Measurement of renal blood flow by phase-contrast magnetic resonance imaging during septic acute kidney injury: a pilot investigation

Focus on oliguria during renal replacement therapy

Oliguria is a clinical symptom characterized by decreased urine output, which can occur at any stage of acute kidney injury and also during renal replacement therapy. In some cases, oliguria may resolve with adjustment of blood purification dose or fluid management, while in others, it may suggest a need for further evaluation and intervention. It is important to determine the underlying cause of oliguria during renal replacement therapy and to develop an appropriate treatment plan. This review looks into the mechanisms of urine production to investigate the mechanism of oliguria during renal replacement therapy from two aspects: diminished glomerular filtration rate and tubular abnormalities. The above conditions all implying a renal oxygen supply-demand imbalance, which is the signal of worsening kidney injury. It also proposes a viable clinical pathway for the treatment and management of patients with acute kidney injury receiving renal replacement therapy.

Assessment of renal perfusion with 82-rubidium PET in patients with normal and abnormal renal function

BACKGROUND

Noninvasive measurement of renal blood flow (RBF) and renal vascular resistance (RVR) is challenging, yet critical in renal pathologies. This study evaluates the correlation between serum renal function markers and RBF/RVR assessed using rubidium PET.

METHODS

Dynamic images from 53 patients who underwent rubidium PET for nonrenal indications were analyzed. RBF was determined using a one-compartment model, and RVR was calculated by dividing mean arterial pressure by RBF.

RESULTS

The study included 51 patients (31 females and 20 males). Among them, 35 had normal renal function [estimated glomerular filtration rate (eGFR) ≥60 ml/min/1.73 m2], and 16 had abnormal renal function (eGFR <60 ml/min/1.73 m2). Patients with normal renal function had significantly higher RBF [median (interquartile range): 443 (297-722) vs 173 (108-380) ml/min/100 g, P = 0.022] and lower RVR [19.1 (12.4-27.2) vs 49.6 (24.4-85.7) mmHg×min×g/ml, P = 0.0011) compared with those with abnormal renal function. There was a moderate correlation between RBF and eGFR (r = 0.62, P < 0.0001) and between RVR and eGFR (r = -0.59, P < 0.0001) in both groups. Among patients with normal renal function, RBF was negatively correlated with age (r = -0.51, P = 0.0017) but there was no correlation among patients with abnormal renal function (r = 0.21, P = 0.44).

CONCLUSION

PET-measured RBF and RVR correlate with renal function markers and differ significantly by renal function status. Further studies are needed to validate rubidium PET's precision and clinical applicability.

Linear Correlation Between Mean Arterial Pressure and Urine Output in Critically Ill Patients

OBJECTIVE

Mean arterial pressure (MAP) plays a significant role in regulating tissue perfusion and urine output (UO). The optimal MAP target in critically ill patients remains a subject of debate. We aimed to explore the relationship between MAP and UO.

DESIGN

A retrospective observational study.

SETTING

A general ICU in a tertiary medical center.

PATIENTS

All critically ill patients admitted to the ICU for more than 10 hours.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

MAP values and hourly UO were collected in 5,207 patients. MAP levels were categorized into 10 groups of 5 mm Hg (from MAP < 60 mm Hg to MAP > 100 mg Hg), and 656,423 coupled hourly mean MAP and UO measurements were analyzed. Additionally, we compared the UO of individual patients in each MAP group with or without norepinephrine (NE) support or diuretics, as well as in patients with acute kidney injury (AKI).Hourly UO rose incrementally between MAP values of 65-100 mm Hg. Among 2,226 patients treated with NE infusion, mean UO was significantly lower in the MAP less than 60 mm Hg group (53.4 mL/hr; 95% CI, 49.3-57.5) compared with all other groups (p < 0.001), but no differences were found between groups of 75 less than or equal to MAP. Among 2500 patients with AKI, there was a linear increase in average UO from the MAP less than 60 mm Hg group (57.1 mL/hr; 95% CI, 54.2-60.0) to the group with MAP greater than or equal to 100 mm Hg (89.4 mL/hr; 95% CI, 85.7-93.1). When MAP was greater than or equal to 65 mm Hg, we observed a statistically significant trend of increased UO in periods without NE infusion.

CONCLUSIONS

Our analysis revealed a linear correlation between MAP and UO within the range of 65-100 mm Hg, also observed in the subgroup of patients treated with NE or diuretics and in those with AKI. These findings highlight the importance of tissue perfusion to the maintenance of diuresis and achieving adequate fluid balance in critically ill patients.

Fluid accumulation syndrome in sepsis and septic shock: pathophysiology, relevance and treatment-a comprehensive review

In this review, we aimed to comprehensively summarize current literature on pathophysiology, relevance, diagnosis and treatment of fluid accumulation in patients with sepsis/septic shock. Fluid accumulation syndrome (FAS) is defined as fluid accumulation (any degree, expressed as percentage from baseline body weight) with new onset organ-failure. Over the years, many studies have described the negative impact of FAS on clinically relevant outcomes. While the relationship between FAS and ICU outcomes is well described, uncertainty exists regarding its diagnosis, monitoring and treatment. A stepwise approach is suggested to prevent and treat FAS in patients with septic shock, including minimizing fluid intake (e.g., by limiting intravenous fluid administration and employing de-escalation whenever possible), limiting sodium and chloride administration, and maximizing fluid output (e.g., with diuretics, or renal replacement therapy). Current literature implies the need for a multi-tier, multi-modal approach to de-resuscitation, combining a restrictive fluid management regime with a standardized early active de-resuscitation, maintenance fluid reduction (avoiding fluid creep) and potentially using physical measures such as compression stockings.Trial registration: Not applicable.

The REPERFUSE study protocol: The effects of vasopressor therapy on renal perfusion in patients with septic shock-A mechanistically focused randomised control trial

INTRODUCTION

Acute kidney injury (AKI) is a common complication of septic shock and together these conditions carry a high mortality risk. In septic patients who develop severe AKI, renal cortical perfusion is deficient despite normal macrovascular organ blood flow. This intra-renal perfusion abnormality may be amenable to pharmacological manipulation, which may offer mechanistic insight into the pathophysiology of septic AKI. The aim of the current study is to investigate the effects of vasopressin and angiotensin II on renal microcirculatory perfusion in a cohort of patients with septic shock.

METHODS AND ANALYSIS

In this single centre, mechanistically focussed, randomised controlled study, 45 patients with septic shock will be randomly allocated to either of the study vasopressors (vasopressin or angiotensin II) or standard therapy (norepinephrine). Infusions will be titrated to maintain a mean arterial pressure (MAP) target set by the attending clinician. Renal microcirculatory assessment will be performed for the cortex and medulla using contrast-enhanced ultrasound (CEUS) and urinary oxygen tension (pO2), respectively. Renal macrovascular flow will be assessed via renal artery ultrasound. Measurement of systemic macrovascular flow will be performed through transthoracic echocardiography (TTE) and microvascular flow via sublingual incident dark field (IDF) video microscopy. Measures will be taken at baseline, +1 and +24hrs following infusion of the study drug commencing. Blood and urine samples will also be collected at the measurement time points. Longitudinal data will be compared between groups and over time.

DISCUSSION

Vasopressors are integral to the management of patients with septic shock. This study aims to further understanding of the relationship between this therapy, renal perfusion and the development of AKI. In addition, using CEUS and urinary pO2, we hope to build a more complete picture of renal perfusion in septic shock by interrogation of the constituent parts of the kidney. Results will be published in peer-reviewed journals and presented at academic meetings.

TRIAL REGISTRATION

The REPERFUSE study was registered on Clinical Trials.gov (NCT06234592) on the 30th Jan 24.

Imaging-based deep learning in kidney diseases: recent progress and future prospects

Kidney diseases result from various causes, which can generally be divided into neoplastic and non-neoplastic diseases. Deep learning based on medical imaging is an established methodology for further data mining and an evolving field of expertise, which provides the possibility for precise management of kidney diseases. Recently, imaging-based deep learning has been widely applied to many clinical scenarios of kidney diseases including organ segmentation, lesion detection, differential diagnosis, surgical planning, and prognosis prediction, which can provide support for disease diagnosis and management. In this review, we will introduce the basic methodology of imaging-based deep learning and its recent clinical applications in neoplastic and non-neoplastic kidney diseases. Additionally, we further discuss its current challenges and future prospects and conclude that achieving data balance, addressing heterogeneity, and managing data size remain challenges for imaging-based deep learning. Meanwhile, the interpretability of algorithms, ethical risks, and barriers of bias assessment are also issues that require consideration in future development. We hope to provide urologists, nephrologists, and radiologists with clear ideas about imaging-based deep learning and reveal its great potential in clinical practice.Critical relevance statement The wide clinical applications of imaging-based deep learning in kidney diseases can help doctors to diagnose, treat, and manage patients with neoplastic or non-neoplastic renal diseases.Key points• Imaging-based deep learning is widely applied to neoplastic and non-neoplastic renal diseases.• Imaging-based deep learning improves the accuracy of the delineation, diagnosis, and evaluation of kidney diseases.• The small dataset, various lesion sizes, and so on are still challenges for deep learning.

Assessment of Acute Kidney Injury using MRI

There has been growing interest in using quantitative magnetic resonance imaging (MRI) to describe and understand the pathophysiology of acute kidney injury (AKI). The ability to assess kidney blood flow, perfusion, oxygenation, and changes in tissue microstructure at repeated timepoints is hugely appealing, as this offers new possibilities to describe nature and severity of AKI, track the time-course to recovery or progression to chronic kidney disease (CKD), and may ultimately provide a method to noninvasively assess response to new therapies. This could have significant clinical implications considering that AKI is common (affecting more than 13 million people globally every year), harmful (associated with short and long-term morbidity and mortality), and currently lacks specific treatments. However, this is also a challenging area to study. After the kidney has been affected by an initial insult that leads to AKI, complex coexisting processes ensue, which may recover or can progress to CKD. There are various preclinical models of AKI (from which most of our current understanding derives), and these differ from each other but more importantly from clinical AKI. These aspects are fundamental to interpreting the results of the different AKI studies in which renal MRI has been used, which encompass different settings of AKI and a variety of MRI measures acquired at different timepoints. This review aims to provide a comprehensive description and interpretation of current studies (both preclinical and clinical) in which MRI has been used to assess AKI, and discuss future directions in the field. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 3.

Physiologically Based Pharmacokinetic Modeling in Neonates: Current Status and Future Perspectives

Rational drug use in special populations is a clinical problem that doctors and pharma-cists must consider seriously. Neonates are the most physiologically immature and vulnerable to drug dosing. There is a pronounced difference in the anatomical and physiological profiles be-tween neonates and older people, affecting the absorption, distribution, metabolism, and excretion of drugs in vivo, ultimately leading to changes in drug concentration. Thus, dose adjustments in neonates are necessary to achieve adequate therapeutic concentrations and avoid drug toxicity. Over the past few decades, modeling and simulation techniques, especially physiologically based pharmacokinetic (PBPK) modeling, have been increasingly used in pediatric drug development and clinical therapy. This rigorously designed and verified model can effectively compensate for the deficiencies of clinical trials in neonates, provide a valuable reference for clinical research design, and even replace some clinical trials to predict drug plasma concentrations in newborns. This review introduces previous findings regarding age-dependent physiological changes and pathological factors affecting neonatal pharmacokinetics, along with their research means. The application of PBPK modeling in neonatal pharmacokinetic studies of various medications is also reviewed. Based on this, we propose future perspectives on neonatal PBPK modeling and hope for its broader application.

The attributable mortality of sepsis for acute kidney injury: a propensity-matched analysis based on multicenter prospective cohort study

BACKGROUND

Both sepsis and AKI are diseases of major concern in intensive care unit (ICU). This study aimed to evaluate the excess mortality attributable to sepsis for acute kidney injury (AKI).

METHODS

A propensity score-matched analysis on a multicenter prospective cohort study in 18 Chinese ICUs was performed. Propensity score was sequentially conducted to match AKI patients with and without sepsis on day 1, day 2, and day 3-5. The primary outcome was hospital death of AKI patients.

RESULTS

A total of 2008 AKI patients (40.9%) were eligible for the study. Of the 1010 AKI patients with sepsis, 619 (61.3%) were matched to 619 AKI patients in whom sepsis did not develop during the screening period of the study. The hospital mortality rate of matched AKI patients with sepsis was 205 of 619 (33.1%) compared with 150 of 619 (24.0%) for their matched AKI controls without sepsis (p = 0.001). The attributable mortality of total sepsis for AKI patients was 9.1% (95% CI: 4.8-13.3%). Of the matched patients with sepsis, 328 (53.0%) diagnosed septic shock. The attributable mortality of septic shock for AKI was 16.2% (95% CI: 11.3-20.8%, p < 0.001). Further, the attributable mortality of sepsis for AKI was 1.4% (95% CI: 4.1-5.9%, p = 0.825).

CONCLUSIONS

The attributable hospital mortality of total sepsis for AKI were 9.1%. Septic shock contributes to major excess mortality rate for AKI than sepsis.

REGISTRATION FOR THE MULTICENTER PROSPECTIVE COHORT STUDY

registration number ChiCTR-ECH-13003934.

Renal MRI: From Nephron to NMR Signal

Renal diseases pose a significant socio-economic burden on healthcare systems. The development of better diagnostics and prognostics is well-recognized as a key strategy to resolve these challenges. Central to these developments are MRI biomarkers, due to their potential for monitoring of early pathophysiological changes, renal disease progression or treatment effects. The surge in renal MRI involves major cross-domain initiatives, large clinical studies, and educational programs. In parallel with these translational efforts, the need for greater (patho)physiological specificity remains, to enable engagement with clinical nephrologists and increase the associated health impact. The ISMRM 2022 Member Initiated Symposium (MIS) on renal MRI spotlighted this issue with the goal of inspiring more solutions from the ISMRM community. This work is a summary of the MIS presentations devoted to: 1) educating imaging scientists and clinicians on renal (patho)physiology and demands from clinical nephrologists, 2) elucidating the connection of MRI parameters with renal physiology, 3) presenting the current state of leading MR surrogates in assessing renal structure and functions as well as their next generation of innovation, and 4) describing the potential of these imaging markers for providing clinically meaningful renal characterization to guide or supplement clinical decision making. We hope to continue momentum of recent years and introduce new entrants to the development process, connecting (patho)physiology with (bio)physics, and conceiving new clinical applications. We envision this process to benefit from cross-disciplinary collaboration and analogous efforts in other body organs, but also to maximally leverage the unique opportunities of renal physiology. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 2.

Renal hemodynamic evaluation protocol based on the pathophysiological mechanism of acute kidney injury: Critical Care UltraSound Guided-A(KI)BCDE

The multiple etiological characteristics of acute kidney injury (AKI) have brought great challenges to its clinical diagnosis and treatment. Renal injury in critically ill patients always indicates hemodynamic injury. The Critical Care UltraSound Guided (CCUSG)-A(KI)BCDE protocol developed by the Chinese Critical Ultrasound Study Group (CCUSG), respectively, includes A(KI) diagnosis and risk assessment and uses B-mode ultrasound, Color doppler ultrasound, spectral Doppler ultrasound, and contrast Enhanced ultrasound to obtain the hemodynamic characteristics of the kidney so that the pathophysiological mechanism of the occurrence and progression of AKI can be captured and the prognosis of AKI can be predicted combined with other clinical information; therefore, the corresponding intervention and treatment strategies can be formulated to achieve targeted, protocolized, and individualized therapy.

CHIP protects against septic acute kidney injury by inhibiting NLRP3-mediated pyroptosis

Septic acute kidney injury (S-AKI), the most common type of acute kidney injury (AKI), is intimately related to pyroptosis and oxidative stress in its pathogenesis. Carboxy-terminus of Hsc70-interacting protein (CHIP), a U-box E3 ligase, modulates oxidative stress by degrading its targeted proteins. The role of CHIP in S-AKI and its relevance with pyroptosis have not been investigated. In this study, we showed that CHIP was downregulated in renal proximal tubular cells in lipopolysaccharide (LPS)-induced S-AKI. Besides, the extent of redox injuries in S-AKI was attenuated by CHIP overexpression or activation but accentuated by CHIP gene disruption. Mechanistically, our work demonstrated that CHIP interacted with and ubiquitinated NLRP3 to promote its proteasomal degradation, leading to the inhibition of NLRP3/ACS inflammasome-mediated pyroptosis. In summary, this study revealed that CHIP ubiquitinated NLRP3 to alleviate pyroptosis in septic renal injuries, suggesting that CHIP might be a potential therapeutic target for S-AKI.

BENEFIT OF HIGHER BLOOD PRESSURE TARGET IN SEVERE ACUTE KIDNEY INJURY TREATED BY CONTINUOUS RENAL REPLACEMENT THERAPY

ABSTRACT

Introduction : The optimal target of mean arterial pressure (MAP) during continuous renal replacement therapy (CRRT) is unknown. Method : We retrospectively collected the hourly MAP data in acute kidney injury patients requiring CRRT who admitted to the intensive care unit in the University of Tokyo hospital during 2011-2019. Patients who died within 48 h of CRRT start and whose average value of hourly MAPs during the first 48 h was <65 mm Hg were excluded. When the average value of MAP was ≤75 mm Hg or >75 mm Hg, patients were allocated to the low or high target group. We estimated the effect of MAP on mortality and RRT independence at 90 days, using multivariable the Cox regression model and Fine and Gray model. Result : Of the 275 patients we analyzed, 95 patients were in the low group. There are no differences in sex, baseline kidney function, and disease severity. At 90 days, the low target group had higher mortality with 38 deaths (40.0%) compared with 57 deaths (31.7%) in the high target group ( P < 0.05). The adjusted hazard ratio of the low target group (≤75 mm Hg) for mortality was 1.72 (95% CI, 1.08-2.74). In addition, the low target group had a lower rate of RRT independence, with 60 patients (63.2%) compared with 136 patients (75.6%) in the high target group ( P < 0.05). The multivariable analysis revealed that the adjusted hazard ratio of the low target group for RRT independence was 0.74 (95% CI, 0.54-1.01). Conclusion : This study found the association with low MAP and mortality. The association with low MAP and delayed renal recovery was not revealed.

Magnetic Resonance Imaging to Evaluate Kidney Structure, Function, and Pathology: Moving Toward Clinical Application

Recent advances in multiparametric magnetic resonance imaging (MRI) allow multiple quantitative measures to assess kidney morphology, tissue microstructure, oxygenation, kidney blood flow, and perfusion to be collected in a single scan session. Animal and clinical studies have investigated the relationship between the different MRI measures and biological processes, although their interpretation can be complex due to variations in study design and generally small participant numbers. However, emerging themes include the apparent diffusion coefficient derived from diffusion-weighted imaging, T1 and T2 mapping parameters, and cortical perfusion being consistently associated with kidney damage and predicting kidney function decline. Blood oxygen level-dependent (BOLD) MRI has shown inconsistent associations with kidney damage markers but has been predictive of kidney function decline in several studies. Therefore, multiparametric MRI of the kidneys has the potential to address the limitations of existing diagnostic methods to provide a noninvasive, noncontrast, and radiation-free method to assess whole kidney structure and function. Barriers to be overcome to facilitate widespread clinical application include improved understanding of biological factors that impact MRI measures, development of a larger evidence base for clinical utility, standardization of MRI protocols, automation of data analysis, determining optimal combination of MRI measures, and health economic evaluation.

A National Case-Crossover Study on the Risk of Kidney Injury Requiring Dialysis after Sepsis

BACKGROUND

Patients with sepsis-associated acute kidney injury (AKI) are at risk of kidney damage, potentially necessitating acute temporary or chronic dialysis. Our study aims to estimate the odds ratio (OR) of preceding sepsis among patients requiring their first dialysis.

METHODS

A nationwide population-based case-only study was conducted using claims records from the National Health insurance database of Taiwan. All patients over 20 years of age who underwent their first dialysis between 2004 and 2016 were included in the study. The six months prior to their first dialysis served as a self-control period.

RESULTS

The study included 147,201 patients who required acute temporary and 75,031 patients who required chronic dialysis. The odds ratios for patients needing acute temporary dialysis after 1, 2, 3, and 4 weeks of exposure periods were 15.8, 10.7, 9.2, and 8.4, respectively. The ORs for patients requiring chronic dialysis were 7.0, 4.1, 4.2, and 3.7, respectively.

CONCLUSIONS

Our findings indicate that sepsis was substantially associated with an increased risk of renal failure. The risk was highest during the first week following sepsis for both acute temporary and chronic dialysis cases.

Role of the Renin Angiotensin Aldosterone System in the Pathogenesis of Sepsis-Induced Acute Kidney Injury: A Systematic Review

BACKGROUND

Sepsis is a life-threatening condition responsible for up to 20% of all global deaths. Kidneys are among the most common organs implicated, yet the pathogenesis of sepsis-induced acute kidney injury (S-AKI) is not completely understood, resulting in the treatment being nonspecific and responsive. In situations of stress, the renin angiotensin aldosterone system (RAAS) may play a role. This systematic review focuses on analyzing the impact of the RAAS on the development of S-AKI and discussing the use of RAAS antagonists as an emerging therapeutic option to minimize complications of sepsis.

METHODS

Studies were identified using electronic databases (Medline via PubMed, Google Scholar) published within the past decade, comprised from 2014 to 2023. The search strategy was conducted using the following keywords: sepsis, S-AKI, RAAS, Angiotensin II, and RAAS inhibitors. Studies on human and animal subjects were included if relevant to the keywords.

RESULTS

Our search identified 22 eligible references pertaining to the inclusion criteria. Treatment of sepsis with RAAS inhibitor medications is observed to decrease rates of S-AKI, reduce the severity of S-AKI, and offer an improved prognosis for septic patients.

CONCLUSION

The use of RAAS antagonists as a treatment after the onset of sepsis has promising findings, with evidence of decreased renal tissue damage and rates of S-AKI and improved survival outcomes.

REGISTRATION

INPLASY202360098.

The future of intensive care: the study of the microcirculation will help to guide our therapies

The goal of hemodynamic resuscitation is to optimize the microcirculation of organs to meet their oxygen and metabolic needs. Clinicians are currently blind to what is happening in the microcirculation of organs, which prevents them from achieving an additional degree of individualization of the hemodynamic resuscitation at tissue level. Indeed, clinicians never know whether optimization of the microcirculation and tissue oxygenation is actually achieved after macrovascular hemodynamic optimization. The challenge for the future is to have noninvasive, easy-to-use equipment that allows reliable assessment and immediate quantitative analysis of the microcirculation at the bedside. There are different methods for assessing the microcirculation at the bedside; all have strengths and challenges. The use of automated analysis and the future possibility of introducing artificial intelligence into analysis software could eliminate observer bias and provide guidance on microvascular-targeted treatment options. In addition, to gain caregiver confidence and support for the need to monitor the microcirculation, it is necessary to demonstrate that incorporating microcirculation analysis into the reasoning guiding hemodynamic resuscitation prevents organ dysfunction and improves the outcome of critically ill patients.

Associations of systolic blood pressure and in-hospital mortality in critically ill patients with acute kidney injury

PURPOSE

Although systolic blood pressure (SBP) is associated with acute renal injury (AKI), the relationship between baseline SBP and prognosis in critically ill patients with AKI is unclear. We aimed to assess the linearity and profile of the relationship between SBP at intensive care unit (ICU) admission and in-hospital mortality in these patients.

METHODS

Data of AKI patients in the ICU settings were extracted from the Medical Information Mart for Intensive Care III database. The association between seven SBP categories (< 100, 100-109, 110-119, 120-129, 130-139, 140-149, and ≥ 150 mmHg) and all-cause in-hospital mortality was assessed by Cox proportional hazard models. Restricted cubic spline analysis for the multivariate Cox model was performed to explore the shape of the relationship between SBP and mortality.

RESULTS

A total of 24,202 patients with AKI were included in this study. A typically U-shaped relationship was found between SBP at admission and in-hospital mortality. Among all SBP categories, the lowest risk of death was observed in patients with SBP around 110-119 mmHg, whereas the highest was noted in patients with extremely low SBP (< 100 mmHg), followed by those with extremely high SBP (≥ 150 mmHg). SBP showed a significant interaction with vasopressor use and AKI stage in relation to the risk of in-hospital mortality.

CONCLUSIONS

SBP upon admission showed a non-linear association with all-cause in-hospital mortality in critically ill patients with AKI. Patients with low or high SBP show an increased risk of mortality compared to patients with normal SBP.

Ultrasound localization microscopy of the human kidney allograft on a clinical ultrasound scanner

Chronic kidney disease is a major medical problem, causing more than a million deaths each year worldwide. Peripheral kidney microvascular damage characterizes most chronic kidney diseases, yet noninvasive and quantitative diagnostic tools to measure this are lacking. Ultrasound Localization Microscopy (ULM) can assess tissue microvasculature with unprecedented resolution. Here, we optimized methods on 35 kidney transplants and studied the feasibility of ULM in seven human kidney allografts with a standard low frame rate ultrasound scanner to access microvascular damage. Interlobar, arcuate, cortical radial vessels, and part of the medullary organization were visible on ULM density maps. The medullary vasa recta can be seen but are not as clear as the cortical vessels. Acquisition parameters were derived from Contrast-Enhanced Ultrasound examinations by increasing the duration of the recorded clip at the same plane. ULM images were compared with Color Doppler, Advanced Dynamic Flow, and Superb Microvascular Imaging with a contrast agent. Despite some additional limitations due to movement and saturation artifacts, ULM identified vessels two to four times thinner compared with Doppler modes. The mean ULM smallest analyzable vessel cross section was 0.3 ± 0.2 mm in the seven patients. Additionally, ULM was able to provide quantitative information on blood velocities in the cortical area. Thus, this proof-of-concept study has shown ULM to be a promising imaging technique for qualitative and quantitative microvascular assessment. Imaging native kidneys in patients with kidney diseases will be needed to identify their ULM biomarkers.

Reliability of rubidium-82 PET/CT for renal perfusion determination in healthy subjects

Background

Changes in renal perfusion may play a pathophysiological role in hypertension and kidney disease, however to date, no method for renal blood flow (RBF) determination in humans has been implemented in clinical practice. In a previous study, we demonstrated that estimation of renal perfusion based on a single positron emission tomography/computed tomography (PET/CT) scan with Rubidium-82 (82Rb) is feasible and found an approximate 5% intra-assay coefficient of variation for both kidneys, indicative of a precise method.This study’s aim was to determine the day-to day variation of 82Rb PET/CT and to test the method’s ability to detect increased RBF induced by infusion of amino acids.

Methods

Seventeen healthy subjects underwent three dynamic 82Rb PET/CT scans over two examination days comprising: Day A, a single 8-minute dynamic scan and Day B, two scans performed before (baseline) and after RBF stimulation by a 2-hour amino acid-infusion. The order of examination days was determined by randomization. Time activity curves for arterial and renal activity with a 1-tissue compartment model were used for flow estimation; the K1 kinetic parameter representing renal 82Rb clearance. Day-to-day variation was calculated based on the difference between the unstimulated K1 values on Day A and Day B and paired t-testing was performed to compare K1 values at baseline and after RBF stimulation on Day B.

Results

Day-to-day variation was observed to be 5.5% for the right kidney and 6.0% for the left kidney (n = 15 quality accepted scans). K1 values determined after amino acid-infusion were significantly higher than pre-infusion values (n = 17, p = 0.001). The mean percentage change in K1 from baseline was 13.2 ± 12.9% (range − 10.4 to 35.5) for the right kidney; 12.9 ± 13.2% (range − 15.7 to 35.3) for the left kidney.

Conclusion

Day-to-day variation is acceptably low. A significant K1 increase from baseline is detected after application of a known RBF stimulus, indicating that 82Rb PET/CT scanning can provide a precise method for evaluation of RBF and it is able to determine changes herein.

Clinical Trial Registration

EU Clinical Trials Register, 2017-005008-88. Registered 18/01/2018.

Sepsis-induced AKI: From pathogenesis to therapeutic approaches

Sepsis is a heterogenous and highly complex clinical syndrome, which is caused by infectious or noninfectious factors. Acute kidney injury (AKI) is one of the most common and severe complication of sepsis, and it is associated with high mortality and poor outcomes. Recent evidence has identified that autophagy participates in the pathophysiology of sepsis-associated AKI. Despite the use of antibiotics, the mortality rate is still at an extremely high level in patients with sepsis. Besides traditional treatments, many natural products, including phytochemicals and their derivatives, are proved to exert protective effects through multiple mechanisms, such as regulation of autophagy, inhibition of inflammation, fibrosis, and apoptosis, etc. Accumulating evidence has also shown that many pharmacological inhibitors might have potential therapeutic effects in sepsis-induced AKI. Hence, understanding the pathophysiology of sepsis-induced AKI may help to develop novel therapeutics to attenuate the complications of sepsis and lower the mortality rate. This review updates the recent progress of underlying pathophysiological mechanisms of sepsis-associated AKI, focuses specifically on autophagy, and summarizes the potential therapeutic effects of phytochemicals and pharmacological inhibitors.

Decreased renal perfusion during acute kidney injury in critical COVID-19 assessed by magnetic resonance imaging: a prospective case control study

BACKGROUND

Renal hypoperfusion has been suggested to contribute to the development of acute kidney injury (AKI) in critical COVID-19. However, limited data exist to support this. We aim to investigate the differences in renal perfusion, oxygenation and water diffusion using multiparametric magnetic resonance imaging in critically ill COVID-19 patients with and without AKI.

METHODS

A prospective case-control study where patients without prior kidney disease treated in intensive care for respiratory failure due to COVID-19 were examined. Kidney Disease: Improving Global Outcomes Creatinine criteria were used for group allocation. Main comparisons were tested using Mann-Whitney U test.

RESULTS

Nineteen patients were examined, ten with AKI and nine without AKI. Patients with AKI were examined in median 1 [0-2] day after criteria fulfillment. Age and baseline Plasma-Creatinine were similar in both groups. Total renal blood flow was lower in patients with AKI compared with patients without (median 645 quartile range [423-753] vs. 859 [746-920] ml/min, p = 0.037). Regional perfusion was reduced in both cortex (76 [51-112] vs. 146 [123-169] ml/100 g/min, p = 0.015) and medulla (28 [18-47] vs. 47 [38-73] ml/100 g/min, p = 0.03). Renal venous saturation was similar in both groups (72% [64-75] vs. 72% [63-84], ns.), as was regional oxygenation (R₂*) in cortex (17 [16-19] vs. 17 [16-18] 1/s, ns.) and medulla (29 [24-39] vs. 27 [23-29] 1/s, ns.).

CONCLUSIONS

In critically ill COVID-19 patients with AKI, the total, cortical and medullary renal blood flows were reduced compared with similar patients without AKI, whereas no differences in renal oxygenation were demonstrable in this setting. Trial registration ClinicalTrials ID: NCT02765191 , registered May 6 2014 and updated May 7 2020.

Cardiovascular Mapping in Cirrhosis From the Compensated Stage to Hepatorenal Syndrome: A Magnetic Resonance Study

INTRODUCTION

Arterial vasodilation and hyperdynamic circulation are considered hallmarks of the pathophysiological mechanisms of decompensation in cirrhosis. However, detailed characterization of peripheral, splanchnic, renal, and cardiac hemodynamic have not previously been published in a spectrum from healthy stage to advanced decompensated liver disease with hepatorenal syndrome-acute kidney injury (HRS-AKI).

METHODS

We included 87 patients with cirrhosis and 27 healthy controls in this prospective cohort study. The population comprised patients with compensated cirrhosis (n = 27) and decompensated cirrhosis (n = 60); patients with decompensated cirrhosis were further separated into subsets of responsive ascites (33), refractory ascites (n = 16), and HRS-AKI (n = 11). We measured portal pressure and assessed regional blood flow by magnetic resonance imaging.

RESULTS

Patients with compensated cirrhosis experienced higher azygos venous flow and higher hepatic artery flow fraction of cardiac index than controls ( P &lt; 0.01), but other flow parameters were not significantly different. Patients with decompensated cirrhosis experienced significantly higher cardiac index ( P &lt; 0.01), higher superior mesenteric artery flow ( P = 0.01), and lower systemic vascular resistance ( P &lt; 0.001) compared with patients with compensated cirrhosis. Patients with HRS-AKI had the highest cardiac output and lowest renal flow of all groups ( P &lt; 0.01 and P = 0.02, respectively). Associations of single hemodynamic parameters were stronger with model for end-stage liver disease than with portal pressure.

DISCUSSION

The regional cardiocirculatory changes seem closely linked to clinical symptoms with 3 distinguished hemodynamic stages from compensated to decompensated cirrhosis and, finally, to HRS-AKI. The attenuated renal perfusion despite high cardiac output in patients with HRS-AKI challenges the prevailing pathophysiological hypothesis of cardiac dysfunction as a causal factor in HRS-AKI. Finally, magnetic resonance imaging seems an accurate and reliable noninvasive method to assess hemodynamics and has potential as a diagnostic tool in patients with cirrhosis.

Programmed Cell Death in Sepsis Associated Acute Kidney Injury

Sepsis-associated acute kidney injury (SA-AKI) is common in patients with severe sepsis, and has a high incidence rate and high mortality rate in ICU patients. Most patients progress to AKI before drug treatment is initiated. Early studies suggest that the main mechanism of SA-AKI is that sepsis leads to vasodilation, hypotension and shock, resulting in insufficient renal blood perfusion, finally leading to renal tubular cell ischemia and necrosis. Research results in recent years have shown that programmed cell death such as apoptosis, necroptosis, pyroptosis and autophagy play important roles. In the early stage of sepsis-related AKI, autophagy bodies form and inhibit various types of programmed cell death. With the progress of disease, programmed cell death begins. Apoptosis promoter represents caspase-8-induced apoptosis and apoptosis effector represents caspase-3-induced apoptosis, however, caspase-11 and caspase-1 regulate gasdermin D-mediated pyroptosis. Caspase-8 and receptor interacting kinase 1 bodies mediate necroptosis. This review focuses on the pathophysiological mechanisms of various programmed cell death in sepsis-related AKI.

Diagnostic value of ultrasound and contrast-enhanced ultrasound in septic acute kidney injury

PURPOSE

This study aimed to explore the clinical value of ultrasonic Doppler examination and contrast-enhanced ultrasound (US) in the circulation of septic acute kidney injury (AKI).

METHODS

Patients with intensive care unit-related infection were divided into AKI group and control groups. The AKI group was divided into three subgroups according to the serum creatinine value: stage 1, stage 2, and stage 3. Relevant parameters and blood flow of the renal artery were measured, and further contrast-enhanced US was performed and time-intensity curve was analyzed.

RESULTS

The renal blood flow (RBF) and time-averaged velocity decreased significantly in the AKI group compared with the control group (p = .021 and p = .001). The peak value decreased and time to peak (TTP) prolonged in the AKI group (p < .001). With the aggravation of the disease, the RBF decreased slightly among subgroups (p = 0.124). However, the peak value gradually decreased and the TTP prolonged (all p < .05). The multiple linear regression model showed that only PI, RI, and TTP were independently and linearly correlated with the serum creatinine value.

CONCLUSIONS

Doppler US and contrast-enhanced US are of great help in the detection of condition changes and prognosis of patients with sepsis-induced AKI.

Maresin conjugates in tissue regeneration-1 suppresses ferroptosis in septic acute kidney injury

Background

Ferroptosis is unique among different types of regulated cell death and closely related to organ injury. Whether ferroptosis occurs in sepsis-associated acute kidney injury (SA-AKI) is not clear. Nuclear factor-erythroid-2-related factor 2 (Nrf2) is crucial to the regulation of ferroptosis. We and others have shown that Maresin conjugates in tissue regeneration 1 (MCTR1) or other members of specialized pro-resolving mediators (SPMs) can actively regulate inflammation resolution and protect organs against injury in inflammatory diseases by activating the Nrf2 signaling. The aim of this study was to determine whether ferroptosis occurs in SA-AKI. Furthermore, we investigated the potential role and mechanism of MCTR1 in the regulation of ferroptosis in SA-AKI, which mainly focus on the Nrf2 signaling.

Results

We demonstrated for the first time that ferroptosis is present in SA-AKI. Moreover, MCTR1 effectively suppressed ferroptosis in SA-AKI. Meanwhile, MCTR1 upregulated the expression of Nrf2 in the kidney of septic mice. Nrf2 inhibitor ML-385 reversed MCTR1-regulated ferroptosis and AKI, implying that Nrf2 is involved in the inhibitory effects of MCTR1 on ferroptosis in SA-AKI. Further, MCTR1 inhibited ferroptosis and elevated the expression of Nrf2 in LPS-induced HK-2 cells. However, Nrf2 siRNA offset the effect of MCTR1 on ferroptosis. Finally, we observed that MCTR1 ameliorates multi-organ injury and improves survival in animal models of sepsis.

Conclusions

These data demonstrate that MCTR1 suppresses ferroptosis in SA-AKI through the Nrf2 signaling. Our study enriches the pathophysiological mechanism of SA-AKI and provides new therapeutic ideas and potential intervention targets for SA-AKI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00734-x.

Innovations and Emerging Therapies to Combat Renal Cell Damage: NAD+ As a Drug Target

Significance: Acute kidney injury (AKI) is a common and life-threatening complication in hospitalized and critically ill patients. It is defined by an abrupt deterioration in renal function, clinically manifested by increased serum creatinine levels, decreased urine output, or both. To execute all its functions, namely excretion of waste products, fluid/electrolyte balance, and hormone synthesis, the kidney requires incredible amounts of energy in the form of adenosine triphosphate. Recent Advances: Adequate mitochondrial functioning and nicotinamide adenine dinucleotide (NAD+) homeostasis are essential to meet these high energetic demands. NAD+ is a ubiquitous essential coenzyme to many cellular functions. NAD+ as an electron acceptor mediates metabolic pathways such as oxidative phosphorylation (OXPHOS) and glycolysis, serves as a cosubstrate of aging molecules (i.e., sirtuins), participates in DNA repair mechanisms, and mediates mitochondrial biogenesis. Critical Issues: In many forms of AKI and chronic kidney disease, renal function deterioration has been associated with mitochondrial dysfunction and NAD+ depletion. Based on this, therapies aiming to restore mitochondrial function and increase NAD+ availability have gained special attention in the last two decades. Future Directions: Experimental and clinical studies have shown that by restoring mitochondrial homeostasis and increasing renal tubulo-epithelial cells, NAD+ availability, AKI incidence, and chronic long-term complications are significantly decreased. This review covers some general epidemiological and pathophysiological concepts; describes the role of mitochondrial homeostasis and NAD+ metabolism; and analyzes the underlying rationale and role of NAD+ aiming therapies as promising preventive and therapeutic strategies for AKI. Antioxid. Redox Signal. 35, 1449-1466.

[Acute kidney injury in intensive care unit: A review]

Acute kidney injury is a common complication in intensive care unit. Its incidence is variable according to the studies. It is considered to occur in more than 50 % of patients. Acute kidney injury is responsible for an increase in morbidity (length of hospitalization, renal replacement therapy) but also for excess mortality. The commonly accepted definition of acute kidney injury comes from the collaborative workgroup named Kidney Disease: Improving Global Outcomes (KDIGO). It made it possible to standardize practices and raise awareness among practitioners about monitoring plasma creatinine and also diuresis. Acute kidney injury in intensive care unit is a systemic disease including circulatory, endothelial, epithelial and cellular function involvement and an acute kidney injury is not accompanied by ad integrum repair. After prolonged injury, inadequate repair begins with a fibrotic process. Several mechanisms are involved (cell cycle arrest, epithelial-mesenchymal transition, mitochondrial dysfunction) and result in improper repair. A continuum exists between acute kidney disease and chronic kidney disease, characterized by different renal recovery phenotypes. Thus, preventive measures to prevent the occurrence of kidney damage play a major role in management. The nephrologist must be involved at every stage, from the prevention of the first acute kidney injury (upon arrival in intensive care unit) to long-term follow-up and the care of a chronic kidney disease.

Renal histopathology in critically ill patients with Septic Acute Kidney Injury(S-AKI)

PURPOSE

To describe the kidney histopathology of patients with S-AKI and correlate the histological findings with AKI severity, presence of septic shock, and the degree of multiple organic dysfunction (MOD) using the SOFA score.

MATERIALS AND METHODS

This was a prospective, observational, and analytical study of a cohort of critically ill patients with S-AKI who died from sepsis at the "Hospital Español" intensive care unit (ICU). Kidney necropsies were performed within 2 h after death.

RESULTS

We considered twenty (20) patients, with all of them exhibiting S-AKI stage 3 at the same time. In renal histopathology analysis, nonspecific tubulointerstitial (TI) lesions were found in almost all patients (95%). The more frequently found nonspecific TI lesions involved leukocyte infiltration (85%). Necrotic TI lesions were found in 6 patients (30%), and necrotic tubular cell casts were the most frequent lesions (50% of patients). It was not possible to demonstrate an association between the presence of necrotic TI lesions and factors such as the APACHE II score, the global SOFA score, ICU stays, AKI length and renal replacement therapy (RRT).

CONCLUSIONS

The main histopathological findings in kidney necropsies in patients with S-AKI KDIGO 3, showed nonspecific TI lesions, and TI necrosis was only observed in 30% of the cases; therefore, S-AKI cannot be considered to be synonymous with acute tubular necrosis (ATN).

Will advances in functional renal magnetic resonance imaging translate to the nephrology clinic?

Characterizing structural and tissue abnormalities of the kidney is fundamental to understanding kidney disease. Functional multi-parametric renal magnetic resonance imaging (MRI) is a noninvasive imaging strategy whereby several sequences are employed within a single session to quantify renal perfusion, tissue oxygenation, fibrosis, inflammation, and oedema without using ionizing radiation. In this review, we discuss evidence surrounding its use in several clinical settings including acute kidney injury, chronic kidney disease, hypertension, polycystic kidney disease and around renal transplantation. Kidney size on MRI is already a validated measure for making therapeutic decisions in the setting of polycystic kidney disease. Functional MRI sequences, T1 mapping and apparent diffusion coefficient, can non-invasively quantify interstitial fibrosis and so may have a near-future role in the nephrology clinic to stratify the risk of progressive chronic kidney disease or transplant dysfunction. Beyond this, multi-parametric MRI may be used diagnostically, for example differentiating inflammatory versus ischaemic causes of renal dysfunction, but this remains to be proven. Changes in MRI properties of kidney parenchyma may be useful surrogate markers to use as end points in clinical trials to assess if drugs prevent renal fibrosis or alter kidney perfusion. Large, multi-centre studies of functional renal MRI are ongoing which aim to provide definitive answers as to its role in the management of patients with renal dysfunction.

Renal Replacement Techniques in Septic Shock

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to an infection; it carries a risk for mortality, considerably exceeding that of a mere infection. Sepsis is the leading cause for acute kidney injury (AKI) and the requirement for renal replacement therapy (RRT) in intensive care unit (ICU) patients. Almost every second critically ill patient with sepsis will develop AKI. In septic shock, the dysregulated host response to infectious pathogens leads to a cytokine storm with uncontrolled production and release of humoral proinflammatory mediators that evoke cellular toxicity and promote the development of organ dysfunction and increased mortality. In addition to treating AKI, RRT techniques can be employed for extracorporeal adsorption of inflammatory mediators using specifically developed adsorption membranes, hemoperfusion sorbent cartridges or columns; these techniques are intended to decrease the level and early deleterious effects of circulating proinflammatory cytokines and endotoxins during the first hours and days of septic shock treatment, in order to improve patient outcomes. Several methods and devices, such as high cut-off membranes, the Oxiris®-AN69 membrane, CytoSorb® and HA380 cytokine hemoadsorption, polymyxin B endotoxin adsorption, and plasmapheresis have been examined in small study series or are under evaluation as ways of improving patient outcomes in septic shock. However, to date, the data on actual outcome benefits have remained controversial, as discussed in this review.

Recent advances in the pharmacological management of sepsis-associated acute kidney injury

INTRODUCTION

Acute kidney injury is a common occurrence in patients with sepsis and portends a high mortality as well as increased morbidity with numerous sequelae including the development of chronic kidney disease. Currently, there are no specific therapies that either prevent AKI or hasten its recovery. Thus, clinicians typically rely on management of the underlying infection, optimization of hemodynamic parameters as well as avoidance of nephrotoxins to maximize outcomes.

AREAS COVERED

Recent advances in understanding the mechanisms of sepsis as well as how these pathways may interact to lead to acute kidney injury have opened the door to the development of new, targeted therapies. This review focuses on the operative pathways in sepsis that have been identified as critical in leading to acute kidney injury and associated therapeutic agents that target these pathways.

EXPERT OPINION

Despite increased understanding of the pathogenesis of sepsis, development of effective therapeutics to decrease the incidence of AKI have lagged. This is likely due to the complex pathophysiology with overlapping pathways and need for multiple therapies guided by specific biomarkers. Biomarkers that detail operative pathways may be able to guide the institution of more specific therapies with the hope for improved outcomes.

Estimation of renal perfusion based on measurement of rubidium-82 clearance by PET/CT scanning in healthy subjects

Background

Changes in renal blood flow (RBF) may play a pathophysiological role in hypertension and kidney disease. However, RBF determination in humans has proven difficult. We aimed to confirm the feasibility of RBF estimation based on positron emission tomography/computed tomography (PET/CT) and rubidium-82 (⁸²Rb) using the abdominal aorta as input function in a 1-tissue compartment model.

Methods

Eighteen healthy subjects underwent two dynamic ⁸²Rb PET/CT scans in two different fields of view (FOV). FOV-A included the left ventricular blood pool (LVBP), the abdominal aorta (AA) and the majority of the kidneys. FOV-B included AA and the kidneys in their entirety. In FOV-A, an input function was derived from LVBP and from AA, in FOV-B from AA. One-tissue compartmental modelling was performed using tissue time activity curves generated from volumes of interest (VOI) contouring the kidneys, where the renal clearance of ⁸²Rb is represented by the K₁ kinetic parameter. Total clearance for both kidneys was calculated by multiplying the K₁ values with the volume of VOIs used for analysis. Intra-assay coefficients of variation and inter-observer variation were calculated.

Results

For both kidneys, K₁ values derived from AA did not differ significantly from values obtained from LVBP, neither were significant differences seen between AA in FOV-A and AA in FOV-B, nor between the right and left kidneys. For both kidneys, the intra-assay coefficients of variation were low (~ 5%) for both input functions. The measured K₁ of 2.80 ml/min/cm³ translates to a total clearance for both kidneys of 766 ml/min/1.73 m².

Conclusion

Measurement of renal perfusion based on PET/CT and ⁸²Rb using AA as input function in a 1-tissue compartment model is feasible in a single FOV. Based on previous studies showing ⁸²Rb to be primarily present in plasma, the measured K₁ clearance values are most likely representative of effective renal plasma flow (ERPF) rather than estimated RBF values, but as the accurate calculation of total clearance/flow is very much dependent on the analysed volume, a standardised definition for the employed renal volumes is needed to allow for proper comparison with standard ERPF and RBF reference methods.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00389-0.

DHHC21 deficiency attenuates renal dysfunction during septic injury

Renal dysfunction is one of the most common complications of septic injury. One critical contributor to septic injury-induced renal dysfunction is renal vascular dysfunction. Protein palmitoylation serves as a novel regulator of vascular function. Here, we examined whether palmitoyl acyltransferase (PAT)-DHHC21 contributes to septic injury-induced renal dysfunction through regulating renal hemodynamics. Multispectral optoacoustic imaging showed that cecal ligation and puncture (CLP)-induced septic injury caused impaired renal excretion, which was improved in DHHC21 functional deficient (Zdhhc21^dep/dep) mice. DHHC21 deficiency attenuated CLP-induced renal pathology, characterized by tissue structural damage and circulating injury markers. Importantly, DHHC21 loss-of-function led to better-preserved renal perfusion and oxygen saturation after CLP. The CLP-caused reduction in renal blood flow was also ameliorated in Zdhhc21^dep/dep mice. Next, CLP promoted the palmitoylation of vascular α1-adrenergic receptor (α1AR) and the activation of its downstream effector ERK, which were blunted in Zdhhc21^dep/dep mice. Vasoreactivity analysis revealed that renal arteries from Zdhhc21^dep/dep mice displayed reduced constriction response to α1AR agonist phenylephrine compared to those from wild-type mice. Consistently, inhibiting PATs with 2-bromopalmitate caused a blunted vasoconstriction response to phenylephrine in small arteries isolated from human kidneys. Therefore, DHHC21 contributes to impaired renal perfusion and function during septic injury via promoting α1AR palmitoylation-associated vasoconstriction.

Sepsis-Pathophysiology and Therapeutic Concepts

Sepsis is a life-threatening condition and a global disease burden. Today, the heterogeneous syndrome is defined as severe organ dysfunction caused by a dysregulated host response to infection, with renewed emphasis on immune pathophysiology. Despite all efforts of experimental and clinical research during the last three decades, the ability to positively influence course and outcome of the syndrome remains limited. Evidence-based therapy still consists of basic causal and supportive measures, while adjuvant interventions such as blood purification or targeted immunotherapy largely remain without proof of effectiveness so far. With this review, we aim to provide an overview of sepsis immune pathophysiology, to update the choice of therapeutic approaches targeting different immunological mechanisms in the course of sepsis and septic shock, and to call for a paradigm shift from the pathogen to the host response as a potentially more promising angle.

Current Development and Applications of Super-Resolution Ultrasound Imaging

Abnormal changes of the microvasculature are reported to be key evidence of the development of several critical diseases, including cancer, progressive kidney disease, and atherosclerotic plaque. Super-resolution ultrasound imaging is an emerging technology that can identify the microvasculature noninvasively, with unprecedented spatial resolution beyond the acoustic diffraction limit. Therefore, it is a promising approach for diagnosing and monitoring the development of diseases. In this review, we introduce current super-resolution ultrasound imaging approaches and their preclinical applications on different animals and disease models. Future directions and challenges to overcome for clinical translations are also discussed.

Pathogenesis of Acute Kidney Injury in Coronavirus Disease 2019

Since the outbreak of Coronavirus Disease 2019 (COVID-19) in Wuhan, China, in December of 2019, it has rapidly become a global pandemic. Although acute respiratory disorder is the main manifestation of COVID-19, acute kidney injury (AKI) is another important extrapulmonary complication, which has a critical impact on the prognosis and mortality of patients. Current understanding about the exact pathogenesis of AKI in COVID-19 is unclear. Several studies have suggested that intrarenal, pre-renal and post-renal factors mediated collaboratively by direct virus attack, overloaded immune responses, drugs, sepsis, coagulation dysfunction, and underlying diseases may all be involved in the pathogenesis of AKI. This article reviews the current understanding of the pathogenesis of AKI in COVID-19.

Sepsis-Associated Acute Kidney Injury

Sepsis-associated acute kidney injury (S-AKI) is a common and life-threatening complication in hospitalized and critically ill patients. It is characterized by rapid deterioration of renal function associated with sepsis. The pathophysiology of S-AKI remains incompletely understood, so most therapies remain reactive and nonspecific. Possible pathogenic mechanisms to explain S-AKI include microcirculatory dysfunction, a dysregulated inflammatory response, and cellular metabolic reprogramming. In addition, several biomarkers have been developed in an attempt to improve diagnostic sensitivity and specificity of S-AKI. This article discusses the current understanding of S-AKI, recent advances in pathophysiology and biomarker development, and current preventive and therapeutic approaches.

Multiparametric MRI assessment of renal structure and function in acute kidney injury and renal recovery

Background

Acute kidney injury (AKI) is associated with a marked increase in mortality as well as subsequent chronic kidney disease (CKD) and end-stage kidney disease. We performed multiparametric magnetic resonance imaging (MRI) with the aim of identifying potential non-invasive MRI markers of renal pathophysiology in AKI and during recovery.

Methods

Nine participants underwent inpatient MRI scans at time of AKI; seven had follow-up scans at 3 months and 1 year following AKI. Multiparametric renal MRI assessed total kidney volume (TKV), renal perfusion using arterial spin labelling, T₁ mapping and blood oxygen level-dependent (BOLD) R₂* mapping.

Results

Serum creatinine concentration had recovered to baseline levels at 1-year post-AKI in all participants. At the time of AKI, participants had increased TKV, increased cortex/medulla T₁ and reduced cortical perfusion compared with the expected ranges in healthy volunteers and people with CKD. TKV and T₁ values decreased over time after AKI and returned to expected values in most but not all patients by 1 year. Cortical perfusion improved to a lesser extent and remained below the expected range in the majority of patients by 1-year post-AKI. BOLD R₂* data showed a non-significant trend to increase over time post-AKI.

Conclusions

We observed a substantial increase in TKV and T₁ during AKI and a marked decrease in cortical perfusion. Despite biochemical recovery at 1-year post-AKI, MRI measures indicated persisting abnormalities in some patients. We propose that such patients may be more likely to have further AKI episodes or progress to CKD and further longitudinal studies are required to investigate this. .

New imaging techniques in AKI

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a common complication in critically ill patients. Understanding the pathophysiology of AKI is essential to guide patient management. Imaging techniques that inform the pathogenesis of AKI in critically ill patients are urgently needed, in both research and ultimately clinical settings. Renal contrast-enhanced ultrasonography (CEUS) and multiparametric MRI appear to be the most promising imaging techniques for exploring the pathophysiological mechanisms involved in AKI.

RECENT FINDINGS

CEUS and MRI can be used to noninvasively and safely evaluate renal macrocirculation and microcirculation and oxygenation in critical ill patients. These techniques show that a decrease in renal blood flow, particularly cortical blood flow, may be observed in septic AKI and may contribute to its development. MRI may be a valuable method to quantify long-term renal damage after AKI that cannot currently be detected using standard clinical approaches.

SUMMARY

CEUS and multiparametric renal MRI are promising imaging techniques but more evidence is needed to show how they can first be more widely used in a research setting to test key hypotheses about the pathophysiology and recovery of AKI, and then ultimately be adopted in clinical practice to guide patient management.

Peritubular Capillary Oxygen Consumption in Sepsis-Induced AKI: Multi-Parametric Photoacoustic Microscopy

Understanding and measuring parameters responsible for the pathogenesis of sepsis-induced AKI (SI-AKI) is critical in developing therapies. Blood flow to the kidney is heterogeneous, partly due to the existence of dynamic networks of capillaries in various regions, responding differentially to oxygen demand in cortex versus medulla. High energy demand regions, especially the outer medulla, are susceptible to hypoxia and subject to damage during SI-AKI. Proximal tubule epithelial cells in the cortex and the outer medulla can also undergo metabolic reprogramming during SI-AKI to maintain basal physiological status and to avoid potential damage. Current data on the assessment of renal hemodynamics and oxygen metabolism during sepsis is limited. Preclinical and clinical studies show changes in renal hemodynamics associated with SI-AKI, and in clinical settings, interventions to manage renal hemodynamics seem to help improve disease outcomes in some cases. Lack of proper tools to assess temporospatial changes in peritubular blood flow and tissue oxygen metabolism is a barrier to our ability to understand microcirculatory dynamics and oxygen consumption and their role in the pathogenesis of SI-AKI. Current tools to assess renal oxygenation are limited in their usability as these cannot perform continuous simultaneous measurement of renal hemodynamics and oxygen metabolism. Multi-parametric photo-acoustic microscopy (PAM) is a new tool that can measure real-time changes in microhemodynamics and oxygen metabolism. Use of multi-parametric PAM in combination with advanced intravital imaging techniques has the potential to understand the contribution of microhemodynamic and tissue oxygenation alterations to SI-AKI.

4D flow MRI for the assessment of renal transplant dysfunction: initial results

OBJECTIVES

(1) Determine inter-observer reproducibility and test-retest repeatability of 4D flow parameters in renal allograft vessels; (2) determine if 4D flow measurements in the renal artery (RA) and renal vein (RV) can distinguish between functional and dysfunctional allografts; (3) correlate haemodynamic parameters with estimated glomerular filtration rate (eGFR), perfusion measured with dynamic contrast-enhanced MRI (DCE-MRI) and histopathology.

METHODS

Twenty-five prospectively recruited renal transplant patients (stable function/chronic renal allograft dysfunction, 12/13) underwent 4D flow MRI at 1.5 T. 4D flow coronal oblique acquisitions were performed in the transplant renal artery (RA) (velocity encoding parameter, VENC = 120 cm/s) and renal vein (RV) (VENC = 45 cm/s). Test-retest repeatability (n = 3) and inter-observer reproducibility (n = 10) were assessed by Cohen's kappa, coefficient of variation (CoV) and Bland-Altman statistics. Haemodynamic parameters were compared between patients and correlated to the estimated glomerular filtration rate, DCE-MRI parameters (n = 10) and histopathology from allograft biopsies (n = 15).

RESULTS

For inter-observer reproducibility, kappa was > 0.99 and 0.62 and CoV of flow was 12.6% and 7.8% for RA and RV, respectively. For test-retest repeatability, kappa was > 0.99 and 0.5 and CoV of flow was 27.3% and 59.4%, for RA and RV, respectively. RA (p = 0.039) and RV (p = 0.019) flow were both significantly reduced in dysfunctional allografts. Both identified chronic allograft dysfunction with good diagnostic performance (RA: AUC = 0.76, p = 0.036; RV: AUC = 0.8, p = 0.018). RA flow correlated negatively with histopathologic interstitial fibrosis score ci (ρ = - 0.6, p = 0.03).

CONCLUSIONS

4D flow parameters had better repeatability in the RA than in the RV. RA and RV flow can identify chronic renal allograft dysfunction, with RA flow correlating with histopathologic interstitial fibrosis score.

KEY POINTS

• Inter-observer reproducibility of 4D flow measurements was acceptable in both the transplant renal artery and vein, but test-retest repeatability was better in the renal artery than in the renal vein. • Blood flow measurements obtained with 4D flow MRI in the renal artery and renal vein are significantly reduced in dysfunctional renal transplants. • Renal transplant artery flow correlated negatively with histopathologic interstitial fibrosis score.

Noninterventional follow-up vs fluid bolus in RESPONSE to oliguria-The RESPONSE trial protocol and statistical analysis plan

BACKGROUND

Oliguria is a frequent trigger for administering a fluid bolus, but the effect of fluid bolus in improving urine output is inadequately demonstrated. Here, we summarize the protocol and detailed statistical analysis plan of the randomized, controlled RESPONSE trial comparing follow-up as the experimental group and a 500 mL crystalloid fluid bolus as the control group for oliguria in critically ill oliguric patients.

METHODS

Our trial is an investigator-initiated, randomized, controlled, pilot trial conducted in three ICUs in two centers. We aim to randomize 1:1 altogether 130 hemodynamically stable oliguric patients either to a 2-hour follow-up without interventions or to receive a crystalloid bolus of 500 mL over 30 minutes. The primary outcome is the change in individual urine output during the 2-hour period compared to 2 hours preceding randomization. Doubling of the urine output is considered clinically significant. Additionally, we record the duration of oliguria, physiological and biochemical variables, adverse events, and the incidences of acute kidney injury and renal replacement therapy.

CONCLUSIONS

Oliguria is a frequent trigger for potentially harmful fluid loading. Therefore, the RESPONSE trial will give information of the potential effect of fluid bolus on oliguria in critically ill patients.

TRIAL REGISTRATION

clinical.trials.gov, NCT02860572.

Prerenal acute kidney injury—still a relevant term in modern clinical practice?

The traditional taxonomy of acute kidney injury (AKI) has remained pervasive in clinical nephrology. While the terms ‘prerenal’, ‘intrarenal’ and ‘postrenal’ highlight the diverse pathophysiology underlying AKI, they also imply discrete disease pathways and de-emphasize the nature of AKI as an evolving clinical syndrome with multiple, often simultaneous and overlapping, causes. In a similar vein, prerenal AKI comprises a diverse spectrum of kidney disorders, albeit one that is often managed by using a standardized clinical algorithm. We contend that the term ‘prerenal’ is too vague to adequately convey our current understanding of hypoperfusion-related AKI and that it should thus be avoided in the clinical setting. Practice patterns among nephrologists indicate that AKI-related terminology plays a significant role in the approaches that clinicians take to patients that have this complex disease. Thus, it appears that precise terminology does impact the treatment that patients receive. We will outline differences in the diagnosis and management of clinical conditions lying on the so-called prerenal disease spectrum to advocate caution when administering intravenous fluids to these clinically decompensated patients. An understanding of the underlying pathophysiology may, thus, avert clinical missteps such as fluid and vasopressor mismanagement in tenuous or critically ill patients.

Evolution of altered tubular metabolism and mitochondrial function in sepsis-associated acute kidney injury

Sepsis-associated acute kidney injury (s-AKI) has a staggering impact in patients and lacks any treatment. Incomplete understanding of the pathogenesis of s-AKI is a major barrier to the development of effective therapies. We address the gaps in knowledge regarding renal oxygenation, tubular metabolism, and mitochondrial function in the pathogenesis of s-AKI using the cecal ligation and puncture (CLP) model in mice. At 24 h after CLP, renal oxygen delivery was reduced; however, fractional oxygen extraction was unchanged, suggesting inefficient renal oxygen utilization despite decreased glomerular filtration rate and filtered load. To investigate the underlying mechanisms, we examined temporal changes in mitochondrial function and metabolism at 4 and 24 h after CLP. At 4 h after CLP, markers of mitochondrial content and biogenesis were increased in CLP kidneys, but mitochondrial oxygen consumption rates were suppressed in proximal tubules. Interestingly, at 24 h, proximal tubular mitochondria displayed high respiratory capacity, but with decreased mitochondrial content, biogenesis, fusion, and ATP levels in CLP kidneys, suggesting decreased ATP synthesis efficiency. We further investigated metabolic reprogramming after CLP and observed reduced expression of fatty acid oxidation enzymes but increased expression of glycolytic enzymes at 24 h. However, assessment of functional glycolysis revealed lower glycolytic capacity, glycolytic reserve, and compensatory glycolysis in CLP proximal tubules, which may explain their susceptibility to injury. In conclusion, we demonstrated significant alterations in renal oxygenation, tubular mitochondrial function, and metabolic reprogramming in s-AKI, which may play an important role in the progression of injury and recovery from AKI in sepsis.

Ultrasound super-resolution imaging provides a noninvasive assessment of renal microvasculature changes during mouse acute kidney injury

Acute kidney injury (AKI) is a risk factor for the development of chronic kidney disease (CKD). One mechanism for this phenomenon is renal microvascular rarefaction and subsequent chronic impairment in perfusion. However, diagnostic tools to monitor the renal microvasculature in a noninvasive and quantitative manner are still lacking. Ultrasound super-resolution imaging is an emerging technology that can identify microvessels with unprecedented resolution. Here, we applied this imaging technique to identify microvessels in the unilateral ischemia-reperfusion injury mouse model of AKI-to-CKD progression in vivo. Kidneys from 21 and 42 day post- ischemia-reperfusion injury, the contralateral uninjured kidneys, and kidneys from sham-operated mice were examined by ultrasound super-resolution and histology. Renal microvessels were successfully identified by this imaging modality with a resolution down to 32 μm. Renal fibrosis was observed in all kidneys with ischemia-reperfusion injury and was associated with a significant reduction in kidney size, cortical thickness, relative blood volume, and microvascular density as assessed by this imaging. Tortuosity of the cortical microvasculature was also significantly increased at 42 days compared to sham. These vessel density measurements correlated significantly with CD31 immunohistochemistry (R²=0.77). Thus, ultrasound super-resolution imaging provides unprecedented resolution and is capable of noninvasive quantification of renal vasculature changes associated with AKI-to-CKD progression in mice. Hence, this technique could be a promising diagnostic tool for monitoring progressive kidney disease.

Acute kidney injury

Acute kidney injury (AKI) is defined by a rapid increase in serum creatinine, decrease in urine output, or both. AKI occurs in approximately 10-15% of patients admitted to hospital, while its incidence in intensive care has been reported in more than 50% of patients. Kidney dysfunction or damage can occur over a longer period or follow AKI in a continuum with acute and chronic kidney disease. Biomarkers of kidney injury or stress are new tools for risk assessment and could possibly guide therapy. AKI is not a single disease but rather a loose collection of syndromes as diverse as sepsis, cardiorenal syndrome, and urinary tract obstruction. The approach to a patient with AKI depends on the clinical context and can also vary by resource availability. Although the effectiveness of several widely applied treatments is still controversial, evidence for several interventions, especially when used together, has increased over the past decade.

Technical recommendations for clinical translation of renal MRI: a consensus project of the Cooperation in Science and Technology Action PARENCHIMA

Purpose

The potential of renal MRI biomarkers has been increasingly recognised, but clinical translation requires more standardisation. The PARENCHIMA consensus project aims to develop and apply a process for generating technical recommendations on renal MRI.

Methods

A task force was formed in July 2018 focused on five methods. A draft process for attaining consensus was distributed publicly for consultation and finalised at an open meeting (Prague, October 2018). Four expert panels completed surveys between October 2018 and March 2019, discussed results and refined the surveys at a face-to-face meeting (Aarhus, March 2019) and completed a second round (May 2019).

Results

A seven-stage process was defined: (1) formation of expert panels; (2) definition of the context of use; (3) literature review; (4) collection and comparison of MRI protocols; (5) consensus generation by an approximate Delphi method; (6) reporting of results in vendor-neutral and vendor-specific terms; (7) ongoing review and updating. Application of the process resulted in 166 consensus statements.

Conclusion

The process generated meaningful technical recommendations across very different MRI methods, while allowing for improvement and refinement as open issues are resolved. The results are likely to be widely supported by the renal MRI community and thereby promote more harmonisation.

Prospective longitudinal observational study of the macro and micro haemodynamic responses to septic shock in the renal and systemic circulations: a protocol for the MICROSHOCK - RENAL study

INTRODUCTION

Septic acute kidney injury (AKI) is the most common complication of septic shock and increases mortality. A large body of experimental data suggests alterations in renal perfusion occur, but this is yet to be fully assessed in humans. The aim of the current study is to observe the macro and microcirculations in both the systemic and renal circulations in a cohort of patients with early septic shock.

METHODS AND ANALYSIS

Single-centre, prospective, longitudinal, observational study of 50 patients with septic shock. Renal microcirculatory assessment will be performed with contrast-enhanced ultrasound, the sublingual microcirculation assessed with incident dark field microscopy and transthoracic echocardiography used to assess global flow. Patients will be enrolled as soon as possible after admission to the intensive care unit and then at +24,+48 and +96 hours. Blood samples of circulatory and renal biomarkers will be collected. Sample groups will be defined by the presence or absence of AKI and then subclassified by the severity (Kidney Disease Improving Global Outcomes (KDIGO) criteria), variables will be compared within and between groups over time.

ETHICS AND DISSEMINATION

Research Ethics Committee (REC) approval has been granted for this study by Yorkshire and the Humber, Leeds West Research Ethics Committee (18/YH/0371) and due to the nature of the patients enrolled with septic shock, capacity for informed consent is likely to be lacking. Therefore, a personal consultee (friend or relative) will be consulted or a nominated consultee (clinician) in their absence. After capacity is regained, consent will then be sought from the patient in accordance with the Mental Capacity Act, UK (2005). This consent process has been approved following REC review. Results will be published in a relevant peer-reviewed journal and presented at academic meetings.