Prognostic value of intraoperative renal tissue oxygenation measurement on early renal transplant function

Investigation of Different Methods of Intraoperative Graft Perfusion Assessment during Kidney Transplantation for the Prediction of Delayed Graft Function: A Prospective Pilot Trial

Delayed graft function (DGF) after renal transplantation is a relevant clinical problem affecting long-term organ function. The early detection of patients at risk is crucial for postoperative monitoring and treatment algorithms. In this prospective cohort study, allograft perfusion was evaluated intraoperatively in 26 kidney recipients by visual and formal perfusion assessment, duplex sonography, and quantitative microperfusion assessment using O2C spectrometry and ICG fluorescence angiography. The O2C tissue spectrometry device provides a quantitative method of microperfusion assessment that can be employed during kidney transplantation as an easy-to-use and highly sensitive alternative to ICG fluorescence angiography. Intraoperative microvascular flow and velocity in the allograft cortex after reperfusion predicted DGF with a sensitivity of 100% and a specificity of 82%. Threshold values of 57 A.U. for microvascular flow and 13 A.U. for microvascular velocity were identified by an ROC analysis. This study, therefore, confirmed that impairment of microperfusion of the allograft cortex directly after reperfusion was a key indicator for the occurrence of DGF after kidney transplantation. Our results support the combined use of intraoperative duplex sonography, for macrovascular quality control, and quantitative microperfusion assessment, such as O2C spectrometry, for individual risk stratification to guide subsequent postoperative management.

Real-time visualization of renal microperfusion using laser speckle contrast imaging

SIGNIFICANCE

Intraoperative parameters of renal cortical microperfusion (RCM) have been associated with postoperative ischemia/reperfusion injury. Laser speckle contrast imaging (LSCI) could provide valuable information in this regard with the advantage over the current standard of care of being a non-contact and full-field imaging technique.

AIM

Our study aims to validate the use of LSCI for the visualization of RCM on ex vivo perfused human-sized porcine kidneys in various models of hemodynamic changes.

APPROACH

A comparison was made between three renal perfusion measures: LSCI, the total arterial renal blood flow (RBF), and sidestream dark-field (SDF) imaging in different settings of ischemia/reperfusion.

RESULTS

LSCI showed a good correlation with RBF for the reperfusion experiment (0.94  ±  0.02; p  <  0.0001) and short- and long-lasting local ischemia (0.90  ±  0.03; p  <  0.0001 and 0.81  ±  0.08; p  <  0.0001, respectively). The correlation decreased for low flow situations due to RBF redistribution. The correlation between LSCI and SDF (0.81  ±  0.10; p  <  0.0001) showed superiority over RBF (0.54  ±  0.22; p  <  0.0001).

CONCLUSIONS

LSCI is capable of imaging RCM with high spatial and temporal resolutions. It can instantaneously detect local perfusion deficits, which is not possible with the current standard of care. Further development of LSCI in transplant surgery could help with clinical decision making.

Relative decrease in hemoglobin and outcomes in patients undergoing kidney transplantation surgery: A retrospective cohort study

BACKGROUND

Recent surgical literature suggests that a relative decrease in hemoglobin (ΔHb) is predictive of adverse outcomes regardless of the absolute level. We aimed to examine the association between perioperative ΔHb and kidney transplantation (KT) outcomes.

METHODS

This was a retrospective cohort study of transplant recipients, where ΔHb = [Hb0- Hb1Hb0]x 100 (Hb₀ = hemoglobin pre-KT and Hb₁ = lowest hemoglobin 24-h post-KT). The main outcome of interest was immediate graft function (IGF).

RESULTS

Of the 899 eligible patients, 38% experienced IGF, and ΔHb was associated with 36% lower odds of IGF. Also, ΔHb was associated with higher all-cause graft failure and longer length of stay but not death-censored graft failure or mortality. ΔHb ≥30% was the threshold beyond which the odds of IGF were significantly lower even if Hb₁ was ≥7 g/dL.

CONCLUSION

ΔHb is associated with inferior outcomes independent of Hb_1; whether it can be used to guide transfusion practices should be explored.

Effect of Perioperative Optimization of Arterial Oxygen Content and Perfusion Pressure on the Function of the Transplanted Kidney in the Retrospective Study of Excretory Function and Assessment of New Markers of Kidney Damage: IL-18, Neutrophil Gelatinase-Associated Lipocalin, and Clusterin

INTRODUCTION

The concept of anesthesia, in which kidney perfusion is optimized, the use of nephrotoxic drugs is avoided, and general anesthesia with protective and preconditioning properties of the graft is applied, is a key element of the therapeutic strategy in kidney transplantation (KTx).

MATERIAL AND METHOD

A total of 86 patients (mean age: 49.4 ± 14.0 years, 66% men) with end-stage renal disease who underwent KTx between 2012 and 2015 were included in this retrospective study. Our aim was to assess the effect of oxygen content in arterial blood and selected hemodynamic parameters on the graft function and the occurrence of delayed graft failure.

RESULTS

No differences were found in baseline characteristics, indication for transplantation, and surgical technique used among study population. No correlation was found between oxygen delivery exponents and both standard markers of renal function and new biochemical markers (eg, IL-18, clusterin, and neutrophil gelatinase-associated lipocalin [NGAL]).

DISCUSSION

In our study, hemodynamic parameters measured at scheduled intervals did not exceed the physiological range, which might have been the reason for the lack of correlation between the function of graft and the described hemodynamic conditions. At the same time, in the observed ranges of perfusion pressure during optimization of the oxygen content, no correlations were found with the postoperative function of the transplanted kidney. That observation could be a valuable conclusion for reducing the tendency of maintaining high blood pressure with the abuse of catecholamines, especially vasoconstrictors, and volume therapy, whose negative effect on tissue perfusion is unequivocal.

Microcirculation changes in gingival tissue after ultrasonic tooth preparation in beagle dogs

OBJECTIVE

Ultrasonic wave technology is widely used during dental treatments. We previously demonstrated that this method protects the gingival tissue. However, the physiological change on the gingival microvasculature caused by this method remains unclear. The aim of this study was to investigate the relationship between the morphological and physiological effects on gingival microcirculation when preparing teeth, using the conventional dental turbine or ultrasonic method.

METHODOLOGY

The lower premolar teeth of beagle dogs were prepared along the gingival margin by using a dental turbine or ultrasonic wave instrument. Gingival vasculature changes were investigated using scanning electron microscopy for corrosion resin casts. Gingival blood flow at the preparation site was determined simultaneously by laser Doppler flowmetry. These assessments were performed immediately (Day 0), at 7 days and 30 days after tooth preparation.

RESULTS

At day 0, in the turbine group, blood vessels were destroyed and some resin leaked. Furthermore, gingival blood flow at the site was significantly increased. In contrast, the ultrasonic group demonstrated nearly normal vasculature and gingival blood flow similar to the non-prepared group for 30 days after preparation. No significant alterations occurred in gingival circulation 30 days after either preparation; however, the turbine group revealed obvious morphological changes.

CONCLUSIONS

Based on multiple approach analyses, this study demonstrated that ultrasonic waves are useful for microvascular protection in tooth preparation. Compared with a dental turbine, ultrasonic wave instruments caused minimal damage to gingival microcirculation. Tooth preparation using ultrasonic wave instruments could be valuable for protecting periodontal tissue.

Monitoring kidney optical properties during cold storage preservation with spatial frequency domain imaging

Transplantation of kidneys results in delayed graft function in as many as 40% of cases. During the organ transplantation process, donor kidneys undergo a period of cold ischemic time (CIT), where the organ is preserved with a cold storage solution to maintain tissue viability. Some complications observed after grafting may be due to damage sustained to the kidney during CIT. However, the effects due to this damage are not apparent until well after transplant surgery has concluded. To this end, we have used spatial frequency domain imaging (SFDI) to measure spatially resolved optical properties of porcine kidneys over the course of 80-h CIT. During this time, we observed an increase in both reduced scattering (μ s& ' ) and absorption (μa) coefficients. The measured scattering b parameter increased until 24 h of CIT, then returned toward baseline during the remaining duration of the imaging sequence. These results show that the optical properties of kidney tissue change with increasing CIT and suggest that continued investigation into the application of SFDI to kidneys under CIT may lead to the development of a noninvasive method for assessing graft viability.

Quantitative assessment of microperfusion by indocyanine green angiography in kidney transplantation resembles chronic morphological changes in kidney specimens

OBJECTIVE

ICG fluorescence angiography enables a quantitative real-time perfusion assessment in kidney transplantation. The results of intraoperative microperfusion of the kidney allograft were compared to the renal chronicity score in pre-transplantation kidney biopsy specimens. The intrarenal resistance index was calculated by duplex sonography as a method of reference.

METHODS

Seventy-seven patients with end-stage renal disease undergoing kidney transplantation were prospectively included in two centers. Correlation analysis of chronic changes in kidney biopsy specimens and the IN of ICG fluorescence signal were investigated.

RESULTS

The results yielded a significantly negative correlation for the renal chronicity (r = -0.294, P = 0.017) as well as the intestinal fibrosis and tubular atrophy score (r = -0.328, P = 0.007). There was a significant inverse relationship between the IN and the mean RI values of the upper pole of the kidney allograft.

CONCLUSIONS

In summary, fluorescence angiography reflects preexisting morphological changes of the renal cortex. ICG angiography may serve as an alternative method for the assessment of microperfusion of the kidney allograft.

Intraoperative assessment of ureteral and graft reperfusion during robotic kidney transplantation with indocyanine green fluorescence videography

BACKGROUND

The aim of this paper is to report the first preliminary experience with intraoperative indocyanine green (ICG) fluorescence videography (IFV) to assess graft and ureteral reperfusion during robot-assisted kidney transplantation (RAKT).

METHODS

We prospectively collected data from consecutive patients undergoing RAKT and IFV from living-donors at our Institution between January 2017 and April 2018. RAKT was performed following the principles of the Vattikuti-Medanta technique. ICG was injected intravenously after vascular anastomoses to quantitate graft and ureteral fluorescence signal. The signal intensity within selected intraoperative snapshots was evaluated for renal parenchyma, ureter and vascular anastomoses. A systematic review of the English-language literature about the topic was performed according to the PRISMA statement recommendations.

RESULTS

Six patients were included. Neither conversions to open surgery nor major intra- or postoperative complications were recorded. At a median follow-up of 12 months (IQR 8-13), median estimated glomerular filtration rate was 64.2 mL/min/1.73 m2 (IQR 45.3-98.4). Intraoperative quantitative assessment of ICG fluorescence was successful in all patients. Of the five studies selected by our review, mostly prospective studies, all including open KT series. Yet, most studies were limited by lack of quantitative measures of IFV fluorescence.

CONCLUSIONS

IFV during RAKT is feasible and safe and provides a reliable assessment of graft reperfusion. Larger studies are needed to standardize the technique and to evaluate the association between fluorescence signal, ultrasound parameters and postoperative kidney function.

Prognostic value of intraoperative measurements of renal tissue oxygenation and microcirculation on renal function in partial nephrectomy

BACKGROUND

Partial nephrectomy (PNx) can be associated with macrocirculatory and microcirculatory alterations, ultimately leading to acute kidney injury (AKI). Measuring kidney tissue oxygenation (μHbO2) and microcirculation during open PNx might be feasible to early detect these alterations and prevent postoperative AKI.

METHODS

μHbO2 and microcirculation were measured in 45 patients undergoing PNx by reflectance spectrophotometry and laser Doppler flowmetry (O2C™, Lea, Germany), related to ischemia time and tumour size. Pre- and postoperative creatinine levels were determined.

RESULTS

μHbO2 was lower after reperfusion than before clamping (72 vs. 75%), while microcirculation and regional haemoglobin did not differ. Ischemia time was 15.7 min on average. μHbO2 was higher without ischemia (80 vs. 70%, p = 0.109) and in T1a- than T1b-tumours, independent of ischemia time and reperfusion. The renal collecting system (RCS) was opened in 19/45 patients with μHbO2 of 68% after reperfusion compared to 74% with intact RCS. Postoperative complications occurred in 6/45 patients (13%). μHbO2 was 68% before clamping vs. 75% without complications. Serum creatinine of patients with T1b was higher compared to T1a (103 vs. 87 µmol/L). Patients with larger tumours had higher postoperative creatinine levels (173 vs. 124 µmol/L; p = 0.052).

CONCLUSION

We showed for the first time that the method is feasible to monitor renal tissue oxygenation at the level of microcirculation non-invasively and reproducibly during PNx. Tumour size seems to have a decisive influence on oxygenation and postoperative renal function. Our results imply that postoperative complications may be predicted by low intraoperative renal oxygenation and microcirculatory flow measurements.

Prognostic Value of Hemoglobin Concentration and Graft Vein Blood Oxygenation on Renal Transplant Outcomes

OBJECTIVE

Our objective was to investigate vein blood gas levels in the transplanted kidney during surgery as a predictive factor for delayed graft function after renal transplant.

MATERIALS AND METHODS

Sixty patients with renal transplant were enrolled in our study from January 2015 to January 2016. After vessels were declamped posttransplant, blood samples from the transplanted kidney veins were taken and acidosis and oxygenation in these samples were measured. Patients were classified based on acidosis and oxygenation of grafted vein and also hemoglobin concentration. We compared delayed graft function in recipients with acidosis versus normal pH, hypoxia versus normal oxygenation, and hemoglobin less than 10 g/dL versus more than 10 g/dL.

RESULTS

Of 60 patients, 6 (10%) experienced delayed graft function and needed hemodialysis. All patients needing hemodialysis were in the acidotic and hypoxic patient groups. Five of six recipients with delayed graft function had hemoglobin concentration < 10 g/dL. Hospital stay was significantly longer in patients with hypoxia, acidosis, and anemia.

CONCLUSIONS

Vein blood gas measurements of the grafted renal vein during surgery can be easily obtained and applied as a prognostic factor for delayed graft function.

Risk factors and outcomes associated with a higher use of inotropes in kidney transplant recipients

Preservation of adequate perfusion pressures to the graft is a main focus of intraoperative management during kidney transplantation. We undertook this study to investigate the incidence of the higher use of inotropes in kidney transplant recipients and identify the patient outcomes and preoperative and intraoperative variables related to this.We retrospectively analyzed 1053 patients who underwent kidney transplantation at Asan Medical Center between January 2006 and February 2012, stratified by their inotropic score ([dopamine] + [dobutamine] + [epinephrine × 100] + [norepinephrine × 100]) <7 versus ≥7, wherein all doses are expressed as μg/kg/min. We evaluated preoperative characteristics, hemodynamic parameters, and intraoperative variables as well as postoperative outcomes, such as length of hospital stay and 1-year rejection and mortality rate.Receiver-operating characteristic analysis was performed to determine inotropic score to predict 1-year mortality. An inotropic score of 7 had the best combined sensitivity and specificity. An inotropic score ≥7 (137 patients, 13.0%) was significantly more prevalent in older patients, those with polycystic kidney disease, and at a 2nd transplant. Anesthesia time, the amounts of crystalloid and 5% albumin infused, and the need for red blood cell transfusion were significantly higher in the inotropic score ≥7 group. The patients with a higher use of inotropes required longer postoperative hospital stay and experienced a >2-fold higher rejection within the 1st year and a 4-fold higher 1-year mortality rate.A higher use of inotropes in kidney transplant recipients is more prevalent in older patients, those with a 2nd transplant and in patients with polycystic kidney disease as their primary renal disease. The postoperative hospital stay, rejection within the 1st year, and 1-year mortality rate are increased in patients with an inotropic score ≥7.

Targeting Endogenous Repair Pathways after AKI

AKI remains a highly prevalent disease associated with poor short- and long-term outcomes and high costs. Although significant advances in our understanding of repair after AKI have been made over the last 5 years, this knowledge has not yet been translated into new AKI therapies. A consensus conference held by the Acute Dialysis Quality Initiative was convened in April of 2014 and reviewed new evidence on successful kidney repair to identify the most promising pathways that could be translated into new treatments. In this paper, we provide a summary of current knowledge regarding successful kidney repair and offer a framework for conceptualizing the therapeutic targeting that may facilitate this process. We outline gaps in knowledge and suggest a research agenda to more efficiently bring new discoveries regarding repair after AKI to the clinic.

Oxygenation measurement by multi-wavelength oxygen-dependent phosphorescence and delayed fluorescence: catchment depth and application in intact heart

Oxygen delivery and metabolism represent key factors for organ function in health and disease. We describe the optical key characteristics of a technique to comprehensively measure oxygen tension (PO(2)) in myocardium, using oxygen-dependent quenching of phosphorescence and delayed fluorescence of porphyrins, by means of Monte Carlo simulations and ex vivo experiments. Oxyphor G2 (microvascular PO(2)) was excited at 442 nm and 632 nm and protoporphyrin IX (mitochondrial PO(2)) at 510 nm. This resulted in catchment depths of 161 (86) µm, 350 (307) µm and 262 (255) µm respectively, as estimated by Monte Carlo simulations and ex vivo experiments (brackets). The feasibility to detect changes in oxygenation within separate anatomical compartments is demonstrated in rat heart in vivo. Schematic of ex vivo measurements.

Sub-nephrotoxic cisplatin sensitizes rats to acute renal failure and increases urinary excretion of fumarylacetoacetase

Nephrotoxicity limits the therapeutic efficacy of the antineoplastic drug cisplatin. Due to dosage adjustment and appropriate monitoring, most therapeutic courses with cisplatin produce no or minimal kidney damage. However, we studied whether even sub-nephrotoxic dosage of cisplatin poses a potential risk for the kidneys by predisposing to acute kidney injury (AKI), specifically by lowering the toxicity threshold for a second nephrotoxin. With this purpose rats were treated with a single sub-nephrotoxic dosage of cisplatin (3mg/kg, i.p.) and after two days, with a sub-nephrotoxic regime of gentamicin (50mg/kg/day, during 6 days, i.p.). Control groups received only one of the drugs or the vehicle. Renal function and renal histology were monitored throughout the experiment. Cisplatin treatment did not cause any relevant functional or histological alterations in the kidneys. Rats treated with cisplatin and gentamicin, but not those under single treatments, developed an overt renal failure characterized by both renal dysfunction and massive tubular necrosis. In addition, the urinary excretion of fumarylacetoacetase was increased in cisplatin-treated animals at subtoxic doses, which might be exploited as a cisplatin-induced predisposition marker. In fact, the urinary level of fumarylacetoacetase prior to the second nephrotoxin correlated with the level of AKI triggered by gentamicin in predisposed animals.

Physiological biomarkers of acute kidney injury: a conceptual approach to improving outcomes

The past 5-10 years have brought significant advances in the identification and validation of novel biochemical biomarkers in the prevention and treatment of acute kidney injury (AKI). These biochemical biomarkers remain research tools but we anticipate that soon they will be employed in clinical practice. A Consensus Conference held by the Acute Dialysis Quality Initiative (ADQI) recently reviewed the evidence, and identified gaps and a research agenda. Furthermore, at this meeting was the birth of an initiative to comprehensively identify new opportunities to characterize the physiological changes during the course of AKI based upon a conceptual framework for the detection and monitoring of renal ischemia-reperfusion injury. This framework includes a transition from monitoring physiological biomarkers of adequate renal perfusion, to pathophysiologic biomarkers of renal hypoperfusion, and finally biomarkers of kidney cell structural injury/damage. Techniques to measure physiological changes in AKI include several physiological variables that might be used in an interactive way to supplement clinical information and biochemical damage biomarkers in the diagnosis and management of AKI. This review summarizes the spectrum of physiological parameters and potential new physiological methods that enable identification of high-risk patients for AKI, facilitate early diagnosis, and differential diagnosis to guide therapeutic management and prognostication. Finally, we propose a research agenda for the next 5 years to facilitate the development and validation of physiological biomarkers in AKI.