Measurement of kidney perfusion in critically ill patients

Comparison of absolute renal uptake by using Tc-99m MAG-3 and Tc-99m DMSA

PURPOSE

The purpose of this study is to compare the value of absolute renal uptake (ARU %) in patients by using Tc-99m MAG-3 and Tc-99m DMSA scan.

MATERIAL AND METHODS

Absolute renal uptake is calculated using Tc-99m MAG-3 and Tc-99m DMSA in renal scintigraphy, Itoh and Tauex kidney depth methods used, respectively. n = 40 adult patients of both genders were included. All patients underwent Tc-99m MAG-3 and Tc-99m DMSA, respectively.

RESULTS

The values of ARU (%) were calculated separately in selected patients n = 40, (left = 17, right = 23 normal functioning kidneys) by MAG-3 and DMSA. Absolute renal uptake (%) of Tc-99m MAG-3 in left kidneys was found to be 15.2 ± 3.4, with spilt renal function 79.2 ± 14.7 and ARU (%) in right kidneys 16.2 ± 3.4 with spilt renal function 77.5 ± 19. Absolute renal uptake of Tc-99m DMSA in left kidneys was 17.5 ± 3.2 and in right kidneys 17.9 ± 4.5 with spilt renal function 81.8 ± 10.7 and 79.3 ± 13.8 for left and right kidney, respectively. Statistical analysis showed strong Pearson correlation.

CONCLUSION

Absolute renal uptake % was found to be more reliable in cases of bilateral compromised kidneys. ARU (%) calculated by Tc-99m MAG-3 solely can be used as predictor of renal function. The use of Tc-99m MAG-3 has more advantages than Tc-99m DMSA alone in renal scintigraphy as dynamic scintigraphy gives less radiation burden to patient, more information regarding renal function, and shorter stay time at hospital in comparison to static renal imaging. SRF % is less reliable than ARU (%).

Contrast-enhanced ultrasonography for identifying acute kidney injury in brain-dead donors

Background

Acute kidney injury (AKI) is frequently found in deceased donors; however, few studies have reported the use of imaging to detect and identify this phenomenon. The purpose of this study was to detect renal microcirculatory perfusion in brain-dead donors using contrast-enhanced ultrasonography (CEUS), investigate the value of CEUS in identifying AKI, and analyze the correlation between CEUS and preimplantation biopsy results and early post-transplant renal function of grafts.

Methods

This prospective study recruited 94 kidneys from brain-dead donors (AKI =44, non-AKI =50) from August 2020 to November 2022. The inclusion criteria were age ≥18 years and brain death. The exclusion criteria encompassed donors maintained with extracorporeal membrane oxygenation (ECMO) and the presence of irregular kidney anatomy. The mean age of the donors was 45.1±10.4 [standard deviation (SD)] years, and the majority were male (86.2%). CEUS was performed prior to organ procurement, and time-intensity curves (TICs) were constructed. The time to peak (TTP) and peak intensity (PI) of kidney segmental artery (KA), kidney cortex (KC), and kidney medulla (KM) were calculated using TIC analysis.

Results

Arrival time (AT) of KA (P<0.001) and TTP of kidney cortex (TTPKC) (P<0.001) of the non-AKI group were significantly shorter than those of the AKI group. The PI of the KA (P=0.003), KM (P=0.005), and kidney cortex (PIKC; P<0.001) of the non-AKI group were significantly higher than those of the AKI group. Multivariable logistic regression analysis showed that serum creatinine [odds ratio (OR) =1.06; 95% CI: 1.03-1.1; P<0.001], TTPKC (OR =1.38; 95% CI: 1.03-1.84; P=0.03), and PIKC (OR =0.95; 95% CI: 0.91-1; P=0.046) were the independent factors of AKI. The area under the receiver operating characteristic curve (AUC) for identifying AKI for TTPKC and PIKC was 0.73 and 0.71, respectively. TTPKC showed a weak correlation with interstitial fibrosis (r=0.23; P=0.03), PIKC showed a weak correlation with arterial intimal fibrosis ((r=-0.29; P=0.004) and arteriolar hyalinosis (r=-0.27; P=0.008), and PIKC showed the strongest correlation with eGFR on postoperative day 7 (r=-0.46; P=0.046) in the donor kidneys with AKI.

Conclusions

CEUS can be used to identify AKI in brain-dead donors. Furthermore, there is a correlation between CEUS-derived parameters and pretransplant biopsy results and early preimplantation renal function of grafts.

Tubular Elabela-APJ axis attenuates ischemia-reperfusion induced acute kidney injury and the following AKI-CKD transition by protecting renal microcirculation

Rationale: Ischemia-reperfusion injury (I/R) is a common cause of acute kidney injury (AKI). Post-ischemic recovery of renal blood supply plays an important role in attenuating injury. Exogenous application of elabela (ELA) peptides has been demonstrated by us and others to alleviate AKI, partly through its receptor APJ. However, the endogenous role of ELA in renal I/R remains unclear. Methods: Renal tubule specific ELA knockout (ApelaKsp KO) mice challenged with bilateral or unilateral I/R were used to investigate the role of endogenous ELA in renal I/R. RNA-sequencing analysis was performed to unbiasedly investigate altered genes in kidneys of ApelaKsp KO mice. Injured mice were treated with ELA32 peptide, Nω-hydroxy-nor-L-arginine (nor-NOHA), prostaglandin E2 (PGE2), Paricalcitol, ML221 or respective vehicles, individually or in combination. Results: ELA is mostly expressed in renal tubules. Aggravated pathological injury and further reduction of renal microvascular blood flow were observed in ApelaKsp KO mice during AKI and the following transition to chronic kidney disease (AKI-CKD). RNA-seq analysis suggested that two blood flow regulators, arginine metabolizing enzyme arginase 2 (ARG2) and PGE2 metabolizing enzyme carbonyl reductases 1 and 3 (CBR1/3), were altered in injured ApelaKsp KO mice. Notably, combination application of an ARG2 inhibitor nor-NOHA, and Paricalcitol, a clinically used activator for PGE2 synthesis, alleviated injury-induced AKI/AKI-CKD stages and eliminated the worst outcomes observed in ApelaKsp KO mice. Moreover, while the APJ inhibitor ML221 blocked the beneficial effects of ELA32 peptide on AKI, it showed no effect on combination treatment of nor-NOHA and Paricalcitol. Conclusions: An endogenous tubular ELA-APJ axis regulates renal microvascular blood flow that plays a pivotal role in I/R-induced AKI. Furthermore, improving renal blood flow by inhibiting ARG2 and activating PGE2 is an effective treatment for AKI and prevents the subsequent AKI-CKD transition.

Intrarenal Doppler approaches in hemodynamics: A major application in critical care

The treatment of severe cases usually requires multimodality hemodynamic monitoring approaches, particularly for tissue and organ perfusion tracking. Currently, only a few studies have investigated renal perfusion status at the bedside. Ultrasound has become increasingly utilized to guide the hemodynamic management of severe patients. Similarly, intrarenal Doppler (IRD) is widely used to assess renal perfusion from both the intrarenal artery and vein perspectives. The renal resistive index (RRI), which reflects the renal arterial blood flow profile, is often applied to predict the reversibility of renal dysfunction and to titrate hemodynamic support. Intrarenal venous flow (IRVF) patterns and the renal venous stasis index (RVSI), which reflects the intrarenal vein blood flow profile, are now being used to assess intravenous congestion. They may also be useful in predicting the risk of acute kidney injury and avoiding fluid overload. IRD can provide diverse and supplemental information on renal perfusion and may help to establish the early diagnosis in severe patients. This review focused on the specific operational methods, influencing factors, and applications of IRD in hemodynamics.

Evaluation of renal microperfusion in hyperuricemic nephropathy by Contrast-Enhanced Ultrasound imaging

Diagnostic tools for the early detection of renal injury caused by hyperuricemia are still lacking. Here, we investigated whether contrast-enhanced ultrasound (CEUS) could be used as a diagnostic tool for hyperuricemic nephropathy (HN). In the HN rat model, CEUS detected a significant decline in renal cortical perfusion compared with that in control rats. Peak intensity (PI) values correlated significantly with serum KIM-1 levels and fibrosis scores in HN rats. An early decline in PI values was also observed in chronic kidney disease (CKD) stage 1 patients with HN compared with the controls (61.1±4.52 dB versus 65.80±7.10 dB) and correlated with renal function in the patients with HN. In contrast, an increase in time to reach PI values was detected in HN patients with stage 1 CKD (15.14±1.75 s versus 14.52±4.75 s) and was more pronounced in CKD stage 4 patients (67.32±3.29 s). CEUS was able to detect abnormal renal perfusion in early CKD with HN, which correlated with renal function decline, suggesting that CEUS could be used as a noninvasive tool for assessing renal function in patients with HN.

Clinical and experimental approaches for imaging of acute kidney injury

Complex molecular cell dynamics in acute kidney injury and its heterogeneous etiologies in patient populations in clinical settings have revealed the potential advantages and disadvantages of emerging novel damage biomarkers. Imaging techniques have been developed over the past decade to further our understanding about diseased organs, including the kidneys. Understanding the compositional, structural, and functional changes in damaged kidneys via several imaging modalities would enable a more comprehensive analysis of acute kidney injury, including its risks, diagnosis, and prognosis. This review summarizes recent imaging studies for acute kidney injury and discusses their potential utility in clinical settings.

New strategies to optimize renal haemodynamics

PURPOSE OF REVIEW

This review discusses the macrocirculatory and microcirculatory aspects of renal perfusion, as well as novel methods by which to measure renal blood flow. Finally, therapeutic options are briefly discussed, including renal-specific microcirculatory effects.

RECENT FINDINGS

The optimal mean arterial pressure (MAP) needed for preservation of renal function has been debated but is most likely a MAP of 60-80 mmHg. In addition, attention should be paid to renal outflow pressure, typically central venous pressure. Heterogeneity in microcirculation can exist and may be mitigated through appropriate use of vasopressors with unique microcirculatory effects. Excessive catecholamines have been shown to be harmful and should be avoided. Both angiotensin II and vasopressin may improve glomerular flow through a number of mechanisms. Macrocirculatory and microcirculatory blood flow can be measured through a number of bedside ultrasound modalities, sublingual microscopy and urinary oxygen measurement, SUMMARY: Acute kidney injury (AKI) is a common manifestation of organ failure in shock, and avoidance of hemodynamic instability can mitigate this risk. Measurement of renal haemodynamics is not routinely performed but may help to guide therapeutic goals. A thorough understanding of pathophysiology, measurement techniques and therapeutic options may allow for a personalized approach to blood pressure management in patients with septic shock and may ultimately mitigate AKI.

Noninvasive Renal Perfusion Measurement Using Arterial Spin Labeling (ASL) MRI: Basic Concept

The kidney is a complex organ involved in the excretion of metabolic products as well as the regulation of body fluids, osmolarity, and homeostatic status. These functions are influenced in large part by alterations in the regional distribution of blood flow between the renal cortex and medulla. Renal perfusion is therefore a key determinant of glomerular filtration. Therefore the quantification of regional renal perfusion could provide important insights into renal function and renal (patho)physiology. Arterial spin labeling (ASL) based perfusion MRI techniques, can offer a noninvasive and reproducible way of measuring renal perfusion in animal models. This chapter addresses the basic concept of ASL-MRI.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This introduction chapter is complemented by two separate chapters describing the experimental procedure and data analysis.

Semi-quantification of renal perfusion using 99mTc-DTPA in systolic heart failure: a feasibility study

BACKGROUND

Renal scintigraphy with ^99mTc-diethylenetriaminepentaacetic acid (DTPA) may be used to study renal perfusion (RP) in heart failure (HF) patients. The goal of this study was to establish a new method to assess RP in patients with systolic HF.

METHODS

In this retrospective, single-center, observational study, 86 subjects with left ventricular ejection fraction ≤ 45% and 31 age-matched subjects without HF underwent renal scintigraphy with ^99mTc-DTPA. Patients with HF were classified into two categories according to the New York Heart Association (NYHA) functional class, i.e., moderate HF with NYHA functional class I or II and severe HF with NYHA functional class III or IV. The first-pass time-activity curve of the renal scintigraph was recorded. The GFR was determined by Gates' method. The time to peak perfusion activity (T_p), the slope of the perfusion phase (S_p), the slope of the washout phase (S_w), and glomerular filtration rate (GFR) in the study were obtained. Differences between groups were assessed by one-way analysis of variance with the Bonferroni post hoc test and rank-sum test.

RESULTS

RP in HF was impaired despite comparable GFRs between the control and HF groups. RP in HF was characterized by a longer T_p and a shallower S_p and S_w. The primary parameter (T_p) was significantly prolonged in patients with HF (41.63 ± 12.22 s in severe HF vs. 26.95 ± 6.26 s in moderate HF vs. 17.84 ± 3.17 s in control, P < 0.001). At a cutoff point of 22 s, there was a high sensitivity (0.895) and specificity (0.935) in identifying patients with HF.

CONCLUSIONS

Renal scintigraphy with ^99mTc-DTPA may represent a new and useful method to noninvasively monitor RP abnormalities in HF.

Clinical and ultrasound variables for early diagnosis of septic acute kidney injury in bitches with pyometra

The aetiology of septic acute kidney injury (AKI) is not completely elucidated. Early identification of AKI in septic patients is considered to improve survival rate since it allows rapid treatment onset. We evaluated clinical, haematological, urinary, B-mode, spectral Doppler, and contrast-enhanced ultrasound variables in 20 bitches with pyometra as sepsis models and 12 healthy controls. All animals with pyometra presented some degree of renal damage on histological examination; however, sequential organ failure assessment (SOFA) classified only 40% cases with sepsis. AKI derived from systemic infection was identified in 57% of cases with hypoperfusion and in 22% with inflammation, being an affection of multifactorial origin. Among the evaluated parameters, urinary protein/creatinine ratio >0.15, serum albumin <2.94 mg/dL, time-averaged minimum velocity <21.5 cm/s, renal length/aorta diameter ratio >5.93, pulsatility index >1.53, haematocrit <45%, time-averaged maximum velocity <45.7 cm/s, haemoglobin <16 g/dL, leukocytes >12.53 × 103/uL, and cortical contrast peak intensity <69%, in the order of accuracy, are significant indicators of septic AKI with an accuracy >80%. Thus, AKI is a very prevalent condition in septic patients, derived mainly from changes in renal perfusion and inflammation. Additionally, reviewing the SOFA score parameters is suggested to identify renal failure.

Renal statistical map for positron emission tomography with [O-15] water

Image statistics are frequently used for functional and molecular imaging research in which images from a patient group with a specific diagnosis are compared with images from a healthy control group who have been matched for demographic variables. The success of image statistics for brain imaging has encouraged us to develop a method for obtaining volumetrically normalized kidney to perform image statistics so that we can locally visualize the statistical significant difference comparing voxel by voxel between certain groups in terms kidney blood flow kinetic parameters. For the development of this evolutionary process, we first volumetrically normalized all subjects, which include healthy control (HC) and chronic renal failure (CRF) patients, 15O water PET image with respect to one HC subject's MRI image using affine transformation. Then 15O kinetic parametric images of normalized kidneys were obtained through the basis function method. Finally, the statistical map of these parametric images was produced using the threshold-free cluster enhancement based permutation method. Kinetic parameters of kidney namely, uptake rate constant (K1), clearance rate constant (k2) and blood volume (Va), were found to be notably lower in CRF than those of in HC and k2 parameter was found to be more stable compared to K1 and Va. The statistical map of these parametric images allowed us to visualize local significant differences statistically (P<0.05) between HC and CRF groups. Though PET and MRI techniques have enormous potentiality for functional and molecular imaging of kidney, these are, at best, in experimental level. It is speculated that statistical mapping of kidney could play a significant role in the successful implementation of functional and molecular kidney imaging. However, more research involving a larger sample size and improved normalization technique will be needed for the robustness of the process.

Protocol for a prospective observational study on the association of variables obtained by contrast-enhanced ultrasonography and sepsis-associated acute kidney injury

INTRODUCTION

Sepsis commonly results in acute kidney injury (AKI), whereas about 50% of AKI cases are due to sepsis. Sepsis-associated acute kidney injury (SA-AKI) increases morbidity and mortality especially among critically ill patients. This study aims to monitor renal microcirculation perfusion during sepsis using contrast-enhanced ultrasonography (CEUS), and to explore whether CEUS is useful for predicting the development of SA-AKI.

METHODS AND ANALYSIS

This prospective observational study will enrol patients who were diagnosed with sepsis-3 definition. The total of septic or septic shock patients were stratified into AKI (including stages 1, 2 and 3) and non-AKI groups according to Kidney Disease Improving Global Outcomes criteria on days 0, 1, 2 and 7 after admission to the emergency intensive care unit, meanwhile, the CEUS technique will be performed to monitor renal microcirculation perfusion. A multivariable model including all CEUS variables were expected to create for predicting the development of AKI during sepsis. Ultrasonography results, demographic information, therapeutic interventions, survival outcomes, laboratory and other clinical datas will also be collected for further analysis.

ETHICS AND DISSEMINATION

The study protocol was approved on 2 August 2017 by the Ethics Committee of Sir Run Run Shaw Hospital (Zhejiang University Medical College) (approval number: 2016C91401). The results will be published in a peer-reviewed journal and shared with the worldwide medical community within 2 years after the start of the recruitment.

TRIAL REGISTRATION NUMBER

ISRCTN14728986.

The PIEPEAR Workflow: A Critical Care Ultrasound Based 7-Step Approach as a Standard Procedure to Manage Patients with Acute Cardiorespiratory Compromise, with Two Example Cases Presented

Critical care ultrasound (CCUS) has been widely used as a useful tool to assist clinical judgement. The utilization should be integrated into clinical scenario and interact with other tests. No publication has reported this. We present a CCUS based "7-step approach" workflow-the PIEPEAR Workflow-which we had summarized and integrated our experience in CCUS and clinical practice into, and then we present two cases which we have applied the workflow into as examples. Step one is "problems emerged?" classifying the signs of the deterioration into two aspects: acute circulatory compromise and acute respiratory compromise. Step two is "information clear?" quickly summarizing the patient's medical history by three aspects. Step three is "focused exam launched": (1) focused exam of the heart by five views: the assessment includes (1) fast and global assessment of the heart (heart glance) to identify cases that need immediate life-saving intervention and (2) assessing the inferior vena cava, right heart, diastolic and systolic function of left heart, and systematic vascular resistance to clarify the hemodynamics. (2) Lung ultrasound exam is performed to clarify the predominant pattern of the lung. Step four is "pathophysiologic changes reported." The results of the focused ultrasound exam were integrated to conclude the pathophysiologic changes. Step five is "etiology explored" diagnosing the etiology by integrating Step two and Step four and searching for the source of infection, according to the clues extracted from the focused ultrasound exam; additional ultrasound exams or other tests should be applied if needed. Step six is "action" supporting the circulation and respiration sticking to Step four. Treat the etiologies according step five. Step seven is "recheck to adjust." Repeat focused ultrasound and other tests to assess the response to treatment, adjust the treatment if needed, and confirm or correct the final diagnosis. With two cases as examples presented, we insist that applying CCUS with 7-step approach workflow is easy to follow and has theoretical advantages. The coming research on its value is expected.

Renal ultrasound provides low utility in evaluating cardiac surgery associated acute kidney injury

BACKGROUND

Renal ultrasonography is part of the algorithm in assessing acute kidney injury (AKI). The purpose of this study was to assess the clinical utility of renal US in postoperative cardiac patients who develop AKI.

METHODS

We conducted a retrospective study of 90 postoperative cardiac surgery patients at a single institution from 1/19/2010 to 3/19/2016 who underwent renal US for AKI. We reviewed provider documentation to determine whether renal US changed management. We defined change as: administration of crystalloid or colloid, addition of inotropic or vasopressor, or procedural interventions on the renal system.

RESULTS

Mean age of study patients was 68 ± 13 years. 48/90 patients (53.3%) had pre-existing chronic kidney disease of varying severity. 48 patients (53.3%) had normal renal US with incidental findings and 31 patients (34.4%) had US evidence of medical kidney disease. 10 patients (11.1%) had limited US results due to poor visualization and 1 patient (1.1%) had mild right-sided hydronephrosis. No patients were found to have obstructive uropathy or renal artery stenosis. Clinical management was altered in only 4/90 patients (4.4%), which included 3 patients that received a fluid bolus and 1 patient that received a fluid bolus and inotropes. No vascular or urologic procedures resulted from US findings.

CONCLUSION

Although renal ultrasound is often utilized in the work-up of AKI, our study shows that renal US provides little benefit in managing postoperative cardiac patients. This diagnostic modality should be scrutinized rather than viewed as a universal measure in the cardiac surgery population.

The utilization of critical care ultrasound to assess hemodynamics and lung pathology on ICU admission and the potential for predicting outcome

Aim

Critical care ultrasound (CCUS) has been used by many Intensive Care Units(ICUs) worldwide, so as to guiding the diagnosis and the treatment. However, none of the publications currently systematically describe the utilization of CCUS to analyze the characteristics of hemodynamics and lung pathology upon the new admission to ICU and its potential role in patients’ prognosis prediction. In this retrospective clinical study, we have demonstrated and analyzed the characteristics of hemodynamics and lung pathology assessed by CCUS and investigated its potential to predict patient outcome.

Methods

We have described and analyzed the epidemic characteristics of hemodynamics and lung pathology assessed by CCUS on ICU admission, which based on our database of 451 cases from the biggest medical center in Western China, between November 2014 and October 2015. The patients’ demographics, clinical characteristics, prognosis and ultrasonic pattern of hemodynamics and lung pathology had been analyzed. A bivariate logistic regression model was established to identify the correlation between the ultrasonic variables on admission and the ICU mortality.

Results

The mean age of the 451 patients was 56.7±18.7 years; the mean APACHE II score was 19.0±7.9, the ICU mortality was 30.6%. Patients received CCUS examination of pericardial, right ventricle (RV) wall motion, left ventricle (LV) wall motion, LV systolic function, LV diastolic function, lung and volume of inferior vena cava (IVC) were 423(93.8%), 418(92.7%), 392(86.9%), 389(86.3%), 383(84.9%), 440(97.6%), 336(74.5%), respectively; The univariate analysis revealed that length of mechanical ventilation was significantly correlated with the diameter of IVC, tricuspid annular plane systolic excursion(TAPSE), mitral annular plane systolic excursion(MAPSE), early diastolic transmitral velocity to early mitral annulus diastolic velocity(E/e’) (p = 0.016, 0.011, 0.000, 0.049, respectively); The TAPSE, ejection fraction(EF), MAPSE, lung ultrasound score (LUS score) (p = 0.000, 0.028, 0.000, 0.011, respectively) were significantly related to ICU mortality. The multivariate analysis demonstrated that APACHE II, age, TAPSE, E/e’ are the independent risk factors for ICU mortality in our study.

Conclusion

CCUS examination on ICU admission which performed by the experienced physician provide valuable information to assist the caregivers in understanding the comprehensive outlook of the characteristics of hemodynamics and lung pathology. Those key variables obtained by CCUS predict the possible prognosis of patients, hence deserve more attention in clinical decision making.

Low mean perfusion pressure is a risk factor for progression of acute kidney injury in critically ill patients - A retrospective analysis

Background

The aim was to investigate whether mean perfusion pressure (MPP) calculated as the difference between mean arterial pressure (MAP) and central venous pressure (CVP) was associated with risk of progression from AKI I to AKI III in critically ill patients.

Methods

Retrospective analysis of adult patients admitted to a multi-disciplinary adult intensive care unit (ICU) between July 2007 and June 2009 who developed AKI I and in whom advanced haemodynamic monitoring was initiated within 12 h of diagnosis of AKI I. We compared patients with a MPP above and below the median value in the first 12 h of diagnosis of AKI. Multivariable logistic regression analyses were performed to identify independent risk factors for progression to AKI III, to explore the impact of MAP and CVP separately, and to investigate the impact of MPP in pre-defined sub-groups.

Results

Among 2118 ICU patients, 790 patients (37%) developed AKI I of whom 205 underwent advanced haemodynamic monitoring within 12 h of AKI stage I. Their median MPP was 59 mmHg. AKI I patients with a MPP ≤59 mmHg had a significantly higher risk of progressing to AKI stage III (48.6% versus 34%, respectively; p = 0.0034). This association was stronger in patients with ischemic heart disease, congestive cardiac failure or without pre-existing hypertension and in patients with a MAP <65 mmHg for >1 h. As individual components, a raised CVP was independently associated with progression to AKI stage III but MAP alone was not an independent risk factor for AKI progression.

Conclusion

MPP <60 mmHg was independently associated with AKI progression. CVP was the key component of MPP.

High-resolution renal perfusion mapping using contrast-enhanced ultrasonography in ischemia-reperfusion injury monitors changes in renal microperfusion

Alterations in renal microperfusion play an important role in the development of acute kidney injury with long-term consequences. Here we used contrast-enhanced ultrasonography as a novel method for depicting intrarenal distribution of blood flow. After infusion of microbubble contrast agent, bubbles were collapsed in the kidney and postbubble destruction refilling was measured in various regions of the kidney. Local perfusion was monitored in vivo at 15, 30, 45, 60 minutes and 24 hours after 28 minutes of bilateral ischemia in 12 mice. High-resolution, pixel-by-pixel analysis was performed on each imaging clip using customized software, yielding parametric perfusion maps of the kidney, representing relative blood volume in each pixel. These perfusion maps revealed that outer medullary perfusion decreased disproportionately to the reduction in the cortical and inner medullary perfusion after ischemia. Outer medullary perfusion was significantly decreased by 69% at 60 minutes postischemia and remained significantly less (40%) than preischemic levels at 24 hours postischemia. Thus, contrast-enhanced ultrasonography with high-resolution parametric perfusion maps can monitor changes in renal microvascular perfusion in space and time in mice. This novel technique can be translated to clinical use in man.

Could Biomarkers Direct Therapy for the Septic Patient?

Sepsis is a serious medical condition caused by a severe systemic inflammatory response to a bacterial, fungal, or viral infection that most commonly affects neonates and the elderly. Advances in understanding the pathophysiology of sepsis have resulted in guidelines for care that have helped reduce the risk of dying from sepsis for both children and older adults. Still, over the past three decades, a large number of clinical trials have been undertaken to evaluate pharmacological agents for sepsis. Unfortunately, all of these trials have failed, with the use of some agents even shown to be harmful. One key issue in these trials was the heterogeneity of the patient population that participated. What has emerged is the need to target therapeutic interventions to the specific patient's underlying pathophysiological processes, rather than looking for a universal therapy that would be effective in a "typical" septic patient, who does not exist. This review supports the concept that identification of the right biomarkers that can direct therapy and provide timely feedback on its effectiveness will enable critical care physicians to decrease mortality of patients with sepsis and improve the quality of life of survivors.

Renal Hemodynamics in AKI: In Search of New Treatment Targets

Novel therapeutic interventions are required to prevent or treat AKI. To expedite progress in this regard, a consensus conference held by the Acute Dialysis Quality Initiative was convened in April of 2014 to develop recommendations for research priorities and future directions. Here, we highlight the concepts related to renal hemodynamics in AKI that are likely to reveal new treatment targets on investigation. Overall, we must better understand the interactions between systemic, total renal, and glomerular hemodynamics, including the role of tubuloglomerular feedback. Furthermore, the net consequences of therapeutic maneuvers aimed at restoring glomerular filtration need to be examined in relation to the nature, magnitude, and duration of the insult. Additionally, microvascular blood flow heterogeneity in AKI is now recognized as a common occurrence; timely interventions to preserve the renal microcirculatory flow may interrupt the downward spiral of injury toward progressive kidney failure and should, therefore, be investigated. Finally, development of techniques that permit an integrative physiologic approach, including direct visualization of renal microvasculature and measurement of oxygen kinetics and mitochondrial function in intact tissue in all nephron segments, may provide new insights into how the kidney responds to various injurious stimuli and allow evaluation of new therapeutic strategies.

Contrast-enhanced ultrasound to evaluate changes in renal cortical perfusion around cardiac surgery: a pilot study

Introduction

Contrast-enhanced ultrasound (CEUS) is a new technique that might enable portable and non-invasive organ perfusion quantification at the bedside. However, it has not yet been tested in critically ill patients. We sought to establish CEUS's feasibility, safety, reproducibility and potential diagnostic value in the assessment of renal cortical perfusion in the peri-operative period in cardiac surgery patients.

Methods

We recruited twelve patients deemed at risk of acute kidney injury (AKI) planned for elective cardiac surgery. We performed renal CEUS with destruction-replenishment sequences before the operation, on ICU arrival and the day following the admission. Enhancement was obtained with Sonovue^® (Bracco, Milano, Italy) at an infusion rate of 1 ml/min. We collected hemodynamic parameters before, during and after contrast agent infusion. At each study time, we obtained five video sequences, which were analysed using dedicated software by two independent radiologists blinded to patient and time. The main output was a perfusion index (PI), corresponding to the ratio of relative blood volume (RBV) over mean transit time (mTT).

Results

All 36 renal CEUS studies, including 24 in the immediate post-operative period could be performed and were well tolerated. Correlation between readers for PI was excellent (R² = 0.96, P < 0.0001). Compared with baseline, there was no overall difference in median PI's on ICU admission. However, the day after surgery, median PI's had decreased by 50% (P < 0.01) (22% decrease in RBV (P = 0.09); 48% increase in mTT (P = 0.04), both suggestive of decreased perfusion). These differences persisted after correction for haemoglobin; vasopressors use and mean arterial pressure. Four patients developed AKI in the post-operative period.

Conclusions

CEUS appears feasible and well-tolerated in patients undergoing cardiac surgery even immediately after ICU admission. CEUS derived-parameters suggest a decrease in renal perfusion occurring within 24 hours of surgery.