Design of clinical trials in AKI: a report from an NIDDK workshop. Trials of patients with sepsis and in selected hospital settings

Patient Preferences and Priorities for the Design of an Acute Kidney Injury Prevention Trial: Findings from a Consensus Workshop

Key Points

Background

High-quality clinical trials are needed to establish the efficacy and safety of novel therapies for AKI prevention. In this consensus workshop, we identified patient and caregiver priorities for recruitment, intervention delivery, and outcomes of a clinical trial of cilastatin to prevent nephrotoxic AKI.

Methods

We included adults with lived experience of AKI, CKD, or risk factors of AKI (e.g., critical care hospitalization) and their caregivers. Using a modified nominal group technique approach, we conducted a series of hybrid in-person/virtual discussions covering three clinical trial topic areas: (1) consent and recruitment, (2) intervention delivery, and (3) trial outcomes. Participants voted on their top preferences in each topic area, and discussion transcripts were analyzed inductively using conventional content analysis.

Results

Thirteen individuals (11 patients, two caregivers) participated in the workshop. For consent and recruitment, participants prioritized technology enabled prescreening and involvement of family members in the consent process. For intervention delivery, participants prioritized measures to facilitate ease of intervention administration and return visits. For trial outcomes, participants identified kidney-related and other clinical outcomes (e.g., AKI, CKD, cardiovascular events) as top priorities. Analysis of transcripts provided insight into care team and family involvement in trial-related decisions, implications of allocation to a placebo arm, and impact of participants' experiences of AKI and critical illness.

Conclusions

Findings from our workshop will directly inform development of a clinical trial protocol of cilastatin for nephrotoxic AKI prevention and can assist others in patient-centered approaches to AKI trial design.

INCREASE IN CHLORIDE IS ASSOCIATED WITH MAJOR ADVERSE KIDNEY EVENTS IN CRITICALLY ILL PATIENTS

ABSTRACT

Purpose: This study aimed to identify the association between hyperchloremia at intensive care unit (ICU) admission and/or the increase of blood chloride levels and the incidence of major adverse kidney events within 30 days (MAKE30) in critically ill adults. Methods: We conducted a retrospective study to analyze the data of all adult patients admitted to the ICU of a tertiary academic hospital in China between April 2020 and April 2022. Patients were categorized based on their admission chloride levels (hyperchloremia ≥110 mmol/L and nonhyperchloremia <110 mmol/L) and stratified on the increased chloride levels 48 h after ICU admission (∆Cl ≥5 mmol/L and ∆Cl <5 mmol/L). The primary outcome was the MAKE30 incidence, including in-hospital death, new receipt of renal replacement therapy (RRT), and persistent renal dysfunction (PRD). Association between hyperchloremia at ICU admission and/or the increase of chloride and the incidence of MAKE30 were assessed using logistic regression. Result: A total of 2,024 patients with a median age of 67 years (interquartile range [IQR], 55-76 years) and a median Acute Physiology and Chronic Health Evaluation II score of 22 (IQR, 17-28) were included. Hyperchloremia occurred in 30.9% (n = 625), and ΔCl ≥5 mmol/L occurred in 18.5% (n = 375) of all ICU patients. The overall MAKE30 incidence was 33.6% (n = 680), including a 10.9% of 30-day hospital mortality (n = 220; as well as overall in-hospital mortality, 11.8% [n = 238]), a 20.2% (n = 408) of PRD, and a 18.0% (n = 365) of new RRT. After adjusted for confounders, it was found that ΔCl ≥5 mmol/L (odds ratio [OR], 1.46; 95% confidence interval [CI], 1.096-1.93; P = 0.010), but not hyperchloremia (OR, 0.99; 95% CI, 0.77-1.28; P = 0.947), was associated with increased incidence of MAKE30. Conclusion: An increased chloride level in the first 48 h of ICU admission was an independent risk factor for MAKE30, whereas hyperchloremia at ICU admission was not associated with an increased incidence of MAKE30. Large-scale prospective studies are needed to verify our findings.

Efficacy of umbilical cord mesenchymal stem cell transfusion for the treatment of severe AKI: a protocol for a randomised controlled trial

INTRODUCTION

Acute kidney injury (AKI) is a common and severe clinical problem that is associated with high mortality, a long hospital stays and high healthcare resource consumption. Approximately a quarter of AKI survivors will develop chronic kidney disease. Mesenchymal stem cells (MSCs) are multipotent stem cells with antiapoptotic, immunomodulatory, antioxidative and proangiogenic properties. Therefore, MSCs have been considered as a potential new therapy for the treatment of AKI. Several clinical trials have been performed, but the results have been inconsistent. This trial investigated whether MSCs can improve renal recovery and mortality in patients with severe AKI.

METHODS AND ANALYSIS

One hundred subjects suffering from severe AKI will participate in this patient-blinded, randomised, placebo-controlled, parallel design clinical trial. Participants will be randomly assigned to receive two doses of MSCs or placebo (saline) on days 0 and 7. Urinary biomarkers of renal injury and repair will be measured using commercially available ELISA kits. The main outcome measures are changes in renal function levels within the first 28 days following MSC infusion.

ETHICS AND DISSEMINATION

The study was approved by the Ethics Committee of the Chinese PLA General Hospital. The findings of the study will be disseminated through public and scientific channels.

TRIAL REGISTRATION NUMBER

NCT04194671.

Utility of bedside ultrasound derived hepatic and renal parenchymal flow patterns to guide management of acute kidney injury

PURPOSE OF REVIEW

Ideal fluid management of critically ill patients is maintaining an adequate perfusion pressure but avoiding venous congestion. Venous excess ultrasound score (VExUS) quantifies venous congestion to guide the management of fluid balance.

RECENT FINDINGS

VExUS of abdominal veins measures fluid tolerance and helps clinicians avoid congestion. VExUS scoring predicts the development of acute kidney injury (AKI) that is a common hospital problem resulting in higher mortality and morbidity. VExUS can predict patients at risk of developing AKI post cardiac surgery. VExUS has been associated with an increase in adverse outcomes in a general intensive care population. Hepatic vein ultrasound can manifest as a sequela of right heart failure and pulmonary hypertension. Intrarenal congestion suggests poorer prognosis in heart failure patients. VExUS score has been used in decision-making to remove fluid in patients with cardiorenal syndrome. VExUS scoring may help curtail overly aggressive fluid resuscitation for patients with septic shock and help avoid iatrogenic 'salt water drowning'.

SUMMARY

We summarize the technique and clinical practice of VExUS to help guide fluid balance across different populations of critically ill patients.

Systemic immune-inflammation index predicts postoperative acute kidney injury in hepatocellular carcinoma patients after hepatectomy

The systemic immune-inflammation index (SII) is an independent prognostic predictor of hepatocellular carcinoma (HCC). The present investigation examined whether an association exists between preoperative SII value and postoperative acute kidney injury (pAKI) in HCC patients.The study included 479 hepatitis B virus (HBV)-associated HCC patients undergoing hepatectomy. The SII was calculated as P × N/L, where P, N, and L represent the counts of platelets, neutrophils, and lymphocytes in routine blood test, respectively. After propensity score matching, logistic regression analysis was used to explore independent predictors of pAKI in HCC patients.pAKI was confirmed in 51 patients (10.8%). The average SII value was higher in patients with pAKI than patients without pAKI. After multivariate logistic regression analysis, SII, history of hypertension, and tumor size, among others, were found to be predictors of pAKI. The optimal threshold value of SII for predicting pAKI was found to be 547.84 × 109/L. Multivariate analysis performed after propensity score matching confirmed that SII ≥ 547.84 × 109/L was an independent predictor of pAKI.The preoperative SII qualifies as a novel, independent predictor of pAKI in HCC patients with HBV infection who underwent hepatectomy.

Balanced Crystalloid Solutions

Intravenous fluid therapy is the most common intervention received by acutely ill patients. Historically, saline (0.9% sodium chloride) has been the most frequently administered intravenous fluid, especially in North America. Balanced crystalloid solutions (e.g., lactated Ringer's, Plasma-Lyte) are an increasingly used alternative to saline. Balanced crystalloids have a sodium, potassium, and chloride content closer to that of extracellular fluid and, when given intravenously, have fewer adverse effects on acid-base balance. Preclinical research has demonstrated that saline may cause hyperchloremic metabolic acidosis, inflammation, hypotension, acute kidney injury, and death. Studies of patients and healthy human volunteers suggest that even relatively small volumes of saline may exert physiological effects. Randomized trials in the operating room have demonstrated that using balanced crystalloids rather than saline prevents the development of hyperchloremic metabolic acidosis and may reduce the need for vasopressors. Observational studies among critically ill adults have associated receipt of balanced crystalloids with lower rates of complications, including acute kidney injury and death. Most recently, large randomized trials among critically ill adults have examined whether balanced crystalloids result in less death or severe renal dysfunction than saline. Although some of these trials are still ongoing, a growing body of evidence raises fundamental concerns regarding saline as the primary intravenous crystalloid for critically ill adults and highlights fundamental unanswered questions for future research about fluid therapy in critical illness.

Carbon monoxide: An emerging therapy for acute kidney injury

Treating acute kidney injury (AKI) represents an important unmet medical need both in terms of the seriousness of this medical problem and the number of patients. There is also a large untapped market opportunity in treating AKI. Over the years, there has been much effort in search of therapeutics with minimal success. However, over the same time period, new understanding of the underlying pathobiology and molecular mechanisms of kidney injury have undoubtedly helped the search for new therapeutics. Along this line, carbon monoxide (CO) has emerged as a promising therapeutic agent because of its demonstrated cytoprotective, and immunomodulatory effects. CO has also been shown to sensitize cancer, but not normal cells, to chemotherapy. This is particularly important in treating cisplatin-induced AKI, a common clinical problem that develops in patients receiving cisplatin therapies for a number of different solid organ malignancies. This review will examine and make the case that CO be developed into a therapeutic agent against AKI.

Roadblocks and Opportunities to the Implementation of Novel Therapies for Acute Kidney Injury: A Narrative Review

Background:

Acute kidney injury (AKI) is a complex and heterogeneous clinical syndrome with limited effective treatment options. Therefore, a coherent research structure considering AKI pathophysiology, treatment, translation, and implementation is critical to advancing patient care in this area.

Purpose of review:

In this narrative review, we discuss novel therapies for AKI from their journey from bench to bedside to population and focus on roadblocks and opportunities to their successful implementation.

Sources of information:

Peer-reviewed articles, opinion pieces from research leaders and research funding agencies, and clinical and research expertise.

Methods:

This narrative review details the challenges of translation of preclinical studies in AKI and highlights trending research areas and innovative designs in the field. Key developments in preclinical research, clinical trials, and knowledge translation are discussed. Furthermore, this article discusses the current need to involve patients in clinical research and the barriers and opportunities for effective knowledge translation.

Key findings:

Preclinical studies have largely been unsuccessful in generating novel therapies for AKI, due both to the complexity and heterogeneity of the disease, as well as the limitations of commonly available preclinical models of AKI. The emergence of kidney organoid technology may be an opportunity to reverse this trend. However, the roadblocks encountered at the bench have not precluded researchers from running well-designed and impactful clinical trials, and the field of renal replacement therapy in AKI is highlighted as an area that has been particularly active. Meanwhile, knowledge translation initiatives are bolstered by the presence of large administrative databases to permit ongoing monitoring of clinical practices and outcomes, with research output from such evaluations having the potential to directly impact patient care and inform the generation of meaningful clinical practice guidelines.

Limitations:

There are limited objective data examining the process of knowledge creation and translation in AKI, and as such the opinions and research areas of the authors are significantly drawn upon in the discussion.

Implications:

The use of an organized knowledge-to-action framework involving multiple stakeholders, especially patient partners, is critical to translating basic research findings to improvements in patient care in AKI, an area where effective treatment options are lacking.

Long-term outcomes in mouse models of ischemia-reperfusion-induced acute kidney injury

Severe acute kidney injury has a high mortality and is a risk factor for progressive chronic kidney disease. None of the potential therapies that have been identified in preclinical studies have successfully improved clinical outcomes. This failure is partly because animal models rarely reflect the complexity of human disease: most preclinical studies are short term and are commonly performed in healthy, young, male mice. Therapies that are effective in preclinical models that share common clinical features seen in patients with acute kidney injury, including genetic diversity, different sexes, and comorbidities, and evaluate long-term outcomes are more likely to predict success in the clinic. Here, we evaluated susceptibility to chronic kidney disease after ischemia-reperfusion injury with delayed nephrectomy by monitoring long-term functional and histological responses to injury. We defined conditions required to induce long-term postinjury renal dysfunction and fibrosis without increased mortality in a reproducible way and evaluate effect of mouse strains, sexes, and preexisting diabetes on these responses.

Capillary rarefaction is more closely associated with CKD progression after cisplatin, rhabdomyolysis, and ischemia-reperfusion-induced AKI than renal fibrosis

Acute kidney injury (AKI) is a strong independent predictor of mortality and often results in incomplete recovery of renal function, leading to progressive chronic kidney disease (CKD). Many clinical trials have been conducted on the basis of promising preclinical data, but no therapeutic interventions have been shown to improve long-term outcomes after AKI. This is partly due to the failure of preclinical studies to accurately model clinically relevant injury and long-term outcomes on CKD progression. Here, we evaluated the long-term effects of AKI on CKD progression in three animal models reflecting diverse etiologies of AKI: repeat-dose cisplatin, rhabdomyolysis, and ischemia-reperfusion injury. Using transdermal measurement of glomerular filtration rate as a clinically relevant measure of kidney function and quantification of peritubular capillary density to measure capillary rarefaction, we showed that repeat-dose cisplatin caused capillary rarefaction and decreased renal function in mice without a significant increase in interstitial fibrosis, whereas rhabdomyolysis-induced AKI led to severe interstitial fibrosis, but renal function and peritubular capillary density were preserved. Furthermore, long-term experiments in mice with unilateral ischemia-reperfusion injury showed that restoration of renal function 12 wk after a contralateral nephrectomy was associated with increasing fibrosis, but a reversal of capillary rarefaction was seen at 4 wk. These data demonstrate that clear dissociation between kidney function and fibrosis in these models of AKI to CKD progression and suggest that peritubular capillary rarefaction is more strongly associated with CKD progression than renal fibrosis.

Buffered solutions versus 0.9% saline for resuscitation in critically ill adults and children

BACKGROUND

Fluid therapy is one of the main interventions provided for critically ill patients, although there is no general consensus regarding the type of solution. Among crystalloid solutions, 0.9% saline is the most commonly administered. Buffered solutions may offer some theoretical advantages (less metabolic acidosis, less electrolyte disturbance), but the clinical relevance of these remains unknown.

OBJECTIVES

To assess the effects of buffered solutions versus 0.9% saline for resuscitation in critically ill adults and children.

SEARCH METHODS

We searched the following databases to July 2018: CENTRAL, MEDLINE, Embase, CINAHL, and four trials registers. We checked references, conducted backward and forward citation searching of relevant articles, and contacted study authors to identify additional studies. We imposed no language restrictions.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) with parallel or cross-over design examining buffered solutions versus intravenous 0.9% saline in a critical care setting (resuscitation or maintenance). We included studies on participants with critical illness (including trauma and burns) or undergoing emergency surgery during critical illness who required intravenous fluid therapy. We included studies of adults and children. We included studies with more than two arms if they fulfilled all of our inclusion criteria. We excluded studies performed in persons undergoing elective surgery and studies with multiple interventions in the same arm.

DATA COLLECTION AND ANALYSIS

We used Cochrane's standard methodological procedures. We assessed our intervention effects using random-effects models, but when one or two trials contributed to 75% of randomized participants, we used fixed-effect models. We reported outcomes with 95% confidence intervals (CIs).

MAIN RESULTS

We included 21 RCTs (20,213 participants) and identified three ongoing studies. Three RCTs contributed 19,054 participants (94.2%). Four RCTs (402 participants) were conducted among children with severe dehydration and dengue shock syndrome. Fourteen trials reported results on mortality, and nine reported on acute renal injury. Sixteen included trials were conducted in adults, four in the paediatric population, and one trial limited neither minimum or maximum age as an inclusion criterion. Eight studies involving 19,218 participants were rated as high methodological quality (trials with overall low risk of bias according to the domains: allocation concealment, blinding of participants/assessors, incomplete outcome data, and selective reporting), and in the remaining trials, some form of bias was introduced or could not be ruled out.We found no evidence of an effect of buffered solutions on in-hospital mortality (odds ratio (OR) 0.91, 95% CI 0.83 to 1.01; 19,664 participants; 14 studies; high-certainty evidence). Based on a mortality rate of 119 per 1000, buffered solutions could reduce mortality by 21 per 1000 or could increase mortality by 1 per 1000. Similarly, we found no evidence of an effect of buffered solutions on acute renal injury (OR 0.92, 95% CI 0.84 to 1.00; 18,701 participants; 9 studies; low-certainty evidence). Based on a rate of 121 per 1000, buffered solutions could reduce the rate of acute renal injury by 19 per 1000, or result in no difference in the rate of acute renal injury. Buffered solutions did not show an effect on organ system dysfunction (OR 0.80, 95% CI 0.40 to 1.61; 266 participants; 5 studies; very low-certainty evidence). Evidence on the effects of buffered solutions on electrolyte disturbances varied: potassium (mean difference (MD) 0.09, 95% CI -0.10 to 0.27; 158 participants; 4 studies; very low-certainty evidence); chloride (MD -3.02, 95% CI -5.24 to -0.80; 351 participants; 7 studies; very low-certainty evidence); pH (MD 0.04, 95% CI 0.02 to 0.06; 200 participants; 3 studies; very low-certainty evidence); and bicarbonate (MD 2.26, 95% CI 1.25 to 3.27; 344 participants; 6 studies; very low-certainty evidence).

AUTHORS' CONCLUSIONS

We found no effect of buffered solutions on preventing in-hospital mortality compared to 0.9% saline solutions in critically ill patients. The certainty of evidence for this finding was high, indicating that further research would detect little or no difference in mortality. The effects of buffered solutions and 0.9% saline solutions on preventing acute kidney injury were similar in this setting. The certainty of evidence for this finding was low, and further research could change this conclusion. Patients treated with buffered solutions showed lower chloride levels, higher levels of bicarbonate, and higher pH. The certainty of evidence for these findings was very low. Future research should further examine patient-centred outcomes such as quality of life. The three ongoing studies once published and assessed may alter the conclusions of the review.

Long-term outcomes after extracorporeal membrane oxygenation in patients with dialysis-requiring acute kidney injury: A cohort study

Background

Acute kidney injury (AKI) is a common complication of extracorporeal membrane oxygenation (ECMO) treatment. The aim of this study was to elucidate the long-term outcomes of adult patients with AKI who receive ECMO.

Materials and methods

The study analyzed encrypted datasets from Taiwan’s National Health Insurance Research Database. The data of 3251 patients who received first-time ECMO treatment between January 1, 2003, and December 31, 2013, were analyzed. Characteristics and outcomes were compared between patients who required dialysis for AKI (D-AKI) and those who did not in order to evaluate the impact of D-AKI on long-term mortality and major adverse kidney events.

Results

Of the 3251 patients, 54.1% had D-AKI. Compared with the patients without D-AKI, those with D-AKI had higher rates of all-cause mortality (52.3% vs. 33.3%; adjusted hazard ratio [aHR] 1.82, 95% confidence interval [CI] 1.53–2.17), chronic kidney disease (13.7% vs. 8.1%; adjusted subdistribution HR [aSHR] 1.66, 95% CI 1.16–2.38), and end-stage renal disease (5.2% vs. 0.5%; aSHR 14.28, 95% CI 4.67–43.62). The long-term mortality of patients who survived more than 90 days after discharge was 22.0% (153/695), 32.3% (91/282), and 50.0% (10/20) in the patients without D-AKI, with recovery D-AKI, and with nonrecovery D-AKI who required long-term dialysis, respectively, demonstrating a significant trend (Pfor trend <0.001).

Conclusion

AKI is associated with an increased risk of long-term mortality and major adverse kidney events in adult patients who receive ECMO.

Balanced Crystalloids versus Saline in Critically Ill Adults

BACKGROUND:

Both balanced crystalloids and saline are used for intravenous fluid administration among critically ill adults. Which results in better clinical outcomes remains unknown.

METHODS:

In a pragmatic, cluster-randomized, multiple-crossover trial in five intensive care units at an academic center, we assigned 15,802 adults to receive saline (0.9% sodium chloride) or balanced crystalloids (lactated Ringer’s solution or Plasma-Lyte A®), according to the randomization of the unit to which they were admitted. The primary outcome was Major Adverse Kidney Events within 30 days (MAKE30), i.e., the composite of death, new renal replacement therapy, or persistent creatinine elevation ≥ 200% of baseline – all censored at the first of hospital discharge or 30 days.

RESULTS:

In the balanced crystalloid group, 1,139 patients (14.3%) experienced MAKE30, compared to 1,211 patients (15.4%) in the saline group (marginal odds ratio, 0.91; 95% confidence interval, 0.84–0.99; conditional odds ratio, 0.90; 95% confidence interval, 0.82–0.99; P=0.04). Thirty-day in-hospital mortality was 10.3% in the balanced crystalloid group and 11.1% in the saline group (P=0.06). The incidence of new renal replacement therapy was 2.5% and 2.9% respectively (P=0.08), and the incidence of persistent creatinine elevation was 6.4% and 6.6% respectively (P=0.60).

CONCLUSIONS:

Among critically ill adults, the use of balanced crystalloids for intravenous fluid administration appeared to reduce the composite outcome of in-hospital mortality, new renal replacement therapy, and persistent renal dysfunction compared with the use of saline. (SMART-MED and SMART-SURG ClinicalTrials.gov numbers, NCT02444988 and NCT02547779.)

Translating Knowledge Into Therapy for Acute Kidney Injury

No therapies have been shown to improve outcomes in patients with acute kidney injury (AKI). Given the high morbidity and mortality associated with AKI this represents an important unmet medical need. A common feature of all of the therapeutic development efforts for AKI is that none were driven by target selection or preclinical modeling that was based primarily on human data. This is important when considering a heterogeneous and dynamic condition such as AKI, in which in the absence of more accurate molecular classifications, clinical cohorts are likely to include patients with different types of injury at different stages in the injury and repair continuum. The National Institutes of Health precision medicine initiative offers an opportunity to address this. By creating a molecular tissue atlas of AKI, defining patient subgroups, and identifying critical cells and pathways involved in human AKI, this initiative has the potential to transform our current approach to therapeutic discovery. In this review, we discuss the opportunities and challenges that this initiative presents, with a specific focus on AKI, what additional efforts will be needed to apply these discoveries to therapeutic development, and how we believe this effort might lead to the development of new therapeutics for subsets of patients with AKI.

The effect of low-dose furosemide in critically ill patients with early acute kidney injury: A pilot randomized blinded controlled trial (the SPARK study)

PURPOSE

Furosemide is commonly prescribed in acute kidney injury (AKI). Prior studies have found conflicting findings on whether furosemide modifies the course and outcome of AKI.

METHODS

Pilot multi-center randomized blinded placebo-controlled trial in adult patients with AKI admitted to three intensive care units. Participants were randomly allocated to furosemide bolus and infusion or 0.9% saline placebo. Primary endpoint was worsening AKI, defined by the RIFLE criteria. Secondary endpoints were kidney recovery, renal replacement therapy (RRT) and adverse events.

RESULTS

The trial was terminated after enrollment of 73 participants (37 to furosemide and 36 to placebo). Mean (SD) age was 61.7 (14.3), 79.5% were medical admissions, mean (SD) APACHE II score was 26.6 (7.8), 90.4% received mechanical ventilation and 61.6% received vasoactives. Groups were similar at baseline. No differences were found in the proportion with worsening AKI (43.2% vs. 37.1%, p=0.6), kidney recovery (29.7% vs. 42.9%, p=0.3), or RRT (27.0% s. 28.6%, p=0.8). Adverse events, mostly electrolyte abnormalities, were more common in furosemide-treated patients (p<0.001). Protocol deviations were common, due often to supplementary furosemide.

CONCLUSIONS

In this pilot trial, furosemide did not reduce the rate of worsening AKI, improve recovery or reduce RRT; however, was associated with greater electrolyte abnormalities.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00978354 registered September 9, 2014.

Bridging translation for acute kidney injury with better preclinical modeling of human disease

The current lack of effective therapeutics for patients with acute kidney injury (AKI) represents an important and unmet medical need. Given the importance of the clinical problem, it is time for us to take a few steps back and reexamine current practices. The focus of this review is to explore the extent to which failure of therapeutic translation from animal studies to human studies stems from deficiencies in the preclinical models of AKI. We will evaluate whether the preclinical models of AKI that are commonly used recapitulate the known pathophysiologies of AKI that are being modeled in humans, focusing on four common scenarios that are studied in clinical therapeutic intervention trials: cardiac surgery-induced AKI; contrast-induced AKI; cisplatin-induced AKI; and sepsis associated AKI. Based on our observations, we have identified a number of common limitations in current preclinical modeling of AKI that could be addressed. In the long term, we suggest that progress in developing better preclinical models of AKI will depend on developing a better understanding of human AKI. To this this end, we suggest that there is a need to develop greater in-depth molecular analyses of kidney biopsy tissues coupled with improved clinical and molecular classification of patients with AKI.

Vagus nerve stimulation mediates protection from kidney ischemia-reperfusion injury through α7nAChR+ splenocytes

The nervous and immune systems interact in complex ways to maintain homeostasis and respond to stress or injury, and rapid nerve conduction can provide instantaneous input for modulating inflammation. The inflammatory reflex referred to as the cholinergic antiinflammatory pathway regulates innate and adaptive immunity, and modulation of this reflex by vagus nerve stimulation (VNS) is effective in various inflammatory disease models, such as rheumatoid arthritis and inflammatory bowel disease. Effectiveness of VNS in these models necessitates the integration of neural signals and α7 nicotinic acetylcholine receptors (α7nAChRs) on splenic macrophages. Here, we sought to determine whether electrical stimulation of the vagus nerve attenuates kidney ischemia-reperfusion injury (IRI), which promotes the release of proinflammatory molecules. Stimulation of vagal afferents or efferents in mice 24 hours before IRI markedly attenuated acute kidney injury (AKI) and decreased plasma TNF. Furthermore, this protection was abolished in animals in which splenectomy was performed 7 days before VNS and IRI. In mice lacking α7nAChR, prior VNS did not prevent IRI. Conversely, adoptive transfer of VNS-conditioned α7nAChR splenocytes conferred protection to recipient mice subjected to IRI. Together, these results demonstrate that VNS-mediated attenuation of AKI and systemic inflammation depends on α7nAChR-positive splenocytes.

A wandering path toward prevention for acute kidney injury

Acute kidney injury (AKI) is a common cause of hospital-related mortality; therefore, strategies to either prevent or treat this complication are of great interest. In this issue of the JCI, Inoue, Abe, and colleagues have uncovered a targetable neuroimmunomodulatory mechanism that protects mice from ischemia-reperfusion injury (IRI) and subsequent AKI. Specifically, the authors demonstrate that vagus nerve stimulation (VNS) activates the cholinergic antiinflammatory pathway (CAP), resulting in activation of antiinflammatory effects via α7 nicotinic acetylcholine receptor-expressing splenic macrophages. Together, the results of this study have potential clinical implications in the prevention of AKI in at-risk individuals.

Inflammation in AKI: Current Understanding, Key Questions, and Knowledge Gaps

Inflammation is a complex biologic response that is essential for eliminating microbial pathogens and repairing tissue after injury. AKI associates with intrarenal and systemic inflammation; thus, improved understanding of the cellular and molecular mechanisms underlying the inflammatory response has high potential for identifying effective therapies to prevent or ameliorate AKI. In the past decade, much knowledge has been generated about the fundamental mechanisms of inflammation. Experimental work in small animal models has revealed many details of the inflammatory response that occurs within the kidney after typical causes of AKI, including insights into the molecular signals released by dying cells, the role of pattern recognition receptors, the diverse subtypes of resident and recruited immune cells, and the phased transition from destructive to reparative inflammation. Although this expansion of the basic knowledge base has increased the number of mechanistically relevant targets of intervention, progress in developing therapies that improve AKI outcomes by modulation of inflammation remains slow. In this article, we summarize the most important recent developments in understanding the inflammatory mechanisms of AKI, highlight key limitations of the commonly used animal models and clinical trial designs that may prevent successful clinical application, and suggest priority approaches for research toward clinical translation in this area.

Diagnostic Criteria for Acute Kidney Injury: Present and Future

Acute kidney injury (AKI) is a clinical diagnosis guided by standard criteria based on changes in serum creatinine, urine output, or both. Severity of AKI is determined by the magnitude of increase in serum creatinine or decrease in urine output. Patients manifesting both oliguria and azotemia and those in which these impairments are persistent are more likely to have worse disease and worse outcomes. Short- and long-term outcomes are worse when patients have some stage of AKI by both criteria. New biomarkers for AKI may substantially aid in the risk assessment and evaluation of patients at risk for AKI.

Furosemide Stress Test and Biomarkers for the Prediction of AKI Severity

Clinicians have access to limited tools that predict which patients with early AKI will progress to more severe stages. In early AKI, urine output after a furosemide stress test (FST), which involves intravenous administration of furosemide (1.0 or 1.5 mg/kg), can predict the development of stage 3 AKI. We measured several AKI biomarkers in our previously published cohort of 77 patients with early AKI who received an FST and evaluated the ability of FST urine output and biomarkers to predict the development of stage 3 AKI (n=25 [32.5%]), receipt of RRT (n=11 [14.2%]), or inpatient mortality (n=16 [20.7%]). With an area under the curve (AUC)±SEM of 0.87±0.09 (P<0.0001), 2-hour urine output after FST was significantly better than each urinary biomarker tested in predicting progression to stage 3 (P<0.05). FST urine output was the only biomarker to significantly predict RRT (0.86±0.08; P=0.001). Regardless of the end point, combining FST urine output with individual biomarkers using logistic regression did not significantly improve risk stratification (ΔAUC, P>0.10 for all). When FST urine output was assessed in patients with increased biomarker levels, the AUC for progression to stage 3 improved to 0.90±0.06 and the AUC for receipt of RRT improved to 0.91±0.08. Overall, in the setting of early AKI, FST urine output outperformed biochemical biomarkers for prediction of progressive AKI, need for RRT, and inpatient mortality. Using a FST in patients with increased biomarker levels improves risk stratification, although further research is needed.

Classifying AKI by Urine Output versus Serum Creatinine Level

Severity of AKI is determined by the magnitude of increase in serum creatinine level or decrease in urine output. However, patients manifesting both oliguria and azotemia and those in which these impairments are persistent are more likely to have worse disease. Thus, we investigated the relationship of AKI severity and duration across creatinine and urine output domains with the risk for RRT and likelihood of renal recovery and survival using a large, academic medical center database of critically ill patients. We analyzed electronic records from 32,045 patients treated between 2000 and 2008, of which 23,866 (74.5%) developed AKI. We classified patients by levels of serum creatinine and/or urine output according to Kidney Disease Improving Global Outcomes staging criteria for AKI. In-hospital mortality and RRT rates increased from 4.3% and 0%, respectively, for no AKI to 51.1% and 55.3%, respectively, when serum creatinine level and urine output both indicated stage 3 AKI. Both short- and long-term outcomes were worse when patients had any stage of AKI defined by both criteria. Duration of AKI was also a significant predictor of long-term outcomes irrespective of severity. We conclude that short- and long-term risk of death or RRT is greatest when patients meet both the serum creatinine level and urine output criteria for AKI and when these abnormalities persist.

The relationship of intravenous fluid chloride content to kidney function in patients with severe sepsis or septic shock

BACKGROUND

Previous studies suggest a relationship between chloride-rich intravenous fluids and acute kidney injury in critically ill patients.

OBJECTIVES

The aim of this study was to evaluate the relationship of intravenous fluid chloride content to kidney function in patients with severe sepsis or septic shock.

METHODS

A retrospective chart review was performed to determine (1) quantity and type of bolus intravenous fluids, (2) serum creatinine (Cr) at presentation and upon discharge, and (3) need for emergent hemodialysis (HD) or renal replacement therapy (RRT). Linear regression was used for continuous outcomes, and logistic regression was used for binary outcomes and results were controlled for initial Cr. The primary outcome was change in Cr from admission to discharge. Secondary outcomes were need for HD/RRT, length of stay (LOS), mortality, and organ dysfunction.

RESULTS

There were 95 patients included in the final analysis; 48% (46) of patients presented with acute kidney injury, 8% (8) required first-time HD or RRT, 61% (58) were culture positive, 55% (52) were in shock, and overall mortality was 20% (19). There was no significant relationship between quantity of chloride administered in the first 24 hours with change in Cr (β = -0.0001, t = -0.86, R(2) = 0.92, P = .39), need for HD or RRT (odds ratio [OR] = 0.999; 95% confidence interval [CI], 0.999-1.000; P = .77), LOS >14 days (OR = 1.000; 95% CI, 0.999-1.000; P = .68), mortality (OR = 0.999; 95% CI, 0.999-1.000; P = .88), or any type of organ dysfunction.

CONCLUSION

Chloride administered in the first 24 hours did not influence kidney function in this cohort with severe sepsis or septic shock.

Validation of cell-cycle arrest biomarkers for acute kidney injury using clinical adjudication

RATIONALE

We recently reported two novel biomarkers for acute kidney injury (AKI), tissue inhibitor of metalloproteinases (TIMP)-2 and insulin-like growth factor binding protein 7 (IGFBP7), both related to G1 cell cycle arrest.

OBJECTIVES

We now validate a clinical test for urinary [TIMP-2]·[IGFBP7] at a high-sensitivity cutoff greater than 0.3 for AKI risk stratification in a diverse population of critically ill patients.

METHODS

We conducted a prospective multicenter study of 420 critically ill patients. The primary analysis was the ability of urinary [TIMP-2]·[IGFBP7] to predict moderate to severe AKI within 12 hours. AKI was adjudicated by a committee of three independent expert nephrologists who were masked to the results of the test.

MEASUREMENTS AND MAIN RESULTS

Urinary TIMP-2 and IGFBP7 were measured using a clinical immunoassay platform. The primary endpoint was reached in 17% of patients. For a single urinary [TIMP-2]·[IGFBP7] test, sensitivity at the prespecified high-sensitivity cutoff of 0.3 (ng/ml)(2)/1,000 was 92% (95% confidence interval [CI], 85-98%) with a negative likelihood ratio of 0.18 (95% CI, 0.06-0.33). Critically ill patients with urinary [TIMP-2]·[IGFBP7] greater than 0.3 had seven times the risk for AKI (95% CI, 4-22) compared with critically ill patients with a test result below 0.3. In a multivariate model including clinical information, urinary [TIMP-2]·[IGFBP7] remained statistically significant and a strong predictor of AKI (area under the curve, 0.70, 95% CI, 0.63-0.76 for clinical variables alone, vs. area under the curve, 0.86, 95% CI, 0.80-0.90 for clinical variables plus [TIMP-2]·[IGFBP7]).

CONCLUSIONS

Urinary [TIMP-2]·[IGFBP7] greater than 0.3 (ng/ml)(2)/1,000 identifies patients at risk for imminent AKI. Clinical trial registered with www.clinicaltrials.gov (NCT 01573962).

Association between AKI and long-term renal and cardiovascular outcomes in United States veterans

BACKGROUND AND OBJECTIVES

AKI is associated with major adverse kidney events (MAKE): death, new dialysis, and worsened renal function. CKD (arising from worsened renal function) is associated with a higher risk of major adverse cardiac events (MACE): myocardial infarction (MI), stroke, and heart failure. Therefore, the study hypothesis was that veterans who develop AKI during hospitalization for an MI would be at higher risk of subsequent MACE and MAKE.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients in the Veterans Affairs (VA) database who had a discharge diagnosis with International Classification of Diseases, Ninth Revision, code of 584.xx (AKI) or 410.xx (MI) and were admitted to a VA facility from October 1999 through December 2005 were selected for analysis. Three groups of patients were created on the basis of the index admission diagnosis and serum creatinine values: AKI, MI, or MI with AKI. Patients with mean baseline estimated GFR<45 ml/min per 1.73 m(2) were excluded. The primary outcomes assessed were mortality, MAKE, and MACE during the study period (maximum of 6 years). The combination of MAKE and MACE-major adverse renocardiovascular events (MARCE)-was also assessed.

RESULTS

A total of 36,980 patients were available for analysis. Mean age±SD was 66.8±11.4 years. The most deaths occurred in the MI+AKI group (57.5%), and the fewest (32.3%) occurred in patients with an uncomplicated MI admission. In both the unadjusted and adjusted time-to-event analyses, patients with AKI and AKI+MI had worse MARCE outcomes than those who had MI alone (adjusted hazard ratios, 1.37 [95% confidence interval, 1.32 to 1.42] and 1.92 [1.86 to 1.99], respectively).

CONCLUSIONS

Veterans who develop AKI in the setting of MI have worse long-term outcomes than those with AKI or MI alone. Veterans with AKI alone have worse outcomes than those diagnosed with an MI in the absence of AKI.

Plasma neutrophil gelatinase-associated lipocalin as a biomarker for acute kidney injury in critically ill patients with suspected sepsis

OBJECTIVES

The aim of this study was to investigate the diagnostic utility of plasma neutrophil gelatinase-associated lipocalin (NGAL) as an early objective biomarker to predict acute kidney injury (AKI) in critically ill patients with suspected sepsis, for whom procalcitonin (PCT) was used for the diagnosis and staging of sepsis.

DESIGN AND METHODS

Plasma NGAL was measured using the Triage NGAL Test (Alere, Inc., San Diego, CA, USA) in 231 samples obtained from patients with suspected sepsis. The results of NGAL were compared with those of Elecsys BRAHMS PCT (Roche Diagnostics, Basel, Switzerland). Renal failure was assessed using the renal subscore of Sepsis-related Organ Failure Assessment (SOFA) score. AKI was defined according to the Acute Kidney Injury Network criteria.

RESULTS

The concentrations of plasma NGAL were significantly different according to the five groups of PCT concentration (P<0.0001) and the renal subscore of SOFA score (P<0.0001). Plasma NGAL was significantly increased in the patients with AKI compared with those without AKI (416.5 ng/mL vs. 181.0 ng/mL, P=0.0223).

CONCLUSION

Plasma NGAL seems to be a highly sensitive and objective predictor of AKI in patients with sepsis. Plasma NGAL can be added for the diagnosis and staging of renal failure in sepsis.

Distinct injury markers for the early detection and prognosis of incident acute kidney injury in critically ill adults with preserved kidney function

The use of novel biomarkers to detect incident acute kidney injury (AKI) in the critically ill is hindered by heterogeneity of injury and the potentially confounding effects of prevalent AKI. Here we examined the ability of urine NGAL (NGAL), L-type Fatty Acid Binding Protein (L-FABP), and Cystatin C to predict AKI development, death, and dialysis in a nested case-control study of 380 critically ill adults with an eGFR over 60 ml/min/1.73 m². One-hundred thirty AKI cases were identified following biomarker measurement and were compared to 250 controls without AKI. Areas under the receiver-operator characteristic curves (AUC-ROCs) for discriminating incident AKI from non-AKI were 0.58(95%CI: 0.52-0.64), 0.59(0.52-0.65), and 0.50(0.48-0.57) for urine NGAL, L-FABP, and Cystatin C, respectively. The combined AUC-ROC for NGAL and L-FABP was 0.59(56-0.69). Both urine NGAL and L-FABP independently predicted AKI during multivariate regression; however, risk reclassification indices were mixed. Neither urine biomarker was independently associated with death or acute dialysis [NGAL hazard ratio 1.35(95%CI: 0.93-1.96), L-FABP 1.15(0.82-1.61)] though both independently predicted the need for acute dialysis [NGAL 3.44(1.73-6.83), L-FABP 2.36(1.30-4.25)]. Thus, urine NGAL and L-FABP independently associated with the development of incident AKI and receipt of dialysis but exhibited poor discrimination for incident AKI using conventional definitions.