND

Renal resistive index (RRI) has been used to evaluate renal blood flow. Our aim was to investigate the relation between RRI and global tissue hypoperfusion indices and their association with clinical outcome, in intensive care unit (ICU) patients.

METHODS

RRI was measured within 24 h of ICU admission. Gas exchange and routine hemodynamic variables at the time of RRI assessment were recorded. An elevated RRI was defined as >0.7. The ratio of central venous-to-arterial carbon dioxide partial pressure difference by arterial-to-central venous oxygen content difference (P(cv-a)CO2/C(a-cv)O2) and lactate were used as global tissue hypoperfusion indices.

RESULTS

A total of 126 patients were included [median age 61 (IQR 28) years, 74% males]. P(cv-a)CO2/C(a-cv)O2 ratio and arterial lactate were significantly higher in patients with RRI >0.7 compared with those with RRI ≤0.7 [2.88 (3.39) vs. 0.62 (0.57) mmol/L and 2.4 (2.2) vs. 1.2 (0.6)] respectively, both P < 0.001)]. RRI was significantly correlated with P(cv-a)CO2/C(a-cv)O2 ratio and arterial lactate for the whole patient population (rho = 0.64, both P < 0.0001) and for the subset of patients with shock (rho = 0.47, P = 0.001; and r = 0.64, P < 0.0001 respectively). Logistic regression models showed a significant association between RRI and P(cv-a)CO2/C(a-cv)O2 ratio with clinical outcome. The combination of RRI with P(cv-a)CO2)/(C(a-cv)O2 ratio and lactate better predicted mortality than RRI alone [AUC 84.8% (95% CI 5.1% -94.4%)] vs. [AUC 74.9% (95% CI 61%-88.8%)] respectively, P < 0.001.

CONCLUSIONS

Renal blood flow assessed by RRI, on ICU admission, correlates with global tissue hypoperfusion indices. In addition, RRI in combination with tissue perfusion estimation better predicts clinical outcome than RRI alone.

Can we predict early renal impairment in pediatric cirrhosis?

AIMS

Published literature on renal dysfunction (RD) in pediatric cirrhosis are limited. We aimed to detect early RD in cirrhotic children by renal resistive index (RI) and plasma aldosterone (PA). We evaluated the effects of large-volume paracentesis (LVP) and albumin infusion on the same.

METHODS

Non-azotemic cirrhotic children with tense ascites (undergoing LVP with albumin infusion) were prospectively enrolled. Blood biochemistry and doppler ultrasonography for RI and PA were measured at regular intervals. RI >0.7 was considered as RD. Outcomes were noted at D90 and 1 year. Chronic liver disease children without ascites were included as controls.

RESULTS

Of the 99 cirrhotic children, tense ascites (n=51) had higher baseline RI than controls (n=48) (p<0.001). Overall, baseline RD was observed in 32% and was significantly higher in tense ascites compared to controls (59% vs. 4%, p<0.001). Tense ascites with RD at admission had higher chances of acute kidney injury (AKI) (p=0.009), ascites recurrence (p=0.043), hospital readmission (p=0.048), and mortality (p=0.009) compared to patients without RD by D90. Significant reduction in RI was noted at 48 h, D7, D30, and D90 compared to baseline after LVP with albumin. Pediatric End-stage Liver Disease (PELD) score and PA had a strong positive correlation with baseline RI (R²=0.51, R²=0.47). Using multivariate analysis, PELD score and PA were predictors of AKI (odds ratio [OR]: 1.14; 95% confidence interval [CI]: 1.04-1.24; p=0.003) and mortality (OR: 1.82; 95% CI: 1.22-2.72; p=0.004), respectively.

CONCLUSIONS

Abnormal baseline RI can be used as an early predictor of RD and predict long-term renal ouctomes in pediatric cirrhosis. Baseline RI correlated well with the severity of liver disease and PA. Paracentesis and albumin infusion effectively reduced RI.

Intraoperative evaluation of renal resistive index with transesophageal echocardiography for the assessment of acute renal injury in patients undergoing coronary artery bypass grafting surgery: A prospective observational study

Background

Acute kidney injury (AKI) is a common complication after on pump coronary artery bypass grafting (CABG) surgery and is associated with a poor prognosis. Postoperative AKI is associated with morbidity, mortality, and increase in length of intensive care unit (ICU) stay and increases the financial burden. Identifying individuals at risk for developing AKI in postoperative period is extremely important to optimize outcomes. The aim of the study is to evaluate the association between the intraoperative transesophageal echocardiography (TEE) derived renal resistive index (RRI) and AKI in patients undergoing on-pump CABG surgery.

Methods

This prospective observational study was conducted in patients more than 18 years of age undergoing elective on pump CABG surgery between July 1, 2018, and December 31, 2019, at a tertiary care center. All preoperative, intraoperative, and postoperative parameters were recorded. TEE measurement was performed in hemodynamically stable patients before the sternum was opened. Postoperative AKI was diagnosed based on the serial measurement of serum creatinine and the monitoring of urine output.

Results

A total of 115 patients were included in our study. Thirty-nine (33.91%) patients had RRI >0.7 while remaining seventy-six (66.08%) patients had RRI <0.7. AKI was diagnosed in 26% (30/115) patients. AKI rates were significantly higher in patients with RRI values exceeding 0.7 with 46.15% (18/39) compared to 15.75% (12/76) in RRI values of less than 0.7. Multivariate analysis revealed that AKI was associated with an increase in RRI and diabetes mellitus. The RRI assessed by receiver operating characteristic (ROC) curve and the area under the curve (AUC) to distinguish between non-AKI and AKI groups were 0.705 (95% CI: 0.588-0.826) for preoperative RRI. The most accurate cut-off value to distinguish non-AKI and AKI groups was a preoperative RRI of 0.68 with a sensitivity of 70% and specificity of 67%.

Conclusions

An increased intraoperative RRI is an independent predictor of AKI in the postoperative period in patients undergoing CABG surgery. The cutoff value of TEE-derived RRI in the intraoperative period should be >0.68 to predict AKI in the postoperative period.

Resistance index of the renal artery measured by doppler ultrasound as a predictor of graft function after kidney transplantation

Background/Aim. As an optimal treatment of choice for patients with the latest stage of chronic kidney failure (CKD), renal transplantation (Tx) is performed. The resistance index (RI) of the renal artery is measured by Doppler ultrasonography routinely at certain time intervals to show the condition of the renal graft. The value of RI > 0.75 is considered abnormal. The aim of the study was to determine the correlation between the values of the RI index and the function of the transplanted kidney. Methods. We analyzed retrospectively 63 patients in whom kidney transplant was done at the Clinic for Nephrology and Clinical Immunology, the University Clinical Center of Vojvodina, Novi Sad, Serbia, in the period from 2013 to 2017. Doppler of renal blood vessels was made to all examined patients in the first month after the renal trans-plantation. In addition to standard demographic data, all patients had the RI index and its relationship to the function of the transplanted kidney analyzed immediately after transplantation, as well as in the 6th, 12th, and 18th month, and in a certain number of patients in the 24th and 48th month after transplantation. Results. Out of 63 patients, 63.5% were men, and 26.5% were women, with an average age of 47.67 ? 13.62 years. The primary diseases in patients which led to the terminal CKD stage were hypertension in 33.3% and different forms of glomerulonephritis; while other diseases (diabetes mellitus, chronic pyelonephritis, eclampsia, polycystic kidneys, kidney agenesia, and unknown cause) were present in a lower percentage. RI < 0.75 was present in 73%, and RI > 0.75 in 27% of patients. There was no statistically significant association between RI and serum creatinine or creatinine clearance at a given time, and there was no connection between RI and gender, as well as length of previous treatment by HD. There was a statistically significant association between RI and age of kidney recipient, as well as Tx type. Conclusion. In the observed group of patients, RI of renal arteries did not prove to be a good predictor of the function of the transplanted kidney either in the early or later post-transplant periods. RI might have greater predictive significance if it were determined on or immediately after the transplantation procedure.

Renal-Resistive Index for Prediction of Acute Kidney Injury in the Setting of Aortic Insufficiency

Acute kidney injury (AKI) is a common postoperative complication after cardiac surgery with cardiopulmonary bypass (CPB), and leads to significant morbidity, mortality, and cost. Although early recognition and management of AKI may reduce the burden of renal disease, reliance on serum creatinine accumulation to confidently diagnose it leads to a significant and important delay (up to 48 hours). Hence, a search for earlier AKI biomarkers is warranted. The renal-resistive index (RRI) is a promising early AKI biomarker that reflects intrarenal arterial pulsatility as reflected by the peak systolic and end-diastolic blood velocities divided by the peak systolic velocity. During cardiac surgery, post-CPB elevation of RRI is correlated with renal injury. The RRI is influenced by intrarenal and extrarenal factors, as well as different hemodynamic states. Understanding its limitations may increase its usefulness as an early AKI biomarker. For example, tachycardia or aortic stenosis typically results in a lower RRI, whereas bradycardia or increased systemic pulse pressure (as seen with aortic insufficiency) are associated with a higher RRI, unrelated to any intrarenal effects. In this E-Challenge, the authors present two cases in which the RRI was used to evaluate a patient's risk of developing AKI.

Determinants of the serial changes in measurements of renal allograft Doppler resistive index in the first postoperative month

Introduction:

The role of single Doppler-derived renal resistive index (RI) in renal allograft management is still a controversial issue, however detection of changes in serial duplex scanning has been reported as more valuable. This study aimed to test the hypothesis that early change in RI following transplantation may be related to factors associated with delayed graft function (DGF).

Material and methods:

113 patients were included, in whom two RI measurements were performed within 30 days post-transplant. According to an RI change (equal to or more than 10%) in the second measurement, patients were assigned to decrease (Group I), no change (Group II), or increase (Group III) group.

Results:

30 subjects had a decrease, 55 had no change, and 28 had an increase in the second RI measurement. The donors were younger in Group III in comparison to Group II. In comparison to Group I, Group III had a higher frequency of deceased donor, DGF, and presence of tubular necrosis and tubular vacuolization in peri-implantation biopsies.

Conclusion:

the increase of RI during the first weeks of the postoperative period seems to be associated with DGF and with tubular necrosis / tubular vacuolization in peri-implantation biopsies, likely related to ischemia reperfusion injury.

Preoperative evaluation of iliac blood vessels for first kidney transplant recipients: Combination of conventional and contrast-enhanced ultrasonography

OBJECTIVE

To assess iliac blood vessels using conventional ultrasound (US) and contrast-enhanced ultrasonography (CEUS) before kidney transplantation (KT) and determine whether US findings related to post-transplant outcomes.

METHODS

A total of 119 patients received US and CEUS before KT waiting-list acceptance. The preoperative iliac blood hemodynamics and vascular conditions were evaluated. The operative strategy and follow-up outcomes were recorded. Logistic regression and correlation analysis were used. The accuracy in determining the patency of iliac blood vessels was calculated before and after the injection of contrast materials.

RESULTS

CEUS can help to significantly improve the visualization of the internal iliac artery, but there was no significant correlation with post-transplant outcomes. In terms of accuracy, there were significant differences in determining the patency of internal iliac arteries between conventional US and CEUS (60.5% and 100%, p < 0.001). The surgical strategy of one patient was regulated and two patients were excluded from KT according to US findings.

CONCLUSIONS

Compared with conventional US, CEUS helps to improve the visualization of the internal iliac artery. Conventional US and CEUS have the potential to serve as effective methods to evaluate anatomy and hemodynamics of iliac vessels and have a potential value while defining clinical algorithms in surgery decision-making.

Renal transplant evaluation: multimodality imaging of post-transplant complications

With advancements in surgical techniques and immuno-suppression, renal transplantation is established as the most effective treatment option in patients with end-stage renal disease. Early detection of renal allograft complications is important for long-term graft survival. Late clinical presentation often causes diagnostic delays till the time allograft failure is advanced and irreversible. Imaging plays a key role in routine surveillance and in management of acute or chronic transplant dysfunction. Multimodality imaging approach is important with ultrasound-Doppler as the first-line imaging study in immediate, early and late post-transplant periods. Additional imaging studies are often required depending on clinical settings and initial ultrasound. Renal functional MRI is a rapidly growing field that has huge potential for early diagnosis of transplant dysfunction. Multiparametric MRI may be integrated in clinical practice as a noninvasive and comprehensive "one-stop" modality for early diagnosis and longitudinal monitoring of renal allograft dysfunctions, which is essential for guiding appropriate interventions to delay or prevent irreversible renal damage. With rapidly increasing numbers of renal transplantation along with improved patient survival, it is necessary for radiologists in all practice settings to be familiar with the normal appearances and imaging spectrum of anatomical and functional complications in a transplant kidney. Radiologist"s role as an integral part of multidisciplinary transplantation team continues to grow with increasing numbers of successful renal transplantation programs across the globe.

Tackling Chronic Kidney Transplant Rejection: Challenges and Promises

Despite advances in post-transplant management, the long-term survival rate of kidney grafts and patients has not improved as approximately forty percent of transplants fails within ten years after transplantation. Both immunologic and non-immunologic factors contribute to late allograft loss. Chronic kidney transplant rejection (CKTR) is often clinically silent yet progressive allogeneic immune process that leads to cumulative graft injury, deterioration of graft function. Chronic active T cell mediated rejection (TCMR) and chronic active antibody-mediated rejection (ABMR) are classified as two principal subtypes of CKTR. While significant improvements have been made towards a better understanding of cellular and molecular mechanisms and diagnostic classifications of CKTR, lack of early detection, differential diagnosis and effective therapies continue to pose major challenges for long-term management. Recent development of high throughput cellular and molecular biotechnologies has allowed rapid development of new biomarkers associated with chronic renal injury, which not only provide insight into pathogenesis of chronic rejection but also allow for early detection. In parallel, several novel therapeutic strategies have emerged which may hold great promise for improvement of long-term graft and patient survival. With a brief overview of current understanding of pathogenesis, standard diagnosis and challenges in the context of CKTR, this mini-review aims to provide updates and insights into the latest development of promising novel biomarkers for diagnosis and novel therapeutic interventions to prevent and treat CKTR.

Present Situation and Research Progress of Kidney Function Recoverability Evaluation of Acute Kidney Injury Patient

Acute kidney injury (AKI) is a critical illness in clinic. The guideline recommendation of kidney disease for improving global outcomes regards urine volume and creatinine as standards to evaluate kidney functions. However, urine volume and creatinine have a certain delay for kidney function evaluation, and these would be interfered by many factors. Whether the renal function of AKI patients can recover is very important, which affects the quality of life of patients. Therefore, the present study reviews the application situation and research progress of the recoverability evaluation of AKI patient kidney function from three aspects: conventional indexes, biomarkers, and imaging methods of kidney function.

Hypertension in Kidney Transplant Recipients: Where Are We Today?

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of death and allograft loss among kidney transplant recipients, and hypertension is an independent risk factor for cardiovascular morbidity of this patient population. The etiology of hypertension is multifactorial, including pre-transplant volume overload, post-transplant recipient and donor-associated variables, and transplant-specific causes (immunosuppressive medications, allograft dysfunction and surgical complications such as transplant artery stenosis).

RECENT FINDINGS

No randomized controlled trials have assessed the optimal blood pressure targets and explored the best antihypertensive regimen for kidney transplant recipients. According to the large observational studies, it is reasonable to achieve a blood pressure goal of equal to or less than 130/80 mmHg in the long-term follow-up for minimizing the cardiovascular morbidity. The selection of antihypertensive agents should be based on the patient's co-morbidities; however, the initial choice could be calcium channel blockers especially in the first few months of transplantation. In patients with cardiovascular indications of renin-angiotensin-aldosterone system inhibition, given the well-described benefits in diabetic and proteinuric patients, it is reasonable to consider the use of renin-angiotensin-aldosterone system inhibitors. There is a need for future prospective trials in the transplant population to define optimal blood pressure goals and therapies.

Introduction of the Grayscale Median for Ultrasound Tissue Characterization of the Transplanted Kidney

Ultrasound examination is advised for early post-kidney transplant assessment. Grayscale median (GSM) quantification is novel in the kidney transplant field, with no systematic assessment previously reported. In this prospective cohort study, we measured the post-operative GSM in a large cohort of adult kidney transplant recipients (KTR) who consecutively underwent Doppler ultrasound directly after transplantation (within 24 h), compared it with GSM in nontransplanted patients, and investigated its association with baseline and follow-up characteristics. B-mode images were used to calculate the GSM in KTR and compared with GSM data in nontransplanted patients, as simulated from summary statistics of the literature using a Mersenne twister algorithm. The association of GSM with baseline and 1-year follow-up characteristics were studied by means of linear regression analyses. In 282 KTR (54 ± 15 years old, 60% male), the median (IQR) GSM was 55 (45–69), ranging from 22 to 124 (coefficient of variation = 7.4%), without differences by type of donation (p = 0.28). GSM in KTR was significantly higher than in nontransplanted patients (p < 0.001), and associated with systolic blood pressure, history of cardiovascular disease, and donor age (std. β = 0.12, −0.20, and 0.13, respectively; p < 0.05 for all). Higher early post-kidney transplant GSM was not associated with 1-year post-kidney transplant function parameters (e.g., measured and estimated glomerular filtration rate). The data provided in this study could be used as first step for further research on the application of early postoperative ultrasound in KTR.

Early changes in renal resistive index and mortality in diabetic and nondiabetic kidney transplant recipients: a cohort study

Background

Renal resistive index (RI) predicts mortality in renal transplant recipients (RTR). However, its predictive value may be different according to the time of measurement. We analysed RI changes between 1 month and 3 months after transplantation and its predictive value for death with a functioning graft (DWFG).

Methods

We conducted a retrospective study in 1685 RTR between 1985 and 2017. The long-term predictive value of changes in RI value from 1 month to 3 months was assessed in diabetic and non-diabetic RTR.

Results

Best survival was observed in RTR with RI < 0.70 both at 1 and 3 months, and the worst survival was found in RTR with RI ≥ 0.70 both at 1 and 3 months (HR = 3.77, [2.71–5.24], p < 0.001). The risk of DWFG was intermediate when RI was < 0.70 at 1 month and ≥ 0.70 at 3 months (HR = 2.15 [1.29–3.60], p = 0.003) and when RI was ≥0.70 at 1 month and < 0.70 at 3 months (HR = 1.90 [1.20–3.03], p = 0.006).

In diabetic RTR, RI was significantly associated with an increased risk of death only in those with RI < 0.70 at 1 month and ≥ 0.70 at 3 months (HR = 4.69 [1.07–20.52], p = 0.040). RI considered as a continuous variable at 1 and 3 months was significantly associated with the risk of DWFG in nondiabetic but not in diabetic RTR.

Conclusion

RI changes overtime and this impacts differently diabetic and nondiabetic RTR. RI short-term changes have a strong prognosis value and refines the risk of DWFG associated with RI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02263-8.

The association between renal resistive index and premature mortality after kidney transplantation is modified by pre-transplant diabetes status: a cohort study

BACKGROUND

Renal resistive index (RI) predicts mortality in renal transplant recipients, but we do not know whether this is true in diabetic patients. The objective of this study was to analyse the long-term predictive value of RI for death with a functioning graft (DWFG) in renal transplant recipients with or without pre-transplant diabetes.

METHODS

We conducted a retrospective study in 1800 renal transplant recipients between 1985 and 2017 who were followed for up to 30 years (total observation period: 14 202 patient years). Donor and recipient characteristics at time of transplantation and at 3 months were reviewed. The long-term predictive value of RI for DWFG and the age-RI and arterial pressure-RI relationships were assessed.

RESULTS

A total of 284/1800 (15.7%) patients had diabetes mellitus before transplantation. RI was <0.75 in 1327/1800 patients (73.7%). High RI was associated with a higher risk of DWFG in non-diabetic patients [hazard ratio (HR) = 3.39, 95% confidence interval 2.50-4.61; P < 0.001], but not in patients with pre-transplant diabetes (HR = 1.25, 0.70-2.19; P = 0.39), even after multiple adjustments. There was no interaction between diabetes and age. In contrast, there was an interaction between RI and pulse pressure.

CONCLUSION

Our study indicates that RI is not a predictor of DWFG in diabetic renal transplant recipients, in contrast to non-diabetic recipients. These findings could be due to a different age-RI or pulse pressure-RI relationship.

Renal resistive index in IgA nephropathy and renal scleroderma vasculopathy

BACKGROUND

Renal Ultra-Sound (US) and Doppler US provide measurements which reflect changes in renal and systemic haemodynamic. The renal resistive index (RRI), obtained through the Doppler spectrum analysis of renal small arteries, is altered in several pathologic conditions. Glomerulonephritis cause minor RRI changes, while renal scleroderma vasculopathy (RSV) leads to significant RRI modifications. The aim of our study was to assess RRI in IgA nephropathy (IgAN) and RSV in a retrospective observational study and to investigate determinants of the RRI in these groups of patients.

METHODS

We enrolled 61 IgAN patients [23 female, median age 41 (33-58) years] and 80 SSc patients [71 female, median age 52 (43-60) years]. RRI was evaluated in all patients at the time of enrolment. Laboratory tests and clinical assessment were evaluated in all patients.

RESULTS

IgAN patients showed lower RRI values than RSV patients [0.70 (0.65-0.73) vs 0.66 (0.62-0.72), p < 0.01], while no significant difference in longitudinal length was observed. Median age was significantly lower in IgAN patients than in RSV patients [41 (33-58) vs 52 (43-60), p < 0.05] while IgAN patients showed a higher prevalence of high blood pressure than RSV patients (39.3% vs 13.8%, p < 0.01). The multiple regression analysis, weighted for age, showed that RRI inversely correlates with estimated glomerular filtration rate (β coefficient = -0.524, p < 0.0001).

CONCLUSION

Higher RRI were found in RSV patients than IgAN patients. IgAN is characterized mainly by glomerular injury, not leading to major RRI changes.

The association between the renal resistive index and the myocardial performance index in the general population

OBJECTIVE

The renal resistive index (RRI) is the most described measure of renal hemodynamics. The myocardial performance index (MPI) is widely used to assess overall myocardial performance. In this study, we aimed to investigate the relationship between renal hemodynamics, assessed by the RRI, and cardiac functions, assessed by the MPI in the general population.

METHODS

This single-center, cross-sectional study included a total of 302 consecutive patients who presented to our outpatient cardiology clinic between October 2019 and February 2020. All patients underwent transthoracic echocardiography and renal Doppler ultrasonography. The study population was divided into two groups: low RRI group (RRI ≤ 0.7, n = 236) and high RRI group (RRI > 0.7, n = 66).

RESULTS

E/A ratio, left ventricular ejection fraction (LVEF), and the MPI were significantly higher in the high RRI group than in the low RRI group (61.3 ± 15.4 vs 55.3 ± 16.4, P = .010 for E velocity; 0.9 ± 0.3 vs 0.7 ± 0.2, P = .008 for E/A ratio; 57.7 ± 4.7 vs 53.2 ± 10.1, P = .029 for LVEF; 0.52 ± 0.1 vs 0.43 ± 0.1, P < .001 for the MPI). A stepwise linear regression analysis demonstrated that LVEF (β = .123, P = .026), E velocity (β = .221, P < .001), and the MPI (β = .392, P < .001) were independently associated with the RRI.

CONCLUSION

Left ventricular ejection fraction and intra-cardiac Doppler blood flow indices, including E velocity and the MPI, were significantly and independently associated with the RRI in the general population.

Postoperative Ultrasound in Kidney Transplant Recipients: Association Between Intrarenal Resistance Index and Cardiovascular Events

Doppler ultrasound, including intrarenal resistance index (RI) measurement, is a widely used modality to assess kidney transplantation (KTx) vascularization. The aim of this study is to gain insight in the associations between early postoperative RI measurements and cardiovascular events (CVEs), all-cause mortality, and death-censored graft survival.

METHODS

From 2015 to 2017, a prospective cohort study was conducted in patients in which RI measurement was performed immediately after KTx. The RI was calculated as (peak systolic velocity-end-diastolic velocity)/peak systolic velocity. End points were CVEs, all-cause mortality, and graft failure. Kaplan-Meier analyses (logrank test) were used for differences in end points. Univariate and multivariate associations were investigated by means of Cox regression analyses.

RESULTS

RI cutoff of 0.70 was used. We included 339 recipients, of which 271 (80%) had an RI ≤ 0.70 and 68 (20%) had an RI > 0.70. CVEs were observed in 27 (8%) patients, 27 (8%) patients died, and 17 (5%) patients had graft failure during a median follow-up of 37 months (interquartile range, 33-43). Kaplan-Meier analyses and univariate Cox regression indicated a significant association with overall CVE-free survival (hazard ratios [HR], 2.79; P = 0.011; logrank test, P = 0.008) and all-cause mortality (HR, 2.59; P = 0.017; logrank test, P = 0.013) for patients with an RI above and below 0.70. An independent association was shown between an RI > 0.70 and CVE-free survival (HR, 2.48; P = 0.042) when deceased donation was not included in the model.

CONCLUSIONS

In the early postoperative period, a high RI showed to be associated with CVEs after adjustment for cardiovascular risk factors, whereas no independent association was found with overall survival and graft failure. For the interpretation of RI measurements after KTx surgery, patients' cardiovascular state should be taken into consideration.

Hemodialysis arteriovenous fistula ligation after renal transplantation: Impact on graft resistive index

BACKGROUND

Kidney allograft resistive index (RI) is prognostic for graft and recipient survivals. Recipient hemodynamics could influence RI. In particular, dialysis arteriovenous fistula (AVF) has been involved in heart function changes, reversible after AVF ligation. Knowledge about AVF and RI is lacking. In this study, we prospectively evaluated RI changes after AVF ligation in kidney transplanted patients.

METHODS

We enrolled 22 stable transplanted patients. Mean RI was measured before AVF ligation (T0), 18 to 24 h (T1) and 6 months (T6) after surgery; mean blood pressure (mBP), heart rate (HR), serum creatinine (sCr), estimated glomerular filtration rate (eGFR), 24 h proteinuria (24 h-P), immunosuppressive drug blood levels (IS) and antihypertensive drugs were also recorded.

RESULTS

AVF ligation was performed 3.1 years (IQR: 2.1-3.8) after transplantation. Median AVF flow (Qa) was 1868 mL/min (IQR: 1538-2712) and 8 AVF were classified as high flow (Qa ≥ 2 L/min). At baseline, median sCr was 1.32 mg/dL (IQR: 1.04-1.76) and median eGFR was 57.1 mL/min. Median RI was 0.71 at T0, 0.69 at T1, 0.66 at T6. RI reduction at T1 and T6 was statistically significant (p < 0.05 and p < 0.001 respectively); in particular, 90.4% of patients had persistently improved values at T6. Furthermore, mBP increased while HR decreased. These changes were independent from sCr, 24 h-P, IS, antihypertensive drugs number, Qa and AVF type.

CONCLUSIONS

AVF ligation improves kidney allograft RI; it may reflect better kidney perfusion.

B-Flow Sonography vs. Color Doppler Sonography for the Assessment of Vascularity in Pediatric Kidney Transplantation

OBJECTIVE

 To compare B-flow sonography (BFS) with color Doppler sonography (CDS) for imaging of kidney transplant vascularization in children.

PATIENTS AND METHODS

 All children receiving a kidney transplantation who underwent a protocol-based ultrasound examination (Loqiq 9, GE Medical Systems, Milwaukee, WI, USA) using the BFS and CDS technique with equal settings and probe position between January 2013 and January 2016 were retrospectively assessed (n = 40). The obtained datasets were visually graded according to the following criteria: (I) delineation of the renal vascular tree (Grade 1 - clear demarcation of interlobar, together with arcuate and interlobular vessels; Grade 2 - clear demarcation of interlobar and cortical vessels, but no distinction of interlobular from arcuate vessels; Grade 3 - only clear demarcation of interlobar vessels, Grade 4 - insufficient demarcation) (II) delineation of cortical vessel density in ventral, lateral, and dorsal part of the transplant, (III) smallest vessel-capsule distance, and (IV) maximum cortical vessel count. Comparison between methods was performed using Fisher's exact and paired sample t-tests.

RESULTS

 Applying a curved transducer (C1-6), BFS showed superior delineation of the renal vascular tree (p < 0.001), a lower vessel-capsule distance (p < 0.001), a higher cortical vessel count (p < 0.001), and a higher cortical vessel density in the superficial cortex (p = 0.01) than CDS. In the dorsal and lateral aspects of the transplant, cortical vessel density was lower with BFS (both p < 0.001). Using a linear high-resolution transducer (ML 6-15), no significant differences between the methods were found.

CONCLUSION

 Improved imaging of kidney transplant vascularization can be achieved in children by adding BFS to a standard protocol. The BFS technique is especially beneficial for overall assessment of the renal vascular tree together with the extent of cortical vascularization on curved array images.

KEY POINTS

  · Depiction of vascular tree and ventral cortical vessels is improved by BFS.. · The dorso-lateral cortex was better represented with CDS because of higher penetration.. · Additional monitoring with BFS improves the monitoring of transplant viability..

CITATION FORMAT

· Dammann E, Groth M, Schild R et al. B-Flow Sonography vs. Color Doppler Sonography for the Assessment of Vascularity in Pediatric Kidney Transplantation. Fortschr Röntgenstr 2021; 193: 49 - 60.

Modeling the hepatic arterial flow in living liver donor after left hepatectomy and postoperative boundary condition exploration

Preoperative and postoperative hepatic perfusion is modeled with one-dimensional (1-D) Navier-Stokes equations. Flow rates obtained from ultrasound (US) data and impedance resulted from structured trees are the inflow and outflow boundary condition (BC), respectively. Structured trees terminate at the size of the arterioles, which can enlarge their size after hepatectomy. In clinical studies, the resistance to pulsatile arterial flow caused by the microvascular bed can be reflected by the resistive index (RI), a frequently used index in assessing arterial resistance. This study uses the RI in a novel manner to conveniently obtain the postoperative outflow impedance from the preoperative impedance. The major emphasis of this study is to devise a model to capture the postoperative hepatic hemodynamics after left hepatectomy. To study this, we build a hepatic network model and analyze its behavior under four different outflow impedance: (a) the same as preoperative impedance; (b) evaluated using the RI and preoperative impedance; (c) computed from structured tree BC with increased radius of terminal vessels; and (d) evaluated using structured tree with both increased radius of root vessel, ie, the outlets of the postoperative hepatic artery, and increased radius of terminal vessels. Our results show that both impedance from (b) and (d) give a physiologically reasonable postoperative hepatic pressure range, while the RI in (b) allows for a fast approximation of postoperative impedance. Since hemodynamics after hepatectomy are not fully understood, the methods used in this study to explore postoperative outflow BC are informative for future models exploring hemodynamic effects of partial hepatectomy.

Shear-Wave Elastography Variability Analysis and Relation with Kidney Allograft Dysfunction: A Single-Center Study

Shear-wave elastography (SWE) showed the absence or presence of significant differences among stable kidney allograft function and allograft dysfunction. We evaluated the variability of kidney allograft stiffness in relation to allograft dysfunction, respectively, in terms of a correlation of stiffness with patients' characteristics. A single-center prospective study on patients who had undergone renal transplantation was conducted between October 2017 and November 2018. Patients were clinically classified as having a stable allograft function or allograft dysfunction. SWE examinations performed by the same radiologist with a LOGIQ E9 were evaluated. Ten measurements were done for Young's modulus (kPa) at the level of allograft cortex and another ten at the level of medulla. Eighty-three SWE examinations from 63 patients, 69 stable allografts, and 14 allografts with dysfunction were included in the analysis. The intra-examinations stiffness showed high variability, with the quantile covariation coefficient ranging from 2.21% to 45.04%. The inter-examinations stiffness showed heterogeneity (from 28.66% to 42.38%). The kidney allograft cortex stiffness showed significantly higher values in cases with dysfunction (median = 28.70 kPa, interquartile range (IQR) = (25.68-31.98) kPa) as compared to those with stable function (median = 20.99 kPa, interquartile range = (16.08-27.68) kPa; p-value = 0.0142). Allograft tissue stiffness (both cortex and medulla) was significantly negatively correlated with body mass index (-0.44, p-value < 0.0001 for allograft cortex and -0.42, p-value = 0.0001 for allograft medulla), and positively correlated with Proteinuria/Creatinuria ratio (0.33, p-value = 0.0021 for allograft cortex and 0.28, p-value = 0.0105 for allograft medulla) but remained statistically significant only in cases with stable function. The cortical tissue stiffness proved significantly higher values for patients with allograft dysfunction as compared to patients with stable function, but to evolve as an additional tool for the evaluation of patients with a kidney transplant and to change the clinical practice, more extensive studies are needed.

A Clinical Association between an Increasing Renal Resistive Index and the Atherosclerotic Burden in Patients with a Preserved Renal Function

Objective A positive correlation is observed between the progression of renal impairment and the increasing risk of cardiovascular disease. Our aim was to examine the relationship between the renal resistive index (RRI) assessed by duplex sonography and the extent of atherosclerosis in patients without renal impairment undergoing vascular imaging studies. Methods The RRI was evaluated pre-procedurally among 106 outpatients with an estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² undergoing clinically-driven coronary computed tomography angiography (CCTA). In those subjects, a carotid artery ultrasound scan was also performed to evaluate carotid artery disease. We investigated the association between the RRI and the atherosclerotic extent, defined by the presence of coronary artery calcium (CAC) >0 and carotid intima-media thickness (cIMT) ≥1.0 mm. Results Multi-site atherosclerosis (CAC>0 and cIMT≥1.0 mm) was found in 31 patients. The RRI was significantly increased with an increasing number of atherosclerotic vessels (absence of atherosclerosis: 0.65±0.04 vs. single-site atherosclerosis: 0.67±0.06 vs. multi-site atherosclerosis: 0.71±0.05, p<0.001). A multivariate logistic regression analysis showed that RRI>0.70 [odds ratio (OR): 4.05, 95% confidence interval (CI), 1.37-12.0, p=0.01], cardio ankle vascular index (CAVI) ≥9.0 (OR: 8.18, 95% CI: 2.47-27.1, p<0.01), diabetes (OR: 4.34, 95% CI: 1.37-13.7, p=0.01) and an eGFR>90 mL/min/1.73 m² (OR: 5.89, 95% CI: 1.39-25.1, p=0.01) were associated with multi-site atherosclerosis. Conclusion The RRI, a sub-clinical renal parameter is an atherosclerotic marker in patients without renal impairment.

Renal vascular resistance is increased in patients with kidney transplant

BACKGROUND

Despite improvement in short-term outcome of kidney transplants, the long-term survival of kidney transplants has not changed over past decades. Kidney biopsy is the gold standard of transplant pathology but it's invasive. Quantification of transplant blood flow could provide a novel non-invasive method to evaluate transplant pathology. The aim of this retrospective cross-sectional pilot study was to evaluate positron emission tomography (PET) as a method to measure kidney transplant perfusion and find out if there is correlation between transplant perfusion and histopathology.

METHODS

Renal cortical perfusion of 19 kidney transplantation patients [average time from transplantation 33 (17-54) months; eGFR 55 (47-69) ml/min] and 10 healthy controls were studied by [15 O]H2O PET. Perfusion and Doppler resistance index (RI) of transplants were compared with histology of one-year protocol transplant biopsy.

RESULTS

Renal cortical perfusion of healthy control subjects and transplant patients were 2.7 (2.4-4.0) ml min- 1 g- 1 and 2.2 (2.0-3.0) ml min- 1 g- 1, respectively (p = 0.1). Renal vascular resistance (RVR) of the patients was 47.0 (36.7-51.4) mmHg mL- 1min- 1g- 1 and that of the healthy 32.4 (24.6-39.6) mmHg mL- 1min-1g-1 (p = 0.01). There was a statistically significant correlation between Doppler RI and perfusion of transplants (r = - 0.51, p = 0.026). Transplant Doppler RI of the group of mild fibrotic changes [0.73 (0.70-0.76)] and the group of no fibrotic changes [0.66 (0.61-0.72)] differed statistically significantly (p = 0.03). No statistically significant correlation was found between cortical perfusion and fibrosis of transplants (p = 0.56).

CONCLUSIONS

[15 O]H2O PET showed its capability as a method in measuring perfusion of kidney transplants. RVR of transplant patients with stage 2-3 chronic kidney disease was higher than that of the healthy, although kidney perfusion values didn't differ between the groups. Doppler based RI correlated with perfusion and fibrosis of transplants.

Intrarenal resistive index conundrum: systemic atherosclerosis versus renal arteriolosclerosis

Background: We aimed to evaluate the relationship between biopsy-proven kidney lesions, subclinical markers of atherosclerosis and intrarenal resistive index (RRI) in chronic kidney disease (CKD) patients.

Methods: This cross-sectional, single-center study prospectively enrolled 44 consecutive CKD patients (57% male gender, 54.1 (95%CI, 49.7–58.6) years, median eGFR 28.1 (15.0–47.7) mL/min) diagnosed by renal biopsy during 6 months in our clinic. RRI, carotid intima-media thickness (IMT), Kauppila score for abdominal aortic calcification (AACs) were assessed. Traditional and nontraditional atheroscleosis risk factors were also evaluated.

Results: Most of the patients had a diagnosis of glomerular nephropathy, with IgA nephropathy and diabetic nephropathy being the most frequent. RRI increased proportionally with CKD stages. Patients with RRI >0.7 (39%) were older, had diabetic and vascular nephropathies more frequently, higher mean arterial blood pressure, increased systemic atherosclerosis burden (IMT and AACs), higher percentage of global glomerulosclerois, GBM thickness, arteriolosclerosis and interstitial fibrosis/tubular atrophy. RRI directly correlated with age (rs = 0.55, p < 0.001) and with all the studied atherosclerosis markers (clinical atherosclerosis score rs = 0.50, p = 0.02; AACs rs = 0.50, p < 0.01; IMT rs = 0.34, p = 0.02). Also, global glomerulosclerosis (rs = 0.31, p = 0.03) and interstitial fibrosis/tubular atrophy (rs = 0.35, p = 0.01) were directly correlated with RRI. In multivariable adjusted binomial logistic regression models, only arteriolosclerosis was retained as independent predictor of RRI >0.7.

Conclusion: The analysis of RRI may be useful in the evaluation of the general vascular condition of the patient with CKD, supplying information about both microvascular and macrovascular impairment. Moreover, RRI correlates well with renal histopathologic characteristics, particularly with arteriolosclerosis.

Resistive index as a predictor of early failure of kidney transplantation

Background

Ultrasonography is a simple and noninvasive examination that can be easily performed after renal transplantation because of the lack of toxicity. The resistive index (RI) was measured using Doppler ultrasound at 7 days postoperatively in patients who underwent renal transplantation. The study aimed to determine the risk of graft loss and premature death within 1 year after transplantation.

Methods

This study was conducted from January 2011 to October 2017 and involved 97 patients who underwent renal transplantation at the Chosun University Hospital, Kwangju, Korea. Brain-dead donors were selected. Several parameters were assessed as recipient variables. In addition, postoperative delayed renal function and complications were examined. At 7 days after surgery, the RI was measured in all patients (the mean value of three measurements taken at different positions was used).

Results

Of the 97 patients, 40 had an RI of ≥0.8 or greater. Of these, four patients died, and a total of seven developed transplant failure. Logistic regression analysis was conducted to predict the risk of transplant failure and mortality based on complex influences of the relevant variables. The RI showed a relative risk value of 12.711 for transplant failure (P=0.003) and was significantly associated with mortality (P=0.001).

Conclusions

The RI was highly correlated with graft loss and recipient mortality after renal transplantation. Measurement of the RI after renal transplantation may lead to a more aggressive management of high-risk patients, and consequently improve the post-transplantation outcome.