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

Real-time organ perfusion monitoring of human kidney transplants using ex vivo normothermic perfusion and reflectance spectroscopy

Transplantation is the standard treatment for end-stage kidney disease but carries with it a non-trivial risk of post-operative complication. There is a need for a continuous, real-time, not additionally invasive method of monitoring organ perfusion. We present an approach to allograft perfusion monitoring using a human kidney model using ex vivo normothermic perfusion (EVNP) and custom spectroscopic optical reflectance probes. Five discarded human kidneys underwent EVNP, spectroscopic measurement and were subjected to perfusion compromising events (rejection, thrombosis or haemorrhage). Oxygenated and deoxygenated haemoglobin spectra were fitted to the spectra acquired from the kidneys in order to estimate the oxygen saturation. Average oxygen saturations before the perfusion compromising events were estimated to be higher than after (or similar in the control cases). Changes in oxygen saturation estimated from measurements made continuously were synchronized well with changes in renal blood flow index measurements. This proof of concept study proves promising in identifying a technique for continuous monitoring of perfusion and oxygenation of a transplanted kidney in vivo with minimal additional invasiveness.

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

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

Current Status of Ultrasound in Acute Rejection After Renal Transplantation: A Review with a Focus on Contrast-Enhanced Ultrasound

Renal transplantation has developed into the best treatment for end-stage renal disease, but severe cases can even lead to loss of renal allograft function due to rejection and complications caused by surgical procedures. If a series of postoperative complications can be reduced or even avoided, the quality of life of recipients will be significantly improved. Acute rejection in a transplanted kidney is one of the main complications after renal transplantation. Early detection and diagnosis will significantly help the prognosis of transplanted kidney patients. As a seminal morphological and hemodynamic examination method, ultrasound can monitor the tissue structure and arteriovenous blood flow of the transplanted kidney, providing information on the transplanted kidney’s gross shape and blood perfusion. Ultrasound is a commonly used detection method after renal transplantation. At present, two-dimensional ultrasound, color Doppler ultrasound, three-dimensional ultrasound, and contrast-enhanced ultrasound have been applied in the monitoring of complications after renal transplantation. Contrast-enhanced ultrasound, as a non-invasive, radiation-free, and easy to perform examination technique, can qualitatively and quantitatively evaluate the microcirculatory blood perfusion of the transplanted kidney. It can reflect the function of the transplanted kidney more objectively and sensitively. In recent years, contrast-enhanced ultrasound has attracted attention as a new technology that can quantitatively monitor the transplanted kidney’s microcirculation perfusion. A large number of studies have shown that contrast-enhanced ultrasound has unique advantages in monitoring acute rejection after renal transplantation compared with other imaging methods, providing a reliable basis for clinical intervention. This article reviews the current status of and recent research on contrast-enhanced ultrasound in acute rejection after renal transplantation.

Prediction Efficiency of Postoperative Acute Kidney Injury in Acute Stanford Type A Aortic Dissection Patients with Renal Resistive Index and Semiquantitative Color Doppler

Objectives

This study is aimed to evaluate the efficiency in early prediction of postoperative persistent acute kidney injury (PAKI) after surgery in acute Stanford type A aortic dissection (AAAD) patients by using Doppler renal resistive index (RRI) and semiquantitative color (SQC) Doppler grade, respectively.

Methods

84 AAAD patients received Sun's surgical management, and 67 patients were enrolled. RRI and SQC Doppler grade were evaluated by ultrasonography, respectively, at 6 hours after surgery. Serum creatinine (sCr) was recorded before operation and at 24 hours, 48 hours, and 72 hours after operation. AKI grade was evaluated according to the classifications of the Acute Kidney Injury Network (AKIN). PAKI is defined as persistent oliguria and/or sCr elevation after 3 days. RRI and SQC Doppler grade were compared, respectively, between the PAKI and non-PAKI groups. Potential predictors were first tested by univariate logistic regression analysis, and a multivariate model was identified to determine the independent predictive ability of RRI and SQC Doppler grade for the PAKI. Receiver operating characteristic (ROC) analysis was performed to compare the diagnostic accuracy between RRI and SQC Doppler grade in early prediction of PAKI by using AKIN classifications as the reference standard.

Results

Of a total of 67 patients enrolled during the study period, 21 (31.3%) patients suffered from PAKI and 8 (11.9%) patients required dialysis. There are significant differences in RRI (0.80 ± 0.09 vs. 0.70 ± 0.05, P=0.002) and SQC Doppler grade (x²=12.193, P=0.007) between the 2 groups with and without PAKI. Univariate analysis showed that RRI, SQC Doppler grade, length of stay in ICU, time of CPB, and length of stay in hospital were significant predictors of PAKI. RRI and the SQC Doppler grade remained independent predictors of PAKI. Area under the curve (AUC) of RRI was 0.855 (95% CI, 0.74–0.96) with cutoff value 0.725 (sensitivity 90.9% and specificity 71.1%), AUC of SQC Doppler grade was 0.642 (95% CI, 0.49–0.79) with cutoff value grade 2 (sensitivity 50% and specificity 73.3%).

Conclusion

Both postoperative RRI and SQC Doppler grade are independent predictors for PAKI after surgery in AAAD patients. Both postoperative RRI and SQC Doppler grade can be obtained rapidly by bedside ultrasound, which is a good tool for early prediction for postoperative PAKI.

Resistive index as a predictor of early failure of kidney transplantation

Background

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

Methods

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

Results

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

Conclusions

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

Rejection evaluation after renal transplantation using MR diffusion tensor imaging

Background Renal allograft dysfunction monitoring is mainly performed using the serum creatinine (SC) level, Doppler ultrasound (US), or renal biopsy. Recently proposed diffusion-based magnetic resonance imaging (MRI) methods have been explored as new, non-invasive tools for assessing renal function after transplantation. Purpose To investigate the value of fractional anisotropy (FA) measurements in the evaluation of acute rejection cases after renal transplant. Material and Methods Doppler US and MRI diffusion tensor imaging (DTI) were performed in 21 patients with graft dysfunction requiring graft biopsy after renal transplantation and in 21 patients with normal graft function. The MR examinations were performed on a 1.5-T MRI using two b-values (0 and 800 s/mm²). FA values were measured from the cortex and medulla of the transplanted kidney at the upper, middle, and lower poles. Results Twenty-one transplant patients diagnosed with acute rejection (Group 1) were compared to the control group of 21 transplant patients with normal graft function (Group 2). The measured FA values of the medulla were 0.19 ± 0.02 and 0.22 ± 0.05 ( P = 0.017) for Groups 1 and 2, respectively. On the other hand, the measured FA values of the renal cortex were 0.18 ± 0.04 and 0.18 ± 0.04 ( P = 0.97) for Groups 1 and 2, respectively. Conclusion The good correlation between the renal medulla FA values and allograft function shows that MR DTI has potential for non-invasive functional assessment of transplanted kidneys. On the other hand, the renal cortex FA values had no correlation with the allograft function.

The Serial Duplex Index Improves Differential Diagnosis of Acute Renal Transplant Dysfunction

OBJECTIVES

Renal duplex sonography represents a standard noninvasive diagnostic procedure to demonstrate morphologic changes in acute kidney transplant dysfunction. We investigated whether a newly developed serial duplex index (SDI) can differentiate between acute cellular rejection and acute vascular rejection more effectively than the established Doppler parameters of the resistive index (RI) and pulsatility index (PI) in recently transplanted patients.

METHODS

Serial duplex scans of patients with histologically proven acute tubular necrosis (n = 25), acute cellular rejection (n = 28), acute vascular rejection (n = 18), and normal graft function (n = 50, partially protocol biopsied) were retrospectively analyzed. For each patient, the RI, PI, and cortex-pelvis proportion (CPP) were included from the day of biopsy (t0) and 3 to 7 days before biopsy (t-1). The sequential CPP ratio (CPP_t0 /CPP_t-1 ), RI ratio (RI_t0 /RI_t-1 ), and PI ratio (PI_t0 /Pi_t-1 ) were determined. The SDI was calculated as: RI ratio × PI ratio/CPP ratio. The diagnostic accuracy of the SDI was compared with that of the RI and PI ratios.

RESULTS

Selected groups were statistically comparable in all routinely determined transplant parameters. The SDI was significantly different between patients with normal graft function, acute cellular rejection, and acute vascular rejection (P < .01, analysis of variance on ranks), whereas the RI and PI ratios were only significantly different between patients with normal graft function and acute vascular rejection (P < .05, analysis of variance on ranks). The indices' ranges were defined by the 95% confidence intervals between the allograft functions.

CONCLUSIONS

The developed SDI was able to detect acute renal transplant rejection with greater sensitivity and specificity than the RI and PI ratios. Since the SDI distinguishes between acute tubular necrosis, acute cellular rejection, and acute vascular rejection, it might be a supportive tool to indicate renal biopsy.