Yitian Fang

Objectives Normothermic machine perfusion (NMP) provides a platform for pre-transplant kidney quality assessment that is essential for the use of marginal donor kidneys. Laser speckle contrast imaging (LSCI) presents distinct advantages as a real-time and non-contact imaging technique for measuring microcirculation. In this study, we aimed to assess the value of LSCI in visualizing renal cortical perfusion and investigate the additional value of dual-side LSCI measurements compared to single aspect measurement during NMP. Methods Porcine kidneys were obtained from a slaughterhouse and then underwent NMP. LSCI was used to measure one-sided cortical perfusion in the first 100 minutes of NMP. Thereafter, the inferior renal artery branch was occluded to induce partial ischemia and LSCI measurements on both ventral and dorsal sides were performed. Results LSCI fluxes correlated linearly with the renal blood flow (R2=0.90, p<0.001). After renal artery branch occlusion, absence of renal cortical perfusion could be visualized and semi-quantified by LSCI. The overall ischemic area percentage of the ventral and dorsal sides was comparable (median [IQR], 38 [24-43]% versus 29 [17-46]%, p=0.43), but heterogenous patterns between the two aspects were observed. There was a significant difference in oxygen consumption (mean ± SD, 2.57 ± 0.63 versus 1.83 ± 0.49 mLO2/min/100g, p<0.001), urine output (median [IQR], 1.3 [1.1-1.7] versus 0.8 [0.6-1.3] mL/min, p<0.05), LDH (mean ± SD, 768 ± 370 versus 905 ± 401 U/L, p<0.05) and AST (mean ± SD, 352 ± 285 versus 462 ± 383 U/L, p<0.01) before and after renal artery occlusion, while no significant difference was found in creatinine clearance, fractional excretion of sodium, total sodium reabsorption and histological damage. Conclusions LSCI fluxes correlated linearly with renal blood flow during NMP. Renal cortical microcirculation and absent perfusion can be visualized and semi-quantified by LSCI. It provides a relative understanding of perfusion levels, allowing for a qualitative comparison between regions in the kidney. Dual-side LSCI measurements are of added value compared to single aspect measurement and renal function markers. Chapter 3 evaluates the value of photoacoustic (PA) imaging in pre-transplant kidney assessment during NMP. Porcine kidneys (n=22) were monitored using 3D PA imaging during a two-hour NMP session. Based on biochemical analyses of perfusate and urine, the kidneys were categorized into "nonfunctional" and "functional" groups. We quantified oxygenation (sO2) within the renal cortical layers of 2 mm, 4 mm, and 6 mm using two-wavelength PA imaging. Next, receiver operating characteristic (ROC) analysis was performed to determine an optimal cortical layer depth and time point for sO2 quantification to discriminate between functional and non-functional organs. Finally, for each depth, we assessed the correlation between sO2 and creatinine clearance (CrCl), oxygen consumption (VO2), and renal blood flow (RBF). We found that hypoxia of the renal cortex is associated with poor renal function. In addition, the determination of sO2 within the 2 mm depth of the renal cortex after 30 minutes of NMP effectively distinguishes between functional and non-functional kidneys. The non-functional kidneys can be detected with a sensitivity and specificity of 80% and 85% respectively, using the cut-off point of sO2 < 39%. Oxygenation significantly correlated with RBF and VO2 in all kidneys. In functional kidneys, sO2 correlated with CrCl, which was not the case for non-functional kidneys. We conclude that the presented technique has high potential for supporting organ selection for kidney transplantation. Chapter 4 evaluates the utility of power Doppler (PD) imaging for kidney quality assessment during NMP. We analyzed 22 porcine kidneys during a 2-hour NMP session, categorizing them into functional and non-functional groups based on biochemical parameters. We quantified PD signals at cortical depths of 2 mm, 4 mm, and 6 mm. The optimal PD depth and time point for discriminating between functional and non-functional organs were determined using receiver operating characteristic (ROC) analysis. Additionally, correlations between PD signals and creatinine clearance (CrCl), oxygen consumption (VO2), and renal blood flow (RBF) were assessed. Our findings show that kidneys with impaired function exhibit lower PD signal intensity. Specifically, PD measurements at 2 mm cortical depth after 30 minutes of NMP effectively distinguished between functional and non-functional kidneys, achieving a sensitivity of 71% and a specificity of 86% with a cut-off point of 19%. PD signal intensity demonstrated a significant correlation with RBF and VO2 across all kidneys, and with CrCl in functional kidneys. The study concludes that PD imaging has significant potential as a real-time, non-invasive tool for objective kidney quality assessment during NMP. Chapter 5 investigates the impact of arterial perfusion pressure on renal function and injury during NMP. Porcine kidneys (n=20) were exposed to 75 minutes of warm ischemia, simulating donation after circulatory death. Kidneys were randomized to undergo NMP at either subphysiological (40 mmHg, n=10) or physiological (70 mmHg, n=10) arterial pressures for 4 hours. Renal blood flow, oxygen consumption, creatinine clearance, and various injury markers (lactate dehydrogenase, aspartate aminotransferase, neutrophil gelatinase-associated lipocalin) were measured. Histological assessment of acute tubular necrosis was also performed. The results showed that kidneys perfused at physiological pressure had significantly higher renal blood flow and oxygen consumption, and better creatinine clearance, compared to those perfused at subphysiological pressure. While there were no significant differences in injury markers, the histological analysis indicated a trend towards reduced acute tubular necrosis in the physiological pressure group. This study demonstrates that physiological arterial pressure during NMP improves renal performance, suggesting that optimizing perfusion pressure could enhance the viability of marginal kidneys. Chapter 6 examines the safety and efficacy of bariatric surgery in patients with end-stage renal disease (ESRD) undergoing kidney transplantation. This propensity score-matched analysis compared 31 patients who underwent bariatric surgery before kidney transplantation with 31 matched controls, and 14 patients who underwent bariatric surgery after kidney transplantation with 14 matched controls, using data from the Dutch Organ Transplantation Registration. Patients undergoing bariatric surgery before transplantation had a significantly higher one-year survival rate (100% vs. 83.9%, p=0.04) and a lower incidence of delayed graft function (12.9% vs. 45.2%, p=0.01) compared to controls. Patient and graft survival at five years were comparable between groups. For patients undergoing bariatric surgery after transplantation, no significant differences were found in patient or graft survival, or incidence of delayed graft function compared to controls. The study concludes that bariatric surgery prior to kidney transplantation is a safe and effective strategy for obese ESRD patients, improving early post-transplant outcomes. Bariatric surgery after transplantation also appears safe, but without significant additional benefits over matched controls. Chapter 7 evaluates the safety and feasibility of kidney transplantation in patients with aortoiliac stenosis (AIS). This retrospective cohort study analyzed 84 ESRD patients with AIS who underwent kidney transplantation between 2004 and 2021, categorized by the severity of stenosis: mild (1-49%), moderate (50-74%), or severe (≥75%). Patients with severe AIS had significantly higher rates of postoperative complications, including vascular complications (20% vs. 0% in mild, p=0.009) and wound complications (30% vs. 13% in mild, p=0.007). One-year patient survival rates were 95% in mild, 93% in moderate, and 85% in severe AIS groups, while five-year survival rates were 85%, 83%, and 70%, respectively. Graft survival rates followed a similar trend. Despite the higher complication rates in severe AIS, overall patient and graft survival remained acceptable, especially considering the survival advantage compared to dialysis. The study suggests that kidney transplantation in patients with AIS is feasible, but careful preoperative assessment and individualized surgical planning are crucial, particularly in cases of severe stenosis. Chapter 8 investigates the efficacy of simultaneous liver-kidney transplantation (SLKT) compared to liver transplantation alone (LTA) in patients with end-stage liver disease (ESLD) and kidney dysfunction. Using data from the Dutch Organ Transplantation Registration (NOTR) from 2005 to 2018, we conducted a propensity score-matched analysis comparing 61 SLKT recipients with 61 LTA recipients. SLKT recipients had significantly higher rates of one-year patient survival (85.2% vs. 70.5%, p=0.03) and one-year graft survival (80.3% vs. 63.9%, p=0.02) compared to LTA recipients. However, at five years, these differences were no longer significant. Subgroup analysis revealed that the survival benefit of SLKT was most pronounced in patients with severe kidney dysfunction (eGFR <30 mL/min/1.73m2). The study concludes that SLKT provides a short-term survival advantage for ESLD patients with kidney dysfunction, particularly those with severe renal impairment, but this benefit diminishes over the long term. Chapter 9 investigates the impact of the 2017 Organ Procurement and Transplantation Network (OPTN) policy on simultaneous liver-kidney transplantation (SLKT) outcomes. Using OPTN/United Network for Organ Sharing (UNOS) registry data, we compared 4,327 SLKTs with 2,427 liver transplant alone (LTA) recipients before and after the policy change. In patients with pre-transplant eGFR ≥30 mL/min/1.73m2, SLKT offered no survival advantage, as LTA recipients achieved comparable or better long-term survival. Conversely, SLKT significantly reduced post-transplant mortality in patients with pre-transplant eGFR <30 mL/min/1.73m2. After the implementation of the 2017 OPTN policy, which introduced stricter SLKT criteria and a "safety net" for kidneys after liver transplantation, the survival benefit of SLKT observed before the policy change was no longer evident. Only 1.4% of LTA recipients underwent kidney transplantation after liver transplantation with priority under the "safety net." This suggests that the new policy appears to optimize organ allocation by reducing unnecessary SLKTs while maintaining favorable outcomes. Chapter 10 investigated the safety and efficacy of ex situ repair followed by autotransplantation in patients with renal artery aneurysms (RAAs) unsuitable for endovascular treatment. We retrospectively analyzed a Dutch cohort of 9 patients with 11 RAAs who underwent ex situ repair and autotransplantation. Eight RAAs were located at the first bifurcation, one on the main trunk, one on the first branch, and one on the second branch. Nephrectomy was performed via laparoscopy (n=7), robot-assisted laparoscopy (n=1), and laparotomy (n=1). Four (44%) patients developed postoperative complications, including bowel obstruction, delirium, pneumonia, and hydronephrosis due to double-J stent dislocation. The median estimated glomerular filtration rate (eGFR) was 83 mL/min/1.73m2 before transplantation and 88 mL/min/1.73m2 after transplantation. After a mean follow-up of 32 months, the vessels of all autotransplanted kidneys were well patent and functional. These findings suggest that ex situ repair with autotransplantation is a safe and feasible option for complex RAAs when endovascular intervention is not possible. Chapter 11 evaluated the predictive value of intraoperative LSCI-derived imaging features, extracted using a convolutional neural network (CNN), for early graft function after living donor kidney transplantation (LDKT). We performed intraoperative LSCI in 110 LDKTs, with early graft function defined by eGFR at 1 week. Across multiple machine learning algorithms, models integrating clinical variables with CNN-derived LSCI features consistently outperformed models using clinical data alone, in both training and test datasets. CNN attention maps showed physiologically relevant feature localization, and intraoperative LSCI additionally enabled the detection and correction of vascular complications, highlighting its potential to improve both perioperative decision-making and early prediction of transplant outcome. Chapter 12 provides a general discussion of this thesis. This chapter synthesizes the key findings across experimental and clinical studies and highlights strategies for extending transplant eligibility, enhancing kidney quality assessment and envision future perspectives such as organ recondition through NMP and centralized organ hubs to optimize transplant outcomes.