Postoperative Ultrasound in Kidney Transplant Recipients: Association Between Intrarenal Resistance Index and Cardiovascular Events

Atherosclerosis and Intrarenal Resistance Index in Kidney Transplant Recipients

Atherosclerosis of the aortoiliac vessels can adversely affect kidney perfusion after kidney transplantation. Atherosclerosis severity can be determined using the calcium score (CaScore). Potential problems with posttransplantation kidney perfusion can be determined using the intrarenal resistance index (RI). This study investigated the association between aortoiliac CaScore and RI in kidney transplant recipients.

Methods

Kidney transplant recipients (2004-2019), for whom the CaScore and RI were determined, were included in this dual-center cohort study. CaScore was measured in 3 aortoiliac segments using noncontrast CT imaging. RI was determined using Doppler ultrasound. Multivariable linear regression analyses were performed between the CaScore and RI, adjusted for confounding variables.

Results

The mean age of the 389 included patients was 59 (±13) y. The mean RI (unitless) was 0.71 (±0.09)' and the median CaScore (unitless) was 3340 (399-7833). In univariable linear regression analyses with RI as the dependent variable, CaScore (β = 0.011; P < 0.001) was positively associated with RI. Moreover, recipient age (β = 0.014; P < 0.001), history of diabetes (β = 0.029; P = 0.003), recipient history of vascular interventions (β = 0.032; P = 0.002), prior dialysis (β = 0.029; P = 0.003), deceased donor transplantation (β = 0.042; P < 0.001), donation after cardiac death (β = 0.036; P = 0.001), an increase in cold ischemia time (β = 0.011; P < 0.001), and the Comprehensive Complication Index (β = 0.006; P = 0.002) were also positively associated with RI, whereas preoperative recipient diastolic blood pressure (β = -0.007; P = 0.030) was inversely associated. In multivariable analyses, CaScore and RI remained significantly (P = 0.010) associated, independent of adjustment for potential confounders. Furthermore, in univariable linear regression analyses, multiple graft function characteristics were associated with RI.

Conclusions

A significant association was found between CaScore and RI, independent of adjustment for multiple potential confounding factors, leading to a better insight into the development and interpretation of RI. Aortoiliac atherosclerosis should be considered when interpreting the RI and determining the possible cause of malperfusion and graft failure after kidney transplantation.

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.

Ultrasonographic study of hemodynamics and CEUS in the rhesus monkey kidney

Nonhuman primates share many developmental similarities with humans. As the world has recognized the rhesus monkey as a standard experimental monkey, studies of rhesus monkey are very important and essential. The purpose of this study was to use gray-scale ultrasound, color Doppler flow imaging (CDFI), and contrast-enhanced ultrasound (CEUS) to study the ultrasound appearance of adult healthy rhesus monkey kidneys and to investigate the relationship between renal ultrasound manifestations and body weight, gender, and the left and right kidneys. Thirty adult healthy rhesus monkeys were studied in the experiments. The size of the kidney and the length and diameter of the renal artery were measured. The peak systolic velocity (PSV), end diastolic velocity (EDV), and resistance index (RI) of the renal artery and intrarenal arteries were measured by CDFI. In CEUS, the time-intensity curve (TIC) was used to obtain microvascular perfusion parameters. There were significant differences in renal size, diameter and length of the renal artery, and hemodynamics of the renal arteries between the different weight groups. In CEUS, there were significant differences in area under curve (AUC), time from peak to one half (THP), intensity peak (PI), time to peak (TTP), mean transit time (MTT), and wash-in-slope (WIS) between the different weight groups. There were no statistical differences between genders or the left and right kidneys. Our study provides valuable reference data for the studies of the kidney and indicates that CEUS can be used to evaluate renal perfusion in rhesus monkeys.

Introduction of the Grayscale Median for Ultrasound Tissue Characterization of the Transplanted Kidney

Ultrasound examination is advised for early post-kidney transplant assessment. Grayscale median (GSM) quantification is novel in the kidney transplant field, with no systematic assessment previously reported. In this prospective cohort study, we measured the post-operative GSM in a large cohort of adult kidney transplant recipients (KTR) who consecutively underwent Doppler ultrasound directly after transplantation (within 24 h), compared it with GSM in nontransplanted patients, and investigated its association with baseline and follow-up characteristics. B-mode images were used to calculate the GSM in KTR and compared with GSM data in nontransplanted patients, as simulated from summary statistics of the literature using a Mersenne twister algorithm. The association of GSM with baseline and 1-year follow-up characteristics were studied by means of linear regression analyses. In 282 KTR (54 ± 15 years old, 60% male), the median (IQR) GSM was 55 (45–69), ranging from 22 to 124 (coefficient of variation = 7.4%), without differences by type of donation (p = 0.28). GSM in KTR was significantly higher than in nontransplanted patients (p < 0.001), and associated with systolic blood pressure, history of cardiovascular disease, and donor age (std. β = 0.12, −0.20, and 0.13, respectively; p < 0.05 for all). Higher early post-kidney transplant GSM was not associated with 1-year post-kidney transplant function parameters (e.g., measured and estimated glomerular filtration rate). The data provided in this study could be used as first step for further research on the application of early postoperative ultrasound in KTR.

Kidney Transplantation and Diagnostic Imaging: The Early Days and Future Advancements of Transplant Surgery

The first steps for modern organ transplantation were taken by Emerich Ullmann (Vienne, Austria) in 1902, with a dog-to-dog kidney transplant, and ultimate success was achieved by Joseph Murray in 1954, with the Boston twin brothers. In the same time period, the ground-breaking work of Wilhelm C. Röntgen (1895) and Maria Sklodowska-Curie (1903), on X-rays and radioactivity, enabled the introduction of diagnostic imaging. In the years thereafter, kidney transplantation and diagnostic imaging followed a synergistic path for their development, with key discoveries in transplant rejection pathways, immunosuppressive therapies, and the integration of diagnostic imaging in transplant programs. The first image of a transplanted kidney, a urogram with intravenous contrast, was shown to the public in 1956, and the first recommendations for transplantation diagnostic imaging were published in 1958. Transplant surgeons were eager to use innovative diagnostic modalities, with renal scintigraphy in the 1960s, as well as ultrasound and computed tomography in the 1970s. The use of innovative diagnostic modalities has had a great impact on the reduction of post-operative complications in kidney transplantation, making it one of the key factors for successful transplantation. For the new generation of transplant surgeons, the historical alignment between transplant surgery and diagnostic imaging can be a motivator for future innovations.