Acute kidney injury and chronic kidney disease after cardiac surgery

Gene networks for use in metabolomic data analysis of blood plasma from patients with postoperative delirium

Postoperative delirium (POD) is considered one of the most severe complications, resulting in impaired cognitive function, extended hospitalization, and higher treatment costs. The challenge of early POD diagnosis becomes particularly significant in cardiac surgery cases, as the incidence of this complication exceeds 50 % in certain patient categories. While it is known that neuroinflammation, neurotransmitter imbalances, disruptions in neuroendocrine regulation, and interneuronal connections contribute significantly to the development of POD, the molecular, genetic mechanisms of POD in cardiac surgery patients, along with potential metabolomic diagnostic markers, remain inadequately understood. In this study, blood plasma was collected from a group of patients over 65 years old after cardiac surgery involving artificial circulation. The collected samples were analyzed for sphingomyelin content and quantity using high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS/MS) methods. The analysis revealed four significantly different sphingomyelin contents in patients with POD compared to those who did not develop POD (control group). Employing gene network reconstruction, we perceived a set of 82 regulatory enzymes affiliated with the genetic coordination of the sphingolipid metabolism pathway. Within this set, 47 are assumed to be regulators of gene expression, governing the transcription of enzymes pivotal to the metabolic cascade. Complementing this, an additional assembly of 35 regulators are considered to be regulators of activity, degradation, and translocation dynamics of enzymes integral to the aforementioned pathway. Analysis of the overrepresentation of diseases with which these regulatory proteins are associated showed that the regulators can be categorized into two groups, associated with cardiovascular pathologies (CVP) and neuropsychiatric diseases (NPD), respectively. The regulators associated with CVP are expectedly related to the effects on myocardial tissue during surgery. It is hypothesized that dysfunction of NPD-associated regulators may specifically account for the development of POD after cardiac surgery. Thus, the identified regulatory genes may provide a basis for planning further experiments, in order to study disorders at the level of expression of these genes, as well as impaired function of proteins encoded by them in patients with POD. The identified significant sphingolipids can be considered as potential markers of POD.

Molecular-genetic pathways of hepatitis C virus regulation of the expression of cellular factors PREB and PLA2G4C, which play an important role in virus replication

The participants of Hepatitis C virus (HCV) replication are both viral and host proteins. Therapeutic approaches based on activity inhibition of viral non-structural proteins NS3, NS5A, and NS5B are undergoing clinical trials. However, rapid mutation processes in the viral genome and acquisition of drug resistance to the existing drugs remain the main obstacles to fighting HCV. Identifying the host factors, exploring their role in HCV RNA replication, and studying viral effects on their expression is essential for understanding the mechanisms of viral replication and developing novel, effective curative approaches. It is known that the host factors PREB (prolactin regulatory element binding) and PLA2G4C (cytosolic phospholipase A2 gamma) are important for the functioning of the viral replicase complex and the formation of the platforms of HCV genome replication. The expression of PREB and PLA2G4C was significantly elevated in the presence of the HCV genome. However, the mechanisms of its regulation by HCV remain unknown. In this paper, using a text-mining technology provided by ANDSystem, we reconstructed and analyzed gene networks describing regulatory effects on the expression of PREB and PLA2G4C by HCV proteins. On the basis of the gene network analysis performed, we put forward hypotheses about the modulation of the host factors functions resulting from protein-protein interaction with HCV proteins. Among the viral proteins, NS3 showed the greatest number of regulatory linkages. We assumed that NS3 could inhibit the function of host transcription factor (TF) NOTCH1 by protein-protein interaction, leading to upregulation of PREB and PLA2G4C. Analysis of the gene networks and data on differential gene expression in HCV-infected cells allowed us to hypothesize further how HCV could regulate the expression of TFs, the binding sites of which are localized within PREB and PLA2G4C gene regions. The results obtained can be used for planning studies of the molecular-genetic mechanisms of viral-host interaction and searching for potential targets for anti-HCV therapy.

Evaluation of acute kidney injury with oxidative stress biomarkers and Renal Resistive Index after cardiac surgery

BACKGROUND

We investigated whether cardiopulmonary bypass (CPB) related oxidative stress mediated glycocalyx degradation can cause an increase in renal resistive index (RRI) or postoperative AKI. Additionally, to evaluate whether RRI and early postoperative serum cystatin C levels could improve the prediction sensitivity of acute kidney injury (AKI).

METHODS

Forty-two patients undergoing cardiac surgery were included in this prospective observational study. RRI was measured pre-operatively and in the cardiac intensive care unit. Blood samples were collected for analyzing of cellular injury biomarkers at preoperative and postoperative second hours. We determined areas under the receiver operating characteristic curve (AUC) and odds ratios for postoperative biomarkers and RRI to predict AKI.

RESULTS

While postoperative cystatin C level (AUC: 0.902, 95% CI = 0.79-1.00, p < .001) and RRI (AUC: 0.748, 95% CI = 0.56-0.93, p = .023) have diagnostic and predictive value in the prediction of AKI, we could not identify any relation between products of oxidative stress and the glycocalyx degradation and AKI.

CONCLUSION

These data suggest that CPB leads to structural and oxidative changes at the protein level and the integrity of glycocalyx is disturbing, but these changes are not specific to kidney injury. Our data suggest that serum cystatin C level and RRI could be used as an early biomarker for postoperative AKI after cardiac surgery.

Postoperative acute kidney injury in adult non-cardiac surgery: joint consensus report of the Acute Disease Quality Initiative and PeriOperative Quality Initiative

Postoperative acute kidney injury (PO-AKI) is a common complication of major surgery that is strongly associated with short-term surgical complications and long-term adverse outcomes, including increased risk of chronic kidney disease, cardiovascular events and death. Risk factors for PO-AKI include older age and comorbid diseases such as chronic kidney disease and diabetes mellitus. PO-AKI is best defined as AKI occurring within 7 days of an operative intervention using the Kidney Disease Improving Global Outcomes (KDIGO) definition of AKI; however, additional prognostic information may be gained from detailed clinical assessment and other diagnostic investigations in the form of a focused kidney health assessment (KHA). Prevention of PO-AKI is largely based on identification of high baseline risk, monitoring and reduction of nephrotoxic insults, whereas treatment involves the application of a bundle of interventions to avoid secondary kidney injury and mitigate the severity of AKI. As PO-AKI is strongly associated with long-term adverse outcomes, some form of follow-up KHA is essential; however, the form and location of this will be dictated by the nature and severity of the AKI. In this Consensus Statement, we provide graded recommendations for AKI after non-cardiac surgery and highlight priorities for future research.

Global epidemiology and outcomes of acute kidney injury

Acute kidney injury (AKI) is a commonly encountered syndrome associated with various aetiologies and pathophysiological processes leading to decreased kidney function. In addition to retention of waste products, impaired electrolyte homeostasis and altered drug concentrations, AKI induces a generalized inflammatory response that affects distant organs. Full recovery of kidney function is uncommon, which leaves these patients at risk of long-term morbidity and death. Estimates of AKI prevalence range from <1% to 66%. These variations can be explained by not only population differences but also inconsistent use of standardized AKI classification criteria. The aetiology and incidence of AKI also differ between high-income and low-to-middle-income countries. High-income countries show a lower incidence of AKI than do low-to-middle-income countries, where contaminated water and endemic diseases such as malaria contribute to a high burden of AKI. Outcomes of AKI are similar to or more severe than those of patients in high-income countries. In all resource settings, suboptimal early recognition and care of patients with AKI impede their recovery and lead to high mortality, which highlights unmet needs for improved detection and diagnosis of AKI and for efforts to improve care for these patients.

The Association of Aortic Valve Pathology With Renal Resistive Index as a Kidney Injury Biomarker

BACKGROUND

Acute kidney injury (AKI) is a common serious complication after cardiac surgery. Doppler-determined renal resistive index (RRI) is a promising early AKI biomarker in this population. However, the relationship between aortic valve pathology (insufficiency and/or stenosis) and RRI is unknown. This study aimed to investigate RRI variability related to aortic valve pathology.

METHODS

In a retrospective review of cardiac surgery patients, RRI and aortic valve pathology were assessed prior to cardiopulmonary bypass using transesophageal echocardiography. Aortic valve status was categorized into four subgroups: normal (insufficiency and stenosis, none/trace/mild), insufficiency (insufficiency, moderate/severe; stenosis, none/trace/mild), combined insufficiency/stenosis (insufficiency and stenosis, moderate/severe), or stenosis (insufficiency, none/trace/mild; stenosis, moderate/severe). RRI and time-matched hemodynamic and Doppler measurements were compared among subgroups.

RESULTS

Of 175 patients, 60 had aortic valve pathology (16 insufficiency, 18 insufficiency/stenosis, 26 stenosis). Compared with the normal subgroup, patients with aortic insufficiency had lower diastolic blood pressure and trough renal Doppler velocities, and higher RRI (0.77 versus 0.69; p < 0.001); patients with combined insufficiency/stenosis also had higher RRI (0.72 versus 0.69, p = 0.042).

CONCLUSIONS

Patients with aortic insufficiency and combined insufficiency/stenosis had higher median RRI values compared with normal patients. For these individuals, diastolic flow differences related to aortic insufficiency may explain why their presurgery RRI values often exceeded postoperative thresholds typically associated with AKI. Strategies to account for the potentially confounding effects of aortic insufficiency on renal flow patterns, independent of renal injury, may add to the value of RRI as an early AKI biomarker.

Neuroendocrine stress response: implications for cardiac surgery-associated acute kidney injury

Surgical stress causes biochemical and physiologic perturbations of every homeostatic axis. These alterations include volume/baroreceptor regulation, sympathetic activation, parasympathetic suppression, neuroendocrine activation, acute phase response protein synthesis and secretion, immune response modulation and long-term behavioral adaptation. The kidney is central to the stress response because of its main role in the maintenance of water, electrolyte balance and hence, intracellular and extracellular compartments, including the intravascular volume. Acute kidney injury after cardiac surgery occurs as a result of numerous factors including ischemia-reperfusion, inflammation, oxidative stress, neurohormonal activation, metabolic factors, and nephrotoxicity or pigment nephropathy. The neuroendocrine stress response has a central role in initiating renal injury during cardiac surgery through an increased release of arginine-vasopressin and activation of the sympathetic nervous system and the intrarenal and systemic renin-angiotensin-aldosterone system. The contribution of an exaggerated neuroendocrine stress response to cardiac surgery and cardiopulmonary bypass as key pathophysiologic mechanism for acute kidney injury after cardiac surgery represents an opportunity for scientific exploration.

Sex and the Risk of AKI Following Cardio-thoracic Surgery: A Meta-Analysis

BACKGROUND AND OBJECTIVES

Being a woman is a well established risk factor for the development of cardiothoracic surgery-associated AKI. In striking contrast, women are less likely to develop AKI associated with noncardiac surgical procedures than men. In an attempt to ascertain why being a woman might be protective for ischemic AKI after general surgery but deleterious in patients undergoing cardiothoracic surgery, we examined cardiothoracic surgery-associated AKI in greater detail.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a systematic review and meta-analysis of cardiothoracic surgery-associated AKI studies published between January of 1978 and December of 2015 to further explore the relationship between sex and cardiothoracic surgery-associated AKI.

RESULTS

Sixty-four studies were identified that provided sex-specific data regarding the incidence of cardiothoracic surgery-associated AKI among 1,057,412 subjects. Using univariate analysis, women were more likely than men to develop AKI postoperatively (odds ratio, 1.21; 95% confidence interval, 1.09 to 1.33; P<0.001). However, when the analysis was restricted to the 120,464 subjects reported in 29 studies that used the Acute Kidney Injury Network criteria, the RIFLE criteria, or the Kidney Disease Improving Global Outcomes criteria to define AKI, there was no significant sex-related difference in risk. Seventeen studies used multivariate analysis to assess risk factors for cardiothoracic surgery-associated AKI and provided sex-specific odd ratios. Among the 1,587,181 individuals included in these studies, the risk of developing cardiothoracic surgery-associated AKI was not significantly associated with sex (odds ratio, 1.04; 95% confidence interval, 0.92 to 1.19; P=0.51). However, when the analysis was restricted to the 5106 subjects reported in four studies that used the Acute Kidney Injury Network criteria to define AKI, the risk of developing AKI was significantly lower in women compared with in men (odds ratio, 0.75; 95% confidence interval, 0.65 to 0.87; P<0.001).

CONCLUSIONS

Our systematic review and meta-analysis contradict the generally held consensus that being a woman is an independent risk factor for the development of cardiothoracic surgery-associated AKI.

Preoperative plasma growth-differentiation factor-15 for prediction of acute kidney injury in patients undergoing cardiac surgery

Background

Growth-differentiation factor-15 (GDF-15) is an emerging humoral marker for risk stratification in cardiovascular disease. Cardiac-surgery-associated acute kidney injury (CSA-AKI), an important complication in patients undergoing cardiac surgery, is associated with poor prognosis. The present secondary analysis of an observational cohort study aimed to determine the role of GDF-15 in predicting CSA-AKI compared with the Cleveland-Clinic Acute Renal Failure (CC-ARF) score and a logistic regression model including variables associated with renal dysfunction.

Methods

Preoperative plasma GDF-15 was determined in 1176 consecutive patients undergoing elective cardiac surgery. Patients with chronic kidney disease stage 5 were excluded. AKI was defined according to Kidney-Disease-Improving-Global-Outcomes (KDIGO) - creatinine criteria. The following variables were screened for association with development of postoperative AKI: age, gender, additive Euroscore, serum creatinine, duration of cardiopulmonary bypass, duration of surgery, type of surgery, total circulatory arrest, preoperative hemoglobin, preoperative oxygen-supplemented cerebral oxygen saturation, diabetes mellitus, hemofiltration during ECC, plasma GDF-15, high sensitivity troponin T (hsTNT), and N-terminal prohormone of B-type natriuretic peptide (NTproBNP).

Results

There were 258 patients (21.9 %) with AKI (AKI stage 1 (AKI-1), n = 175 (14.9 %); AKI-2, n = 6 (0.5 %); AKI-3, n = 77 (6.5 %)). The incidence of AKI-1 and AKI-3 increased significantly from the lowest to the highest tertiles of GDF-15. In logistic regression, preoperative GDF-15, additive Euroscore, age, plasma creatinine, diabetes mellitus, and duration of cardiopulmonary bypass were independently associated with AKI. Inclusion of GDF-15 in a logistic regression model comprising these variables significantly increased the area under the curve (AUC 0.738 without and 0.750 with GDF-15 included) and the net reclassification ability to predict AKI. Comparably, in receiver operating characteristic analysis the predictive capacity of the CC-ARF score (AUC 0.628) was improved by adding GDF-15 (AUC 0.684) but this score also had lower predictability than the logistic regression model. In random forest analyses the predictive capacity of GDF-15 was especially pronounced in patients with normal plasma creatinine.

Conclusion

This suggests that preoperative plasma GDF-15 independently predicts postoperative AKI in patients undergoing elective cardiac surgery and is particularly helpful for risk stratification in patients with normal creatinine.

Trial registration

NCT01166360 on July 20, 2010.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1482-3) contains supplementary material, which is available to authorized users.

High Postoperative Blood Pressure After Cardiac Surgery Is Associated With Acute Kidney Injury and Death

OBJECTIVES

Gaps and uncertainty exist regarding the understanding of optimal clinical goals for perioperative (ie, preoperative, intraoperative, and postoperative) blood pressure (BP) management in patients undergoing cardiac surgery and the consequences of achieving or failing to achieve those goals. In this setting, it is understood that preoperative hypertension is predictive of poor postoperative outcomes, with a growing appreciation that current, clinically acceptable changes in intraoperative BP also may be associated independently with adverse short- and long-term outcomes. In contrast, the impact of postoperative BP on outcomes after cardiac surgery remains less clear.

DESIGN

This study was a retrospective outcome analysis.

SETTING

The study included all cardiac surgery patients cared for at a single institution over a 7-year period. Consequences of the success or failure of meeting postoperative BP targets on medical outcomes and health resource utilization were evaluated.

RESULTS

The study comprised 5,225 patients. Hypertensive postoperative patients experienced a higher in-hospital mortality rate compared with matched-case normotensive patients (4.97% v 1.32%, p<0.001) and a longer hospital stay (p = 0.024). In hypertensive patients, serum creatinine levels from postoperative day 1 through postoperative day 7 were increased compared with baseline and postoperative renal dysfunction according to the Kidney Disease: Improving Global Outcomes criteria occurred significantly more often (25.3% v 19.7%, p = 0.027).

CONCLUSIONS

Postoperative hypertension is associated with compromised outcome as reflected by higher mortality, longer length of stay, and higher incidence of renal dysfunction.

Minor Postoperative Increases of Creatinine Are Associated with Higher Mortality and Longer Hospital Length of Stay in Surgical Patients

BACKGROUND

Surgical patients frequently experience postoperative increases in creatinine levels. The authors hypothesized that even small increases in postoperative creatinine levels are associated with adverse outcomes.

METHODS

The authors examined the association of postoperative changes from preoperative baseline creatinine with all-cause in-hospital mortality and hospital length of stay (HLOS) in a retrospective analysis of surgical patients at a single tertiary care center between January 2006 and June 2012.

RESULTS

The data of 39,369 surgical patients (noncardiac surgery n = 37,345; cardiac surgery n = 2,024) were analyzed. Acute kidney injury (AKI)-by definition of the Kidney Disease: Improving Global Outcome group-was associated with a five-fold higher mortality (odds ratio [OR], 4.8; 95% CI, 4.1 to 5.7; P < 0.001) and a longer HLOS of 5 days (P < 0.001) after adjusting for age, sex, comorbidities, congestive heart failure, preoperative hemoglobin, preoperative creatinine, exposure to radiocontrast agent, type of surgery, and surgical AKI risk factors. Importantly, even minor creatinine increases (Δcreatinine 25 to 49% above baseline but < 0.3 mg/dl) not meeting AKI criteria were associated with a two-fold increased risk of death (OR, 1.7; 95% CI, 1.3 to 2.4; P < 0.001) and 2 days longer HLOS (P < 0.001). This was more pronounced in noncardiac surgery patients. Patients with minor creatinine increases had a five-fold risk of death (OR, 5.4; 95% CI, 1.5 to 20.3; P < 0.05) and a 3-day longer HLOS (P < 0.01) when undergoing noncardiac surgery.

CONCLUSIONS

Even minor postoperative increases in creatinine levels are associated with adverse outcomes. These results emphasize the importance to find effective therapeutic approaches to prevent or treat even mild forms of postoperative kidney dysfunction to improve surgical outcomes.

Incidence and risk factors for early renal dysfunction after liver transplantation

AIM: To determine renal dysfunction post liver transplantation, its incidence and risk factors in patients from a Belgian University Hospital.

METHODS: Orthotopic liver transplantations performed from January 2006 until September 2012 were retrospectively reviewed (n = 187). Patients with no renal replacement therapy (RRT) before transplantation were classified into four groups according to their highest creatinine plasma level during the first postoperative week. The first group had a peak creatinine level below 12 mg/L, the second group between 12 and 20 mg/L, the third group between 20 and 35 mg/L, and the fourth above 35 mg/L. In addition, patients who needed RRT during the first week after transplantation were also classified into the fourth group. Perioperative parameters were recorded as risk factors, namely age, sex, body mass index (BMI), length of preoperative hospital stay, prior bacterial infection within one month, preoperative ascites, preoperative treatment with β-blocker, angiotensin-converting enzyme inhibitor or non steroidal anti-inflammatory drugs, preoperative creatinine and bilirubin levels, donor status (cardiac death or brain death), postoperative lactate level, need for intraoperative vasopressive drugs, surgical revision, mechanical ventilation for more than 24 h, postoperative bilirubin and transaminase peak levels, postoperative hemoglobin level, amount of perioperative blood transfusions and type of immunosuppression. Univariate and multivariate analysis were performed using logistic ordinal regression method. Post hoc analysis of the hemostatic agent used was also done.

RESULTS: There were 78 patients in group 1 (41.7%), 46 in group 2 (24.6%), 38 in group 3 (20.3%) and 25 in group 4 (13.4%). Twenty patients required RRT: 13 (7%) during the first week after transplantation. Using univariate analysis, the severity of renal dysfunction was correlated with presence of ascites and prior bacterial infection, preoperative bilirubin, urea and creatinine level, need for surgical revision, use of vasopressor, postoperative mechanical ventilation, postoperative bilirubin and urea, aspartate aminotransferase (ASAT), and hemoglobin levels and the need for transfusion. The multivariate analysis showed that BMI (OR = 1.1, P = 0.004), preoperative creatinine level (OR = 11.1, P < 0.0001), use of vasopressor (OR = 3.31, P = 0.0002), maximal postoperative bilirubin level (OR = 1.44, P = 0.044) and minimal postoperative hemoglobin level (OR = 0.059, P = 0.0005) were independent predictors of early post-liver transplantation renal dysfunction. Neither donor status nor ASAT levels had significant impact on early postoperative renal dysfunction in multivariate analysis. Absence of renal dysfunction (group 1) was also predicted by the intraoperative hemostatic agent used, independently of the extent of bleeding and of the preoperative creatinine level.

CONCLUSION: More than half of receivers experienced some degree of early renal dysfunction after liver transplantation. Main predictors were preoperative renal dysfunction, postoperative anemia and vasopressor requirement.

Advanced oxidation protein products in predicting acute kidney injury following cardiac surgery

To test the hypothesis whether serum advanced oxidation protein products (AOPP) are associated with increased acute kidney injury (AKI) after cardiopulmonary bypass (CPB) and could serve as a biomarker in this aspect, we performed a prospective cohort study. Thirty-five (22.3%) patients developed AKI, and 32 age- and gender-matched patients without AKI were selected as control. Serum AOPP 1 h after CPB were significantly higher among AKI patients compared with non-AKI patients (81.8 ± 18.6 versus 67.4 ± 12.5 μmol/L, p < 0.001), with an area under the receiver-operating characteristic (ROC) curve of 0.714. An optimal serum AOPP 1 h after CPB cutoff of 69.9 μmol/L had a sensitivity of 74%, specificity of 63% and a positive predictive value of 68% for predicting AKI. These results demonstrated that serum AOPP might be an early biomarker for AKI after CPB.

Evidence for preoperative aspirin improving major outcomes in patients with chronic kidney disease undergoing cardiac surgery: a cohort study

BACKGROUND

Effects of aspirin on patients with chronic kidney disease (CKD) remains unclear. This study aimed to examine the effect of preoperative aspirin use on postoperative renal function and 30-day mortality in patients with CKD undergoing cardiac surgery.

METHODS

A retrospective cohort study was performed on consecutive patients (n = 5175) receiving cardiac surgery in 2 tertiary hospitals. Of all patients, 3585 met the inclusion criteria and underwent the analysis to determine the association of preoperative aspirin with incidence of acute kidney injury (AKI) and death based on estimated glomerular filtration rate (eGFR).

RESULTS

Of 3585 patients, 31.5% had CKD (eGFR < 60 mL/min/1.73 m2) at baseline and 27.6% had AKI postoperatively. The baseline eGFR had a nonlinear relationship with the incidence and stages of AKI. As eGFR decreased to 15 to 30 from more than or equal to 90 mL/min/1.73 m2, AKI and 30-day mortality increased to 50.5% from 23.5% and to 11.9% from 2.6%, respectively (P < 0.001). However, preoperative aspirin use was associated with a significant decrease in postoperative AKI and 30-day mortality in patients with CKD undergoing cardiac surgery, in particular, the survival benefit associated with aspirin was greater in patients with CKD (vs normal kidney function): 30-day mortality was reduced by 23.3%, 58.2%, or 70.0% for patients with baseline eGFR more than or equal to 90, 30 to 59, or 15 to 30 mL/min/1.73 m2, respectively (P trend < 0.001).

CONCLUSIONS

For patients with CKD undergoing cardiac surgery, preoperative aspirin therapy was associated with renal protection and mortality decline. The magnitude of the survival benefit was greater in patients with CKD than normal kidney function.

Pathophysiology of Cardiopulmonary Bypass

The techniques and equipment of cardiopulmonary bypass (CPB) have evolved over the past 60 years, and numerous numbers of cardiac surgical procedures are conducted around the world using CPB. Despite more widespread applications of percutaneous coronary and valvular interventions, the need for cardiac surgery using CPB remains the standard approach for certain cardiac pathologies because some patients are ineligible for percutaneous procedures, or such procedures are unsuccessful in some. The ageing patient population for cardiac surgery poses a number of clinical challenges, including anemia, decreased cardiopulmonary reserve, chronic antithrombotic therapy, neurocognitive dysfunction, and renal insufficiency. The use of CPB is associated with inductions of systemic inflammatory responses involving both cellular and humoral interactions. Inflammatory pathways are complex and redundant, and thus, the reactions can be profoundly amplified to produce a multiorgan dysfunction that can manifest as capillary leak syndrome, coagulopathy, respiratory failure, myocardial dysfunction, renal insufficiency, and neurocognitive decline. In this review, pathophysiological aspects of CPB are considered from a practical point of view, and preventive strategies for hemodilutional anemia, coagulopathy, inflammation, metabolic derangement, and neurocognitive and renal dysfunction are discussed.

The association of postcardiac surgery acute kidney injury with intraoperative systolic blood pressure hypotension

Background. Postoperative acute kidney injury (AKI) is associated with high mortality and substantial cost after aortocoronary bypass graft (CABG) surgery. We tested the hypothesis that intraoperative systolic blood pressure variation is associated with postoperative AKI. Methods. We gathered demographic, procedural, blood pressure, and renal outcome data for 7,247 CABG surgeries at a single institution between 1996 and 2005. A development/validation cohort methodology was randomly divided (66% and 33%, resp.). Peak postoperative serum creatinine rise relative to baseline (%ΔCr) was the primary AKI outcome variable. Markers reflective of intraoperative systolic blood pressure variation were derived for each patient including (1) peak and nadir values (absolute and relative to baseline) and (2) excursion episodes beyond selected thresholds (by duration, frequency, and duration × degree). Each marker of systolic blood pressure variation was then separately evaluated for association with AKI using linear regression models with adjustment for several known risk factors (age, aprotinin use, congestive heart failure, previous myocardial infarction, baseline creatinine, bypass time, diabetes, weight, concomitant valve surgery, gender, and preoperative pulse pressure). Results. An association was identified between systolic blood pressure relative to baseline and postoperative AKI (P < 0.006). Conclusions. In CABG surgery patients, intraoperative systolic blood pressure decrease relative to baseline systolic blood pressure is independently associated with postoperative AKI.

Extracardiac complications in adults with congenital heart disease

With the increasing number of adults living with repaired, or unrepaired, congenital heart disease, there is a growing incidence of extracardiac comorbidities. These comorbidities can affect various organ systems in complex ways, and may have a significant impact on a patient's quality of life and survival. Many of these potential complications may go undiagnosed until there is already a significant bearing on the patient's life. Therefore, it is important for physicians who care for the adult congenital patient to be mindful of these potential extracardiac complications, and actively assess for these complications in their adult congenital practice. Continued research to identify modifiable risk factors is needed so that both preventative and therapeutic management options for these extracardiac complications may be developed.

Transfusion and risk of acute kidney injury in cardiac surgery

Acute kidney injury (AKI) is a serious and common complication of major surgery. This narrative review focuses on the relationship between perioperative red blood cell transfusion and AKI after cardiac surgery with cardiopulmonary bypass (CPB). Numerous observational studies have shown that these two factors are independently associated with each other. Several lines of evidence suggest that the nature of this association is one of cause and effect. The pathophysiological mechanism by which transfusions might harm the kidney has not been fully elucidated, but it is known that erythrocytes undergo irreversible morphological and biochemical changes during storage. As a result, after transfusion, they can promote a pro-inflammatory state, impair tissue oxygen delivery, and exacerbate tissue oxidative stress. This in turn can cause AKI in susceptible patients undergoing cardiac surgery with CPB, such as those with pre-existing kidney dysfunction or anaemia. Interventions aimed at avoiding perioperative blood transfusion might, therefore, reduce the risk of AKI after cardiac and other types of surgery.

Advanced oxidation protein products as prognostic biomarkers for recovery from acute kidney injury after coronary artery bypass grafting

Recovery from acute kidney injury (AKI) is related to long-term prognosis. This study, involving 56 patients with AKI and 56 controls from a prospective cohort undergoing coronary artery bypass grafting (CABG), investigated the prognostic performance of serum levels of advanced oxidation protein products (AOPPs) for predicting non-recovered AKI and non-completely recovered AKI. AOPP levels increased significantly 7 days after surgery in patients with non-recovered or non-completely recovered AKI. Increased AOPP levels were associated with both types of poor recovery from AKI. Results from receiver-operating characteristic (ROC) curves demonstrated that AOPP levels had good prognostic value for predicting non-recovered and non-completely recovered AKI.

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

AKI remains an important clinical problem, with a high mortality rate, increasing incidence, and no Food and Drug Administration-approved therapeutics. Advances in addressing this clinical need require approaches for rapid diagnosis and stratification of injury, development of therapeutic agents based on precise understanding of key pathophysiological events, and implementation of well designed clinical trials. In the near future, AKI biomarkers may facilitate trial design. To address these issues, the National Institute of Diabetes and Digestive and Kidney Diseases sponsored a meeting, "Clinical Trials in Acute Kidney Injury: Current Opportunities and Barriers," in December of 2010 that brought together academic investigators, industry partners, and representatives from the National Institutes of Health and the Food and Drug Administration. Important issues in the design of clinical trials for interventions in AKI in patients with sepsis or AKI in the setting of critical illness after surgery or trauma were discussed. The sepsis working group discussed use of severity of illness scores and focus on patients with specific etiologies to enhance homogeneity of trial participants. The group also discussed endpoints congruent with those endpoints used in critical care studies. The second workgroup emphasized difficulties in obtaining consent before admission and collaboration among interdisciplinary healthcare groups. Despite the difficult trial design issues, these clinical situations represent a clinical opportunity because of the high event rates, severity of AKI, and poor outcomes. The groups considered trial design issues and discussed advantages and disadvantages of several short- and long-term primary endpoints in these patients.

Prevention of post-cardiopulmonary bypass acute kidney injury by endothelin A receptor blockade

OBJECTIVE

The aim of this study was to determine whether administration of a specific endothelin A receptor antagonist, sitaxsentan sodium, would prevent the development of post-cardiopulmonary bypass acute kidney injury in swine.

DESIGN

Experimental study.

SETTING

Cardiovascular Research Institute.

INTERVENTIONS

Adult pigs (n = 8 per group) were randomized to undergo a sham procedure, cardiopulmonary bypass, or cardiopulmonary bypass plus administration of endothelin A receptor antagonist (RA), with recovery and reassessment at 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Cardiopulmonary bypass resulted in a significant reduction in creatinine clearance relative to sham pigs (mean difference for cardiopulmonary bypass vs. sham, -50.3 mL/min [95% confidence interval -89.2 to -11.4 mL/min], p = .008). This was reversed by the administration of endothelin A RA during cardiopulmonary bypass (mean difference for cardiopulmonary bypass + endothelin A RA vs. cardiopulmonary bypass, +43.3 mL/min [95% confidence interval +3.3 to +83.4 mL/min], p = .030). Cardiopulmonary bypass also resulted in a significant rise in the specific urinary biomarker of acute kidney injury interleukin-18 compared to sham procedures (mean difference +209 pg/mL [95% confidence interval +119 to +299 pg/mL], p < .001) that was reversed by endothelin A receptor antagonist administration. Post-cardiopulmonary bypass kidney injury was associated with vascular endothelial injury and dysfunction, reduced nitric oxide bioavailability, inflammation, and a significant increase in the expression of the paracrine vasoconstrictors adenosine and endothelin-1. In post-cardiopulmonary bypass kidneys at 24 hrs there was persistent hypoxia at the level of the outer medulla, cortical adenosine triphosphate depletion, and evidence of proximal tubule epithelial cell stress manifest as phenotypic change. There was no evidence of acute tubular necrosis. Administration of endothelin A RA to cardiopulmonary bypass pigs reversed endothelial dysfunction, regional hypoxia, inflammation, and tubular changes.

CONCLUSION

In this model, post-cardiopulmonary bypass acute kidney injury is associated with endothelial dysfunction, regional tissue hypoxia, and proximal tubular epithelial cell stress but not acute tubular necrosis. Antagonism of the endothelin-1 A receptor reversed these changes and may represent a therapeutic target for the prevention of post-cardiac surgery acute kidney injury.

Impact of estimated glomerular filtration rate after valve and combined valve and coronary surgery

Preoperative renal impairment predicts postoperative mortality in patients undergoing cardiac surgery. We examined the impact of three equations for glomerular filtration rate (GFR) estimation on mortality. This is a retrospective, observational study on patients undergoing valve (n = 594) and combined valve and coronary procedures (n = 412). Glomerular filtration rate was estimated with modification in diet and renal disease (MDRD), Cockcroft-Gault (CG) equation, and Mayo-Clinic (MC) equation. Mean age was 65 ± 11 years and mean logistic EuroSCORE was 9.0 [95% confidence interval (CI): 8.4-9.7]. Preoperative kidney dysfunction (eGFR <60 ml/min/1.73 m²) is associated with increased risk for mortality. Hazard ratios for 30-day mortality differed between eGFR equations [MC 2.6 (95% CI: 1.6-4.1); MDRD 2.9 (95% CI: 1.9-4.4); CG 3.9 (95% CI: 2.2-5.2)]. Discriminatory performance of GFR equations was comparable with logistic EuroSCORE, but CG and MC discriminated significantly better than MDRD. Median intensive care unit stay did not differ, but Bland-Altman plots showed considerable variation between eGFR equations, indicating that they cannot be used interchangeably. Substantial amount of agreement was achieved with CG and MDRD. Only one equation should be used in one institution. The bias between equations varied considerably. Impaired preoperative kidney dysfunction is associated with increased risk for mortality irrespective of the formula used.

Effect of remote ischemic preconditioning on renal dysfunction after complex valvular heart surgery: a randomized controlled trial

OBJECTIVE

Acute kidney injury after cardiac surgery with cardiopulmonary bypass is closely related to systemic inflammatory reactions and oxidative stresses. Remote ischemic preconditioning is a systemic protective strategy whereby brief limb ischemia confers systemic protection against prolonged ischemia and inflammatory reactions in distant organs. This study investigated whether remote ischemic preconditioning provides systemic protective effect on kidneys that are not directly exposed to ischemia-reperfusion injury during complex valvular heart surgery.

METHODS

Seventy-six adult patients undergoing complex valvular heart surgery were randomly assigned to either remote ischemic preconditioning group (n = 38) or control group (n = 38). Remote ischemic preconditioning consisted of 3 10-minute cycles of lower limb ischemia and reperfusion with an automated cuff inflator. Primary end points were comparisons of biomarkers of renal injury including serum creatinine, cystatin C and neutrophil gelatinase-associated lipocalin, and incidence of acute kidney injury. Secondary end points were comparisons of myocardial enzyme release and pulmonary parameters.

RESULTS

There were no significant differences in serum levels of biomarkers of renal injury between groups throughout the study period. The incidence of acute kidney injury did not differ between groups. Creatine kinase isoenzyme MB at 24 hours after surgery was lower, and intensive care unit stay was shorter in the remote ischemic preconditioning group than in the control group.

CONCLUSIONS

In patients undergoing complex valvular heart surgery, remote ischemic preconditioning did not reduce degree of renal injury or incidence of acute kidney injury whereas it did reduce myocardial injury and intensive care unit stay.

Validation of clinical scores predicting severe acute kidney injury after cardiac surgery

BACKGROUND

Acute kidney injury (AKI) requiring renal replacement therapy (RRT) in patients undergoing cardiac surgery is associated strongly with adverse patient outcomes. Recently, 3 predictive risk models for RRT have been developed. The aims of our study are to validate the predictive scoring models for patients requiring postoperative RRT and test applicability to the broader spectrum of patients with postoperative severe AKI.

STUDY DESIGN

Diagnostic test study.

SETTING & PARTICIPANTS

12,096 patients undergoing cardiac surgery with cardiopulmonary bypass at Mayo Clinic, Rochester, MN, from 2000 through 2007.

INDEX TEST

Cleveland Clinic score, Mehta score, and Simplified Renal Index (SRI) score.

REFERENCE TEST OR OUTCOME

Incidence of postoperative RRT or composite outcome of severe AKI, defined as serum creatinine level >2.0 mg/dL, and a 2-fold increase compared with the preoperative baseline creatinine level or RRT.

RESULTS

RRT was used in 254 (2.1%) patients, whereas severe AKI was present in 467 (3.9%). Discrimination for the prediction of RRT and severe AKI was good for all scoring models measured using areas under the receiver operating characteristic curve (AUROCs): 0.86 (95% CI, 0.84-0.88) for RRT and 0.81 (95% CI, 0.79-0.83) for severe AKI using the Cleveland score, 0.81 (95% CI, 0.78-0.86) and 0.76 (95% CI, 0.73-0.80) using the Mehta score, and 0.79 (95% CI, 0.77-0.82) and 0.75 (95% CI, 0.72-0.77) using the SRI score. The Cleveland score and Mehta score consistently showed significantly better discrimination compared with the SRI score (P < 0.001). Despite lower AUROCs for the prediction of severe AKI, the Cleveland score AUROC was still >0.80. The Mehta score is applicable in only a subgroup of patients.

LIMITATIONS

Single-center retrospective cohort study.

CONCLUSIONS

The Cleveland scoring system offers the best discriminative value to predict postoperative RRT and covers most patients undergoing cardiac surgery. It also can be used for prediction of the composite end point of severe AKI, which enables broader application to patients at risk of postoperative kidney dysfunction.

Cardiac surgery and acute kidney injury: emerging concepts

PURPOSE OF REVIEW

To review recent advances in understanding of the occurrence, pathophysiology, prophylaxis and treatment of cardiac surgery-associated acute kidney injury (AKI).

RECENT FINDINGS

New definitions and prompt diagnostic tools, enhanced risk stratification strategies, avoidance of nephrotoxins and procedure selection are all areas in which recent contributions to the literature have improved perioperative care for cardiac surgery patients. Although evidence continues to confirm the adverse effects of extreme hemodilution and transfusion as part of cardiac surgery, the previously believed advantages of tight perioperative glucose control for the kidney are being questioned in recent studies. Although very little evidence from randomized trials in cardiac surgery populations supports specific interventions to protect or prevent AKI, recent reports indicate reduced AKI associated with some procedural innovations, and the hope that promising findings for agents such as sodium bicarbonate that require further study may yield effective therapies.

SUMMARY

The vexing problem of AKI following cardiac surgery is common and unsolved. Clinical strategies that stress avoidance rather than treatment remain the mainstay of effective management of patients at high renal risk.

Minimized extracorporeal circulation cannot prevent acute kidney injury but attenuates early renal dysfunction after coronary bypass grafting

We studied the impact of minimized extracorporeal circulation (MECC) on acute kidney injury (AKI) after coronary bypass grafting. A retrospective, observational study with 1,685 patients with MECC and 3,046 patients with conventional bypass was done. Primary outcome was AKI defined as a decline > or = 50% in estimated glomerular filtration rate (eGFR) within 48 hours after surgery. Secondary outcome was temporary dialysis. MECC exerts beneficial hemodynamic effects but does not prevent AKI. Fewer patients developed a decline in eGFR <60 mL/min/1.73 m(2) (MECC) compared with conventional extracorporeal circulation (ECC) (30.7% versus 45.5%, p < 0.001). The incidence of eGFR decrease by > or = 50% did not differ (1.8% versus 2.7%, p = 0.20). Temporary dialysis was required in 61 patients with ECC (2%) and in 16 patients with MECC (0.9%, p < 0.001). A preoperative eGFR <60 mL/min/1.73 m(2) increased in both groups the risk for mortality compared with patients with an eGFR >60 mL/min/1.73 m(2) (ECC: odds ratio 3.6, 95% confidence interval 2.6-4.9; MECC: odds ratio 4.9, 95% confidence interval 2.8-8.6). MECC is renoprotective in the early postoperative period but cannot prevent AKI. An impaired preoperative eGFR increases the risk for mortality irrespective of the cardiopulmonary bypass system used.

Trends in cardiac surgery-associated acute renal failure in the United States: a disproportionate increase after heart transplantation

Acute renal failure (ARF) is common after cardiac surgery and more frequent after complex cardiac surgery. While the incidence of ARF is increasing after coronary artery bypass graft (CABG) surgery, trends in other forms of cardiac surgery remain unclear. We investigated the trend of ARF in various cardiac procedures and compared patterns using CABG surgery as a reference group. The study population consisted of discharges from the Nationwide Inpatient Sample from 1988 to 2003, grouped according to surgery as: CABG, CABG with mitral valve, CABG with other valve, valve alone, and heart transplant. Standard diagnostic codes were used to identify ARF among discharges. Multivariable regression was used to determine trends in ARF among various procedures with CABG as a reference group. The incidence of ARF increased in all five groups (p < 0.001) over the 16-year period. The ARF incidence was highest in the heart transplant group (17%). Compared to the CABG population, patients following heart transplantation developed ARF at higher rates during the study period. In contrast, while ARF increased over time in other groups, the rates of rise were slower than in CABG patients. Among heart surgery procedures, ARF incidence is highest in heart transplantation. The incidence of ARF is also increasing at a faster rate in this group of patients in contrast to other procedure groups when compared to CABG surgery. The disproportionate increase in ARF burden after heart transplantation is a concern due to its strong association with chronic kidney disease and mortality.

Age- and gender-specific values of estimated glomerular filtration rate among 6232 patients undergoing cardiac surgery

Impaired preoperative renal function as estimated by glomerular filtration rate (GFR) is an independent risk factor for mortality after cardiac surgery. Little is known about the actual prevalence of renal dysfunction among patients undergoing cardiac surgery in Germany. We performed a retrospective analysis of 6232 patients from 20 to 80 years. GFR was estimated with the modification of diet in renal disease (MDRD) formula. There was an age-dependent decrease in estimated glomerular filtration rates (eGFR) among both men and women. There is a stepwise age-dependent increase of chronic kidney disease (CKD) stages 3-5 (<60 ml/min/1.73 m(2)). The lower the eGFR the higher the risk for mortality [odds ratio 2.93 95%-confidence interval (CI) 1.92-4.53] for eGFR<30 ml/min/1.73 m(2); odds ratio 1.93 (95%-CI 1.56-2.39) for eGFR 30-60 ml/min/1.73 m(2) compared to patients with an eGFR>60 ml/min/1.73 m(2). The actual mortality rates varied between 6.3% (307/4869) for patients with an eGFR>60 ml/min/1.73 m(2), 11.3% (137/1051) for patients with an eGFR of 30-60 ml/min/1.73 m(2) and 16.6% (27/163) for patients with an eGFR<30 ml/min/1.73 m(2). Estimated GFR declines are age- and gender-dependent. Preoperative renal dysfunction is an important predictor of in-hospital mortality after cardiac surgery.

Emerging concepts in acute kidney injury following cardiac surgery

Acute kidney injury (AKI) remains a significant cause of morbidity and mortality following cardiac surgery. Through a more thorough understanding of perioperative genomics and the evolving role of early biomarkers of AKI, the authors seek to improve meaningful outcomes among cardiac surgery patients. In this review, the focus will be on advances in risk stratification, evolving definitions and improving early diagnosis of AKI, identification of effective individualized therapies, and future directions.