Doppler spectrum analysis to diagnose rejection during posttransplant acute renal failure

Color Doppler Ultrasound and Hemodynamics for Evaluating Graft Dysfunction in Recurrent Immunoglobulin A Nephropathy

BACKGROUND The aim of this study was to investigate the diagnostic and prognostic utility of color Doppler ultrasound for graft dysfunction in recurrent immunoglobulin A nephropathy (IgAN). MATERIAL AND METHODS We selected a series of 78 biopsies diagnostic of recurrent IgAN following living-donor transplantation from July 2004 to January 2019. Based on Lee's classification, Doppler parameters in different degrees of histopathological injury were retrospectively analyzed. RESULTS The 4-year cumulative graft survival rate after biopsy was 66.3%, and the difference among the Kaplan-Meier curves of Lee's classification (P<0.01) was significant. Doppler parameters showed that echo enhancement, decreasing blood flow distribution, decreasing end-diastolic velocity (EDV) of the main renal artery (MRA), segmental renal atery (SRA) and interlobar renal artery (IRA), and an elevated resistance index (RI) of the arcuate renal artery (ARA) were significantly different among grades I-V of Lee's classification (P<0.05). Logistic multivariate analysis indicated that echo enhancement (HR 13.6, 95% CI 2.7-68.4) and decreasing EDV of the SRA (HR 1.1 for a 1-cm/s, 95% CI 1.0-1.2) were independent predictors of severe injury (IV-V). The ROC curve fitted by echo enhancement and decreasing EDV of the SRA had an area under the curve of 0.87. The cutoff was 17.5 cm/s (decreasing EDV of the SRA) without echo enhancement. The sensitivity and specificity were 72.2% and 91.7%, respectively. CONCLUSIONS Color Doppler ultrasound successfully evaluated the graft dysfunction in recurrent IgAN; a decreasing EDV of the SRA indicated severe histopathological injury and poor prognosis.

Sonography of the renal allograft: Correlation between doppler sonographic resistance index (RI) and histopathology

INTRODUCTION

Allograft rejection (AR), chronic allograft injury (CAI) and acute tubular necrosis (ATN) can lead to renal allograft dysfunction after kidney transplantation. Interstitial fibrosis/tubular atrophy (Banff classification 2005) describes chronic allograft injury with no specific etiology, thus explaining the common final endpoint of various (immunologic and non immunologic) etiologies. The aim of this study was to evaluate correlations between the Doppler sonographic RI-values and histopathological changes of renal allografts biopsies during rejection, acute tubular necrosis and chronic allograft injury as well as the influence of donor and recipient features on the intrarenal RI-values.

METHODS

102 allograft biopsies and ultrasound reports of 69 patients with kidney transplantation performed at the hospital Klinikum rechts der Isar (Technische Universität München, Germany) between 2009 and 2013 were analyzed retrospectively (41 biopsies of living donors, 61 biopsies of deceased donors). Chronic allograft injury was described using the IFTA (interstitial fibrosis and tubular atrophy) or the ECAI score (extended chronic allograft injury score). The ECAI score was built out of the chronic histological lesions glomerulopathy, interstitial fibrosis, tubular atrophy and fibrous intimal thickening (cg + ci + ct + cv) of the BANFF scoring.

RESULTS

Intrarenal RI-values were significantly higher in patients with allograft rejection than without rejection (median 0,79 vs. 0,73; inter quartile range: 0,20 vs. 0,13; p = 0,018). The same was found for T-and non-T cell mediated rejection (median 0,78 vs. 0,73; inter quartile range 0,20 vs. 0,13; p = 0,039). There were no significant differences in the RI-values between the subtypes of T-cell mediated rejection (type IA-IIB). Furthermore, there were no significant differences of RI-values regarding antibody-mediated rejection (present vs. not present) or type of rejection (T-cell- vs. antibody mediated rejection). Patients with rejection and simultaneously chronic allograft injury showed significantly higher RI-values than patients with only chronic allograft injury. Analyses using the IFTA or the ECAI score showed comparable results (IFTA p = 0,043; Score p = 0,021). The intrarenal RI-value was neither able to detect chronic allograft injury nor to distinguish between acute tubular necrosis and rejection. The intrarenal RI-value showed a significant correlation with recipient age (p < 0,001) but not with donor features.

CONCLUSION

In summary, the intrarenal RI-value can indicate a rejection but gives no clear hint to acute tubular necrosis and cannot differentiate from it. Since patients with rejection can have normal RI-values, a biopsy should always be performed in case of suspected rejection. The intrarenal RI-value has no unambiguous validity to determine intrinsic values of the renal allograft, but should rather be understood and interpreted as a systemic parameter influenced by multiple factors.

Biological modulation of renal ischemia-reperfusion injury

PURPOSE OF REVIEW

Biological modulation of renal ischemia-reperfusion injury holds the potential to reduce the incidence of early graft dysfunction and to safely expand the donor pool with kidneys that have suffered prolonged ischemic injury before organ recovery.

RECENT FINDINGS

In the current review, we will discuss clinical studies that compare kidney transplant recipients with and without early graft dysfunction in order to elucidate the pathophysiology of ischemic acute allograft injury. We will specifically review the mechanisms leading to depression of the glomerular filtration rate and activation of the innate immune system in response to tissue injury.

SUMMARY

We conclude that the pathophysiology of delayed graft function after kidney transplantation is complex and shares broad similarity with rodent models of ischemic acute kidney injury. Given the lack of specific therapies to prevent delayed graft function in transplant recipients, comprehensive efforts should be initiated to translate the promising findings obtained in small animal models into clinical interventions that attenuate ischemic acute kidney injury after transplantation.

Role of resistive index measurement in diagnosis of acute rejection episodes following successful kidney transplantation

OBJECTIVE

This study was performed to evaluate the role of resistive index (RI) in the diagnosis of rejection episodes following successful kidney transplantation.

MATERIALS AND METHODS

One hundred and one unrelated living first kidney allograft adult recipients (75 males and 26 females) of overall mean age of 39 years were enrolled and prospectively followed for 6 months. The measurement of RI by Doppler ultrasonography was performed in all patients on days 3 and 7 as well as at months 1, 3, and 6 in addition to when there was graft dysfunction. We determined serum creatinine and cyclosporine levels.

RESULTS

Twenty-seven patients (26.7%) experienced 33 acute rejection episodes during the follow-up. There were significant differences between mean RI among patients with normal function vs rejection: 0.606 +/- 0.065 vs 0.866 +/- 0.083 (P < .05), respectively. Overall, elevated levels of cyclosporine, ischemic acute tubular necrosis (ATN), and renal artery thrombosis were observed in 8, 5, and 3 patients, respectively. No association was observed between these factors and RI.

CONCLUSIONS

RI was significantly higher in patients with acute rejection episodes. It had no association with ATN or cyclosporine toxicity. Hence, RI may be useful to diagnose acute renal allograft rejection following renal transplantation.

Imaging of the renal donor and transplant recipient

Renal transplant remains the mainstay of the treatment of end-stage renal disease. With improvement in management strategies and the diverse imaging options, the yearly survival of recipients with functional kidneys has improved significantly. This improved survival is attributed to factors such as immunosuppressive therapy planning in recipients, human leukocyte antigen matching, surgeon experience, and recipient's age. Transplantation offers the closest thing to a normal state if the transplanted kidney can replace the failed kidneys. Living-donor kidney transplants are playing a vital role in bridging the gap between decreased supply of, and increased demand for, kidneys for transplant. Early detection and characterization of complications in the recipient are of immense clinical relevance, allowing timely intervention to prevent graft failure.

Three-block electrical model of renal impedance

In this study, we measured the characteristic renal impedance profiles of Wistar rats and simulated the profiles using an electrical model with three series connected Windkessel blocks containing inductance. It is expected that a complete renal impedance profile ought to provide better physical properties information and have more diagnostic power than the pulsatility (PI) and resistive indices (RI) as a result of frequency dependency. A characteristic peak value at the third harmonic on the renal impedance amplitude curve was observed and the phase curve decreased with increasing harmonic numbers. From least mean square fitted parameters, the three blocks were given distinct physical properties and identified as: (1) the renal artery, (2) the small arteries plus the afferent arteriole and (3) the residual kidney (i.e., the efferent arteriole plus the post glomerular capillary structures). These allocations were made according to respective physical properties reported in previous research. These classifications were further confirmed when we compressed the kidney or infused Ang II. Variations in electrical parameters concurred with the likely affected blood vessels reported. This model describes renal impedance characteristics well; and it provides useful hints on the physical properties of the renal vascular system as well as allows for distinctions in possible physiologically affected locations during functional disturbance. It has potential for development as a clinical non-invasive diagnostic tool.

Imaging in Renal Transplantation

Renal transplantation is the best treatment option for chronic renal failure, with marked improvement in social activity, work, and family life. In addition to these obvious improvements, it is an extremely cost-effective procedure when successful. Ultrasonography plays a major role in the imaging of these patients, and ultrasound (including color Doppler) is helpful to the transplant physician in detecting graft dysfunction and peritransplant collections, some of which may be drained under ultrasound guidance. It is also helpful in the diagnosis of chronic vascular complications including transplant artery stenosis and arteriovenous fistula. It has no specific application in the diagnosis of chronic rejection.

Severely elevated intrarenal arterial impedance and abnormal venous flow pattern in a normal functioning kidney graft

Serial Doppler sonographic impedance measurements represent the most common diagnostic method for noninvasive monitoring of kidney grafts. Severely elevated arterial impedance is almost always associated with graft dysfunction. However, we describe in the present work a renal transplant recipient with optimal graft function despite permanently elevated arterial impedance (pulsatility index (PI) ranging from 2.9-3.0, and resistive index (RI) = 1.0 as well as an abnormal venous flow pattern. In contrast, the contralateral graft from the same cadaver donors transplanted into a 17-year-old female patient displayed normal range PI and RI values in conjunction with a normal serum creatinine. Known causes of arterial impedance elevation such as rejection, cyclosporine, urinary obstruction, and external graft compression were excluded. Other extrarenal causes of high impedance, such as aortic insufficiency and reduced aortic compliance, were also excluded. No evidence of impaired venous outflow at the site of the anastomosis of the main renal vein to the iliac vein was found. Those findings support the view that impedance indexes are hemodynamic rather than functional parameters.

Ultrasound of renal transplantation

The most effective primary treatment of chronic renal failure is renal transplantation. A significant improvement in lifestyle and family life in conjunction with it being an extremely cost-effective procedure has resulted in an intense monitoring and imaging programme to help ensure a successful outcome. Ultrasound, both grey-scale and colour-flow Doppler, are useful monitoring techniques when interpreted in the clinical context, and in the delineation of peri-transplant collections, some of which can be drained under ultrasound guidance. After the early post-operative period it can also be utilized in the diagnosis of chronic vascular complications including transplant artery stenosis and arteriovenous fistula, although it is of limited use in the diagnosis of chronic rejection. This article will discuss the role of ultrasound in all its guises and how its efficacy in both the early transplant period in the monitoring of graft dysfunction and in the detection of the more chronic conditions including transplant artery stenosis and arteriovenous fistulae. A more limited role for ultrasound also exists in the long-term follow-up of patients and to aid the detection of complications including susceptibility to malignancy.

Quantitative assessment of power Doppler mapping in the detection of renal allograft complications

PURPOSE

We evaluated the usefulness of power Doppler (PD) imaging with a quantitative parameter in the identification of renal transplant complications.

METHODS

One hundred eight transplanted kidneys were subjected to PD examinations. The blood flow area ratio (BFAR), defined as the percentage of the area of color pixels within a given cross-sectional area placed over a region of a transplanted kidney, was measured using built-in color histogram software and used as a quantitative parameter for evaluating the status of allograft blood perfusion. The mean BFARs in the normal, acute rejection (AR), acute tubular necrosis (ATN), chronic rejection (CR), and cytomegalovirus infection (CMV) groups were compared.

RESULTS

The BFAR in the normal group tended to decrease gradually with the time interval since transplantation, but the mean value, 0.68+/-0.08, was significantly higher than that in the complication groups: AR, 0.43+/-0.18; ATN, 0.43+/-0.14; CR, 0.15+/-0.14; and CMV, 0.36+/-0.10 (p < 0.01 for all). When a BFAR of 0.60 or greater was used as the diagnostic criterion for normal allografts, a sensitivity, specificity, and accuracy of more than 90% could be achieved in the diagnosis of complications. However, owing to overlapping BFARs among the complication groups, the BFAR alone had a limited ability to differentiate the types of complications.

CONCLUSIONS

Although PD imaging has some limitations in identifying the nature of renal allograft complications, the use of the quantitative parameter BFAR in the PD assessment of renal allografts may be useful in detecting complications. Further studies are needed to explore the BFAR's clinical value.

Evaluation of renal hemodynamics in awake and isoflurane-anesthetized cats with pulsed-wave Doppler and quantitative renal scintigraphy

The feasibility and reproducibility of obtaining the pulsed-wave Doppler measurements of resistive index (RI) and pulsatility index (PI) were investigated in intrarenal arteries of normal, nonsedated cats, and cats anesthetized with isoflurane. In addition, relative renal function and relative renal blood flow were evaluated using quantitative renal scintigraphy. The percentage of injected dose uptake, time to peak activity, and two indices of renal blood flow (K/A ratio and flow index) obtained during the first pass of 99mTc-MAG3, were determined for both awake and anesthetized cats. Results indicate that measuring RI and PI in nonsedated cats is readily accomplished and that the results are reproducible within an animal. Mean RI and PI values in the awake cats were 0.55 and 0.8, respectively. Significant differences between the awake and anesthetized cats were found for all pulsed-wave Doppler and quantitative renal scintigraphic measurements evaluated.