Emerging concepts in acute kidney injury following cardiac surgery

Evaluating the Prevalence of Cardiac Surgery-associated Acute Kidney Injury After Septal Myectomy Combined With Concomitant Procedures in Obstructive Hypertrophic Cardiomyopathy

OBJECTIVES

Hypertrophic obstructive cardiomyopathy (HOCM) may be treated by septal myectomy. Cardiac surgery-associated acute kidney injury (CSA-AKI) is a common complication, but little is known about its incidence after septal myectomy. The objectives of this work were to evaluate the prevalence of CSA-AKI after septal myectomy and identify potential perioperative and phenotype-related factors contributing to CSA-AKI.

DESIGN

This was a retrospective database analysis with new data analysis.

SETTING

The study occurred in a single university academic expertise center for septal myectomy HOCM patients.

PARTICIPANTS

Data from 238 HOCM patients with septal myectomy operated on between 2005 and 2022 were collected.

INTERVENTIONS

CSA-AKI was stratified according to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines using measurement of creatinine and urine production. Important HOCM phenotype-related and perioperative factors were analyzed for their possible associations with CSA-AKI.

MEASUREMENTS AND MAIN RESULTS

CSA-AKI occurred in 45% of patients; of these, 55% were classified as KDIGO stage I and the remaining 45% as stage II, with no chronic kidney damage observed. Moreover, there were no phenotypical or perioperative characteristics that were more prevalent in the CSA-AKI cohort. However, the use of beta-blockers and coronary artery disease were more prevalent in the CSA-AKI cohort.

CONCLUSIONS

CSA-AKI is a common complication after septal myectomy but was transient, and kidney function recovered in all patients.

Cardiac Surgery-Associated Acute Kidney Injury

AKI is a common and serious complication of cardiac surgery that has a significant impact on patient morbidity and mortality. The Kidney Disease Improving Global Outcomes definition of AKI is widely used to classify and identify AKI associated with cardiac surgery (cardiac surgery-associated AKI [CSA-AKI]) on the basis of changes in serum creatinine and/or urine output. There are various preoperative, intraoperative, and postoperative risk factors for the development of CSA-AKI which should be recognized and addressed as early as possible to expedite its diagnosis, reduce its occurrence, and prevent or ameliorate its devastating complications. Crucial issues are the inaccuracy of serum creatinine as a surrogate parameter of kidney function in the perioperative setting of cardiothoracic surgery and the necessity to discover more representative markers of the pathophysiology of AKI. However, except for the tissue inhibitor of metalloproteinase-2 and insulin-like growth factor binding protein 7 ratio, other diagnostic biomarkers with an acceptable sensitivity and specificity are still lacking. This article provides a comprehensive review of various aspects of CSA-AKI, including pathogenesis, risk factors, diagnosis, biomarkers, classification, prevention, and treatment management.

The impact of statin use before intensive care unit admission on patients with acute kidney injury after cardiac surgery

Background: Cardiac surgery-associated acute kidney injury (CSA-AKI) is a common and serious complication after cardiac surgery. The influence of statin use before surgery on the renal outcome of patients undergoing cardiac surgery is controversial. The purpose of this study was to evaluate the effect of statins on postoperative renal outcomes in patients undergoing cardiac surgery. Methods: We included CSA-AKI patients in the Medical Information Mart for Intensive Care (MIMIC)-IV database and were divided into statin group and non-statin group according to whether they used statins before entering intensive care units (ICU). The main outcomes were hospitalization and 30-day mortality, and the secondary outcomes were 60-day mortality and 90-day mortality. We used propensity score matching (PSM) to adjust for confounding factors. The 95% confidence interval (CI) and risk ratio (RO) were calculated by the COX proportional regression model. At the same time, stratified analysis was used to explore whether the relationship between the statins use before intensive care units and mortality was different in each subgroup and whether the relationship between different doses of Atorvastatin and mortality was different. Result: We identified 675 pre-ICU statin users and 2095 non-statin users. In the COX proportional regression model, pre-ICU statin use was associated with decreased in-hospital (HR = 0.407, 95%confidence interval 0.278-0.595, p < 0.001) and 30-day mortality (HR = 0.407, 95%CI 0.279-0.595, p < 0.001). The survival rate of patients who took statins before entering ICU was significantly higher than that of those who did not use statins at 30 days, 60 days and 90 days. There is a significant interaction between patients with aged>65 years (HR = 0.373, 95%CI 0.240-0.581, p < 0.001), Acute kidney injury grade I (HR = 0.244, 95%CI 0.118-0.428, p < 0.001), and without post-myocardial infarction syndrome (HR = 0.344, 95%CI 0.218-0.542, p < 0.001). The mortality in hospital and 60 days of CSA-AKI patients treated with ≥80 mg Atorvastatin before operation was significantly reduced (p < 0.05). Conclusion: The pre-ICU statin use was significantly associated with decreased risk in hospital and 30-day mortality. The preoperative use of ≥80 mg Atorvastatin may improve the prognosis of CSA-AKI.

Microvascular dysfunction following cardiopulmonary bypass plays a central role in postoperative organ dysfunction

Despite significant advances in surgical technique and strategies for tissue/organ protection, cardiac surgery involving cardiopulmonary bypass is a profound stressor on the human body and is associated with numerous intraoperative and postoperative collateral effects across different tissues and organ systems. Of note, cardiopulmonary bypass has been shown to induce significant alterations in microvascular reactivity. This involves altered myogenic tone, altered microvascular responsiveness to many endogenous vasoactive agonists, and generalized endothelial dysfunction across multiple vascular beds. This review begins with a survey of in vitro studies that examine the cellular mechanisms of microvascular dysfunction following cardiac surgery involving cardiopulmonary bypass, with a focus on endothelial activation, weakened barrier integrity, altered cell surface receptor expression, and changes in the balance between vasoconstrictive and vasodilatory mediators. Microvascular dysfunction in turn influences postoperative organ dysfunction in complex, poorly understood ways. Hence the second part of this review will highlight in vivo studies examining the effects of cardiac surgery on critical organ systems, notably the heart, brain, renal system, and skin/peripheral tissue vasculature. Clinical implications and possible areas for intervention will be discussed throughout the review.

Massive Bleeding After Surgical Repair in Acute Type A Aortic Dissection Patients: Risk Factors, Outcomes, and the Predicting Model

Background

Massive bleeding throughout aortic repair in acute type A aortic dissection (ATAAD) patients is a common but severe condition that can cause multiple serious clinical problems. Here, we report our findings regarding risk factors, short-term outcomes, and predicting model for massive bleeding in ATAAD patients who underwent emergent aortic repair.

Methods

A universal definition of perioperative bleeding (UDPB) class 3 and 4 were used to define massive bleeding and comprehensively evaluate patients. A total of 402 consecutive patients were enrolled in this retrospective study during 2019. Surgical strategies used to perform aortic arch procedures included total arch and hemiarch replacements. In each criterion, patients with massive bleeding were compared with remaining patients. Multivariable regression analyses were used to identify independent risk factors for massive bleeding. Logistic regression was used to build the model, and the model was evaluated with its discrimination and calibration.

Results

Independent risk factors for massive bleeding included male sex (OR = 6.493, P &lt; 0.001), elder patients (OR = 1.029, P = 0.05), low body mass index (BMI) (OR = 0.879, P = 0.003), emergent surgery (OR = 3.112, P = 0.016), prolonged cardiopulmonary bypass time (OR = 1.012, P = 0.002), lower hemoglobin levels (OR = 0.976, P = 0.002), increased D-dimer levels (OR = 1.000, P = 0.037), increased fibrin degradation products (OR = 1.019, P = 0.008), hemiarch replacement (OR = 5.045, P = 0.037), total arch replacement (OR = 14.405, P = 0.004). The early-stage mortality was higher in massive bleeding group (15.9 vs. 3.9%, P = 0.001). The predicting model showed a well discrimination (AUC = 0.817) and calibration (χ2 = 5.281, P = 0.727 &gt; 0.05).

Conclusion

Massive bleeding in ATAAD patients who underwent emergent aortic repair is highly associated with gender, emergent surgery, increased D-dimer levels, longer CPB time, anemia, and use of a complex surgical strategy. Since massive bleeding may lead to worse outcomes, surgeons should choose suitable surgical strategies in patients who are at a high risk of massive bleeding.

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.

Apolipoprotein L1 (APOL1) Coding Variants Are Associated With Creatinine Rise After Cardiac Surgery

OBJECTIVE

Acute kidney injury (AKI) is a complication of cardiac surgery that is considerably more common in African Americans (1.5-fold). Although homozygous status for apolipoprotein L1 (APOL1) risk alleles is associated with chronic kidney disease in individuals of African ancestry, whether these coding variants confer AKI risk is unknown. The present study examined whether APOL1 homozygous risk allele status was associated with AKI in African Americans after cardiac surgery.

DESIGN

Retrospective analysis of a cohort.

SETTING

Single-center university hospital.

PARTICIPANTS

African American patients from the CATHeterization GENetics study cohort who underwent cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

Genotyping of APOL1 alleles.

MEASUREMENTS AND MAIN RESULTS

Data from 125 African American patients included 12 APOL1 risk (ie, homozygous for risk alleles) patients and 113 APOL1 control (ie, wildtype or heterozygous for risk alleles) patients. The primary outcome to reflect AKI was peak serum creatinine rise after surgery relative to the preoperative creatinine (%ΔCr). The secondary outcome was Kidney Disease: Improving Global Outcomes (KDIGO) AKI criteria. In the primary analysis, peak creatinine rise was higher in risk compared with control patients in both univariate (%ΔCr 69.1 v 29.6%; p = 0.005) and multivariate regression (%ΔCr 88.5 v 43.7%; p = 0.006) analyses. For the secondary outcome, a trend toward KDIGO AKI development was noted in APOL1 risk patients, but this was not statistically significant.

CONCLUSIONS

African American cardiac surgery patients homozygous for APOL1 chronic kidney disease risk variants averaged a more than 2-fold higher postoperative creatinine rise even after adjustment for other risk factors, suggesting these alleles also are independent risk factors for AKI.

Regional thigh tissue oxygen saturation during cardiopulmonary bypass predicts acute kidney injury after cardiac surgery

Cardiopulmonary bypass-associated acute kidney injury may appear postoperatively, but predictive factors are unclear. We investigated the potential of regional tissue oxygen saturation as a predictor of cardiopulmonary bypass-associated acute kidney injury. We analyzed the clinical data of 150 adult patients not on dialysis who underwent elective cardiac surgical procedures during January 2015-March 2017. Near-infrared spectroscopy was used to measure regional oxygen saturation. Sensors were placed on the patients' forehead, abdomen, and thigh. The incidence of acute kidney injury was 2% at the end of surgery, 13% at 24 h, and 9% at 48 h, with the highest at 24 h after surgery. The multiple regression analysis revealed that the thigh regional oximetry during cardiopulmonary bypass, oxygen delivery index, and neutrophil count at the end of cardiopulmonary bypass and surgery were independent risk factors for acute kidney injury. The receiver-operating characteristic curve analysis suggested that a cutoff of regional oxygen saturation at the thigh of ≤ 67% was predictive of acute kidney injury within 24 h after surgery. In conclusion, the regional oxygen saturation at the thigh during cardiopulmonary bypass is a crucial marker to predict postoperative acute kidney injury in adults undergoing cardiac surgery.

Predictors of acute kidney injury in patients undergoing adult cardiac surgery

Background

Acute kidney injury (AKI) after cardiac surgery (CS) is not uncommon and has serious effects on mortality and morbidity. A majority of patients suffer mild forms of AKI. There is a paucity of Indian data regarding this important complication after CS.

Aims and Objectives

The primary objective was to study the incidence of AKI associated with CS in an Indian study population. Secondary objectives were to describe the risk factors associated with AKI-CS in our population and to generate outcome data in patients who suffer this complication.

Methods

Serial patients (n = 400) presenting for adult CS (emergency/elective) at a tertiary referral care hospital in South India from August 2016 to November 2017 were included as the study individuals. The incidence of AKI-CS AKI network (AKIN criteria), risk factors associated with this condition and the outcomes following AKI-CS are described.

Results

Out of 400, 37 (9.25%) patients developed AKI after CS. AKI associated with CS was associated with a mortality of 13.5% (no AKI group mortality 2.8%, P = 0.001 [P < 0.05]). When AKI was severe enough to need renal replacement therapy, the mortality increased to 75%. Patients with AKI had a mean hospital stay 16.92 ± 12.75 days which was comparatively longer than patients without AKI (14 ± 7.98 days). Recent acute coronary syndrome, postoperative atrial fibrillation, and systemic hypertension significantly predicted the onset of AKI-CS in our population.

Conclusions

The overall incidence of AKI-CS was 9.25%. The incidence of AKI-CS requiring dialysis (Stage 3 AKIN) AKI-CS was lower (2%). However, mortality risks were disproportionately high in patients with AKIN Stage 3 AKI-CS (75%). There is a need for quality improvement in the care of patients with AKI-CS in its most severe forms since mortality risks posed by the development of Stage 3 AKIN AKI is higher than reported in other index populations from high resource settings.

Risk Factors and Outcome of Acute Kidney Injury after Isolated CABG Surgery: a Prospective Cohort Study

BACKGROUND

Acute kidney injury (AKI) is a frequent event after cardiac surgery with increased mortality and morbidity. We explored frequency, risk factors, and associated morbidity and mortality of AKI after isolated coronary artery bypass grafting (CABG) surgery at a single institution.

METHODS

All consecutive adults undergoing CABG surgery from March 2013 to October 2016 were assessed for development and severity of AKI based on Acute Kidney Injury Network (AKIN) criteria. The patients were also investigated regarding their need for renal replacement therapy (RRT), predictive risk factors, and associated outcomes, including duration of mechanical ventilation, mortality, intensive care unit (ICU) and hospital length of stay.

RESULTS

Of 1737 patients in the study, 275 (15.8%) developed AKI. Twenty-five (12.8%) cases required RRT. Patients with AKI had longer ventilation time, ICU and hospital length of stay (P<0.001). Mortality rates were 28 (10.2%) and 22 (1.5%) in patients with and without AKI, respectively (P<0.001). There was a strong association between advanced age (aOR=1.016, 95% CI=1.002-1.030, P=0.028), diabetes (aOR=1.36, 95% CI=1.022-1.809, P=0.035), on-pump surgery (aOR=2.63, 95% CI=1.543-4.483, P<0.001), transfusion of more than 1 unit of red blood cells (aOR=2.154, 95% CI=1.237-3.753, P=0.007), and prolonged mechanical ventilation and development of AKI (aOR=2.697, 95% CI=1.02407.071, P<0.001). AKI was seen less frequently in those with opium abuse (aOR=0.613, 95% CI=0.409-0.921, P=0.018).

CONCLUSION

We demonstrated that advanced age, diabetes, on-pump surgery, red blood cell transfusion, and prolonged mechanical ventilation were independent positive risk factors for the development of AKI after isolated CABG while opium abuse was a protective factor.

Predicting acute kidney injury: current status and future challenges

Acute kidney injury (AKI) is characterized by an acute decline in renal function and is associated to increased mortality rate, hospitalization time, and total health-related costs. The severity of this ‘fearsome’ clinical complication might depend on, or even be worsened by, the late detection of AKI, when the diagnosis is based on the elevation of serum creatinine (SCr). For these reasons, in recent years a great number of new tools, biomarkers and predictive models have been proposed to clinicians in order to improve diagnosis and prevent the development of AKI. The purpose of this narrative paper is to review the current state of the art in prediction and early detection of AKI and outline future challenges.

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.

Cardiac surgery-associated acute kidney injury

Cardiac surgery-associated acute kidney injury (CSA-AKI) is a well-recognized complication resulting with the higher morbid-mortality after cardiac surgery. In its most severe form, it increases the odds ratio of operative mortality 3-8-fold, length of stay in the Intensive Care Unit and hospital, and costs of care. Early diagnosis is critical for an optimal treatment of this complication. Just as the identification and correction of preoperative risk factors, the use of prophylactic measures during and after surgery to optimize renal function is essential to improve postoperative morbidity and mortality of these patients. Cardiopulmonary bypass produces an increased in tubular damage markers. Their measurement may be the most sensitive means of early detection of AKI because serum creatinine changes occur 48 h to 7 days after the original insult. Tissue inhibitor of metalloproteinase-2 and insulin-like growth factor-binding protein 7 are most promising as an early diagnostic tool. However, the ideal noninvasive, specific, sensitive, reproducible biomarker for the detection of AKI within 24 h is still not found. This article provides a review of the different perspectives of the CSA-AKI, including pathogenesis, risk factors, diagnosis, biomarkers, classification, postoperative management, and treatment. We searched the electronic databases, MEDLINE, PubMed, EMBASE using search terms relevant including pathogenesis, risk factors, diagnosis, biomarkers, classification, postoperative management, and treatment, in order to provide an exhaustive review of the different perspectives of the CSA-AKI.

Creatinine, Neutrophil Gelatinase-Associated Lipocalin, and Cystatin C in Determining Acute Kidney Injury After Heart Operations Using Cardiopulmonary Bypass

Acute kidney injury (AKI) represents frequent complication after cardiac surgery using cardiopulmonary bypass (CPB). In the hope to enhance earlier more reliable characterization of AKI, we tested the utility of neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C (CysC) in addition to standard creatinine for early determination of AKI after cardiac surgery using CPB. Forty-one patients met the inclusion criteria. Arterial blood samples collected after induction of general anesthesia were used as baseline, further sampling occurred at CPB termination, 2 h after CPB, on the first and second day after surgery. According to AKIN classification 18 patients (44%) developed AKI (AKI1-2 groups) and 23 (56%) did not (non-AKI group). Groups were similar regarding demographics and operative characteristics. CysC levels differed already preoperatively (non-AKI vs. AKI2; P = 0.045; AKI1 vs. AKI2; P = 0.011), while postoperatively AKI2 group differed on the first day and AKI1 on the second regarding non-AKI group (P = 0.004; P = 0.021, respectively). NGAL and creatinine showed significant difference already 2 h after CPB between groups AKI2 and non-AKI and later on the first postoperative day between groups AKI1 and AKI2 (P = 0.028; P = 0.014, respectively). This study shows similar performance of early plasma creatinine and NGAL in patients with preserved preoperative renal function. It demonstrates that creatinine, as well as NGAL, differentiate subsets of patients developing AKI of clinically more advanced grade early after 2 h, also when used single and uncombined.

Kidney Injury Molecule-1 and Cardiovascular Diseases: From Basic Science to Clinical Practice

Despite the recent findings concerning pathogenesis and novel therapeutic strategies, cardiovascular disease (CVD) still stays the leading cause of morbidity and mortality in patients with renal dysfunction, especially acute kidney injury (AKI). Early detection of patients with impaired renal function with cardiovascular risk may help ensure more aggressive treatment and improve clinical outcome. Kidney injury molecule-1 (KIM-1) is a new, promising marker of kidney damage which is currently the focus of countless studies worldwide. Some recent animal and human studies established KIM-1 as an important marker of acute tubular necrosis (ATN) and reliable predictor of development and prognosis of AKI. Food and Drug Administration (FDA) in USA acclaimed KIM-1 as an AKI biomarker for preclinical drug development. Recent data suggest the importance of monitoring of KIM-1 for early diagnosis and clinical course not only in patients with various forms of AKI and other renal diseases but also in patients with cardiorenal syndrome, heart failure, cardiopulmonary bypass, cardiothoracic surgical interventions in the pediatric emergency setting, and so forth. The aim of this review article is to summarize the literature data concerning KIM-1 as a potential novel marker in the early diagnosis and prediction of clinical outcome of certain cardiovascular diseases.

Novel biomarkers for cardiac surgery-associated acute kidney injury: a skeptical assessment of their role

Cardiac surgery-associated acute kidney injury (AKI) is common and is associated with a high mortality rate. Traditional biomarkers of AKI (creatinine and urea) increase slowly in response to renal injury, are insensitive to mild degrees of AKI, and are influenced by nonrenal factors. There is considerable interest in novel biomarkers of AKI such as neutrophil gelatinase-associated lipocalin that increase rapidly after renal injury, detect mild degrees of AKI, and are less subject to nonrenal factors. It has been postulated that the early diagnosis of cardiac surgery-associated AKI using novel biomarkers will result in improved outcomes. However, there is little evidence that interventions started early in the course of evolving AKI enhance renal recovery. Until effective therapies are developed that significantly improve the outcome from AKI, there is little benefit from early diagnosis using novel biomarkers.

Cardio-renal syndrome: new perspective in diagnostics

Chronic heart failure and chronic renal failure are at epidemic proportions. These patients have significantly altered cardiac, renal, and all-cause outcomes. Much of the current research has focused on treating these individual organs in isolation. Although there are positive data on outcomes with neurohormonal modulation, they, however, remain underused. At present, data lacks for novel treatment options, while evidence continues to point at significantly worsened prognosis. Current diagnostic tools that detect acute changes in renal function or renal injury appear retrospective, which often hinder meaningful diagnostic and therapeutic decisions. This review is aimed at exploring the importance of accurate assessment of renal function for the heart failure patient by providing a synopsis on cardio-renal physiology and establishing the possibility of novel approaches in bridging the divide.

Update on acute kidney injury after cardiac surgery

OBJECTIVES

To review the current state of clinical practice and discuss recent advances in the diagnosis and management of acute kidney injury (AKI) in the context of cardiac surgery.

METHODS

A review of the published data pertaining to AKI in the setting of cardiac surgery and cardiothoracic surgical critical care medicine was conducted, and the relevant data were synthesized from appropriate interventional and observational study reports.

RESULTS

Significant advances have occurred in the diagnosis of AKI, and consensus has been reported on a system of diagnosis using the serum creatinine and urine output. New biomarkers of injury and function are available that are likely to improve the interval to diagnosis of AKI after cardiac surgery. The adverse effect on outcome of small changes in serum creatinine is appreciated. Novel prevention and rescue therapies are now entering phase I and II studies. Urinary alkalinization was effective in a phase II blinded clinical trial and is now the subject of a multicenter, double-blind, randomized clinical trial of cardiac surgery patients.

CONCLUSIONS

In 2011, the field of AKI could be emerging from a period of stagnation that has lasted more than 2 decades. The failure to translate successful animal model interventions to the clinic might have resulted from delays in diagnosis that might now be avoidable with the advent of novel diagnostic biomarkers.

Preoperative Estimated Glomerular Filtration Rate and RIFLE-Classified Postoperative Acute Kidney Injury Predict Length of Stay Post-Coronary Bypass Surgery in an Australian Setting

We investigated the influence of preoperative estimated glomerular filtration rate and postoperative acute kidney injury on outcomes after coronary bypass surgery in a local setting, with the focus on length of stay.

A retrospective analysis of prospectively collected data for 3302 consecutive patients who underwent coronary artery bypass graft surgery (June 1997 through to January 2007) at St Vincent's Public Hospital, Melbourne, was undertaken. Preoperative estimated glomerular filtration rate was calculated and categorised using US National Kidney Foundation cut-offs for chronic kidney disease (normal function; mild, moderate and severe dysfunction). Postoperative acute kidney injury was categorised using serum creatinine RIFLE criteria (no acute kidney injury, risk, injury and failure). Postoperative intensive care and hospital length of stay was determined.

The hazard ratios for time to hospital discharge up to one month decreased (indicating a longer length of stay) as severity of preoperative renal dysfunction category increased when compared to those with normal renal function: mild hazard ratio=1.02 (95% confidence interval: 0.91 to 1.15, P=0.70), moderate 0.87 (0.76 to 1.00, P=0.047), severe 0.47 (0.35 to 0.64, P < 0.001). Hazard ratios also decreased as severity of postoperative acute kidney injury category increased, when compared to those with no acute kidney injury: risk 0.67 (0.58 to 0.77, P <0.001), injury 0.52 (0.41 to 0.65, P <0.001), failure 0.35 (0.20 to 0.60, P <0.001).

The increasing severity of preoperative renal dysfunction and postoperative acute kidney injury were associated with increased hospital length of stay. This has implications for resource use, informed consent and case selection.