The renal arterial resistive index and stage of chronic kidney disease in patients with renal allograft

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.

Elevated renal resistive index is independently predicted by older age, but not by the presence of chronic kidney disease: A retrospective cohort study

PURPOSE

Renal resistive index (RRI), which reflects intra-renal arterial impedance is routinely measured when undertaking renal Doppler ultrasonography (RDU). We investigated the relationship between elevated RRI and presence of chronic kidney disease (CKD), and examined whether elevated RRI at baseline is associated with decline in estimated glomerular filtration rate (eGFR) on follow-up.

METHODS

This retrospective observational study examined the association of elevated RRI (>0.7) with the presence of CKD (eGFR <60 mL/min for >3 months), demographic and clinical factors in multivariable models. We also examined the effect of elevated RRI on eGFR decline on follow-up using mixed models.

RESULTS

Of the 346 patients undergoing RDU (median age 69.7 years, 46.2% male), 180 had elevated RRI. There was a strong inverse association between RRI and eGFR at baseline, 1 and 2 years (rho = -0.53, -0.51, -0.53, all p < 001). Elevated RRI was independently predicted by older age (Odds Ratio 3.29, 95% CI: 2.25-4.8, p < 0.001) and diabetes (Odds Ratio 2.65, 95% CI: 1.21-5.80, p = 0.015) but not CKD using multivariate logistic regression. Decline of eGFR was not different between RRI categories on follow-up.

CONCLUSION

Elevated RRI was predicted by older age and diabetes, but not by the presence of CKD. Baseline RRI was not associated with eGFR decline. This article is protected by copyright. All rights reserved.

The Correlation of Intraabdominal Pressure With Renal Resistive Index

BACKGROUND

To evaluate the correlation between intraabdominal pressure (IAP) measured via the bladder and renal resistive index (RRI) measured by Doppler ultrasonography (USG).

METHODS

Eighty consecutive surgical patients were included into this study. Before Doppler USG evaluation, IAP was measured by a Foley catheter via the bladder. The left and right RRI, the diameters of the inferior vena cava and portal vein were measured by colored Doppler USG. Spearman correlation analysis was used to evaluate the correlation between different measurements. Intraabdominal hypertension (IAH) was defined as of IAP ≥ 12 mmHg. Significantly different variables from the univariate analysis between patients with and without IAH were entered into backward stepwise binary logistic regression analysis of IAH as the dependent variable. P values < 0.05 were accepted as statistically significant.

RESULTS

In total, 80 patients were included into study. In 27 patients (34%) IAP was normal and in 53 patients (66%) IAH was diagnosed. The Spearman correlation analysis of IAP and the ultrasonographic measurements revealed a strong correlation between RRI and IAP (P < 0.001). Patients with IAH were more likely to be diabetic and had abdominal incisional hernia compared with patients with normal IAP (P < 0.05). The results of the multivariate logistic regression analysis revealed right RRI as the only independent predictor of IAH (B: 57.04, S. E.: 13.7, P < 0.001).

CONCLUSIONS

There is a strong correlation between IAP and RRI. RRI can be an alternative, noninvasive technique for the diagnosis and follow-up of IAH after further evaluations in different patient groups.

Role of remodeling of small diameter kidney arteries in the prognosis of progression of tubulointerstitial fibrosis in patients with chronic glomerulonephritis

Aim. To assess the role of remodeling of small diameter kidney arteries in the prognosis of progression of tubulointerstitial fibrosis in patients with chronic glomerulonephritis.

Material and methods. The study involved 97 patients with primary glomerulonephritis. The average age of patients was 37,27±1,2 years. The inclusion criterion was the presence of indications for renal biopsy. Renal biopsy was used to analyze renal tissue, in particular, for determining of tubulointerstitial fibrosis (TIF). Based on TIF sign, the patients were divided in 2 groups. The first group includes patients with TIF, the second — without TIF. Vasometry, a measurement of the renal arteries structures, was performed as part of renal biopsy. Parameters of internal and external diameters, wall thickness, intima, media, intima-media complex, vascular mass were analyzed.

Results. The influence of the size of the inner and outer diameters of the interlobular artery (MA) on the studied risk was established. Probability of TIF developing increases with decreasing of MA inner diameter (χ2-criterion =5,34, p=0,02) and increasing of MA outer diameter (χ2-criterion =7,77, p=0,005). Intimal thickness does not have a statistically significant effect on the risk of TIF developing (p=0,29), whereas media thickness has a high statistical significance in renal tissue remodeling (χ2-criterion =13,71, p=0,0002). A statistically significant effect of an increase in the vascular mass on the risk of TIF was determined (χ2-criterion =6,55, p=0,01).

Conclusion. We established that changes in the structure of small diameter kidney arteries in chronic glomerulonephritis occurs according to a hypertrophic type. Remodeling of small diameter kidney arteries plays significant role on the risk of TIF.

Increased renal cortical stiffness obtained by share-wave elastography imaging significantly predicts the contrast-induced nephropathy in patients with preserved renal function

PURPOSE

We aimed to investigate the relation between renal cortical stiffness (CS) obtained by shear-wave elastography (SWE) and contrast-induced nephropathy (CIN) development in interventional treatment-planned acute coronary syndrome (ACS) patients.

METHODS

Our study group consisted of 465 ACS patients. Routine laboratory assessments, B-mode, Doppler, and SWE renal ultrasonography (USG) evaluations were performed. Renal resistive index (RRI), renal pulsatility index (RPI), and acceleration time (AT) and CS were measured. Patients were grouped as with and without CIN.

RESULTS

Among the study group, 55 patients (11.8%) had CIN. Age, diabetes mellitus (DM), hypertension (HT), basal creatinine, CK-MB and troponin I levels, contrast volume, contrast volume/weight ratio, SYNTAX score, RRI, RPI, AT, and CS values were significantly higher in patients with CIN. eGFR was lower in patients who developed CIN. Age, contrast volume/weight ratio, and CS were determined as independent predictors of CIN occurrence in logistic regression analysis. In multivariate logistic analysis, increase of age (each year), contrast volume/weight (each 0.2 mL/kg), and CS (each 1 kPa) were found to augment the development of CIN by 7.1, 59.5, and 62.3%, respectively. In the ROC analysis, CS had the highest AUROC value. The cutoff value of CS obtained by the ROC curve analysis was 7 kPa for the CIN development (sensitivity: 74.5%, specificity: 72.5%).

CONCLUSION

CS value is a simple, cheap, reproducible, noninvasive, and objective parameter for the detection of CIN development. ACS patients should be directed to renal USG, and routine CS value should be written besides USG measurements in reports.

Cold Pulsatile Machine Perfusion versus Static Cold Storage in Kidney Transplantation: A Single Centre Experience

Introduction

We present our experience with hypothermic machine perfusion (HMP) versus cold storage (CS) in relation to kidney transplant outcomes.

Methods

Retrospective analysis of 33 consecutive HMP kidney transplant outcomes matched with those of 33 cold stored: delayed graft function (DGF), length of hospital stay (LOS), estimated glomerular filtration rate (eGFR), and patient and graft survival were compared. Renal Resistive Indexes (RIs) during HMP in relation to DGF were also analysed.

Results

In the HMP group, mean HMP time was 5.7 ± 3.9 hours with a mean cold ischaemic time (CIT) of 15 ± 5.6 versus 15.1 ± 5.3 hours in the CS group. DGF was lower in the HMP group (p=0.041), and donation after Circulatory Death (DCD) was a predictor for DGF (p<0.01). HMP decreased DGF in DCD grafts (p=0.036). Patient and graft survival were similar, but eGFR at 365 days was higher in the HMP cohort (p<0.001). RIs decreased during HMP (p<0.01); 2-hours RI ≥ 0.45 mmHg/mL/min predicted DGF in DCD kidneys (75% sensitivity, 80% specificity; area under the curve 0.78); 2-hours RI ≥ 0.2 mmHg/ml/min predicted DGF in DBD grafts (sensitivity 100%, specificity 91%; area under the curve 0.87).

Conclusion

HMP decreased DGF compared to CS, offering viability assessment pretransplant and improving one-year renal function of the grafts.

The impact of functioning hemodialysis arteriovenous accesses on renal graft perfusion: Results of a pilot study

Introduction:

After a kidney transplant, it is unknown whether the maintenance of a functioning hemodialysis arteriovenous access could have deleterious effects on renal grafts. We hypothesize that maintaining an arteriovenous access can deviate a significant proportion of the cardiac output from the renal graft. The aim of this study was to investigate whether a temporary closure of the arteriovenous access could lead to an increase in graft perfusion.

Methods:

We conducted a study in 17 kidney-transplanted patients with a functioning arteriovenous access. We evaluated, at baseline and 30 s after compression of the arteriovenous access (access flow occlusion), the hemodynamic parameters and the renal resistive index of the graft by Doppler ultrasound.

Results:

After arteriovenous access occlusion 82.4% (n = 14) of the patients had a decrease in resistive index. All patients had a decrease in heart rate (67 vs 58 bpm, p < 0.001) and 14 (82.4%) had an increase in mean blood pressure (98.3 vs 101.7 mm Hg, p = 0.044). There was a significant decrease in the resistive index (ΔRI) after the access occlusion (0.68 vs 0.64, p = 0.030). We found a negative correlation in Qa (r2 = −0.55, p = 0.022) with the ΔRI, and Qa was an independent predictor of ΔRI in a model adjusted to pre-occlusion resistive index.

Conclusion:

Our results showed that temporary occlusion of an arteriovenous access causes a significant decline in renal graft resistive index and this decline is higher with the occlusion of accesses with higher Qa. These results suggest that the maintenance of arteriovenous accesses, mainly those with higher Qa, can decrease renal graft perfusion.

Renal Resistive Index as a Novel Indicator for Renal Complications in High-Fat Diet-Fed Mice

BACKGROUND/AIMS

The renal resistive index (RI) is a novel candidate as a renal injury prognostic indicator, but it remains unclear how renal RI levels correspond to renal injury in diabetic nephropathy.

METHODS

To examine this issue, we compared 8-week-old male C57BL/6 mice fed with high-fat diet (HFD) versus chow diet (CHD) for 16 weeks. At 8 and 12 weeks, the glomerular filtration rate (GFR), urinary albumin-to-creatinine ratio (UACR), and inflammatory factors (IL-1β, IL-6, TNFα, and MCP-1) were measured, along with the increase in renal RI.

RESULTS

Our study suggests RI values positively correlate with GFR for the first 12 weeks of HFD feeding. In contrast, the GFR of 16-week HFD feeding is lower than that of 12-week HFD feeding, whereas RI levels are significantly increased. Additionally, our study suggests RI values accurately indicate the renal fibrosis and renal injury in HFD-fed mice treated with lovastatin.

CONCLUSION

This study seems to confirm the utility of a noninvasive and repeatable ultrasound parameter to rapidly evaluate renal fibrosis in a HFD-induced type 2 diabetic mouse model in vivo. This highly sensitive and comparable renal RI measurement could monitor the whole procedure of disease development in real-time. RI measurement of the renal artery is capable of differentiating responses to standard therapy with lovastatin in HFD-fed mice from the CHD group.

B-mode and Doppler ultrasound of chronic kidney disease in dogs and cats

Ultrasound is the imaging test of choice for renal evaluation, because it provides information about the position, size, shape, internal architecture and hemodynamics of the kidneys without harming the patient. In chronic kidney disease, the main findings observed in B-mode ultrasound images are increased cortical echogenicity, loss of corticomedullary differentiation, reduced renal volume and irregular renal contour, and when these changes are associated, they are indicative of end-stage renal disease. However, the cause of kidney disease cannot be determined by ultrasonography, but must be confirmed by means of biopsy, although the presence of ultrasonographic changes indicative of the end-stage of the disease may contraindicate this procedure. The Doppler ultrasound test complements the ultrasonic B-mode examination and enables the assessment of renal perfusion based on a calculation of the hemodynamic indices, which are increased in cases of chronic kidney lesions, with higher values ​​in the most severe cases. Thus, ultrasound examinations are not only useful in diagnostics but also play an important role in defining the prognosis of patients with chronic kidney disease.

Pre-procedural renal resistive index accurately predicts contrast-induced acute kidney injury in patients with preserved renal function submitted to coronary angiography

The study aimed to evaluate the clinical utility of ultrasonographic intra-renal blood flow parameters, together with the wide range of different risk factors, for the prediction of contrast-induced acute kidney injury (CI-AKI) in patients with preserved renal function, referred for coronary angiography or percutaneous coronary interventions (CA/PCI). This prospective study covered 95 consecutive patients (69.5% men; median age 65 years) subject to elective or urgent CA/PCI. Data regarding 128 peri-procedural variables were collected. Ultrasonographic intra-renal blood flow parameters, including renal resistive index (RRI) and pulsatility index (RPI), were acquired directly before the procedure. CI-AKI was defined as ≥50% relative or ≥0.3 mg/dL absolute increase of serum creatinine 48 h after procedure. CI-AKI was confirmed in nine patients (9.5%). Patients with CI-AKI had higher SYNTAX score (p = 0.0002), higher rate of left main disease (p < 0.00001), peripheral artery disease (PAD; p = 0.02), coronary artery anomaly (p = 0.017), more frequently underwent surgical revascularization (p = 0.0003), ‘had greater...’ intima-(p = 0.004) and extra-medial thickness (p = 0.001), and received higher contrast media dose (p = 0.049), more often overused non-steroidal anti-inflammatory drugs (p = 0.001), and had substantially higher pre-procedural RRI (0.69 vs. 0.62; p = 0.005) and RPI values (1.54 vs. 1.36; p = 0.017). Logistic regression confirmed age, SYNTAX score, presence of PAD, diabetes mellitus, and pre-procedural RRI independently predicted CI-AKI onset (AUC = 0.95; p < 0.0001). Pre-procedural RRI > 0.69 had 78% sensitivity and 81% specificity in CI-AKI prediction. High pre-procedural RRI seems to be a useful novel risk factor for CI-AKI in patients with preserved renal function. Coronary, peripheral and renal vascular pathology contribute to the development of CI-AKI following CA/PCI.

The comparison of resistivity index and strain index values in the ultrasonographic evaluation of chronic kidney disease

OBJECTIVES

Chronic kidney disease (CKD) is a disorder progressing to end-stage kidney failure. Early diagnosis and treatment are important for medical care. The aim of this prospective study was to define the strain index (SI) and resistivity index (RI) values in the same CKD group for each kidney separately at the same time, and also to compare the efficacy of SI and RI in the differentiation of normal population and CKD patients.

MATERIALS AND METHODS

Toshiba Aplio 500 USG device and 3.5-5 MHz convex probe were used for USG, CDUSG, and USG elastography examinations. The patients were referred to radiology clinique from nephrology and endocrinology cliniques after GFR calculation. Patients with renal cyst, tumor, or obstructive renal disease were excluded. Healthy volunteers according to laboratory and clinical examinations were selected from non-kidney disease patients.

RESULTS

A total of 121 CKD (68 men, 53 women) and 40 healthy volunteers (19 men, 21 women) were participated. The mean SI and RI values of CKD were significantly higher than the normal healthy volunteers (p < 0.05). The SI and RI values of right and left kidney did not show any difference in CKD patients (p values were 0.381 for SI and 0.821 for RI). The sensitivity and the specificity of the SI were higher than RI.

CONCLUSION

The RI and SI values of kidneys in CKD patients were significantly higher than those of apparently normal kidneys. SI was more sensitive than RI in our study. Determining cut-off SI and RI values between normal and damaged renal parenchyma can help in the diagnosis and follow up of CKD patients.

ADVANCES IN KNOWLEDGE

To the best of our knowledge, this is the first study comparing RI and SI in CKD patients, and SI is found to be more sensitive than RI for the evaluation of CKD.

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.

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.