Effects of Different Doses of Remote Ischemic Preconditioning on Kidney Damage Among Patients Undergoing Cardiac Surgery: A Single-Center Mechanistic Randomized Controlled Trial

How Would We Prevent Our Own Acute Kidney Injury After Cardiac Surgery?

Acute Kidney Injury (AKI) is a common complication after cardiac surgery affecting up to 40% leading to increased morbidity and mortality. To date, there is no specific treatment for AKI, thus, clinical research efforts are focused on preventive measures. The only pharmacological preventive intervention that has demonstrated a beneficial effect on AKI in a high-quality, double-blind, randomized controlled trial is a short perioperative infusion of a balanced mixture of amino acid solution. Amino acid infusion reduced the incidence of AKI by recruiting renal functional reserve and, therefore, increasing the glomerular filtration rate. The beneficial effect of amino acids was further confirmed for severe AKI and applied to patients with chronic kidney disease. Among non-pharmacological interventions, international guidelines on AKI suggest the implementation of a bundle of good clinical practice measures to reduce the incidence of perioperative AKI or to improve renal function whenever AKI occurs. The Kidney Disease Improving Global Outcomes (KDIGO) bundle includes the discontinuation of nephrotoxic agents, volume status and perfusion pressure assessment, renal functional hemodynamic monitoring, serum creatine, and urine output monitoring, and the avoidance of hyperglycemia and radiocontrast procedures. However, pooled data from a meta-analysis did not find a significant reduction in AKI. The aim of this review is to delineate the most appropriate evidence-based approach to prevent AKI in cardiac surgery patients.

A wide scope, pan-comparative, systematic meta-analysis of the efficacy of prophylactic strategies for cardiac surgery-associated acute kidney injury

Acute kidney injury (AKI) is the most common complication of cardiac surgery. Cardiac surgery-associated AKI (CSA-AKI) is caused by systemic and renal hemodynamic impairment and parenchymal injury. Prophylaxis of CSA-AKI remains an unmet priority, for which preventive strategies based on drug therapies, hydration procedures, and remote ischemic preconditioning (RIPC) have been tested in pre-clinical and clinical studies, with variable success. Contradicting reports and scarce or insufficiently pondered information have blurred conclusions. Therefore, with an aim to contribute to consolidating the available information, we carried out a wide scope, pan-comparative meta-analysis including the accessible information about the most relevant nephroprotective approaches assayed. After a thorough examination of 1892 documents retrieved from PubMed and Web of Science, 150 studies were used for the meta-analysis. Individual odds ratios of efficacy at reducing AKI incidence, need for dialysis, and plasma creatinine elevation were obtained for each alleged protectant. Also, the combined class effect of drug families and protective strategies was also meta-analyzed. Our results show that no drug family or procedure affords substantial protection against CSA-AKI. Only, a mild but significant reduction in the incidence of CSA-AKI by preemptive treatment with dopaminergic and adrenergic drugs, vasodilators, and the RIPC technique. The integrated analysis suggests that single-drug approaches are unlikely to cope with the variety of individual pathophysiological scenarios potentially underlying CSA-AKI. Accordingly, a theragnostic approach involving the etiopathological diagnosis of kidney frailty is necessary to guide research towards the development of pharmacological combinations concomitantly and effectively addressing the key mechanisms of CSA-AKI.

Cardiopulmonary Protection of Modified Remote Ischemic Preconditioning in Mitral Valve Replacement Surgery: A Randomized Controlled Trial

Background: Remote ischemic preconditioning (RIPC) is reported to have early-phase and delayed-phase organ-protective effects. Previous studies have focused on the organ protection of a single RIPC protocol, and the clinical outcomes remain uncertain. Whether the modified RIPC (mRIPC) protocol performed repeatedly provides cardiopulmonary protection is still uncertain. Methods: In this single-center, randomized, controlled trial, 86 patients undergoing elective mitral valve replacement (MVR) surgery were randomized 1:1 to receive either mRIPC or no ischemic preconditioning (control). Three cycles of 5 min ischemia and 5 min reperfusion induced by a blood pressure cuff served as the RIPC stimulus. mRIPC was induced at the following three time points: 24 h, 12 h, and 1 h before surgery. Blood samples were withdrawn at 10 min after intubation (T0), at 1 h after aortic declamping (T1), and at 6 h (T2), 12 h (T3), and 24 h (T4) after surgery to measure the serum concentrations of myocardial enzymes and other biomarkers, including cardiac troponin I (cTnI), which was the primary endpoint of this study. Creatine kinase isoenzyme (CK-MB), lactate dehydrogenase (LDH), inotropic score (IS), and inflammatory mediators were also measured. Blood gas analysis was conducted to calculate the PaO2/FiO2 ratio and A-aDO2, and the incidence of acute lung injury (ALI) was also recorded. Results: mRIPC significantly decreased the serum concentrations of cTnI, CK-MB, and LDH at T2, T3, and T4 (p < 0.01), and the IS decreased compared with that in the control group (12.0 ± 1.0 vs. 14.2 ± 1.1, p < 0.01). In addition, the incidence of ALI in the mRIPC group was decreased (32.6% vs. 51.2%, p = 0.039), and the PaO2/FiO2 was higher at T4 (p < 0.05). Compared with those in the control group, the levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were decreased at T1, T2, T3, and T4 (p < 0.05) in the mRIPC group, and the level of IL-10 increased at the same time. Conclusions: mRIPC decreased the incidence of myocardial and lung injury in MVR surgery, providing new evidence for the clinical application of RIPC in valve surgery. Trial Registration: ClinicalTrials.gov (NCT01406678).

Myocardial protection in cardiac surgery: a comprehensive review of current therapies and future cardioprotective strategies

Cardiac surgery with cardiopulmonary bypass results in global myocardial ischemia-reperfusion injury, leading to significant postoperative morbidity and mortality. Although cardioplegia is the cornerstone of intraoperative cardioprotection, a number of additional strategies have been identified. The concept of preconditioning and postconditioning, despite its limited direct clinical application, provided an essential contribution to the understanding of myocardial injury and organ protection. Therefore, physicians can use different tools to limit perioperative myocardial injury. These include the choice of anesthetic agents, remote ischemic preconditioning, tight glycemic control, optimization of respiratory parameters during the aortic unclamping phase to limit reperfusion injury, appropriate choice of monitoring to optimize hemodynamic parameters and limit perioperative use of catecholamines, and early reintroduction of cardioprotective agents in the postoperative period. Appropriate management before, during, and after cardiopulmonary bypass will help to decrease myocardial damage. This review aimed to highlight the current advancements in cardioprotection and their potential applications during cardiac surgery.

Remote ischemic conditioning reduces postoperative bleeding in adult cardiac surgical patients: a systematic review and meta-analysis

INTRODUCTION

The current study was designed to systemically investigate the impact of remote ischemic conditioning (RIC) on intra- and postoperative bleeding and transfusion in patients undergoing cardiac surgery.

EVIDENCE ACQUISITION

We included all randomized controlled trials (RCTs) comparing RIC with control on intra- and postoperative blood loss and blood transfusion. The inclusion criteria were as follows: 1) adult patients undergoing cardiac surgery; 2) RCT; 3) perioperative administration of RIC compared to control; 4) outcomes of interest reported. Exclusion criteria included: 1) case reports, reviews, or abstracts; 2) animal or cell studies; 3) duplicate publications; 4) studies lacking information about outcomes of interest.

EVIDENCE SYNTHESIS

Databases search yielded 24 RCTs including 3530 patients, 1765 patients were allocated into RIC group and 1765 into control group. The current study suggested that RIC administration was associated with reduced postoperative blood loss (WMD=-57.89; 95% CI: -89.89 to -25.89; P=0.0004). RIC did not affect the volume of intraoperative blood loss (WMD=-4.02; 95% CI: -14.09 to 6.05; P=0.43), the volume of intra- and postoperative transfusion of red blood cell (RBC) (WMD=-15.66; 95% CI: -39.35 to 8.03; P=0.20), the re-exploration for bleeding (WMD=-0.01; 95% CI: -0.03 to 0.01; P=0.21).

CONCLUSIONS

The current study demonstrated that, RIC reduced post-operative blood loss in adult patients undergoing cardiac surgeries. It also indicated that, RIC reduced intra-operative RBC transfusion in adult patients undergoing coronary artery bypass grafting. However, RIC did not influence intra-operative bleeding, post-operative blood transfusion.

Is Renal Ischemic Preconditioning an Alternative to Ameliorate the Short- and Long-Term Consequences of Acute Kidney Injury?

Acute kidney injury (AKI) is a global health problem and has recently been recognized as a risk factor for developing chronic kidney disease (CKD). Unfortunately, there are no effective treatments to reduce or prevent AKI, which results in high morbidity and mortality rates. Ischemic preconditioning (IPC) has emerged as a promising strategy to prevent, to the extent possible, renal tissue from AKI. Several studies have used this strategy, which involves short or long cycles of ischemia/reperfusion (IR) prior to a potential fatal ischemic injury. In most of these studies, IPC was effective at reducing renal damage. Since the first study that showed renoprotection due to IPC, several studies have focused on finding the best strategy to activate correctly and efficiently reparative mechanisms, generating different modalities with promising results. In addition, the studies performing remote IPC, by inducing an ischemic process in distant tissues before a renal IR, are also addressed. Here, we review in detail existing studies on IPC strategies for AKI pathophysiology and the proposed triggering mechanisms that have a positive impact on renal function and structure in animal models of AKI and in humans, as well as the prospects and challenges for its clinical application.

[New aspects of perioperative organ protection]

BACKGROUND

Acutely occurring organ damage significantly contributes to morbidity and mortality in the perioperative context.

OBJECTIVE

This article highlights new clinical perspectives on how perioperative organ damage can be prevented and ameliorated by influencing the high mobility group box 1 protein (HMGB1) signaling.

MATERIAL AND METHODS

A MEDLINE search was performed in the fields of clinical and basic research. The presentation of basic mechanisms of perioperative organ damage and the discussion of the importance of HMGB1 in prevention and treatment by pharmaceutical and nonpharmaceutical interventions are the focus of the review.

RESULTS

The HMGB1 is a central element in the pathogenesis of septic and aseptic inflammation-induced organ damage. Remote ischemic preconditioning (RIPC) and dexmedetomidine are highly effective approaches to mitigate or prevent organ damage.

CONCLUSION

The RIPC and dexmedetomidine offer protective properties in ischemia-reperfusion injury as well as in inflammation-related organ damage, which are mediated by HMGB1, among others. This effectively protects the kidneys, heart, lungs, liver and brain. The application of these concepts should be considered in routine clinical practice.

Strategies for post-cardiac surgery acute kidney injury prevention: A network meta-analysis of randomized controlled trials

Objects

Cardiac surgery is associated with acute kidney injury (AKI). However, the effects of various pharmacological and non-pharmacological strategies for AKI prevention have not been thoroughly investigated, and their effectiveness in preventing AKI-related adverse outcomes has not been systematically evaluated.

Methods

Studies from PubMed, Embase, and Medline and registered trials from published through December 2021 that evaluated strategies for preventing post-cardiac surgery AKI were identified. The effectiveness of these strategies was assessed through a network meta-analysis (NMA). The secondary outcomes were prevention of dialysis-requiring AKI, mortality, intensive care unit (ICU) length of stay (LOS), and hospital LOS. The interventions were ranked using the P-score method. Confidence in the results of the NMA was assessed using the Confidence in NMA (CINeMA) framework.

Results

A total of 161 trials (involving 46,619 participants) and 53 strategies were identified. Eight pharmacological strategies {natriuretic peptides [odds ratio (OR): 0.30, 95% confidence interval (CI): 0.19-0.47], nitroprusside [OR: 0.29, 95% CI: 0.12-0.68], fenoldopam [OR: 0.36, 95% CI: 0.17-0.76], tolvaptan [OR: 0.35, 95% CI: 0.14-0.90], N-acetyl cysteine with carvedilol [OR: 0.37, 95% CI: 0.16-0.85], dexmedetomidine [OR: 0.49, 95% CI: 0.32-0.76;], levosimendan [OR: 0.56, 95% CI: 0.37-0.84], and erythropoietin [OR: 0.62, 95% CI: 0.41-0.94]} and one non-pharmacological intervention (remote ischemic preconditioning, OR: 0.76, 95% CI: 0.63-0.92) were associated with a lower incidence of post-cardiac surgery AKI with moderate to low confidence. Among these nine strategies, five (fenoldopam, erythropoietin, natriuretic peptides, levosimendan, and remote ischemic preconditioning) were associated with a shorter ICU LOS, and two (natriuretic peptides [OR: 0.30, 95% CI: 0.15-0.60] and levosimendan [OR: 0.68, 95% CI: 0.49-0.95]) were associated with a lower incidence of dialysis-requiring AKI. Natriuretic peptides were also associated with a lower risk of mortality (OR: 0.50, 95% CI: 0.29-0.86). The results of a sensitivity analysis support the robustness and effectiveness of natriuretic peptides and dexmedetomidine.

Conclusion

Nine potentially effective strategies were identified. Natriuretic peptide therapy was the most effective pharmacological strategy, and remote ischemic preconditioning was the only effective non-pharmacological strategy. Preventive strategies might also help prevent AKI-related adverse outcomes. Additional studies are required to explore the optimal dosages and protocols for potentially effective AKI prevention strategies.

Remote ischemic preconditioning causes transient cell-cycle arrest and renal protection by a NF-kB-dependent Sema5B pathway

Acute kidney injury increases morbidity and mortality, and previous studies have shown that remote ischemic preconditioning (RIPC) reduces the risk of acute kidney injury after cardiac surgery. RIPC increases urinary high mobility group box protein-1 (HMGB1) levels in patients, and this correlates with kidney protection. Here, we show that RIPC reduces renal ischemia-reperfusion injury and improves kidney function in mice. Mechanistically, RIPC increases HMGB1 levels in the plasma and urine, and HMGB1 binds to TLR4 on renal tubular epithelial cells, inducing transcriptomic modulation of renal tubular epithelial cells and providing renal protection, whereas TLR4 activation on nonrenal cells was shown to contribute to renal injury. This protection is mediated by activation of induction of AMPKα and NF-κB; this induction contributes to the upregulation of Sema5b, which triggers a transient, protective G₁ cell cycle arrest. In cardiac surgery patients at high risk for postoperative acute kidney injury, increased HMGB1 and Sema5b levels after RIPC were associated with renal protection after surgery. The results may help to develop future clinical treatment options for acute kidney injury.

Effects of preoperative high-oral protein loading on short- and long-term renal outcomes following cardiac surgery: a cohort study

BACKGROUND

Post-cardiac surgery acute kidney injury (AKI) is associated with increased mortality. A high-protein meal enhances the renal blood flow and glomerular filtration rate (GFR) and might protect the kidneys from acute ischemic insults. Hence, we assessed the effect of a preoperative high-oral protein load on post-cardiac surgery renal function and used experimental models to elucidate mechanisms by which protein might stimulate kidney-protective effects.

METHODS

The prospective "Preoperative Renal Functional Reserve Predicts Risk of AKI after Cardiac Operation" study follow-up was extended to postoperative 12 months for 109 patients. A 1:2 ratio propensity score matching method was used to identify a control group (n = 214) to comparatively evaluate the effects of a preoperative protein load and standard care. The primary endpoints were AKI development and postoperative estimated GFR (eGFR) loss at 3 and 12 months. We also assessed the secretion of tissue inhibitor of metalloproteases-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7), biomarkers implicated in mediating kidney-protective mechanisms in human kidney tubular cells that we exposed to varying protein concentrations.

RESULTS

The AKI rate did not differ between the protein loading and control groups (13.6 vs. 12.3%; p = 0.5). However, the mean eGFR loss was lower in the former after 3 months (0.1 [95% CI - 1.4, - 1.7] vs. - 3.3 [95% CI - 4.4, - 2.2] ml/min/1.73 m²) and 12 months (- 2.7 [95% CI - 4.2, - 1.2] vs - 10.2 [95% CI - 11.3, - 9.1] ml/min/1.73 m²; p < 0.001 for both). On stratification based on AKI development, the eGFR loss after 12 months was also found to be lower in the former (- 8.0 [95% CI - 14.1, - 1.9] vs. - 18.6 [95% CI - 23.3, - 14.0] ml/min/1.73 m²; p = 0.008). A dose-response analysis of the protein treatment of the primary human proximal and distal tubule epithelial cells in culture showed significantly increased IGFBP7 and TIMP-2 expression.

CONCLUSIONS

A preoperative high-oral protein load did not reduce AKI development but was associated with greater renal function preservation in patients with and without AKI at 12 months post-cardiac surgery. The potential mechanisms of action by which protein loading may induce a kidney-protective response might include cell cycle inhibition of renal tubular epithelial cells. Clinical trial registration ClinicalTrials.gov: NCT03102541 (retrospectively registered on April 5, 2017) and ClinicalTrials.gov: NCT03092947 (retrospectively registered on March 28, 2017).

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.