Immediate renal Doppler ultrasonography findings (<24 h) and its association with graft survival

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.

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.

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.

Current status of imaging diagnosis in the transplanted kidney. A review of the literature with a special focus on contrast-enhanced ultrasonography

Objectives

Ultrasonographic scanning is currently the most widespread imaging diagnostic procedure. The method provides real-time morphological, vascular and elastographic information in a non-invasive manner. In recent years, harmonic vascular examination has become accessible using intravenous contrast agents. In urological pathology, this procedure is used in the detection and evaluation of vascular and ischemic complications, in the classification of complex cysts according to the Bosniak system, also in the renal lesions with uncertain etiology and in acute pyelonephritis for the detection of abscesses. The contrast agent (SonoVue) is angiospecific and can be used in patients transplanted immediately after surgery without adverse effects or impaired renal function. Thus, it is desirable to be used in the nephrological pathology of the renal graft and to develop diagnostic models based on the evaluation of renal microvascularization, as well as the quantitative data resulting from the graphical representation of the specific parameters. The purpose of this review is to evaluate the current state of the literature regarding the place and role of contrast substance ultrasound in the early diagnosis of acute renal graft dysfunction and to make a differential diagnosis of this pathological entity.

Method

This review quantifies the role of contrast ultrasound in the diagnosis of acute complications of the renal graft. The research was conducted based on the databases PubMed, MedScape, Cochrane, according to the search criteria such as contrast-enhanced ultrasound + kidney transplant, “time intensity curves” + “kidney transplant”, filtered for the period 2004–2018.

Results

In the nephrological pathology of the renal graft, contrast-enhanced ultrasound is a valuable tool, superior to Doppler ultrasound in predicting the evolution of the renal graft, identifying very small early defects in renal microvascularization. A number of studies succeeded in identifying acute graft dysfunction, some of which establish its etiology - humoral rejection versus acute tubular necrosis. On the other hand, the contrast-enhanced ultrasound parameters do not have the ability to distinguish between cellular and humoral rejection.

Conclusions

If, at present, the histopathological examination is the only one that can differentiate with certainty the cause of acute renal graft dysfunction, we consider that contrast-enhanced ultrasound, as a non-invasive imaging technique, opens a favorable perspective for increasing the survival of the renal graft and decreasing the complications in the renal transplant. The combination of other ultrasound techniques, together with contrast-enhanced ultrasound, could lead to the development of new diagnostic models.

Increase in Serum Amylase and Resistive Index After Kidney Transplant Are Biomarkers of Delayed Graft Function

BACKGROUND

Both amylase and resistive index (RI) are routinely measured after kidney transplant and proposed as markers of delayed graft function (DGF).

MATERIAL AND METHODS

This retrospective cross-sectional study analyzed amylase and RI in 269 renal transplant recipients before and after transplantation, and at discharge. An increase above 20% of total amylase with/without RI>0.7 were evaluated as prognostic markers of DGF, hospitalization length and risk of rejection.

RESULTS

Serum amylase increase >20% was found in 103/269 (38.3%) patients who showed DGF (45.6% vs. 25.3%, p=0.001) and had lower estimated glomerular filtration rate compared to those with an amylase increase <20% (42.0±21.7 vs. 49.8±23.2 ml/min, p=0.007). The double condition consisting of concomitant amylase increase >20% and RI>0.7 was associated with higher DGF occurrence (65% vs. 24%, p<0.001), longer hospital stay, lower eGFR at discharge, and higher risk of rejection.

CONCLUSION

Patients with concomitant amylase increase >20% and RI>0.7 might require closer monitoring to diagnose DGF early and modify the therapeutic approach accordingly.

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.

Imaging in pediatric renal transplantation

Renal transplantation is the therapy of choice in children with ESKD. Radiological investigations are required in both pre- and post-transplant assessment, although there is paucity of both consensus-based statements and evidence-based imaging guidelines in pediatric renal transplantation. The phases of pediatric ESKD management that require imaging are pretransplantation recipient assessment and post-transplantation surveillance for detection of potential complications. We present suggestions for imaging algorithms for both pre- and post-transplant assessment in pediatric renal transplant recipients.

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.

Functional MRI detects perfusion impairment in renal allografts with delayed graft function

Delayed graft function (DGF) after kidney transplantation is not uncommon, and it is associated with long-term allograft impairment. Our aim was to compare renal perfusion changes measured with noninvasive functional MRI in patients early after kidney transplantation to renal function and allograft histology in biopsy samples. Forty-six patients underwent MRI 4–11 days after transplantation. Contrast-free MRI renal perfusion images were acquired using an arterial spin labeling technique. Renal function was assessed by estimated glomerular filtration rate (eGFR), and renal biopsies were performed when indicated within 5 days of MRI. Twenty-six of 46 patients had DGF. Of these, nine patients had acute rejection (including borderline), and eight had other changes (e.g., tubular injury or glomerulosclerosis). Renal perfusion was significantly lower in the DGF group compared with the group with good allograft function (231 ± 15 vs. 331 ± 15 ml·min−1·100 g−1, P < 0.001). Living donor allografts exhibited significantly higher perfusion values compared with deceased donor allografts ( P < 0.001). Renal perfusion significantly correlated with eGFR ( r = 0.64, P < 0.001), resistance index ( r = −0.57, P < 0.001), and cold ischemia time ( r = −0.48, P < 0.01). Furthermore, renal perfusion impairment early after transplantation predicted inferior renal outcome and graft loss. In conclusion, noninvasive functional MRI detects renal perfusion impairment early after kidney transplantation in patients with DGF.

Complications of kidney transplantation with grafts from expanded criteria donors

PURPOSE

The limited availability of kidneys for transplantation has been addressed by expanding the criteria for allowing a donor kidney to be transplanted, but this tendency may cause suboptimal kidneys to be implanted and could be associated with greater risk of complications.

METHODS

A retrospective study of 407 kidney transplantations was done to compare complications of transplantation with non-expanded (n = 244) and expanded criteria donors (n = 163). Expanded criteria donors were donors older than 60 years, or donors aged 50-60 years who had ≥ 2 of the following risk factors: hypertension, diabetes mellitus (type 2), creatinine >1.5 mg/dL, or death caused by stroke.

RESULTS

Compared with transplant recipients from non-expanded criteria donors, transplant recipients from expanded criteria donors had significantly greater frequency of graft loss, delayed graft function, pneumonia, overall surgical complications, early reoperation, wound eventration, hydronephrosis, postoperative hemorrhage, and wound infection. When analyzing surgical complications types, a significant greater frequency of urologic, wound, vascular, early and late surgical complications was found. In terms of severity, expanded donor criteria transplantation was related to Clavien I, III, and IV complications.

CONCLUSIONS

Transplantation of kidneys from expanded criteria donors is associated with a significant higher risk of medical and surgical complications than kidneys from non-expanded criteria donors.

Early ultrasound assessment of renal transplantation as the valuable biomarker of long lasting graft survival: a cross-sectional study

Background:

To date, there has been little agreement on the use of ultrasonographic parameters in predicting the long-term outcome after transplantation. This study evaluates whether ultrasonography of the graft performed in the early stage after transplantation is a valuable predictor for long-term-outcome.

Objectives:

The aim of this study was to evaluate the association of ultrasonographic parameters (resistive index [RI], pulsatility index[PI], end diastolic velocity [EDV], graft length and graft parenchymal volume) measured within the first week after transplantation with 6 months graft function.

Patients and Methods:

A cross-sectional study was performed on 91 (46 males and 45 females) living renal transplants between April 2011 and February 2013. All patients underwent an ultrasonography at the first week after transplantation. Intrarenal Doppler indices including RI, PI and EDV were measured at the interlobar artery level and the graft length and parenchymal volume were defined with gray scale ultrasonography. Graft function was estimated at 6months by glomerular filtration rate (GFR). Unpaired t-test and multivariate-linear and logistic regression analysis were used to estimate the relationship between ultrasonographic parameters and GFR.

Results:

Fourteen patients (15.4%) had impaired graft function after 6 months (GFR less than 60 ml/min/1.73m2). Multivariate linear regression analysis showed significant correlation between GFR at 6 months and RI, PI and EDV with a P value of 0.026, 0.016 and 0.015, respectively. Logistic regression analysis showed that GFR<60 ml/min/1.73 m2 at 6 months was significantly associated with RI>0.7 (odds ratio=2.20, P value=0.004) and PI>1.3 (odds ratio=2.74, P value<0.001) and EDV<9 cm/Sec (odds ratio=1.83, P value=0.03).

Conclusions:

In this study, kidney transplant recipients with a lower RI and PI and a higher EDV at 1week showed better graft function at 6 months after transplantation.

Relation of resistive and pulsatility indices with graft function after renal transplant

OBJECTIVES

There are conflicting data regarding the use of some measured indices by Doppler ultrasound such as the resistive index and the pulsatility index in predicting renal allograft dysfunction. This study sought to evaluate the association of early postoperative Doppler indices and 3-month serum creatinine levels in renal transplant recipients.

MATERIALS AND METHODS

During a 1-year period, all patients who underwent renal transplant at our hospital were recruited into a prospective study. Doppler ultrasound was performed on all patients 6 days and 3 months after the transplant and the resistive index and the pulsatility index were calculated for each patient. Then, the association between these indices and 3-month outcomes of patients were investigated.

RESULTS

Thirty-eight patients including 21 men (mean age, 36.6 ± 13.1 y) were evaluated. There was a positive correlation between the resistive index and the pulsatility index at 6 days after transplant and the serum creatinine measured at the same day (P < .001 and r=0.570 for resistive index; P < .001 and r=0.547 for pulsatility index). There was also a positive correlation between the pulsatility index and the resistive index at 6 days after transplant and 3-month serum creatinine level (P = .009 and r=0.420 for resistive index; P = .009 and r=0.417 for pulsatility index). There were negative correlations between the resistive index and the pulsatility index on the sixth day after surgery and creatinine clearance measured at 6 days and 3 months after transplant.

CONCLUSIONS

This study reveals a strong-to-medium correlation between the resistive index and the pulsatility index, serum creatinine level, measured 6 days after transplant.

Recipient and donor risk factors for surgical complications following kidney transplantation

OBJECTIVE

The aim of this study was to evaluate recipient and donor risk factors that are related to surgical complications after renal transplantation.

MATERIAL AND METHODS

In total, 419 kidney transplantations were analysed with regard to the influence of recipient and donor risk factors on the main postoperative surgical complications.

RESULTS

The mean follow-up for the entire group was 72.8 months (± 54.2 SD). Vascular complications were independently associated with donor age; and urological complications with recipient age >65 years and cyclosporine rather than tacrolimus therapy. Wound complications were independently associated with recipient age, preoperative dialysis time, recipient body mass index (BMI) and cyclosporine rather than tacrolimus therapy. Collections were independently associated with retransplantation, type 2 diabetes mellitus and wound complications. Overall surgical complications were associated with donor age and delayed graft function. In terms of severity, grade I complications were independently associated with recipient age and surgical revision, grade II with recipient age >50 years, grade III with recipient BMI, and grade IV with donor age.

CONCLUSIONS

Recipient characteristics are the primary determinants of wound, urological and minor (Clavien grades I, II and III) complications; however, graft or donor characteristics are the primary risk factors for vascular, overall and major (Clavien grade IV) surgical complications.