Early assessment of renal resistance index after kidney transplant can help predict long-term renal function

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.

Predictive value of the renal resistive index in the immediate postoperative period after kidney transplantation on short- and long-term graft and patient outcomes

INTRODUCTION

During the postoperative stay in the intensive care unit after kidney transplantation, the renal resistive index (RI) is routinely measured. An increased RI, measured months posttransplant, is associated with a higher mortality. We wanted to investigate the value of the RI immediately posttransplant in predicting both short- and long-term outcome.

METHODS

We performed a retrospective single-center study. The RI was collected <48 h posttransplant in patients undergoing kidney transplantations between 2005 and 2014. Short-term outcome was evaluated by delayed graft function (DGF). The long-term endpoints were kidney function and mortality at 30 days, 1 year and 5 years.

RESULTS

We included 478 recipients, 91.4% of whom reached the end of the 5-year follow-up. A higher RI < 48 h posttransplant was significantly associated with DGF. This association was particularly strong in patients receiving grafts from donors after brain death and expanded criteria donors. A higher RI also correlated with mortality and death with functioning graft but not with graft failure. After adjustment for confounders, we found an association between increased RI and DGF, but not with long-term kidney function or mortality.

CONCLUSION

The RI routinely measured <48 h posttransplant is an independent predictor of short-term kidney function.

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.

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.

Machine Retrograde Perfusion of Deceased Donor Kidneys: A Prospective Study

Objective: To maximize the utilization of potential kidneys, improving perfusion and preservation techniques is necessary.

Methods: We investigated the safety and efficacy of retrograde machine perfusion of kidneys from deceased donors. A total of 30 kidneys were included and all the grafts were preserved in the Kidney Transporter machines. A total of 15 kidneys that received retrograde perfusion (RP) were selected as the RP group (n = 15) and their counterparts received standard antegrade perfusion (AP) as the control group (n = 15).

Results: All the recipients were followed up for 6 months. Renal resistance in the RP group remained stable during the perfusion. There was no primary nonfunction. No difference in the incidence of delayed graft function was found in both groups (3 in RP vs. 2 in AP, p = 0.62). The RP group had lower serum creatinine (RP vs. AP, 102.20 vs. 138.67, p = 0.05) and blood urea nitrogen (RP vs. AP, 6.44 vs. 8.71, p = 0.05) than that in the AP group at 6 months. Both the groups had comparable estimated glomerular filtration rate and cystatin C within 6 months.

Conclusion: This novel technique may be an effective and safe alternative for kidney preservation.

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.

Deceased vs. living donor kidney transplantation in prediction of acute renal allograft rejection using Tc-99m DTPA renal scan

OBJECTIVES

No data are available regarding different prognostic values of Tc-99m diethylenetriaminepentaacetic acid (DTPA) renal scan in kidney transplantation (KT) recipients according to two distinct donor types: deceased donor KT (DDKT) and living donor KT (LDKT). We evaluated whether the interpretation of Tc-99m DTPA renal scan should be different by the donor type in predicting acute renal allograft rejection (AR).

METHODS

One hundred and seven KT recipients (61 DDKT and 46 LDKT) were included in this study. Tc-99m DTPA renal scan was performed 1 week after KT. AR was defined as pathological evidence of renal allograft rejection during the first 6 months of KT. Clinical factors and Tc-99m DTPA renal scan findings were compared between patients with and without AR. To further analyze the effect of the donor type, they were again compared within DDKT and LDKT recipients, respectively.

RESULTS

AR occurred in 15 patients (7 DDKT and 8 LDKT recipients). Among all patients, time to peak uptake (TTP) of the cortex (TTP_CX) measured by Tc-99m DTPA renal scan was independently predictive of AR. Moreover, TTP_KD (TTP of the whole transplanted kidney) and TTP_CX were the only predictors of AR among DDKT recipients. The most accurate predictors were TTP_CX and kidney area on renal scan for DDKT and LDKT, respectively. However, these parameters could not predict AR for the opposite donor type.

CONCLUSIONS

AR could be effectively predicted by Tc-99m DTPA renal scan obtained at 1 week post-KT. Different parameters should be applied according to the donor type in the prediction of AR.

WITHDRAWN: Impact on Delayed Graft Function of the Renal Resistive Index in the Immediate Postoperative Period After Kidney Transplantation: A Cohort Analysis

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Impact on renal resistive index of diabetes in renal transplant donors and recipients: A retrospective analysis of 1827 kidney transplant recipients

High renal resistive index (RI) is observed in diabetes and is associated with poor patient survival, but whether it is primarily due to renal vascular resistance or systemic vascular alterations is unclear. The respective impact of kidney transplant from diabetic donors or to diabetic recipients on RI would shed some light on this issue. The objective of the study was to analyze the impact of donor and recipient diabetes on RI in order to understand the respective impact of the kidney and the vascular environment. The authors conducted a retrospective study in 1827 renal transplant recipients who received a kidney between 1985 and 2017, and had Doppler measurements at 3 months after transplant. Donor and recipient characteristics at the time of transplant and at 3 months were reviewed. Both donor diabetes and recipient diabetes were associated with RI in univariate analysis, but only recipient diabetes remained significantly associated in stepwise multivariate analyses (effect estimate on RI: +0.03 ± 0.005, P < 0.001). These findings were confirmed when RI was expressed as a binary variable using a cutoff of 0.75 (OR = 2.50 [1.77, 3.54], P < 0.001). Other determinants of RI were recipient characteristics (age, sex, systolic and diastolic blood pressure, and duration of dialysis). Donor characteristics were not associated with RI. Our results suggest that high RI observed in diabetic recipients shortly after transplant is primarily due to the new vascular environment, rather than to characteristics of the transplanted kidney. Therefore, RI reflects systemic rather than intra-renal changes.

Use of Intraoperative Duplex Ultrasound and Resistance Index Reduces Complications in Living Renal Donor Transplantation

BACKGROUND

The treatment of choice in end-stage renal disease is transplantation. Hemodynamic disturbances can evoke graft loss, while early ultrasound identification of vascular problems improves outcome. The aim of this study was to identify differences in postoperative complications with and without systematic intraoperative Doppler ultrasound use.

METHODS

The primary outcome was the postoperative rate of complications and the secondary aim was to find a predictive resistance index cut-off value, which would show where surgical reintervention was necessary. Over a 10-year period, 108 renal transplants were performed from living donors at our institution. In group 1 (n = 67), intraoperative duplex ultrasound and intraparenchymatous resistance index measurements assessed patients, while in group 2 (n = 41), no ultrasound was performed.

RESULTS

There were no intergroup differences in the overall postoperative complication rate or in benefit to graft or patient survival with Doppler use. However, significantly more vascular complications (10% vs 0%, P = .02) and more acute rejections (37% vs 10%) occurred in group 2 than in group 1. Therefore, an intraoperative cut-off value of the resistance index 0.5 was proposed to justify immediate surgical revision.

CONCLUSIONS

This is the first report demonstrating benefits of systematic intraoperative Doppler ultrasound on postoperative complications in renal transplantation from living donors. Our results support surgical revision with a resistance index <0.5.

Early experience with hypothermic machine perfusion of living donor kidneys - a retrospective study

Although hypothermic machine perfusion (HMP) has been shown to be beneficial to deceased donor kidneys, the effect of HMP on living donor kidneys (LDK) is unknown. LDK are subjected to minutes of normothermic ischemia at the time of recovery. Comparison of 16 LDK preserved by HMP with 16 LDK preserved by static cold storage (SCS). Outcomes of interest are resistive indices (RI), both while on HMP and postoperatively, and creatinine clearance (CrCl). Injury markers NGAL and LDH were seen in the perfusate of LDK in amounts similar to what is found for donation after neurological determination of death kidneys. Compared to SCS kidneys, CrCl was significantly higher in the HMP group from days 2 through 7 post-transplant [ie: day 7 (78.8 ± 5.4 vs. 54.0 ± 4.6 ml/min, P = 0.005)]. CrCl at 1 year was higher in the HMP group (81.2 ± 5.8 vs. 70.0 ± 5.3 ml/min, P = 0.03). Early post-transplant RI was significantly lower in the HMP group (0.61 ± 0.02 vs. 0.71 ± 0.02, P < 0.0001). Our data support the assertion that injury does occur during LDK procurement and suggest that some of this injury may be reversed with HMP, resulting in more favorable early RI and graft function compared to SCS kidneys.

Relationship Between 'Immediate' Resistive Index Measurement After Renal Transplantation and Renal Allograft Outcomes

BACKGROUND

The arterial resistive index, also referred to as the resistive index (RI) or Pourcelot Index, is a measure of pulsatile blood flow. Previous studies have demonstrated the usefulness of the RI as a predictor of allograft outcomes based on RI measurement in the later stages after transplantation. However, there is little evidence of the predictive value of "immediate" RI measurement within 24 hours after transplantation.

METHODS

We performed a retrospective cohort study of 305 adult renal transplants carried out between 2003 and 2013. The associations between immediate RI measurement (within 24 hours after transplantation) and donor, recipient, and surgical factors were analyzed. In addition, the correlations between immediate RI measurement and renal allograft outcomes, including delayed graft function (DGF) and transplant failure (TF), also were evaluated.

RESULTS

From a cohort of 305 patients, 52 were excluded on the basis of on confounding factors. Of the remaining 253 patients, the mean age was 48.4 years, 57.5% were male, and approximately one-third had diabetes. Two hundred twenty-six patients had an RI < 0.8, whereas only 27 had an RI ≥ 0.8. Significant associations were found between elevated RI (≥0.8) and both DGF (odds ratio = 3.22, P = .006) and TF (odds ratio = 3.54, P = .008).

CONCLUSIONS

Immediate RI measurement after renal transplantation is a strong predictor of both DGF and TF.

The predictive value of resistive index obtained by Doppler ultrasonography early after renal transplantation on long-term allograft function

DUSG is a useful diagnostic tool for the follow-up of renal transplant recipients. The measurement of intrarenal arterial RI by DUSG has been proven to predict short-term AF. The aim of the study was to evaluate the predictive value of DUSG performed during the early after RTx on long-term AF. Seventy patients were enrolled into study. DUSG was performed at third and seventh days after RTx. Patients were divided into two groups according to rate of recovery of graft function as patients with normal graft function and abnormal graft function. Although the RI values were correlated with the AF early after transplantation, they were not correlated with long-term AF. However, the rate of recovery of graft function at early period after RTx was correlated with creatinine level at first year and with glomerular filtration rate at first year and last visit. Although the RI has no predictive value for long-term AF, the rate of recovery of graft function at early post-transplantation period has predictive value for long-term AF; patients with higher RI values early after RTx should be followed carefully for the development of chronic allograft injury.

The inability of an early post-transplantation intrarenal resistive index to predict renal allograft function at 12 weeks after engraftment in young adults

Background The intrarenal resistive index (RI) is a promising tool for predicting renal graft outcomes. Due to the complexity of graft function and the presence of diverse contributing factors, however, the available data are inconclusive. Purpose To examine the performance of the RI 1 week after transplant in predicting allograft function at week 12, with an emphasis on the type of intrarenal artery used in the examination. Material and Methods A total of 58 first-time living-donor kidney-allograft-transplantation patients aged less than 50 years underwent Doppler ultrasonography (US) of the intrarenal arteries 1 week after engraftment. The RI was calculated for both the segmental (RI-C) and interlobar-arcuate (RI-P) arteries. Serum creatinine level and the creatinine reduction ratio (CRR) were determined at weeks 1 and 12 post transplantation. Results While the RI did not correlate with serum creatinine level and CRR at week 1, significant correlations were present between the RI and serum creatinine level (r = 0.28, P = 0.03 for both RI-C and RI-P) and CRR (r = -0.25, P = 0.05 for both RI-C and RI-P) at week 12. The sensitivity, specificity, positive predictive value, and negative predictive value of using RI-C in predicting abnormal 12-week serum creatinine level were 51.2%, 52.9%, 72.4%, and 31.3%, respectively; and 53.7%, 47.1%, 70.9%, and 29.6% for RI-P, respectively ( P > 0.99 for all comparisons). Conclusion Early post-transplantation RI correlates significantly with both serum creatinine level and creatinine reduction ratio 12 weeks after engraftment with intermediate predictive accuracy.

High Resistive Index in Transplant Kidneys Is a Possible Predictor for Biopsy Complications

BACKGROUND

Transplant kidney biopsies are performed to determine a histological diagnosis for specific patient treatment. The aim of this study was to investigate if Resistive Index (RI) could be a predictor for biopsy complications.

METHODS

In this study, 220 consecutive transplant kidney biopsies (136 men and 84 women; median age, 55.5 years) were prospectively included. RI (median, 0.7) was measured by use of ultrasound. Histological diagnoses and biopsy complications were registered. Biopsy needles were either 16- or 18-gauge. Biopsies were performed by radiologists and were carried out as an outpatient procedure (70%) or an inpatient procedure (30%). Usually three passes per biopsy were performed.

RESULTS

The overall complication rate was 6.8%, divided into major (4.5%) and minor (2.3%) complications. An RI ≥0.8 predicts major (13.3% versus 3.2%; risk ratio [RR], 4.2; confidence interval [CI], 1.3-14.1; P = .03) and overall biopsy complications (16.7% versus 5.3%; RR, 3.2; CI, 1.2-8.6; P = .04) compared with RI <0.8. In the group <0.8, RI correlated with age (r_s = 0.28, P < .001) and systolic blood pressure (r_s = 0.18, P = .02). In the group ≥0.8, RI correlated with degree of interstitial fibrosis (r_s = 0.65, P = .006) and systolic blood pressure (r_s = 0.40, P = .03). The multiple regression analysis showed that in the group <0.8, the RI correlated only with age (P < .001), whereas in the group ≥0.8, RI correlated only with the degree of interstitial fibrosis (P = .003).

CONCLUSIONS

An RI ≥0.8 indicates greater risk for major and overall biopsy complications and should result in greater caution after biopsy.

Contrast-enhanced ultrasonography in the early period after kidney transplantation predicts long-term allograft function

INTRODUCTION

Real-time contrast-enhanced sonography (CES) can assess microvascular tissue perfusion using gas-filled microbubbles. The purpose of the study was to evaluate the feasibility of early CES in predicting long-term kidney allograft function in comparison to color Doppler ultrasonography (CDUS).

METHODS

We prospectively studied 68 consecutive kidney transplant recipients using CES and conventional CDUS investigation 1 week after transplantation. Transplant tissue perfusion imaging was performed by low-power imaging during intravenous administration of the sonocontrast SonoVue. Renal tissue perfusion was assessed quantitatively using flash replenishment kinetics of microbubbles to estimate renal blood flow (RBF). The obtained sonography values were correlated with clinical data 1 week up to 1 year after transplantation.

RESULTS

In contrast with conventional CDUS resistive indices, RBF estimated by CES 1 week posttransplantation significantly correlated with kidney function after 1 year (r = 0.67; P < .001). Determination of RBF by CES revealed a significant correlation with donor age but not recipient age, whereas conventional CDUS resistive index was significantly correlated to recipient age (r = 0.54; P < .001) but not donor age. Furthermore RBF was associated with vascular fibrosis and intimal thickening of the engraftment biopsies.

CONCLUSION

This is the first prospective study demonstrating the prognostic value of CES early after kidney transplantation. In contrast with CDUS, CES reveals information about kidney allograft perfusion independent of recipient vascular compliance.

Effect of Donor- and Recipient-Related Factors on Arterial Resistance Index After Kidney Transplant

BACKGROUND

The assessment of color Doppler resistance index (RI) of the intra-renal arteries has been shown to be a good predictor of short-term and long-term graft survival after kidney transplant. In this study, we investigated the influence of donor- and recipient-related factors on RI evaluated early after kidney transplant.

METHODS

We prospectively analyzed 90 kidney transplant patients who underwent RI assessment within the first month after the transplant, subdivided into 2 groups according their RI values lower (group A) or higher (group B) than 0.646 (median value).

RESULTS

Patients in group A had a lower human leukocyte antigen (HLA) mismatch number (3.3 ± 1 versus 3.9 ± 0.9, P = .007) and were significantly younger (42.8 ± 11 years versus 47.8 ± 11 years, P = .03) than patients in group B. All the others variables examined were not significantly different between the 2 groups. Multivariate logistic regression analysis confirmed that HLA mismatch number (P = .03) and recipient age (P = .03) are independent predictors of RI.

CONCLUSIONS

Our data suggest that HLA mismatches and donor age can influence recipient kidney vascular resistance in the early period after transplantation.

Initial kidney graft resistance index and the long-term cardiovascular mortality in transplanted patients: a paired grafts analysis

BACKGROUND

Cardiovascular complications remain the most frequent cause of death in kidney transplant recipients. We analysed the prognostic value of early measured resistance index (RI) in the aspect of long-term cardiovascular mortality. In order to eliminate potential donor-related confounders, we analysed the mortality of recipients, transplanted with organs procured from the same donor, in whom the initial RI values substantially differed.

METHODS

Doppler sonography was performed in 725 consecutive kidney graft recipients early after transplantation. We identified 133 pairs (266 patients) who received their kidney grafts from the same donor and their initial RI values differed by >0.1.

RESULTS

During 109 ± 37 months of follow-up after transplantation, 84 patients lost their graft and 29 died, 14 of them due to cardiovascular causes. Two groups of paired patients with higher RI and lower RI did not differ significantly with respect to their age, BMI, HLA mismatch and cold ischaemia time. There were more patients with diabetes in the higher RI group (14.3 versus 6.8%). Survival analysis revealed a higher mortality for cardiovascular (8.3 versus 2.3%, P = 0.02) and all causes (14.3 versus 7.5%, P = 0.06) among patients with higher initial RI values. In the Cox regression model, not including age, a higher RI value was a strong predictor of cardiovascular death (HR = 4.88), independent of previous cardiovascular episodes (HR = 6.78). Both these variables lost its significance as a predictors after inclusion of age in the regression model.

CONCLUSION

Increased intrarenal resistance index in the early posttransplant period may help to identify the recipients with increased cardiovascular risk.

Hypothermic machine perfusion improves Doppler ultrasonography resistive indices and long-term allograft function after renal transplantation: a single-centre analysis

OBJECTIVES

To evaluate whether hypothermic machine perfusion (HMP) of transplanted kidneys can improve long-term renal allograft function compared with static cold storage (CS).

METHODS

We evaluated whether graft Doppler ultrasonography resistive indices improved with the use of HMP compared with CS preservation, and examined whether these improvements were predictive of long-term graft function. A total of 30 kidney transplants (15 pairs) were examined. One of the kidney pairs was placed on CS and transplanted first (CS group, n = 15). The other kidney of each pair was placed on HMP and transplanted after the CS group (HMP group, n = 15). Doppler ultrasonography was performed on days 1 and 7 after transplantation and resistive indices were evaluated. The estimated glomerular filtration rate (eGFR) was monitored for 24 months after transplantation.

RESULTS

Despite longer cold ischaemia times, kidneys maintained with HMP had lower resistive indices (P = 0.005) with correspondingly higher eGFR throughout the follow-up. Subgroup analysis showed that the HMP-induced improvement in postoperative eGFR was greatest in kidneys obtained from donation after cardiac death (DCD), even at 2 years after transplantation (P = 0.008).

CONCLUSIONS

HMP of transplant kidneys appears to improve vascular resistance after transplantation and has a positive impact on long-term allograft function compared with CS in the population of recipients of DCD kidneys.

Ultrasound Doppler renal resistive index: a useful tool for the management of the hypertensive patient

The Doppler-derived renal resistive index has been used for years in a variety of clinical settings such as the assessment of chronic renal allograft rejection, detection and management of renal artery stenosis, evaluation of progression risk in chronic kidney disease, differential diagnosis in acute and chronic obstructive renal disease, and more recently as a predictor of renal and global outcome in the critically ill patient. More recently, evidence has been accumulating showing that an increased renal resistive index not only reflects changes in intrarenal perfusion but is also related to systemic hemodynamics and the presence of subclinical atherosclerosis, and may thus provide useful prognostic information in patients with primary hypertension. On the basis of these results, the evaluation of renal resistive index has been proposed in the assessment and management of patients with primary hypertension to complement other signs of renal abnormalities.

Renal transplantation parenchymal complications: what Doppler ultrasound can and cannot do

Kidney transplantation is the treatment of choice in end-stage renal disease, given the better quality of life of transplanted patients when compared with patients on maintenance dialysis. In spite of surgical improvements and new immunosuppressive regimens, parts of transplanted grafts still develop chronic dysfunction. Ultrasonography, both in B-mode and with Doppler ultrasound, is an important diagnostic tool in case of clinical conditions which might impair kidney function. Even though ultrasonography is considered fundamental in the diagnosis of vascular and surgical complications of the transplanted kidney, its role is not fully understood in case of parenchymal complications of the graft. The specificity of Doppler is low both in case of acute complications, such as acute tubular necrosis, drugs toxicity and acute rejection, and in case of chronic conditions, such as chronic allograft nephropathy. Single determinations of resistance indices present low diagnostic accuracy, which is higher in case of successive measurements performed during the follow-up of the graft. Modern techniques such as tissue pulsatility index, maximal fractional area and contrast-enhanced ultrasound increase ultrasonography diagnostic power in case of parenchymal complications of the transplanted kidney.

The Maintenance Immunosuppression Scheme Influences Early C4d Urinary Excretion in Kidney Graft Recipients but Does Not Affect the Long-term Graft Survival

C4d urinary excretion varies according to the risk of graft rejection or progression of chronic allograft nephropathy. The most common maintenance immunosuppression (IS) schemes include cyclosporine (CSA) or tacrolimus (TAC) with azathiopryne (AZA) or mycophenolate mophetil (MMF). The chosen IS may influence kidney transplant outcomes and possibly modify urinary C4d. The aim of the study was to determine whether early C4d urinary excretion varies in patients after kidney allograft transplantation (KTx) regarding administered IS and if these factors may help to predict long-term KTx outcomes. The study involved 185 patients who underwent KTx. The urinary specimens were assessed by enzyme-linked immunosorbent assay test for C4d excretion. To increase the objectivity, C4d excretion was divided by urinary creatinine excretion (ng/mgCr). The study population was grouped according to the IS scheme, that is, CSA + AZA, CSA + MMF, and TAC + MMF. At baseline, the greatest C4d urinary excretion was noticed in patients treated with CSA + AZA, 199.5 ± 175.9 ng/mL (5.3 ± 7.1 ng/mgCr) and the lowest in those in whom tacrolimus and mycophenolate mophetil was administered, 166.6 ± 186.3 ng/mL (3.9 ± 6.2 ng/mgCr). In the CSA + MMF group, C4d excretion was 195.6 ± 200.3 ng/mL (5.0 ± 6.6 ng/mgCr). Statistically significant differences were seen only between the CSA + AZA and TAC + MMF groups, analysis of variance P < 0.05 (P < 0.01 for C4d/urinary creatinine ratio). No statistically significant differences were found in graft survival rates between different immunosuppressive regimens. Although early C4d measurements vary in patients after kidney allograft transplantation regarding administered IS, this IS dependant variation does not seem to affect the long-term graft survival.

Absence of C4d urinary excretion in the early post-transplant period is associated with improved long-term kidney graft survival

INTRODUCTION

C4d urinary excretion varies according to the risk of graft rejection or progression of chronic allograft nephropathy, but its influence on long-term kidney transplant (KTx) outcomes remains unclear. The aim of the study was to determine whether the initial (1-3 months post KTx) level of C4d urinary excretion may help to predict long-term kidney allograft transplantation outcomes.

MATERIALS AND METHODS

The study involved 185 patients who had undergone KTx. The urinary specimens taken from the morning urine portion were assessed by ELISA test for C4d excretion. To increase the objectivity of the assessment, all measurements were divided by urinary creatinine excretion (ng/mgCr). The study population was grouped according to the C4d excretion cut-off value into low (LC4d, 109 participants) and high (HC4d, 76 participants) C4d excretion groups. Additionally a subgroup with absence of C4d in the urine (ZC4d, 26 patients) was formed.

RESULTS

The calculated Roc curve indicated the cut off value of the urinary C4d excretion as 12.4ng/mgCr (AUC 0.77; 95%CI 0.73-0.95). The mean C4d urinary excretions in LC4d and HC4d were 1.9±3.27 and 20.6±4.6ng/mgCr, respectively, whereas after exclusion of ZC4d subgroup, the mean C4d was 14.9±6.3ng/mgCr in the remainder. Kaplan-Meier curve analysis demonstrated a slightly higher graft survival rate (GSR) in LC4d than in HC4d group (p=0.04 by log-rank). The subsequent analysis showed the highest GSR in ZC4d subgroup (p=0.0006 by log-rank).

CONCLUSION

Although lower C4d urinary excretion in the early post-transplant period seems to be associated with better long-term kidney allograft transplantation outcomes, only its absence in the urine appears to be a solid predictor of improved graft survival.

Renal arterial resistive index is associated with severe histological changes and poor renal outcome during chronic kidney disease

Background

Chronic kidney disease (CKD) is a growing public health problem and end stage renal disease (ESRD) represents a large human and economic burden. It is important to identify patients at high risk of ESRD. In order to determine whether renal Doppler resistive index (RI) may discriminate those patients, we analyzed whether RI was associated with identified prognosis factors of CKD, in particular histological findings, and with renal outcome.

Methods

RI was measured in the 48 hours before renal biopsy in 58 CKD patients. Clinical and biological data were collected prospectively at inclusion. Arteriosclerosis, interstitial fibrosis and glomerulosclerosis were quantitatively assessed on renal biopsy in a blinded fashion. MDRD eGFR at 18 months was collected for 35 (60%) patients. Renal function decline was defined as a decrease in eGFR from baseline of at least 5 mL/min/ 1.73 m²/year or need for chronic renal replacement therapy. Pearson’s correlation, Mann–Whitney and Chi-square tests were used for analysis of quantitative and qualitative variables respectively. Kaplan Meier analysis was realized to determine renal survival according to RI value using the log-rank test. Multiple logistic regression was performed including variables with p < 0.20 in univariate analysis.

Results

Most patients had glomerulonephritis (82%). Median age was 46 years [21–87], eGFR 59 mL/min/ 1.73m² [5–130], percentage of interstitial fibrosis 10% [0–90], glomerulosclerosis 13% [0–96] and RI 0.63 [0.31-1.00]. RI increased with age (r = 0.435, p = 0.0063), pulse pressure (r = 0.303, p = 0.022), renal atrophy (r = −0.275, p = 0.038) and renal dysfunction (r = −0.402, p = 0.0018). Patients with arterial intima/media ratio ≥ 1 (p = 0.032), interstitial fibrosis > 20% (p = 0.014) and renal function decline (p = 0.0023) had higher RI. Patients with baseline RI ≥ 0.65 had a poorer renal outcome than those with baseline RI < 0.65 (p = 0.0005). In multiple logistic regression, RI≥0.65 was associated with accelerated renal function decline independently of baseline eGFR and proteinuria/creatininuria ratio (OR=13.04 [1.984-85.727], p = 0.0075). Sensitivity, specificity, predictive positive and predictive negative values of RI ≥ 0.65 for renal function decline at 18 months were respectively 77%, 86%, 71% and 82%.

Conclusions

Our results suggest that RI ≥ 0.65 is associated with severe interstitial fibrosis and arteriosclerosis and renal function decline. Thus, RI may contribute to identify patients at high risk of ESRD who may benefit from nephroprotective treatments.

Color Doppler indexes in early phase after kidney transplantation and their association with kidney function on six month follow up

BACKGROUND

Doppler ultrasonography (DU) and measurement of its indexes, resistive index (RI) and pulsatility index (PI), is used to investigate transplanted kidney hemodynamic status and function. The aim of this study was to determine the correlation between Doppler indexes in the early phase after transplantation with long-term transplanted kidney function.

MATERIALS AND METHODS

In this cross-sectional study on 38 newly kidney transplant patients, we performed DU with assessment of its indexes within 48 hours, 1 week, and 6 months after kidney transplantation. Serum creatinine after stability and 6 months after kidney transplantation were assessed. Cyclosporine level was measured 1 week after kidney transplantation and compared with DU indexes.

RESULTS

About 71% of kidney transplanted patients reached their normal initial creatinine level(cr<1.5 mg/ dl) and 28% of all patients were involved in kidney dysfunction after 6 months (increase in basic creatinine level more than 25%).There was no significant difference between mean RI and PI in patients with normal and disturbed kidney function based on creatinine level in early posttransplantation period but there was linear correlation between mean RI and PI within 48 hours and 1 week with kidney function after 6 months. Also no association between cyclosporine level and RI and PI was shown. There was a direct association between age and the levels of RI and PI 6 months after transplantation.

CONCLUSION

This study suggests assessment of RI and PI in early period after transplantation and can be used as predictive parameters for long-term function of transplanted kidney and RI more than 0.80 in early phase after transplantation has an acceptable sensitivity and specificity to predict long-term kidney dysfunction.

Impact of early kidney resistance index on kidney graft and patient survival during a 5-year follow-up

BACKGROUND

Resistance index (RI) measured by Doppler sonography during the early post-transplant period reflects interstitial oedema within the transplanted kidney. We have prospectively analysed the relationship between RI measured shortly after kidney transplantation (KTx), patient and graft survival, as well as kidney graft function during a 5-year follow-up.

METHODS

RI was measured at the second to fourth day after KTx in 364 consecutive patients, who were divided into tertiles, according to baseline RI value (Group 1: RI < 0.73, Group 2: RI between 0.73 and 0.85 and Group 3: RI > 0.85). The kidney graft function [estimated glomerular filtration rate (eGFR)] during the follow-up period was calculated according to the Modification of Diet in Renal Disease formula.

RESULTS

During the 5-year follow-up period, 23 patients died (2.6 versus 6.5 versus 9.6% in RI tertiles, respectively) and 59 lost their kidney graft (12.1 versus 17.7 versus 18.4%, respectively). Survival analyses showed that the effect of RI was significant for a combined outcome [graft loss or death; hazard ratio (HR) = 10.88] and in relation to death, it was of borderline significance (HR = 45.3, P = 0.09). The effect of delayed graft function (DGF) was only significant on graft loss (HR = 1.73). eGFR in the highest tertile was lower than in the lowest tertile during the entire follow-up period.

CONCLUSIONS

High RI values measured in segmental arteries in the very early post-transplant period predict worse kidney graft function and increased risk of all-cause graft loss, including patient death in the 5-year follow-up period. (ii) The predictive value of RI is not completely independent from the adverse influence of DGF on the premature graft loss.

Prognostic impact of renal arterial resistance index upon renal allograft survival: the time point matters

BACKGROUND

The renal arterial resistance index (RI) is reported to be a significant predictive parameter for renal allograft failure or death. The influence of the time point after renal transplantation on its predictive power has not been sufficiently evaluated. We performed a retrospective analysis of RI and its power to predict renal allograft failure or death with special emphasis on the time point of RI measurement.

METHODS

The present analysis is based on ultrasonographically recorded intrarenal arterial RI measurements, routinely obtained in our outpatient department, over a period of 13 years. Altogether, 88 patients with an RI measurement 0-3, 3-6 and 12-18 months after transplantation were included and retrospectively stratified into two groups according to the RI: those with an index >0.75 and those with an index of ≤0.75.

RESULTS

Twenty patients (23%) reached the combined end point, i.e. allograft failure with a return to dialysis or death. The RI measured early after transplantation (0-3 and 3-6 months) did not predict the end point, whereas the RI obtained between 12 and 18 months showed a significant predictive value for renal transplant failure or death in a univariate approach [Wald test, P = 0.0013, hazard ratio (HR) 4.787, 95% confidence interval (CI) 1.846-12.411]. At 12-18 months after transplantation, 14% (12 patients) of the study population had an RI >0.75. Seven (58%) of these patients reached the end point versus 13 of 76 patients (17%) with an RI ≤0.75. In a multivariate Cox model, the RI measured between 12 and 18 months after transplantation exhibited the highest hazard ratio (HR 6.191, 95% CI 2.288-16.756, P = 0.0003) for transplant failure or death.

CONCLUSION

In our hands, the RI obtained during the first 6 months after transplantation failed to predict renal allograft failure or death, whereas the RI measured 12-18 months after transplantation appeared useful to predict long-term allograft outcomes.

Early kidney graft size and Doppler parameters are associated with kidney graft function 1 year after transplantation

BACKGROUND

The aim of this study was to assess the association of various ultrasonography (US) and Doppler parameters of kidney graft as measured at 1 month posttransplant with 1-year graft function.

MATERIALS AND METHODS

The study cohort included 125 adult recipients of deceased donor kidney transplantations between January 2006 and February 2009. All patients underwent an US-Doppler examination performed by a trained nephrologist at 1 month posttransplant using an Acuson-Siemens Sequoia 512. Graft length and intrarenal Doppler indices were measured at the midsegmental artery level. Relative graft size was calculated by dividing graft length with body mass index. Graft function was assessed at 1 year by estimated glomerular filtration rate (eGFR) using the 4-variable Modification of Diet in Real Disease study equation. Linear and logistic regression analyses were used to assess the relationship between US-Doppler parameters and eGFR.

RESULTS

Univariate linear regression showed a significant correlation between eGFR at 1 year and graft length at 1 month (P = .009), relative graft length <0.50 cm per kg/m(2) (P = .004), resistance index >0.75 (P = .031), and end-diastolic velocity <9 cm/sec (P = .006). Logistic regression analyses showed that eGFR <60 mL/min/1.73 m(2) at 1 year was significantly associated with graft length <12 cm at 1 month (odds ratio [OR], 2.4; 95% confidence interval [CI], 1.16-4.92; P = .017), relative graft length <0.5 cm per kg/m(2) (OR, 2.54; 95% CI, 1.20-5.35; P = .014), resistance index >0.75 (OR, 2.86; 95% CI, 1.30-6.29; P = .009), and end-diastolic velocity <9 cm/sec (OR, 2.37; 95% CI, 1.01-5.56; P = .047).

CONCLUSION

In this retrospective analysis, kidney transplant recipients with greater graft length at 1 month, specifically when standardized to body size, showed better graft function at 1 year posttransplantation. Higher intrarenal diastolic blood flow and lower resistance index at 1 month were also predictive of better graft function at 1 year.

Donor effect on cortical perfusion intensity in renal allograft recipients: a paired kidney analysis

BACKGROUND

The contributions of donor- and recipient-related factors to renal allograft hemodynamics are difficult to dissect due to methodological reasons. We analyzed 28 pairs of kidneys (each pair from the same donor) transplanted to 56 different recipients in order to define the contributions of the donor and the recipient to allograft hemodynamics.

METHODS

Two different techniques based on color-coded duplex ultrasound were used: renal resistance index (RI; measured in 3 different segmental arteries) and cortical perfusion intensity (PI; calculated as the average PI of selected cortical parenchymal regions during one heart cycle in standardized registered and processed ultrasound videos). All measurements were performed during the same study visit.

RESULTS

Donor age was 56 years (median, range 17-78) and recipient age at examination 54 years (range 30-77). Median time after transplant (at the date of examination) was 2.4 years (range 0.7-5.5). RI correlated with pulse pressure (r = 0.64; p < 0.001) and recipient age (r = 0.42; p < 0.03), but not with donor age or transplant function expressed as estimated glomerular filtration rate (eGFR) or PI. In within- and between-pairs ANOVA, donor-derived factors determined eGFR (p < 0.02) and cortical PI (p < 0.03), but not RI.

CONCLUSIONS

Intrinsic donor-derived factors are associated with GFR and cortical parenchymal perfusion intensity, but not the RI of segmental arteries in renal allografts.

Significant increase in 1-year posttransplant renal arterial index predicts graft loss

BACKGROUND AND OBJECTIVES

Conflicting data have been reported concerning the use of kidney graft arterial resistance index (RI) measured by Doppler to predict death-censored graft loss. We hypothesized that changes in RI values could carry better information than a single measure of RI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Four hundred twenty-five renal transplant recipients were included in the study. We tested whether changes in renal arterial resistance index between 4 and 12 months after transplant (ΔRI(4→12)) were predictive of graft loss.

RESULTS

Neither 4-month nor 1-year RI predicted graft loss. The area under the receiver operating characteristics curve of ΔRI(4→12) for graft loss was 0.75. A ΔRI(4→12) ≥10% had the best sensitivity and specificity. One year after transplant, 22% of the study population had ΔRI(4→12) ≥10%. Fifty-five patients (12.9%) experienced graft loss during follow-up. The annual incidence of graft loss was higher in patients with ΔRI(4→12) ≥10% (3.5 versus 1.3%; P = 0.009). In multivariate analysis, patients with ΔRI(4→12) ≥10% had an increased risk of graft loss (hazard ratio, 6.21; 95% confidence interval, 1.99 to 22.15; P = 0.002).

CONCLUSIONS

A variation in RI ≥10% in the first year after transplant is an independent risk factor for death-censored graft loss in renal transplant recipients.

Early assessment of renal resistance index and long-term renal function in renal transplant recipients

BACKGROUND

The effect of the intrarenal arterial resistance index (RI) on long-term renal functions is not well known. We examined the predictive value of intrarenal RI on long-term allograft outcomes.

METHODS

We retrospectively investigated 121 stable renal transplant recipients, followed for a mean of 63.21 +/- 19.9 months after renal transplant. Patients with complications during the first six months after transplant were not included. Color Doppler ultrasonography was done to calculate the intrarenal RI within the first four weeks after transplant.

RESULTS

Older recipient age, high pulse pressure, active smoking, and proteinuria were associated with a higher intrarenal RI. Multivariate analyses revealed that renal RI and donor age were independent predictors of allograft outcome. Kaplan-Meier estimates of cumulative graft survival were significantly worse in patients who had an RI of 0.7 or more than they were in patients who had an RI of less than 0.7 (p = .005). Development of chronic allograft nephropathy (CAN) was significantly higher in patients who had an RI of 0.7 or more (p = .02).

CONCLUSIONS

Renal RI determined within the first month after renal transplant predicts long-term allograft function and development of CAN in renal transplant recipients.

Prediction of the severity and outcome of acute tubular necrosis based on continuity of Doppler spectrum in the early period after kidney transplantation

BACKGROUND

Doppler flow spectrum, quantified in the segmental arteries of the graft early after kidney transplantation (KTx), reflects the exacerbation of interstitial oedema. In some patients, the spectrum is characterized by the absence of blood flow during part or during the whole diastole of the cardiac cycle. We have previously observed that such discontinuous flow is associated with a more severe clinical course of acute tubular necrosis (ATN). In order to further verify this hypothesis, we have quantified prospectively the timing of blood flow in Doppler spectrum within the cardiac cycle.

METHODS

Doppler sonography was performed in 173 recipients between 2 and 4 days after KTx. A total of 18 patients with a diagnosed episode of acute rejection or primary graft non-function were excluded from the analysis. Fifty-three out of 155 patients (34%) developed ATN, defined as a requirement for more than one haemodialysis session after KTx. In patients with a discontinuous spectrum of flow, we have quantified the ratio of time during the whole cardiac cycle in which the flow is present [flow time index (FTI) expressed as %].

RESULTS

The discontinuous spectrum of flow was present in 35 out of 53 (66.0%) patients with ATN but only in 6 out of 102 (5.9%) patients with immediate or slow graft function. The relative risk of ATN occurrence for patients with discontinuous spectrum of flow was 5.98 (3.83-9.34) and the duration of ATN in these patients was twice as long-12 (10-14) versus 6 (5-8) days. In patients with ATN a significant correlation was found between FTI and duration of ATN (r = -0.357, P = 0.035).

CONCLUSION

The discontinuous spectrum of flow in the segmental arteries of the kidney graft in the early period after KTx is typical for ATN and predicts its duration.