Acute kidney injury following cardiac surgery: current understanding and future directions

Is the use of hydroxyethyl starch as priming solution during cardiac surgery advisable? A randomized, single-center trial

Introduction:

The use of cardiopulmonary bypass (CPB) leads to increased fluid filtration and edema. The use of artificial colloids to counteract fluid extravasation during cardiac surgery is controversial. Beneficial effects on global fluid loading, leading to better cardiac performance and hemodynamics, have been claimed. However, renal function and coagulation may be adversely affected, with unfavorable impact on outcome following cardiac surgery.

Methods:

Forty patients were randomly allocated to study groups receiving either acetated Ringer’s solution (CT group) or hydroxyethyl starch (HES group, Tetraspan®) as CPB priming solution. Fluid balance, bleeding and hemodynamics, including cardiac output, were followed postoperatively. The occurrence of acute kidney injury was closely registered.

Results:

Two patients were excluded from further analyzes due to surgical complications. Fluid accumulation was attenuated in the HES group (3374 (883) ml) compared with the CT group (4328 (1469) ml) (p=0.024). The reduced perioperative fluid accumulation was accompanied by an increased cardiac index immediately after surgery (2.7 (0.4) L/min/m2 in the HES group and 2.1 (0.3) L/min/m2 in the CT group (p<0.001)). No increase in bleeding could be demonstrated in the HES group. Three patients, all of them in the HES group, experienced acute kidney injury postoperatively.

Conclusions:

CPB priming with HES solution lowers fluid loading during bypass and improves cardiac function in the early postoperative period. The manifestation of acute kidney injury exclusively in the HES group of patients raises doubts about the use of HES products in conjunction with cardiac surgery. ( https://clinicaltrials.gov/ct2/show/NCT01511120 )

Ethyl pyruvate is renoprotective against ischemia-reperfusion injury under hyperglycemia

BACKGROUND

Hyperglycemia (HG) is common in cardiovascular surgeries due to diabetes, inflammation, and the neuroendocrine stress response. HG aggravates renal ischemia-reperfusion (I/R) injury through an increased inflammatory response, and blunts the protective effect of various measures. Ethyl pyruvate (EP) provides anti-inflammatory effects against I/R injury via inhibition of high-mobility group box 1 protein (HMGB1) release. This study aimed to determine the renoprotective effect of EP against I/R injury under HG.

METHODS

Sprague-Dawley rats were randomly assigned at random to 8 groups: normoglycemia (NG)-sham, NG-I/R-control, NG-EP-I/R (pretreatment), NG-I/R-EP (posttreatment), HG-sham, HG-I/R-control, HG-EP-I/R, and HG-I/R-EP. Renal I/R was induced by 45 minutes of ischemia (clamping of renal arteries), followed by 24 hours of reperfusion. EP (50 mg/kg) was administered intraperitoneally at 1 h before ischemia (pretreatment) or on reperfusion (posttreatment).

RESULTS

I/R injury under HG significantly aggravated the degree of renal tubular apoptosis and damage compared with the NG groups, which could be attenuated by both pretreatment and posttreatment of EP. I/R-induced increases in HMGB1 and Toll-like receptors (TLRs), activation of NF-kB, and resultant alterations in interleukin-1β, tumor necrosis factor-α, proapoptotic Bax, and antiapoptotic Bcl-2 were all favorably modulated by EP treatment in both the NG and HG groups compared with their corresponding control groups.

CONCLUSIONS

Despite aggravation of renal I/R injury by HG through amplified inflammation, EP administration showed similar suppression of the HMGB1-TLR-NF-kB pathway in the HG and NG groups. EP retained anti-inflammatory, antiapoptotic, and renoprotective effects in the HG groups, whether administered before ischemia or on reperfusion.

Perioperative levosimendan in cardiac surgery: A systematic review with meta-analysis and trial sequential analysis

BACKGROUND

Several studies suggested beneficial effects of perioperative levosimendan on postoperative outcome after cardiac surgery. However, three large randomized controlled trials (RCTs) have been recently published and presented neutral results. We performed a systematic review with meta-analysis and trial sequential analysis (TSA) to assess benefits and harms of perioperative levosimendan therapy in cardiac surgery.

METHODS

Electronic databases were searched up to September 2017 for RCTs on preoperative levosimendan versus any type of control. The Cochrane methodology was employed. We calculated odds ratio (OR) or Risk Ratio (OR) and 95% confidence interval (CI) using fixed-effects meta-analyses and we further performed TSA.

RESULTS

We included data from 40 RCTs and 4246 patients. Pooled analysis of 5 low risk of bias trials (1910 patients) showed no association between levosimendan and mortality (OR 0.86 [95% CI, 0.62, 1.18], p=0.34, TSA inconclusive), acute kidney injury, need of renal replacement therapy, myocardial infarction, ventricular arrhythmias, and serious adverse events, but an association with higher incidence of supraventricular arrhythmias (RR 1.11 [95% CI, 1.00, 1.24], p=0.05, TSA inconclusive) and hypotension (RR 1.15 [95% CI, 1.01, 1.30], p=0.04, TSA inconclusive). Analysis including all 40 trials found that levosimendan was associated with lower postoperative mortality (OR 0.56 [95% CI, 0.44, 0.71], p<0.00001, TSA conclusive), acute kidney injury, and renal replacement therapy, and higher incidence of hypotension.

CONCLUSIONS

There is not enough high-quality evidence to neither support nor discourage the systematic use of levosimendan in cardiac surgery.

Pathophysiology of AKI

Acute kidney injury (AKI) is common in the perioperative and intensive care setting. Although AKI is usually multifactorial, haemodynamic instability, sepsis and drug toxicity are commonly implicated. Independent of the exact aetiology, several different pathophysiologic processes occur simultaneously and in sequence, including endothelial dysfunction, alteration of the microcirculation, tubular injury, venous congestion and intrarenal inflammation. A multitude of different immune cells from within the kidney and the systemic circulation play a role in the development, maintenance and recovery phase of AKI. In this review, we describe the common processes involved in AKI and their connections, with particular emphasis on the perioperative and critical care setting.

Role of Body Mass Index in Acute Kidney Injury Patients after Cardiac Surgery

Background/Aims

To explore the association of body mass index (BMI) with the risk of developing acute kidney injury after cardiac surgery (CS-AKI) and for AKI requiring renal replacement therapy (AKI-RRT) after cardiac surgery.

Methods

Clinical data of 8,455 patients undergoing cardiac surgery, including demographic preoperative, intraoperative, and postoperative data were collected. Patients were divided into underweight (BMI <18.5), normal weight (18.5≤ BMI <24), overweight (24≤ BMI <28), and obese (BMI ≥28) groups. The influence of BMI on CS-AKI incidence, duration of hospital, and intensive care unit (ICU) stays as well as AKI-related mortality was analyzed.

Results

The mean age of the patients was 53.2 ± 13.9 years. The overall CS-AKI incidence was 33.8% (n = 2,855) with a hospital mortality of 5.4% (n = 154). The incidence of AKI-RRT was 5.2% (n = 148) with a mortality of 54.1% (n = 80). For underweight, normal weight, overweight, and obese cardiac surgery patients, the AKI incidences were 29.9, 31.0, 36.5, and 46.0%, respectively (p < 0.001). The hospital mortality of AKI patients in the 4 groups was 9.5, 6.0, 3.8, and 4.3%, whereas the hospital mortality of AKI-RRT patients in the 4 groups was 69.2, 60.8, 36.4, and 58.8%, both significantly different (p < 0.05). Hospital and ICU stay durations were not significantly different in the 4 BMI groups.

Conclusion

The hospital prognosis of AKI and AKI-RRT patients after cardiac surgery was best when their BMI was in the 24-28 range.

Mechanism of myocardial ischemia/reperfusion-induced acute kidney injury through DJ-1/Nrf2 pathway in diabetic rats

The objective of the present study was to investigate acute kidney injury (AKI) induced by myocardial ischemia/reperfusion (MIR) in diabetic rats and elucidate its underlying mechanism. A rat model of MIR was established by left anterior descending coronary artery occlusion for 30 min, followed by reperfusion for 2 h. Rats were randomly divided into four groups: i) Sham group, ii) sham + MIR group, iii) diabetic group and iv) diabetes + MIR group. Myocardial injury was detected by plasma creatine kinase isoenzyme MB and lactate dehydrogenase assays. AKI induced by MIR in diabetic rats was characterized by increases in cystatin C and β2-microglobulin levels. Oxidative stress injury was accompanied by an increase of malondialdehyde levels and a decrease of total antioxidative capacity in the renal tissues. Immunohistochemistry and western blot analysis demonstrated that the expression of DJ-1 and nuclear factor erythroid 2-related factor 2 (Nrf2) were significantly increased in the diabetes + MIR group compared with that in the sham + MIR and diabetic groups. Taken together, these results suggested that AKI induced by MIR in diabetic rats may be associated with activation of the DJ-1/Nrf2 pathway.

Acute kidney injury after cardiac surgery is associated with mid-term but not long-term mortality: A cohort-based study

Acute kidney injury (AKI) in cardiac surgery is associated with complications, early and late mortality and increased health care expenditures. The overall dynamic comorbidity-adjusted contributions of an episode of AKI on mortality during long-term follow-up have not been fully explored. A longitudinal cohort of 7075 adult patients admitted for cardiac surgery were enrolled in the study. Follow-up data were obtained through telephonic survey after 1, 5, 10, and 15 years or from the National Mortality Registry. All-cause mortality was assessed at five time intervals: I) 30 days after surgery to 1 year; II) 1 to 3 years; III) 3 to 5 years; IV) 5 to 10 years; and V) 10 to 15 years. For the adjustment of mortality for comorbidity and pre-, intra- and postoperative variables, Cox proportional hazard regression models were conducted within each period. The overall incidence of AKI was 36.1%. AKI was an independent predictor of death only during the first five years after surgery (30 days to 1 year: HR 1.834, 95% CI 1.459 to 2.306; 1 to 3 years: HR 1.285, 95% CI 1.023 to 1.610; and 3 to five years: HR 1.330, 95% CI 1.123 to 1.750). Only age, diabetes mellitus and CHF were associated with increased risk of death over the entire follow-up period. Our study demonstrates a transient association of AKI with long-term mortality that progressively decreases and vanishes five years after surgery. The knowledge of this dynamic is crucial to understanding this complex association, planning health care and allocating resources.

IL-17A blockade or deficiency does not affect progressive renal fibrosis following renal ischaemia reperfusion injury in mice

Objectives

IL-17A contributes to acute kidney injury and fibrosis. Therefore, we asked whether IL-17A deficiency or treatment with a IL-17A blocking antibody impacts severe renal ischaemia reperfusion injury (IRI) and the progression to chronic kidney disease (CKD).

Methods

IL-17A-deficient and wild-type (WT) mice underwent transient unilateral renal pedicle clamping for 45 min to induce IRI and subsequent renal fibrosis. Furthermore, a neutralizing anti-IL-17A antibody (mAb) was injected into WT mice before induction of renal IRI intravenously. On days 1, 7 and 21, inflammation, fibrosis, leukocyte infiltration and pro-inflammatory and pro-fibrotic cytokine expression were assessed in kidneys using histology, qPCR and flow cytometry.

Key findings

IL-17A was significantly increased after renal IRI in WT kidneys. Levels of pro-inflammatory (MCP-1) cytokine and pro-fibrotic (collagen 1α1, fibronectin) transcripts were similar in the experimental groups studied. IL-17A deficiency had no effect on renal T-cell influx or the number, inflammatory phenotype, or spatial distribution of macrophages. Similarly, administration of an IL-17A blocking antibody did not attenuate inflammation.

Conclusions

Despite the effects of IL-17 in other inflammation models, neither genetic IL-17A deficiency nor treatment with an IL-17A blocking antibody attenuated IRI and progression to CKD. We conclude that in severe renal IRI IL-17A is not crucially involved in disease progression.

Right atrium positioning for exposure of right pulmonary veins during off-pump atrial fibrillation ablation

OBJECTIVES

Concomitant surgical ablation of atrial fibrillation (AF) is recommended for patients undergoing off-pump coronary revascularization in the presence of this arrhythmia. Achievement of optimal visualization of pulmonary veins while maintaining stable haemodynamic conditions is crucial for proper completion of the ablation procedure. This study evaluates the safety and feasibility of right atrial positioning using a suction-based cardiac positioner as opposed to compressive manoeuvres for exposure during off-pump surgical ablation for AF.

METHODS

Thirty-four consecutive patients underwent pulmonary vein isolation, ganglionated plexi ablation and left atrial appendage occlusion during off-pump coronary artery bypass grafting. Right atrial suction positioning was used to visualize right pulmonary veins. Safety and feasibility end points were analysed intraoperatively and in the early postoperative course.

RESULTS

In all patients, right atrial positioning created optimal conditions to complete transverse and oblique sinus blunt dissection, correct placement of a bipolar ablation probe, detection and ablation of ganglionated plexi and conduction block assessment. In all patients, this entire right-sided ablation procedure was completed with a single exposure manoeuvre. Feasibility end points were achieved in all study patients.

CONCLUSIONS

This report documents the safety and feasibility of right atrial exposure using a suction-based cardiac positioner to complete ablation for AF concomitant with off-pump coronary revascularization. This technique may be widely adopted to create stable haemodynamic conditions and optimal visualization of the right pulmonary veins.

Do lipid microemboli induce acute kidney injury during cardiopulmonary bypass?

BACKGROUND

Acute kidney injury (AKI) following cardiopulmonary bypass affects 5% of patients, representing significant postoperative morbidity and mortality. Animal models have shown an increased uptake of lipid microemboli (LME) into the renal vasculature, potentially indicating ischaemic causation. This study tested a new lipid filtration system (RemoweLL) against a conventional system with no lipid-depleting capacity to determine the efficacy of the filtration system and its effects on renal function.

METHODS

Thirty consecutive patients underwent coronary artery bypass graft surgery using either the RemoweLL filtration system (15 patients) or a conventional cardiopulmonary bypass circuit (15 patients). Renal function was assessed using cystatin C concentrations as a surrogate marker of glomerular injury, as well as perioperative glomerular filtration rate (GFR) and serum creatinine concentrations. Patients were defined as having acute renal injury if there was an increase in absolute serum creatinine ⩾3 mg/dL (26.4 µmol/L) or 1.5-fold increase from baseline as categorised using the AKIN criteria.

RESULTS

Postoperative differences in LME count between the two groups were highly significant [p<0.001]. Analysis of peak cystatin C concentrations showed significantly lower levels in the LME filtration group on the 2^nd postoperative morning [p=0.04]. Two-factor ANOVA revealed a trend towards interaction, but this failed to reach significance [p=0.06]. There were no differences throughout the study period in serum creatinine or GFR [p>0.05]. There were no differences in any of the serum or urinary electrolytes.

CONCLUSIONS

This study has shown a trend towards improved cystatin C removal with LME filtration; with significantly lower peak concentrations, although no further evidence of renoprotection could be demonstrated. Further research is warranted to establish possible renal benefits of LME filtration in patients undergoing cardiac surgery.

Functional MRI for characterization of renal perfusion impairment and edema formation due to acute kidney injury in different mouse strains

Purpose

The purpose was to characterize acute kidney injury (AKI) in C57BL/6 (B6)- and 129/Sv (Sv)-mice by noninvasive measurement of renal perfusion and tissue edema using functional MRI.

Methods

Different severities of AKI were induced in B6- and Sv-mice by renal ischemia reperfusion injury (IRI). Unilateral clamping of the renal pedicle for 35 min (moderate AKI) or 45 min (severe AKI) was done. MRI (7-Tesla) was performed 1, 7 and 28 days after surgery using a flow alternating inversion recovery (FAIR) arterial spin labeling (ASL) sequence. Maps of perfusion and T1-relaxation time were calculated. Relative MRI-parameters of the IRI kidney compared to the contralateral not-clipped kidney were compared between AKI severities and between mouse strains using unpaired t-tests. In addition, fibrosis was assessed by Masson Trichrome and collagen IV staining.

Results

After moderate AKI relative perfusion impairment was significantly higher in B6- than in Sv-mice at d7 (55±7% vs. 82±8%, p<0.05) and d28 (76±7% vs. 102±3%, p<0.01). T1-values increased in the early phase after AKI in both mouse strains. T1-increase was more severe after prolonged ischemia times of 45 min compared to 35 min in both mouse strains, measured in the renal cortex and outer stripe of outer medulla. Kidney volume loss (compared to the contralateral kidney) occurred already after 7 days but proceeded markedly towards 4 weeks in severe AKI. Early renal perfusion impairment was predictive for later kidney volume loss. The progression to chronic kidney disease (CKD) in the severe AKI model was similar in both mouse strains as revealed by histology.

Conclusion

Quantification of renal perfusion and tissue edema by functional MRI allows characterization of strain differences upon AKI. Renal perfusion impairment was stronger in B6- compared to Sv-animals following moderate AKI. Prolonged ischemia times were associated with more severe perfusion impairment and edema formation in the early phase and progression to CKD within 4 weeks of observation.

The correlation between CVP-derived parameters and the prognosis of critically ill patients

OBJECTIVE

To investigate the effect of central venous pressure on the organ dysfunction and prognosis of critically ill patients.

METHODS

We conducted a retrospective observational cohort study of 488 ICU patients with central venous pressure and its derived parameters in a half-year period in one single ICU centre to compare the length of ICU stay, critical illness scores (SOFA and APACHE II), serum creatinine and lactate levels.

RESULTS

The initial, peak and mean CVP levels of critically ill patients and length of ICU stay, peak lactate levels and SOFA scores were significantly correlated. While the peak CVP and peak creatinine levels were significantly correlated, the correlation of initial and mean CVP levels with peak creatinine was not significant. Subgroup analysis showed that in the patients with a peak CVP value above 12mmHg, the length of stay was significantly prolonged, organ function was significantly worse, and the SOFA score was significantly higher. ROC analysis showed peak levels of CVP above 11.5mmHg had the greatest ability to predict mortality of critically ill patients.

CONCLUSION

Exposure to higher levels of central venous pressure in critically ill patients is associated with a poorer prognosis and worse organ function. Therefore, central venous pressure should be kept as low as possible during hemodynamic therapy in critically ill patients.

Continuous administration of recombinant human B-type natriuretic peptide can improve heart and renal function in patients after cardiopulmonary bypass surgery

BACKGROUND

Any cardiac surgery under cardiopulmonary bypass (CPB) will induce ischemia-reperfusion injury and systematic inflammatory response, which may lead to exacerbation. Conventional therapy strategy is to use inotropes, diuretics and vasodilator drugs, yet, the therapeutic effects of which need to be improved. Recombinant human B-type natriuretic peptide (rhBNP) has been shown to be efficacious in the treatment of acute decompensated heart failure and acute myocardial infarction. However, the effects of rhBNP on patients carried out CPB surgery is unknown.

METHODS

We retrospect 357 patients carried out CPB surgery between Jan 1st 2014 and Dec 31st 2015 of our department. And according the use of rhBNP, these patients were divided into two groups: rhBNP group and control group. Patients in rhBNP group were received continuous intravenous rhBNP (0.0075-0.01 µg/kg/min) in 6 hours after CPB surgery, for a period of 72 h. Hemodynamic parameters were measured immediately after CPB surgery, and then at 2, 4, 8, 12 and 24 h after surgery. Blood samples were obtained immediately after surgery and thereafter once a day at 6:00 AM within the first 3 days after surgery. The daily urine volume as well as the time of tracheal intubation, ICU stay and chest drainage were also recorded.

RESULTS

The baseline characteristics and heart functions were well balanced between two groups, and no patient died in the surgery. It showed significant differences in time-dependent changes in both groups of MAP (P<0.0001, within groups), MPAP (P<0.0001, within groups), PAWP (P<0.0001, within groups), CI (P<0.0001, within groups), SVRI (P<0.0001, within groups), serum BNP (P<0.0001, within groups), CK-MB (P<0.0001, within groups), troponin (P<0.0001, within groups) and creatinine (P<0.0001, within groups). It also showed significant differences in time-dependent changes between the two groups of MAP (P=0.04, between groups), PAWP (P=0.04, between groups), serum troponin (P<0.0001, between groups), serum creatinine (P<0.0001, between groups) and urine volume (P<0.0001, between groups). Interestingly, our results showed that patients in rhBNP group tended to wean off the respirator half a day later than those in control group (P=0.05), while no significant difference showed in both the length of chest drainage time and intensive care unit stay between the two groups.

CONCLUSIONS

The administration of rhBNP can improve heart and renal function in patients underwent CPB surgery as well as accelerating the recovery from myocardial injury. But the prognosis of the patients who were administrated rhBNP did not improve in our study.

Relationship among Mortality of Patients with Acute Kidney Injury after Cardiac Surgery, Fluid Balance and Ultrafiltration of Renal Replacement Therapy: An Observational Study

Background/Aims: The study aimed to investigate the relationship among mortality of patients with cardiac surgery-associated acute kidney injury (CSA-AKI), fluid balance, and ultrafiltration of renal replacement therapy (RRT). Methods: From January 2009 to October 2015, hospitalized patients with CSA-AKI receiving continuous or prolonged intermittent RRT were screened. The effects of fluid balance and ultrafiltration of RRT on clinical outcome were analyzed. Results: The 30-day mortality of all the 63 patients in the study was 58.6%. Compared with the death group, the survival group had a significantly lower fluid balance, larger ultrafiltration volume, and similar ultrafiltration rate during the first 3 days of RRT. Multivariate Cox regression analysis revealed that positive fluid balance during the first day of RRT, cardiac function of grade IV, and higher Sequential Organ Failure Assessment score were independent risk factors of 30-day mortality. Conclusion: Fluid balance was more relevant to short-term prognosis of CSA-AKI-RRT patients than ultrafiltration volume or ultrafiltration rate.

Preoperative Statin Treatment for the Prevention of Acute Kidney Injury in Patients Undergoing Cardiac Surgery: A Meta-Analysis of Randomised Controlled Trials

BACKGROUND

The effect of preoperative statin treatment (PST) on the risk of postoperative acute kidney injury (AKI) after cardiac surgery remains controversial. We performed a meta-analysis of randomised controlled trials (RCT) to investigate whether PST could improve the renal outcomes in patients undergoing cardiac surgery.

METHODS

We conducted a comprehensive search on PubMed, Embase and Cochrane Central Register of Controlled Trials. Randomised controlled trials which reported incidence of AKI and renal replacement treatment (RRT), mean change of serum creatine (SCr) and C-reactive protein (CRP), length of stay in intensive care unit (LOS-ICU) and hospital (LOS-HOS) were included.

RESULTS

A total of nine RCTs, covering 3,201 patients were included. Based on the results of our meta-analysis, PST could not reduce the incidence of AKI (risk ratio (RR) 1.12, 95% confidence interval (CI) 0.97 to 1.29, p=0.37), and RRT (RR 1.13, 95% CI 0.45 to 2.85, p=0.80). Furthermore, SCr was not likely to be improved by PST (weighted mean difference (WMD) 0.03, 95% CI 0.00 to 0.06, p=0.055). However, the level of CRP (WMD -5.93, 95% CI 11.71 to 0.15, p=0.044) in patients treated with PST was significantly lower than that of patients administered with placebo. In addition, no significant difference was observed in LOS-ICU and LOS-HOS between PST and control groups.

CONCLUSION

Our meta-analysis suggests that PST cannot provide any benefit for improving renal complications and clinical outcomes, but may slightly reduce postoperative inflammation in patients undergoing cardiac surgery. In the future, more powerful RCTs will be needed to confirm these findings.

Using central venous catheter for suprapubic catheterization in cardiac surgery

Suprapubic catheterization is an alternative method for urinary drainage that is used when transurethral catheterization fails. Traditionally, inserted large-bore suprapubic catheters may cause fatal complications. During the past decade, we used a small central venous catheter (CVC) suprapubicly in 16 male patients for the purpose of urinary drainage, when transurethral catheterization failed. The procedure is performed in no more than 10 minutes. Success rate was 100% and this approach did not lead to any complications. In conclusion, placing a CVC for suprapubic drainage is a safe method with a high success rate and we recommend it in patients with failed transurethral catheterization after a few attempts (2–3 attempts).