Acute kidney injury: definitions and new paradigms

Urinary L-FABP Assay in the Detection of Acute Kidney Injury following Haematopoietic Stem Cell Transplantation

Background: Acute Kidney Injury (AKI) is a condition that affects a significant proportion of acutely unwell patients and is associated with a high mortality rate. Patients undergoing haemopoietic stem cell transplantation (HSCT) are in an extremely high group for AKI. Identifying a biomarker or panel of markers that can reliably identify at-risk individuals undergoing HSCT can potentially impact management and outcomes. Early identification of AKI can reduce its severity and improve prognosis. We evaluated the urinary Liver type fatty acid binding protein (L-FABP), a tubular stress and injury biomarker both as an ELISA and a point of care (POC) assay for AKI detection in HSCT. Methods: 85 patients that had undergone autologous and allogenic HSCT (35 and 50, respectively) had urinary L-FABP (uL-FABP) measured by means of a quantitative ELISA and a semi-quantitative POC at baseline, day 0 and 7 post-transplantation. Serum creatinine (SCr) was also measured at the same time. Patients were followed up for 30 days for the occurrence of AKI and up to 18 months for mortality. The sensitivity and specificity of uL-FABP as an AKI biomarker were evaluated and compared to the performance of sCr using ROC curve analysis and logistic regression. Results: 39% of participants developed AKI within 1 month of their transplantation. The incidence of AKI was higher in the allogenic group than in the autologous HTSC group (57% vs. 26%, p = 0.008) with the median time to AKI being 25 [range 9-30] days. This group was younger (median age 59 vs. 63, p < 0.001) with a lower percentage of multiple myeloma as the primary diagnosis (6% vs. 88%, p < 0.001). The median time to AKI diagnosis was 25 [range 9-30] days. uL-FABP (mcg/gCr) at baseline, day of transplant and on the 7th day post-transplant were 1.61, 5.39 and 10.27, respectively, for the allogenic group and 0.58, 4.36 and 5.14 for the autologous group. Both SCr and uL-FABP levels rose from baseline to day 7 post-transplantation, while the AUC for predicting AKI for baseline, day 0 and day 7 post-transplant was 0.54, 0.59 and 0.62 for SCr and for 0.49, 0.43 and 0.49 uL-FABP, respectively. Univariate logistic regression showed the risk of AKI to be increased in patients with allogenic HSCT (p = 0.004, 95%CI [0.1; 0.65]) and in those with impaired renal function at baseline (p = 0.01, 95%CI [0.02, 0.54]). The risk of AKI was also significantly associated with SCr levels on day 7 post-transplant (p = 0.03, 95%CI [1; 1.03]). Multivariate logistic regression showed the type of HSCT to be the strongest predictor of AKI at all time points, while SCr levels at days 0 and 7 also correlated with increased risk in the model that included uL-FABP levels at the corresponding time points. The POC device for uL-FABP measurement correlated with ELISA (p < 0.001, Spearman 'correlation' = 0.54) Conclusions: The urinary biomarker uL-FABP did not demonstrate an independent predictive value in the detection of AKI at all stages. The most powerful risk predictor of AKI in this setting appears to be allograft recipients and baseline renal impairment, highlighting the importance of clinical risk stratification. Urinary L-FAPB as a POC biomarker was comparable to ELISA, which provides an opportunity for simple and rapid testing. However, the utility of LFABP in AKI is unclear and needs further exploration. Whether screening through rapid testing of uL-FABP can prevent or reduce AKI severity is unknown and merits further studies.

Therapeutic Drug Monitoring of Vancomycin in Adult Patients with Methicillin-Resistant Staphylococcus aureus Bacteremia or Pneumonia

Background

Vancomycin remains widely used for methicillin-resistant Staphylococcus aureus (MRSA) infections; however, treatment failure rates up to 50% have been reported. At the authors' institution, monitoring of trough concentration is the standard of care for therapeutic drug monitoring of vancomycin. New guidelines support use of the ratio of 24-hour area under the concentration-time curve to minimum inhibitory concentration (AUC₂₄/MIC) as the pharmacodynamic index most likely to predict outcomes in patients with MRSA-associated infections.

Objectives

To determine the discordance rate between trough levels and AUC₂₄/MIC values and how treatment failure and nephrotoxicity outcomes compare between those achieving and not achieving their pharmacodynamic targets.

Methods

This retrospective cohort study involved patients with MRSA bacteremia or pneumonia admitted to the study hospital between March 1, 2014, and December 31, 2018, and treated with vancomycin. Data for trough concentrations were collected, and minimum concentrations (C _min) were extrapolated. The AUC₂₄/MIC values were determined using validated population pharmacokinetic models. The C _min and AUC₂₄/MIC values were characterized as below, within, or above pharmacodynamic targets (15-20 mg/L and 400-600, respectively). Discordance was defined as any instance where a patient's paired C _min and AUC₂₄/MIC values fell in different ranges (i.e., below, within, or above) relative to the target ranges. Predictors of treatment failure and nephrotoxicity were determined using logistic regression.

Results

A total of 128 patients were included in the analyses. Of these, 73 (57%) received an initial vancomycin dose less than 15 mg/kg. The discordance rate between C _min and AUC₂₄/MIC values was 21% (27/128). Rates of treatment failure and nephrotoxicity were 34% (43/128) and 18% (23/128), respectively. No clinical variables were found to predict discordance. Logistic regression identified initiation of vancomycin after a positive culture result (odds ratio [OR] 4.41, 95% confidence interval [CI] 1.36-14.3) and achievement of target AUC₂₄/MIC after 4 days (OR 3.48, 95% CI 1.39-8.70) as modifiable predictors of treatment failure.

Conclusions

The relationship between vancomycin monitoring and outcome is likely confounded by inadequate empiric or initial dosing. Before any modification of practice with respect to vancomycin monitoring, empiric vancomycin dosing should be optimized.

High Central Venous Pressure after Cardiac Surgery Might Depict Hemodynamic Deterioration Associated with Increased Morbidity and Mortality

Background: Cardiac surgery patients represent a high-risk cohort in intensive care units (ICUs). Central venous pressure (CVP) measurement seems to remain an integral part in hemodynamic monitoring, especially in cardio-surgical ICUs. However, its value as a prognostic marker for organ failure is still unclear. Therefore, we analyzed postoperative CVP values after adult cardiac surgery in a large cohort with regard to its prognostic value for morbidity and mortality. Methods: All adult patients admitted to our ICUs between 2006 and 2019 after cardiac surgery were eligible for inclusion in the study (n = 11,198). We calculated the median initial CVP (miCVP) after admission to the ICU, which returned valid values for 9802 patients. An ROC curve analysis for optimal cut-off miCVP to predict ICU mortality was conducted with consecutive patient allocation into a (a) low miCVP (LCVP) group (≤11 mmHg) and (b) high miCVP (HCVP) group (>11 mmHg). We analyzed the impact of high miCVP on morbidity and mortality by propensity score matching (PSM) and logistic regression. Results: ICU mortality was increased in HCVP patients. In addition, patients in the HCVP group required longer mechanical ventilation, had a higher incidence of acute kidney injury, were more frequently treated with renal replacement therapy, and showed a higher risk for postoperative liver dysfunction, parametrized by a postoperative rise of ≥ 10 in MELD Score. Multiple regression analysis confirmed HCVP has an effect on postoperative ICU-mortality and intrahospital mortality, which seems to be independent. Conclusions: A high initial CVP in the early postoperative ICU course after cardiac surgery is associated with worse patient outcome. Whether or not CVP, as a readily and constantly available hemodynamic parameter, should promote clinical efforts regarding diagnostics and/or treatment, warrants further investigations.

Bioanalytical Assessment of Plasma Concentrations of Angiotensin-Converting Enzyme II Inhibitors and Angiotensin Receptor Blockers: A Pilot Study Among Patients Hospitalized With Acute Heart Failure

BACKGROUND

Although angiotensin-converting enzyme II inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) improve chronic heart failure (HF) outcomes, their potential harms and benefits in acute HF (AHF) is less clear.

STUDY QUESTION

We explored the relationship between ACEI or ARB plasma concentrations among patients with AHF with in-hospital change in estimated glomerular filtration rate (eGFR).

DATA SOURCES AND STUDY DESIGN

From August 2016-June 2017, patients with AHF prescribed an outpatient ACEI or ARB were enrolled before AHF treatment. All patients were given twice their home dose of diuretic intravenously and received clinical care at the discretion of the medical team. Of 61 patients in the parent study, saved plasma from 34 who were prescribed an outpatient ACEI or ARB was included in this substudy.

MEASURES AND OUTCOMES

Liquid chromatography-tandem mass spectrometry was performed to assess ACEI or ARB plasma concentrations before AHF treatment. Change in eGFR was computed using the Chronic Kidney Disease Epidemiology Collaboration equation, which adjusts for age, sex, and race; diuretic dose and enrollment eGFR were used to adjust for HF severity. Multiple linear regression adjusting for enrollment eGFR and diuretic dose was performed to examine the relationship between drug concentration (undetectable/low vs. in/above-range) and in-hospital change in eGFR.

RESULTS

Of 34 patients with AHF, median age was 63 years (interquartile range, 58-78 years), 19 (55.9%) were women, median eGFR at enrollment was 55.6 mL/min (interquartile range, 35.2-75.3 mL/min), and for 11 (32.4%), no ACEI or ARB was detectable in plasma. Medication concentrations in- or above-reference range were associated with in-hospital decrease in eGFR of 8.3 mL/min (95% confidence interval, 15.3-1.3 mL/min decrease), after adjusting for enrollment eGFR and diuretic treatment.

CONCLUSIONS

Bioanalytical assessment of medication levels may be useful to guide in-hospital ACEI and ARB therapy for patients with AHF.

Early Blood Pressure Reduction by Intravenous Vasodilators Is Associated With Acute Kidney Injury in Patients With Hypertensive Acute Decompensated Heart

BACKGROUND

Intravenous vasodilators are commonly used in patients with hypertensive acute decompensated heart failure (ADHF), but little is known about their optimal use in blood pressure (BP) management to avoid acute kidney injury (AKI). The purpose of this study was to investigate the association between systolic BP (SBP) changes and the incidence of AKI in patients with hypertensive ADHF.

METHODS AND RESULTS

Post-hoc analysis was performed on a prospectively enrolled cohort. We investigated 245 patients with ADHF and SBP >140 mmHg on arrival (mean age, 76 years; 40% female). We defined "SBP-fall" as the maximum percent reduction in SBP 6 h after intravenous treatment. AKI was defined as serum creatinine (SCr) ≥0.3 mg/dL, or urine output <0.5 mL/kg/h (n=66) at 48 h. Mean SBP and SCr levels on arrival were 180 mmHg and 1.21 mg/dL, respectively. Patients with AKI had significantly larger SBP-fall than the others (36.7±15.3% vs. 27.2±15.3%, P<0.0001). Logistic regression analysis showed an odds ratio per 10% SBP-fall for AKI of 1.49 (95% confidence interval 1.29-1.90, P=0.001). SBP-fall was significantly associated with the number of concomitant used intravenous vasodilators (P=0.001). The administration of carperitide was also independently associated with increased incidence of AKI.

CONCLUSIONS

Larger SBP-fall from excessive vasodilator use is associated with increased incidence of AKI in patients with hypertensive ADHF.

Postoperative Acute Kidney Injury and Blood Product Transfusion After Synthetic Colloid Use During Cardiac Surgery

OBJECTIVES

This study assessed the effect of 2 types of hydroxyethyl starches (HES) on renal integrity and blood transfusion in cardiac surgery patients.

DESIGN

Retrospective investigation.

SETTING

Patients from a single tertiary medical center.

PARTICIPANTS

Inclusion criteria included coronary artery bypass graft (CABG) and/or valve surgery that included cardiopulmonary bypass with aortic cross-clamping.

INTERVENTIONS

Intraoperative HES and blood product administration.

MEASUREMENTS AND MAIN RESULTS

The study comprised 1,265 patients who met inclusion criteria. Of these patients, 70% received HES, and of these, 47% received<1,000 mL and 53% received≥1,000 mL. There was no difference in the development of acute kidney injury between the 2 groups. A parsimonious propensity model for colloids showed that combined CABG and valve surgery were less likely to be associated with HES administration than was CABG alone (OR 0.68, confidence interval [CI] 0.46-0.97; p = 0.04). Intra-aortic balloon pump use was less likely to be associated with HES administration (OR 0.57, CI 0.38-0.86; p = 0.007). Patients with chronic kidney disease, stages 3 to 5, were less likely to receive HES, with an OR of 0.56 (CI 0.38-0.84; p = 0.004); 0.51 (CI 0.20-1.33; p = 0.170); and 0.23 (CI 0.12-0.44; p<0.0001), respectively, for each stage. No difference was noted in red blood cell transfusion. However, fresh frozen plasma, cryoprecipitate, and platelet transfusions were significantly higher with larger volumes of HES, with an OR of 2.03 (CI 1.64-2.52; p<0.001); 1.60 (CI 1.30-1.97; p<0.000); and 1.62 (CI 1.21-2.15; p = 0.006), respectively. No differences in surgical mortality were found between the colloid and noncolloid groups.

CONCLUSIONS

This study showed no association of postoperative acute kidney injury and red blood cell transfusion between the colloid and noncolloid groups. Although the complication rate was higher with HES administration, there was no difference in surgery mortality between the 2 groups.

Matrix Metalloproteinases in Kidney Disease: Role in Pathogenesis and Potential as a Therapeutic Target

Matrix metalloproteinases (MMPs) are large family of proteinases. In addition to a fundamental role in the remodeling of the extracellular matrix, they also cleave a number of cell surface proteins and are involved in multiple cellular processes. MMP activity is regulated via numerous mechanisms, including inhibition by endogenous tissue inhibitors of metalloproteinases (TIMPs). Similar to MMPs, a role for TIMPs has been established in multiple cell signaling pathways. Aberrant expression of MMPs and TIMPS in renal pathophysiology has long been recognized, and with the generation of specific knockout mice, the mechanistic role of several MMPs and TIMPs is becoming more understood and has revealed both pathogenic and protective roles. This chapter will focus on the expression and localization of MMPs and TIMPs in the kidney, as well as summarizing the current information linking these proteins to acute kidney injury and chronic kidney disease. In addition, we will summarize studies suggesting that MMPs and TIMPs may be biomarkers of renal dysfunction and represent novel therapeutic targets to attenuate kidney disease.

The optimal definition of contrast-induced acute kidney injury for prediction of inpatient mortality in patients undergoing percutaneous coronary interventions

BACKGROUND

It is unknown which definition of contrast-induced acute kidney injury (CI-AKI) in the setting of percutaneous coronary interventions is best associated with inpatient mortality and whether this association is stable across patients with various preprocedural serum creatinine (SCr) values.

METHODS

We applied logistic regression models to multiple CI-AKI definitions used by the Kidney Disease Improving Global Outcomes guidelines and previously published studies to examine the impact of preprocedural SCr on a candidate definition's correlation with the adverse outcome of inpatient mortality. We used likelihood ratio tests to examine candidate definitions and identify those where association with inpatient mortality remained constant regardless of preprocedural SCr. These definitions were assessed for specificity, sensitivity, and positive and negative predictive values to identify an optimal definition.

RESULTS

Our study cohort included 119,554 patients who underwent percutaneous coronary intervention in Michigan between 2010 and 2014. Most commonly used definitions were not associated with inpatient mortality in a constant fashion across various preprocedural SCr values. Of the 266 candidate definitions examined, 16 definition's association with inpatient mortality was not significantly altered by preprocedural SCr. Contrast-induced acute kidney injury defined as an absolute increase of SCr ≥0.3 mg/dL and a relative SCr increase ≥50% was selected as the optimal candidate using Perkins and Shisterman decision theoretic optimality criteria and was highly predictive of and specific for inpatient mortality.

CONCLUSIONS

We identified the optimal definition for CI-AKI to be an absolute increase in SCr ≥0.3 mg/dL and a relative SCr increase ≥50%. Further work is needed to validate this definition in independent studies and to establish its utility for clinical trials and quality improvement efforts.

Nephrotoxicity comparison of two commercially available generic vancomycin products

To date, no comparative clinical studies have investigated the effects of different vancomycin products on nephrotoxicity. The objective of this single-center, retrospective, matched-cohort study was to investigate the impact of two different vancomycin products on the development of nephrotoxicity. The study population included adults receiving a single vancomycin product, from either Pfizer or Hospira, for their entire course of therapy. Patients were matched based on underlying nephrotoxicity risk factors. Secondary outcomes included the need for renal replacement therapy, length of hospital stay, and in-hospital mortality. One-hundred forty-six matched pairs (n = 292) were included, and they had no significant differences in demographics, comorbid conditions, severity of illness, or vancomycin-associated nephrotoxicity risk factors. The frequency of nephrotoxicity was 8.9% in the Pfizer group and 11.0% in the Hospira group as defined by the 2009 consensus vancomycin guidelines (P = 0.56), 17.1% in the Pfizer group and 13.0% in the Hospira group as defined by the Acute Kidney Injury Network (AKIN) (P = 0.33), and 10.3% in the Pfizer group and 11.6% in the Hospira group as defined by RIFLE (risk, injury, failure, loss, and end-stage renal disease) criteria (P = 0.71). There were no differences between groups in regard to nephrotoxicity by any definition or in secondary outcomes. In multivariate analysis of overall nephrotoxicity risk factors, the type of vancomycin product was not independently associated with increased odds of developing nephrotoxicity according to the RIFLE criteria. Based on our results, there are no discernible differences between Pfizer and Hospira vancomycin products in the frequency of nephrotoxicity. Confirmation of these results with other types of vancomycin and different patient populations is warranted.

Clinical and prognostic role of ammonia in advanced decompensated heart failure. The cardio-abdominal syndrome?

BACKGROUND

Advanced heart failure is associated with end-organ damage. Recent literature suggested an intriguing crosstalk between failing heart, abdomen and kidneys. Venous ammonia, as a by-product of the gut, could be a marker of abdominal injury in heart failure patients. The aim of the study was to investigate the clinical and prognostic role of ammonia in patients with advanced decompensated heart failure (ADHF).

METHODS & RESULTS

90 patients admitted with ADHF were prospectively studied. The prognostic role of ammonia at admission was evaluated. Primary end-points were: a composite of cardiac death, urgent heart transplantation and mechanical circulatory support at 3 months and need for renal replacement therapies (RRT). In the study cohort (age 59.0 ± 12.0 years, FE 21.6 ± 9.0%, INTERMACS profile 3.7 ± 0.9, creatinine 1.71 ± 0.95 mg/dl) 27 patients (30%) underwent the cardiac composite endpoint, while 9 patients (10%) needed RRT. At ROC curve analysis ammonia ≥ 130 μg/dl (abdominal damage) showed the best diagnostic accuracy. At multivariate analysis abdominal damage predicted the cardiac composite endpoint. Abdominal damage further increased risk among patient with cold profile at admission (HR 2.7, 95% CI 1.1-7.0, p = 0.046). At multivariate analysis abdominal damage also predicted need for RRT (OR 10.8, 95% CI 1.5-75.8, p = 0.017). The combined use of estimated right atrial pressure and ammonia showed the highest diagnostic accuracy and a very high specificity in prediction of need for RRT.

CONCLUSION

In a selected population admitted for ADHF ammonia, as a marker of abdominal derangement, predicted adverse cardiac events and need for RRT.

The aging kidney: increased susceptibility to nephrotoxicity

Three decades have passed since a series of studies indicated that the aging kidney was characterized by increased susceptibility to nephrotoxic injury. Data from these experimental models is strengthened by clinical data demonstrating that the aging population has an increased incidence and severity of acute kidney injury (AKI). Since then a number of studies have focused on age-dependent alterations in pathways that predispose the kidney to acute insult. This review will focus on the mechanisms that are altered by aging in the kidney that may increase susceptibility to injury, including hemodynamics, oxidative stress, apoptosis, autophagy, inflammation and decreased repair.

Recombinant factor VII is associated with worse survival in complex cardiac surgical patients

BACKGROUND

Recombinant activated factor VII (rFVIIa) decreases requirements for allogeneic blood transfusion and chest reexploration in patients undergoing cardiac surgery. Whether rFVIIa increases the risk of postoperative adverse events is unclear. We tested whether rFVIIa administration was associated with increased mortality and neurologic and renal morbidity in patients undergoing cardiac surgery. Risk of thromboembolic complications and the dose-response of rFVIIa on mortality and morbidity were also evaluated.

METHODS

Of 27,977 patients who had complex cardiac surgery, 164 patients (0.59%) received rFVIIa perioperatively. Using propensity-matching techniques, patients were matched to a maximum of 3 control patients. Patients who received rFVIIa were compared with control patients on risk of mortality, neurologic and renal morbidity, and thromboembolic complications, including a composite of myocardial infarction, pulmonary embolism, and deep venous thrombosis. A corresponding dose-response analysis using multivariable logistic regression was also performed.

RESULTS

Propensity techniques successfully matched 144 patients (88%) with 359 control patients. Of patients who received rFVIIa, 40% experienced in-hospital mortality compared with 18% of control patients (odds ratio, 2.82; 98.3% confidence interval, 1.64 to 4.87; p<0.001). Furthermore, 31% of patients treated with rFVIIa versus 17% of control patients experienced renal morbidity (odds ratio, 2.07; 98.3% confidence interval, 1.19 to 3.62; p=0.002); however, neurologic morbidity and thromboembolic complications were not different among groups. High-dose rFVIIa (>60 μg/kg) did not increase the risk for mortality compared with treatment with low-dose rFVIIa (<60 μg/kg).

CONCLUSIONS

Administration of rFVIIa is associated with increased mortality and renal morbidity in patients undergoing cardiac surgery.

Acute kidney injury clinical trial design: old problems, new strategies

Apart from supportive dialysis there are no universally accepted interventions in acute kidney injury (AKI). We have summarized the outcomes of all published randomized, placebo-controlled studies of non-dialysis treatment of AKI. Forty-nine trials were identified, only one of which was in a paediatric population. Sixteen trials had positive outcomes; these trials are not comparable in terms of methodology used or outcomes assessed, and they share many of the problems of the negative trials. We discuss the flaws in clinical trial design that have contributed to poor or uncertain outcomes and propose minimum requirements for future trials. In particular, future trials should incorporate biomarkers specific to the etiology of the AKI, and treatment should match the phase of injury.

Cytochrome c: potential as a noninvasive biomarker of drug-induced acute kidney injury

INTRODUCTION

Acute kidney injury (AKI) in critically ill patients is closely associated with increased morbidity and mortality, yet there remains continued reliance on increased serum creatinine and blood urea nitrogen to diagnose AKI. These biomarkers increase only after significant renal structural damage has occurred. Recent research efforts have focused on discovery and validation of novel serum and urine biomarkers to detect AKI prior to extensive structural damage. Cytochrome c is best known as an indicator of cell death burden in any organ or tissue. It is released during mitochondrial damage that is associated with processing of apoptosis, cell lysis during necrosis and even reversible mitochondrial and cell injury.

AREAS COVERED

This article reviews the current literature on the potential for cytochrome c as an early biomarker of AKI. The article is based on PubMed searches, using the terms 'acute kidney injury,' 'renal failure,' 'biomarker,' 'toxicity' and 'cytochrome c', with a focus on experimental and clinical data.

EXPERT OPINION

Cytochrome c, as a biomarker, has the potential to improve outcome for AKI patients. Its release indicates mitochondrial damage, one of the earliest changes in cell injury and death. New mitochondrial-targeted therapeutics may be designed around this molecule. Its disadvantages include only transient increase at expression levels that are easily measurable and nonspecificity for kidney injury. The appropriate and optimal utilization of cytochrome c as a biomarker for AKI will be realized only after its complete characterization in experimental and clinical arenas.

Clearance and beyond: the complementary roles of GFR measurement and injury biomarkers in acute kidney injury (AKI)

Acute kidney injury (AKI) is a common and frequently fatal illness in critically ill patients. The reliance on daily measurements of serum creatinine as a surrogate of glomerular filtration rate (GFR) not only delays diagnosis and development of successful therapies but also hinders insight into the pathophysiology of human AKI. Measurement of GFR under non-steady-state conditions remains an elusive gold standard against which biomarkers of renal injury need to be judged. Approaches to the rapid (near real-time) measurement of GFR are explored. Even if real-time GFR was available, absent baseline information will always limit diagnosis of AKI based on GFR or serum creatinine to a detection of change. Biomarkers of renal cellular injury have provided new strategies to facilitate detection and early intervention in AKI. However, the diagnostic and predictive performance of urinary biomarkers of injury vary, depending on both the time after renal injury and on the preinjury GFR. Progress in understanding the role of each novel biomarker in the causal pathways of AKI promises to enhance their diagnostic potential. We predict that combining rapid measures of GFR with biomarkers of renal injury will yield substantive progress in the treatment of AKI.

Changes in renal markers and acute kidney injury after marathon running

BACKGROUND

The impact of marathon running on kidney function has not been previously described.

METHODS

From 425 marathon runners, 13 women and 12 men were randomly selected and cardiovascular magnetic resonance imaging (MRI) and blood/urine biomarkers were performed 4 weeks before (baseline), immediately after (peak), and 24 h after the race (recovery).

RESULTS

Participants were 38.7 ± 9.0 years old and completed the marathon in 256.2 ± 43.5 min. A total of 10/25 (40.0%) met the Acute Kidney Injury Network definition of acute kidney injury (AKI) based on a rise in serum creatinine. There were parallel and similar mean rises in serum creatinine and cystatin C from baseline, to peak, and return to normal in recovery. Urine neutrophil gelatinase-associated lipocalin rose from 8.2 ± 4.0 to 47.0 ± 28.6 and returned to 10.6 ± 7.2 ng/mL, P < 0.0001. Likewise, the mean urinary kidney injury molecule-1 levels were 2.6 ± 1.6, 3.5 ± 1.6 and 2.7 ± 1.6 ng/mL (P = 0.001). The mean and minimum pre- and post-IVC (inferior vena cava) diameters by MRI were 24.9, 18.8 and 25.3, 17.5 mm, respectively, suggesting that runners were not volume depleted at the first post-race measurement.

CONCLUSION

Approximately 40% of marathon runners experience a transient rise in serum creatinine that meets criteria of AKI with a parallel elevation of cystatin C, and supportive elevations of neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 in the urine. All biomarker elevations resolved by 24 h. These data suggest that AKI with a transient and minor change in renal filtration function occurs with the stress of marathon running. The impact of repetitive episodes of AKI with long-distance running is unknown.

Presurgical serum cystatin C and risk of acute kidney injury after cardiac surgery

BACKGROUND

Acute kidney injury (AKI) after cardiac surgery is associated with poor outcomes, but is challenging to predict from information available before surgery.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

The TRIBE-AKI (Translational Research Investigating Biomarker Endpoints in Acute Kidney Injury) Consortium enrolled 1,147 adults undergoing cardiac surgery at 6 hospitals from 2007-2009; participants were selected for high AKI risk.

PREDICTORS

Presurgical values for cystatin C, creatinine, and creatinine-based estimated glomerular filtration rate (eGFR) were categorized into quintiles and grouped as "best" (quintiles 1-2), "intermediate" (quintiles 3-4), and "worst" (quintile 5) kidney function.

OUTCOMES

The primary outcome was AKI Network (AKIN) stage 1 or higher; ≥0.3 mg/dL or 50% increase in creatinine level.

MEASUREMENTS

Analyses were adjusted for characteristics used clinically for presurgical risk stratification.

RESULTS

Average age was 71 ± 10 years (mean ± standard deviation); serum creatinine, 1.1 ± 0.3 mg/dL; eGFR-Cr, 74 ± 9 mL/min/1.73 m(2); and cystatin C, 0.9 ± 0.3 mg/L. 407 (36%) participants developed AKI during hospitalization. Adjusted odds ratios for intermediate and worst kidney function by cystatin C were 1.9 (95% CI, 1.4-2.7) and 4.8 (95% CI, 2.9-7.7) compared with 1.2 (95% CI, 0.9-1.7) and 1.8 (95% CI, 1.2-2.6) for creatinine and 1.0 (95% CI, 0.7-1.4) and 1.7 (95% CI, 1.1-2.3) for eGFR-Cr categories, respectively. After adjustment for clinical predictors, the C statistic to predict AKI was 0.70 without kidney markers, 0.69 with creatinine, and 0.72 with cystatin C. Cystatin C also substantially improved AKI risk classification compared with creatinine, based on a net reclassification index of 0.21 (P < 0.001).

LIMITATIONS

The ability of these kidney biomarkers to predict risk of dialysis-requiring AKI or death could not be assessed reliably in our study because of a small number of patients with either outcome.

CONCLUSIONS

Presurgical cystatin C is better than creatinine or creatinine-based eGFR at forecasting the risk of AKI after cardiac surgery.

Chronic critical illness: prevalence, profile, and pathophysiology

The syndrome of chronic critical illness has well-documented emotional, social, and financial burdens for individuals, caregivers, and the health care system. The purpose of this article is to provide experienced acute and critical care clinicians with essential information about the prevalence and profile of the chronically critically ill patient needed for comprehensive care. In addition, pathophysiology contributing to chronic critical illness is addressed, though the exact mechanism underlying the conversion of acute critical illness to chronic critical illness is unknown. Clinicians can use this information to identify at-risk intensive care unit patients and to institute proactive care to minimize burden and distress experienced by patients and their caregivers.

Fresh and cryopreserved, uncultured adipose tissue-derived stem and regenerative cells ameliorate ischemia-reperfusion-induced acute kidney injury

Background. Acute kidney injury (AKI) represents a major clinical problem with high mortality and limited causal treatments. The use of cell therapy has been suggested as a potential modality to improve the course and outcome of AKI.

Methods. We investigated the possible renoprotection of freshly isolated, uncultured adipose tissue-derived stem and regenerative cells (ADRCs) before and after cryopreservation in a rat ischemia–reperfusion (I–R) model of AKI.

Results. We demonstrated that ADRC therapy drastically reduced mortality (survival 100% vs. 57%, ADRC vs. controls, respectively) and significantly reduced serum creatinine (sCr on Day 3: 3.03 ± 1.58 vs. 7.37 ± 2.32 mg/dL, ADRC vs. controls, respectively). Histological analysis further validated a significantly reduced intratubular cast formation, ameliorated acute tubular epithelial cell necrosis and mitigated macrophage infiltration. Furthermore, a reduced RNA expression of CXCL2 and IL-6 was found in the ADRC group which could explain the reduced macrophage recruitment. Use of cryopreserved ADRCs resulted in an equally high survival (90% vs. 33% in the control group) and similarly improved renal function (sCr on Day 3: 4.64 ± 2.43 vs. 7.24 ± 1.40 mg/dL in controls).

Conclusions. Collectively, these results suggest a potential clinical role for ADRC therapy in patients with AKI. Importantly, cryopreservation of ADRCs could offer an autologous treatment strategy for patients who are at high risk for AKI during planned interventions.

Urinary cystatin C is diagnostic of acute kidney injury and sepsis, and predicts mortality in the intensive care unit

Introduction

To evaluate the utility of urinary cystatin C (uCysC) as a diagnostic marker of acute kidney injury (AKI) and sepsis, and predictor of mortality in critically ill patients.

Methods

This was a two-center, prospective AKI observational study and post hoc sepsis subgroup analysis of 444 general intensive care unit (ICU) patients. uCysC and plasma creatinine were measured at entry to the ICU. AKI was defined as a 50% or 0.3-mg/dL increase in plasma creatinine above baseline. Sepsis was defined clinically. Mortality data were collected up to 30 days. The diagnostic and predictive performances of uCysC were assessed from the area under the receiver operator characteristic curve (AUC) and the odds ratio (OR). Multivariate logistic regression was used to adjust for covariates.

Results

Eighty-one (18%) patients had sepsis, 198 (45%) had AKI, and 64 (14%) died within 30 days. AUCs for diagnosis by using uCysC were as follows: sepsis, 0.80, (95% confidence interval (CI), 0.74 to 0.87); AKI, 0.70 (CI, 0.64 to 0.75); and death within 30 days, 0.64 (CI, 0.56 to 0.72). After adjustment for covariates, uCysC remained independently associated with sepsis, AKI, and mortality with odds ratios (CI) of 3.43 (2.46 to 4.78), 1.49 (1.14 to 1.95), and 1.60 (1.16 to 2.21), respectively. Concentrations of uCysC were significantly higher in the presence of sepsis (P < 0.0001) or AKI (P < 0.0001). No interaction was found between sepsis and AKI on the uCysC concentrations (P = 0.53).

Conclusions

Urinary cystatin C was independently associated with AKI, sepsis, and death within 30 days.

Trial registration

Australian New Zealand Clinical Trials Registry ACTRN012606000032550.

Rapid detection of acute kidney injury by plasma cystatin C in the intensive care unit

BACKGROUND

Plasma cystatin C (pCysC) has been proposed as an alternative to plasma creatinine (pCr) as a measure of renal function. We compared the detection of functional change by both biomarkers in critically ill patients.

METHODS

pCysC and pCr were measured on admission to one of two intensive care units (ICU) and then daily over 7 days. Patients were classified according to the analyte that first increased by either ≥25 or ≥50% above the admission value. The proportion of patients in each class was compared using McNemar's chi-square test. Sustained acute kidney injury (AKI, a ≥50% increase in pCr from baseline for ≥24 h), dialysis and death within 30 days were recorded. The ability of pCysC and pCr on admission to predict sustained AKI, dialysis or death was assessed from the area under the receiver operator characteristic curve (AUC).

RESULTS

Of 442 patients, 83 had a ≥50% increase in one analyte, 17 in both and 342 in neither. Comparable numbers for a ≥25% increase were 163 in one analyte, 45 in both and 234 in neither. pCysC increased prior to pCr more frequently than vice versa in both the cohort with a ≥50% increase (P < 0.0001) and with a ≥25% increase (P < 0.0001). pCysC predicted sustained AKI with an AUC of 0.80 [95% confidence interval (CI) = 0.71-0.88]. pCysC and pCr were similarly moderately predictive of death or dialysis with AUCs of 0.61 [95% CI = 0.53-0.68] and 0.60 [95% CI = 0.51-0.67], respectively.

CONCLUSION

pCysC was an effective and earlier surrogate marker of decreased renal function than pCr in a general ICU population.

Early intervention with erythropoietin does not affect the outcome of acute kidney injury (the EARLYARF trial)

We performed a double-blind placebo-controlled trial to study whether early treatment with erythropoietin could prevent the development of acute kidney injury in patients in two general intensive care units. As a guide for choosing the patients for treatment we measured urinary levels of two biomarkers, the proximal tubular brush border enzymes gamma-glutamyl transpeptidase and alkaline phosphatase. Randomization to either placebo or two doses of erythropoietin was triggered by an increase in the biomarker concentration product to levels above 46.3, with a primary outcome of relative average plasma creatinine increase from baseline over 4 to 7 days. Of 529 patients, 162 were randomized within an average of 3.5 h of a positive sample. There was no difference in the incidence of erythropoietin-specific adverse events or in the primary outcome between the placebo and treatment groups. The triggering biomarker concentration product selected patients with more severe illness and at greater risk of acute kidney injury, dialysis, or death; however, the marker elevations were transient. Early intervention with high-dose erythropoietin was safe but did not alter the outcome. Although these two urine biomarkers facilitated our early intervention, their transient increase compromised effective triaging. Further, our study showed that a composite of these two biomarkers was insufficient for risk stratification in a patient population with a heterogeneous onset of injury.

Secondary prevention of acute kidney injury

PURPOSE OF REVIEW

Secondary prevention follows identification of acute kidney injury (AKI), in which functional outcome is incomplete. Secondary prevention requires biomarkers for early diagnosis and response to appropriate treatment, on-going injury and repair, and meaningful metrics to monitor outcome. This review summarizes recent research in these areas.

RECENT FINDINGS

Proteomics and genetic studies have identified new risk factors and biomarkers of AKI. Biomarker performance studies reveal differences in prognostic performance according to population and AKI definition. The first early secondary prevention study utilizing a urinary biomarker of AKI as a triaging tool to randomize to treatment has been completed. Recent creatinine-kinetic modelling has highlighted issues with defining AKI which continue to make comparison of treatment outcomes difficult. Biomarkers to monitor repair are emerging.

SUMMARY

The prognostic performance of novel biomarkers of AKI in a range of clinical settings is encouraging and critical to effective secondary prevention. Identification of cause and time-course of specific biomarkers are required before biomarker panels for secondary prevention are developed. Agreed standards around reporting of biomarker studies would facilitate comparisons between studies. Phase-specific biomarkers are required to triage to phase-specific treatment.

Exertional rhabdomyolysis and acute kidney injury

Skeletal muscle breakdown occurs normally with exercise, followed by muscle repair and physiologic adaptation. Strenuous, unaccustomed, prolonged, and repetitive exercise, particularly when associated with other risk factors such as hot and humid climate or sickle cell trait can cause clinically significant exertional rhabdomyolysis (ER). Although most cases are asymptomatic and resolve without sequelae, ER is the most common cause of exercise-related myoglobinuric acute renal injury and acute renal failure in athletes. Exercise-related muscle pain, elevated serum creatine kinase (CK), and "cola-colored" urine have been described as a classic presentation of ER. The exact mechanism of ER has not been clearly elucidated. Most studies suggest a cascade of events that include depletion of adenosine triphosphate (ATP), impaired function of the Na+- K+ ATPase system, intracellular excess calcium accumulation, sarcolemma damage, and release of intracellular proteins and other substances into blood. Excess myoglobin that is filtered at the glomerulus can lead to myoglobinuric acute renal injury. Cessation of physical activity, relative rest during clinical recovery, and early aggressive fluid replacement are mainstays of treatment. Return to play after recovery from ER is influenced by associated risk factors that may predispose the athlete to recurrence and is guided by signs, symptoms, and CK levels. This article reviews the definitions, pathophysiology, diagnosis, and management of ER with specific relevance to acute kidney injury.