Renal function and oxygenation are impaired early after liver transplantation despite hyperdynamic systemic circulation

Optimization and Protection of Kidney Health in Liver Transplant Recipients: Intra- and Postoperative Approaches

Postoperative acute kidney injury after liver transplant (LT) has long-term implications for kidney health. LT recipients are at risk of acute kidney injury due to a number of factors related to the donor liver, intraoperative factors including surgical technique, as well as recipient factors, such as pre-LT kidney function and postoperative complications. This review discusses these factors in detail and their impact on posttransplant kidney function. Long-term risk factors such as calcineurin inhibitors have also been discussed. Additionally, the impact of liver allocation policies on pre- and post-LT kidney health is discussed.

Hyperglycemia and Hyperlipidemia with Kidney or Liver Transplantation: A Review

Although solid organ transplantation in persons with diabetes mellitus is often associated with hyperglycemia, the risk of hyperlipidemia in all organ transplant recipients is often underestimated. The diagnosis of diabetes often predates transplantation; however, in a moderate percentage of allograft recipients, perioperative hyperglycemia occurs triggered by antirejection regimens. Post-transplant prescription of glucocorticoids, calcineurin inhibitors and mTOR inhibitors are associated with increased lipid concentrations. The existence of diabetes mellitus prior to or following a liver transplant is associated with shorter times of useful allograft function. A cycle involving Smad, TGF beta, m-TOR and toll-like receptors has been identified in the contribution of rejection and aging of allografts. Glucocorticoids (prednisone) and calcineurin inhibitors (cyclosporine and tacrolimus) induce hyperglycemia associated with insulin resistance. Azathioprine, mycophenolate and prednisone are associated with lipogenesis. mTOR inhibitors (rapamycin) are used to decrease doses of atherogenic agents used for immunosuppression. Post-transplant medication management must balance immune suppression and glucose and lipid control. Concerns regarding rejection often override those relative to systemic and organ vascular aging and survival. This review focuses attention on the underlying mechanism of relationships between glycemia/lipidemia control, transplant rejection and graft aging.

Liver Graft Proteomics Reveals Potential Incipient Mechanisms behind Early Renal Dysfunction after Liver Transplantation

Acute kidney injury (AKI) is frequent after liver transplantation (LT) and correlates with later development of chronic kidney disease. Its etiology is multifactorial and combines pre-, intra-, and postoperative factors. Additionally, the liver graft itself seems an important element in the development of AKI, yet the detailed mechanisms remain unclear. We hypothesized that grafts of LT recipients developing significant early AKI may show distinct proteomic alterations, and we set out to identify proteome differences between LT recipients developing moderate or severe AKI (n = 7) and LT recipients without early renal injury (n = 7). Liver biopsies obtained one hour after reperfusion were assessed histologically and using quantitative proteomics. Several cytokines and serum amyloid A2 (SAA2) were analyzed in serum samples obtained preoperatively, 2−4 h, and 20−24 h after graft reperfusion, respectively. LT induced mild histological alterations without significant differences between groups but uniformly altered liver function tests peaking on postoperative day 1, with a trend towards more severe alterations in patients developing AKI. Global quantitative proteomic analysis revealed 136 proteins differing significantly in their expression levels (p < 0.05, FC 20%): 80 proteins had higher and 56 had lower levels in the AKI group. Most of these proteins were related to immune and inflammatory responses, host defense, and neutrophil degranulation. No differences between the studied pro- and anti-inflammatory cytokines or SAA2 between groups were found at any moment. Our results suggest that grafts of LT patients who develop early AKI reveal a distinct proteome dominated by an early yet prominent activation of the innate immunity. These findings support the hypothesis that AKI after LT may be favored by certain graft characteristics.

Perioperative kidney injury in liver transplantation: a prospective study with renal histology and measured glomerular filtration rates

BACKGROUND

Acute kidney injury (AKI) is frequent after liver transplantation (LT), with impact on graft function, morbidity and mortality. Although multifactorial, the pathophysiology of perioperative kidney injury remains unclear. Our aims were to analyze the frequency, evolution and risk factors for kidney impairment during the peri- and early post-operative period.

METHODS

In a prospective, single-center study of 27 adult patients undergoing first single-organ LT, we analyzed measured glomerular filtration rate (mGFR) pre-transplant, at post-operative day (POD) 10, and at 1, 3, 12 and 36 months. Kidney and liver graft biopsies were performed during LT.

RESULTS

A median mGFR decline of 45% was detected from pre-transplant to POD 10, correlating strongly with the mGFR evolution from baseline to 12 months (rs = 0.80, p<.001) and baseline to 36 months (rs = 0.82, p<.001). AKI occurred in 59% of recipients within 48 h of LT, notably before the introduction of calcineurin inhibitors on POD 3. AKI was strongly associated with mGFR at 12 and 36 months. Kidney and liver graft biopsies showed only minor histological changes. Donor and recipient body mass index, recipient age, model of end-stage liver disease score, diagnosis of hepatitis C, donor cause of death, as well as bleeding, transfusions and duration of the anhepatic phase correlated with early kidney dysfunction.

CONCLUSION

The greatest decline in mGFR was evident within 10 days and AKI within hours of LT, irrespective of baseline mGFR and before introduction of calcineurin inhibitors. Very early post-LT kidney injury has substantial consequences for long-term kidney function.

Current aspects of renal dysfunction after liver transplantation

The development of chronic kidney disease (CKD) after liver transplantation (LT) exerts a severe effect on the survival of patients. The widespread adoption of the model for end-stage liver disease score strongly impacted CKD incidence after the procedure, as several patients are transplanted with previously deteriorated renal function. Due to its multifactorial nature, encompassing pre-transplantation conditions, perioperative events, and nephrotoxic immunosuppressor therapies, the accurate identification of patients under risk of renal disease, and the implementation of preventive approaches, are extremely important. Methods for the evaluation of renal function in this setting range from formulas that estimate the glomerular filtration rate, to non-invasive markers, although no option has yet proved efficient in early detection of kidney injury. Considering the nephrotoxicity of calcineurin inhibitors (CNI) as a factor of utmost importance after LT, early nephroprotective strategies are highly recommended. They are based mainly on delaying the application of CNI during the immediate postoperative-period, reducing their dosage, and associating them with other less nephrotoxic drugs, such as mycophenolate mofetil and everolimus. This review provides a critical assessment of the causes of renal dysfunction after LT, the methods of its evaluation, and the interventions aimed at preserving renal function early and belatedly after LT.

Biomarkers for detecting and improving AKI after liver transplantation: From diagnosis to treatment

Orthotopic liver transplantation (OLT) is a well-established treatment for patients with liver failure. The shortage of donor organs and postoperative complications remain major obstacles for improving patient survival. Among these complications, acute kidney injury (AKI) is one of the most frequent types, contributing to graft loss. The timely detection and reversal of AKI can reduce its adverse influences on graft and patient outcomes. Traditional markers for detecting AKI are often limited with regard to their accuracy and specificity, and the discovery of better AKI markers and therapeutic targets assumes great importance. During past decades, studies directed toward early detection and treatment of AKI in OLT have been available. This review summarizes the evidence of these biomarkers for the prediction, diagnosis, treatment and prognosis stratification of AKI associated with OLT.

Renal Hemodynamics, Function, and Oxygenation in Critically Ill Patients and after Major Surgery

This review outlines the available data from the work of our group on renal hemodynamics, function, and oxygenation in patients who are critically ill with acute renal dysfunction, such as those with postoperative AKI, those in early clinical septic shock, in patients undergoing cardiac surgery with cardiopulmonary bypass, or in patients undergoing liver transplantation. We also provide information on renal hemodynamics, function, and oxygenation in patients with chronic renal impairment due to congestive heart failure. This review will argue that, for all of these groups of patients, the common denominator is that renal oxygenation is impaired due to a lower renal oxygen delivery or a pronounced increase in renal oxygen consumption.

Renal Near-Infrared Spectroscopy for Assessment of Renal Oxygenation in Adults Undergoing Cardiac Surgery: A Method Validation Study

OBJECTIVE

To investigate the correlation between invasively measured renal venous oxygen saturation (SrvO₂) and tissue oxygenation (rSO₂) measured with near-infrared spectroscopy (NIRS) in adult patients undergoing cardiac surgery.

DESIGN

Prospective observational study.

SETTING

Single cardiac surgery center at a university hospital.

PARTICIPANTS

Thirteen adult patients with skin- to- kidney distance ≤4 cm undergoing open cardiac surgery with cardiopulmonary bypass (CPB).

INTERVENTIONS

All patients received renal vein catheters for invasive measurement of SrvO₂, and NIRS electrodes for assessment of renal rSO₂ were placed over the kidney using ultrasound guidance. Measurements were made before CPB, during CPB at 3 different flow rates (2.4, 2.7, and 3.0 L/min/m²), and after CPB.

MEASUREMENTS AND MAIN RESULTS

Repeated- measures correlation analyses and Bland-Altman plots were used to study the correlation and agreement between rSO₂ and SrvO₂. For all measurement points, renal rSO₂ correlated with SrvO₂ (r_rm = 0.61, p < 0.001), and the mean difference (bias) between rSO₂ and SrvO₂ was -2.71 ± 7.22 (p = 0.002), with an error of 17.6%. When measurements during CPB and before and after CPB were studied separately, rSO₂ and SrvO₂ were correlated (r_rm = 0.51, p < 0.007 and r_rm = 0.73, p < 0.001, respectively). During CPB, renal rSO₂ predicted SrvO₂ with a bias of -3.41 ± 7.76 (p = 0.009) and an error of 18.8%. Before and after CPB, the mean difference was -1.93 ± 6.60 (p = 0.092), with an error of 16.2%.

CONCLUSIONS

Renal rSO₂ is correlated to and predicts SrvO₂ with a small bias and acceptable agreement. Further studies are needed before renal NIRS can be used as a surrogate marker of renal oxygenation in clinical practice.

Intraoperative Oxygen Delivery and Acute Kidney Injury after Liver Transplantation

Although intraoperative hemodynamic variables were reported to be associated with acute kidney injury (AKI) after liver transplantation, the time-dependent association between intraoperative oxygen delivery and AKI has not yet been evaluated. We reviewed 676 cases of liver transplantation. Oxygen delivery index (DO2I) was calculated at least ten times during surgery. AKI was defined according to the Kidney Disease Improving Global Outcomes criteria. The area under the curve (AUC) was calculated as below a DO2I of 300 (AUC < 300), 400 and 500 mL/min/m2 threshold. Also, the cumulative time below a DO2I of 300 (Time < 300), 400, and 500 mL/min/m2 were calculated. Multivariable logistic regression analysis was performed to evaluate whether AUC < 300 or time < 300 was independently associated with the risk of AKI. As a sensitivity analysis, propensity score matching analysis was performed between the two intraoperative mean DO2I groups using a cutoff of 500 ml/min/m2, and the incidence of AKI was compared between the groups. Multivariable analysis showed that AUC < 300 or time < 300 was an independent predictor of AKI (AUC < 300: odds ratio [OR] = 1.10, 95% confidence interval [CI] 1.06-1.13, time < 300: OR = 1.10, 95% CI 1.08-1.14). Propensity score matching yielded 192 pairs of low and high mean DO2I groups. The incidence of overall and stage 2 or 3 AKI was significantly higher in the lower DO2I group compared to the higher group (overall AKI: lower group, n = 64 (33.3%) vs. higher group, n = 106 (55.2%), P < 0.001). In conclusion, there was a significant time-dependent association between the intraoperative poor oxygen delivery <300 mL/min/m2 and the risk of AKI after liver transplantation. The intraoperative optimization of oxygen delivery may mitigate the risk of AKI.

Renal effects of norepinephrine-induced variations in mean arterial pressure after liver transplantation: A randomized cross-over trial

BACKGROUND

Acute kidney injury is commonly seen after liver transplantation. The optimal perioperative target mean arterial pressure (MAP) for renal filtration, perfusion and oxygenation in liver recipients is not known. The effects of norepinephrine-induced changes in MAP on renal blood flow (RBF), oxygen delivery (RDO₂ ), glomerular filtration rate (GFR) and renal oxygenation (=renal oxygen extraction, RO₂ Ex) were therefore studied early after liver transplantation.

METHODS

Ten patients with an intra- and post-operative vasopressor-dependent systemic vasodilation were studied early after liver transplantation during sedation and mechanical ventilation. To achieve target MAP levels of 60, 75 and 90 mm Hg, the norepinephrine infusion rate was randomly and sequentially titrated. At each target MAP, data on cardiac index (CI), RBF and GFR were obtained by transpulmonary thermodilution (PiCCO), the renal vein thermodilution technique and renal extraction of chromium ethylenediaminetetraaceticacid (⁵¹ Cr-EDTA), respectively. Renal oxygen consumption (RVO₂ ) and extraction (RO₂ Ex) were calculated according to standard formulas.

RESULTS

At a target MAP of 75 mm Hg, CI (13%), RBF (18%), RDO₂ (24%), GFR (31%) and RVO₂ (20%) were higher while RO₂ Ex was unchanged compared to a target MAP of 60 mm Hg. Increasing MAP from 75 up to 90 mm Hg increased RVR by 38% but had no further effects on CI, RBF, RDO₂ or GFR.

CONCLUSIONS

In patients undergoing liver transplantation, RBF and GFR are pressure-dependent at MAP levels below 75 mm Hg. Our results suggest that MAP should probably be targeted to approximately 75 mm Hg for optimal perioperative renal filtration, perfusion and oxygenation in patients undergoing liver transplantation.

Comparison of acute kidney injury of different etiology reveals in-common mechanisms of tissue damage

Acute kidney injury (AKI) is a syndrome of reduced glomerular filtration rate and urine production caused by a number of different diseases. It is associated with renal tissue damage. This tissue damage can cause tubular atrophy and interstitial fibrosis that leads to nephron loss and progression of chronic kidney disease (CKD). This review describes the in-common mechanisms behind tissue damage in AKI caused by different underlying diseases. Comparing six high-quality microarray studies of renal gene expression after AKI in disease models (gram-negative sepsis, gram-positive sepsis, ischemia-reperfusion, malignant hypertension, rhabdomyolysis, and cisplatin toxicity) identified 5,254 differentially expressed genes in at least one of the AKI models; 66% of genes were found only in one model, showing that there are unique features to AKI depending on the underlying disease. There were in-common features in the form of four genes that were differentially expressed in all six models, 49 in at least five, and 215 were found in common between at least four models. Gene ontology enrichment analysis could be broadly categorized into the injurious processes hypoxia, oxidative stress, and inflammation, as well as the cellular outcomes of cell death and tissue remodeling in the form of epithelial-to-mesenchymal transition. Pathway analysis showed that MYC is a central connection in the network of activated genes in-common to AKI, which suggests that it may be a central regulator of renal gene expression in tissue injury during AKI. The outlining of this molecular network may be useful for understanding progression from AKI to CKD.