Dopamine increases renal oxygenation: a clinical study in post-cardiac surgery patients

Factors that mediate change in creatinine and acute kidney injury after the Norwood operation: insights from high-fidelity haemodynamic monitoring data

BACKGROUND

Acute kidney injury is a common postoperative complication of paediatric cardiac surgery associated with increased morbidity and mortality. The purpose of this study is to characterise associations between haemodynamic parameters, clinical parameters, and medical interventions, on acute kidney injury.

METHODS

Nine patients with univentricular physiology undergoing the Norwood procedure from a single-centre tertiary care paediatric cardiac ICU were included (September 2022 to March 2023). Patients were monitored with the T3 software. Data were analysed using a Fisher exact test, Mann-Whitney-U test, LASSO-based machine learning techniques, and receiver operator curve analyses.

RESULTS

Over 27,000 datapoints were included. Acute kidney injury occurred in 2 patients (22%) during this period. Net fluid balance and renal oxygen extraction were independently associated with acute kidney injury, while commonly used metrics of pressure (systolic, diastolic, or mean arterial blood pressure) were not. The resulting acute kidney injury risk score was (4.1 × fluid balance) + (1.9 × renal oxygen extraction). The risk score was significantly higher in acute kidney injury with a score of 32.9 compared to 7.9 (p < 0.01). Optimal cut-offs for fluid balance (7 mL/hr) and renal oxygen extraction (29%) were identified. Higher serum creatinine:baseline creatinine ratio was associated with a higher mean airway pressure, higher renal oxygen extraction, higher mean arterial blood pressure, higher vasoactive inotropic score, and fluid balance.

CONCLUSION

Among patients with univentricular physiology undergoing the Norwood procedure, renal oxygen extraction and a higher net fluid balance are independently associated with increased risk of acute kidney injury. Renal perfusion pressure is not significantly associated with acute kidney injury.

Assessment of pharmacologically induced changes in canine kidney function by multiparametric magnetic resonance imaging and contrast enhanced ultrasound

Introduction

Dynamic contrast-enhanced (DCE) MRI and arterial spin labeling (ASL) MRI enable non-invasive measurement of renal blood flow (RBF), whereas blood oxygenation level-dependent (BOLD) MRI enables non-invasive measurement of the apparent relaxation rate (R2*), an indicator of oxygenation. This study was conducted to evaluate the potential role of these MRI modalities in assessing RBF and oxygenation in dogs. The correlation between contrast-enhanced ultrasound (CEUS) and the MRI modalities was examined and also the ability of the MRI modalities to detect pharmacologically induced changes.

Methods

RBF, using CEUS, ASL- and DCE-MRI, as well as renal oxygenation, using BOLD-MRI of eight adult beagles were assessed at two time-points, 2–3 weeks apart. During each time point, the anesthetized dogs received either a control (0.9% sodium chloride) or a dopamine treatment. For each time point, measurements were carried out over 2 days. An MRI scan at 3 T was performed on day one, followed by CEUS on day two.

Results

Using the model-free model with caudal placement of the arterial input function (AIF) region of interest (ROI) in the aorta, the DCE results showed a significant correlation with ASL measured RBF and detected significant changes in blood flow during dopamine infusion. Additionally, R2* negatively correlated with ASL measured RBF at the cortex and medulla, as well as with medullary wash-in rate (WiR) and peak intensity (PI). ASL measured RBF, in its turn, showed a positive correlation with cortical WiR, PI, area under the curve (AUC) and fall time (FT), and with medullary WiR and PI, but a negative correlation with medullary rise time (RT). During dopamine infusion, BOLD-MRI observed a significant decrease in R2* at the medulla and entire kidney, while ASL-MRI demonstrated a significant increase in RBF at the cortex, medulla and the entire kidney.

Conclusion

ASL- and BOLD-MRI can measure pharmacologically induced changes in renal blood flow and renal oxygenation in dogs and might allow detection of changes that cannot be observed with CEUS. However, further research is needed to confirm the potential of ASL- and BOLD-MRI in dogs and to clarify which analysis method is most suitable for DCE-MRI in dogs.

Therapeutic Potential of Dopamine and Related Drugs as Anti-Inflammatories and Antioxidants in Neuronal and Non-Neuronal Pathologies

Dopamine (DA), its derivatives, and dopaminergic drugs are compounds widely used in the management of diseases related to the nervous system. However, DA receptors have been identified in nonneuronal tissues, which has been related to their therapeutic potential in pathologies such as sepsis or septic shock, blood pressure, renal failure, diabetes, and obesity, among others. In addition, DA and dopaminergic drugs have shown anti-inflammatory and antioxidant properties in different kinds of cells.

AIM

To compile the mechanism of action of DA and the main dopaminergic drugs and show the findings that support the therapeutic potential of these molecules for the treatment of neurological and non-neurological diseases considering their antioxidant and anti-inflammatory actions.

METHOD

We performed a review article. An exhaustive search for information was carried out in specialized databases such as PubMed, PubChem, ProQuest, EBSCO, Scopus, Science Direct, Web of Science, Bookshelf, DrugBank, Livertox, and Clinical Trials.

RESULTS

We showed that DA and dopaminergic drugs have emerged for the management of neuronal and nonneuronal diseases with important therapeutic potential as anti-inflammatories and antioxidants.

CONCLUSIONS

DA and DA derivatives can be an attractive treatment strategy and a promising approach to slowing the progression of disorders through repositioning.

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.

Use of Levosimendan in Intensive Care Unit Settings: An Opinion Paper

Levosimendan is an inodilator that promotes cardiac contractility primarily through calcium sensitization of cardiac troponin C and vasodilatation via opening of adenosine triphosphate–sensitive potassium (K_ATP) channels in vascular smooth muscle cells; the drug also exerts organ-protective effects through a similar effect on mitochondrial K_ATP channels. This pharmacological profile identifies levosimendan as a drug that may have applications in a wide range of critical illness situations encountered in intensive care unit medicine: hemodynamic support in cardiogenic or septic shock; weaning from mechanical ventilation or from extracorporeal membrane oxygenation; and in the context of cardiorenal syndrome. This review, authored by experts from 9 European countries (Austria, Belgium, Czech republic, Finland, France, Germany, Italy, Sweden, and Switzerland), examines the clinical and experimental data for levosimendan in these situations and concludes that, in most instances, the evidence is encouraging, which is not the case with other cardioactive and vasoactive drugs routinely used in the intensive care unit. The size of the available studies is, however, limited and the data are in need of verification in larger controlled trials. Some proposals are offered for the aims and designs of these additional studies.

The Effect of Levosimendan Versus Milrinone on the Occurrence Rate of Acute Kidney Injury Following Congenital Heart Surgery in Infants: A Randomized Clinical Trial

OBJECTIVES

It has been shown that, in contrast to other inotropic agents, levosimendan improves glomerular filtration rate after adult cardiac surgery. The aim of this study was to investigate the efficacy of levosimendan, compared with milrinone, in preventing acute kidney dysfunction in infants after open-heart surgery with cardiopulmonary bypass.

DESIGN

Two-center, double-blinded, prospective, randomized clinical trial.

SETTING

The study was performed in two tertiary pediatric centers, one in Sweden (Gothenburg) and one in Finland (Helsinki).

PATIENTS

Infants between 1 and 12 months old, diagnosed with Tetralogy of Fallot, complete atrioventricular septal defect or nonrestrictive ventricular septal defect, undergoing total corrective cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

Seventy-two infants were randomized to receive a perioperative infusion of levosimendan (0.1 µg/kg/min) or milrinone (0.4 µg/kg/min). The infusion was initiated at the start of cardiopulmonary bypass and continued for 26 hours.

MEASUREMENTS AND MAIN RESULTS

The primary outcome variable was the absolute value of serum creatinine data on postoperative day 1. Secondary outcomes included the following: 1) acute kidney injury according to the serum creatinine criteria of the Kidney Diseases: Improving Global Outcomes; 2) acute kidney injury with serum creatinine corrected for fluid balance; 3) plasma neutrophil gelatinase-associated lipocalin; 4) cystatin C; 5) urea; 6) lactate; 7) hemodynamic variables; 8) use of diuretics in the PICU; 9) need of dialysis; 10) length of ventilator therapy; and 11) length of PICU stays. There was no significant difference in postoperative serum creatinine between the treatment groups over time (p = 0.65). The occurrence rate of acute kidney injury within 48 hours was 46.9% in the levosimendan group and 39.5% in the milrinone group (p = 0.70). There were no significant differences in other secondary outcome variables between the groups.

CONCLUSIONS

Levosimendan compared with milrinone did not reduce the occurrence rate of acute kidney injury in infants after total corrective heart surgery for atrioventricular septal defect, ventricular septal defect, or Tetralogy of Fallot.

Differential Effects of Levosimendan and Dobutamine on Glomerular Filtration Rate in Patients With Heart Failure and Renal Impairment:A Randomized Double-Blind Controlled Trial

Background The management of the cardiorenal syndrome in advanced heart failure is challenging, and the role of inotropic drugs has not been fully defined. Our aim was to compare the renal effects of levosimendan versus dobutamine in patients with heart failure and renal impairment. Methods and Results In a randomized double-blind study, we assigned patients with chronic heart failure (left ventricular ejection fraction <40%) and impaired renal function (glomerular filtration rate <80 mL/min per 1.73 m2) to receive either levosimendan (loading dose 12 μg/kg+0.1 μg/kg per minute) or dobutamine (7.5  μg/kg per minute) for 75 minutes. A pulmonary artery catheter was used for measurements of systemic hemodynamics, and a renal vein catheter was used to measure renal plasma flow by the infusion clearance technique for PAH (para-aminohippurate) corrected by renal extraction of PAH . Filtration fraction was measured by renal extraction of chromium ethylenediamine tetraacetic acid. A total of 32 patients completed the study. Following treatment, the levosimendan and dobutamine groups displayed similar increases in renal blood flow (22% and 26%, respectively) with no significant differences between groups. Glomerular filtration rate increased by 22% in the levosimendan group but remained unchanged in the dobutamine group ( P=0.012). Filtration fraction was not affected by levosimendan but decreased by 17% with dobutamine ( P=0.045). Conclusions In patients with chronic heart failure and renal impairment, levosimendan increases glomerular filtration rate to a greater extent than dobutamine and thus may be the preferred inotropic agent for treating patients with the cardiorenal syndrome. Clinical Trial Registration URL: https://www.clinicaltrials.gov . Unique identifier: NCT 02133105.

Renal haemodynamics and oxygenation during and after cardiac surgery and cardiopulmonary bypass

Acute kidney injury (AKI) is a common complication following cardiac surgery performed on cardiopulmonary bypass (CPB) and has important implications for prognosis. The aetiology of cardiac surgery-associated AKI is complex, but renal hypoxia, particularly in the medulla, is thought to play at least some role. There is strong evidence from studies in experimental animals, clinical observations and computational models that medullary ischaemia and hypoxia occur during CPB. There are no validated methods to monitor or improve renal oxygenation during CPB, and thus possibly decrease the risk of AKI. Attempts to reduce the incidence of AKI by early transfusion to ameliorate intra-operative anaemia, refinement of protocols for cooling and rewarming on bypass, optimization of pump flow and arterial pressure, or the use of pulsatile flow, have not been successful to date. This may in part reflect the complexity of renal oxygenation, which may limit the effectiveness of individual interventions. We propose a multi-disciplinary pathway for translation comprising three components. Firstly, large-animal models of CPB to continuously monitor both whole kidney and regional kidney perfusion and oxygenation. Secondly, computational models to obtain information that can be used to interpret the data and develop rational interventions. Thirdly, clinically feasible non-invasive methods to continuously monitor renal oxygenation in the operating theatre and to identify patients at risk of AKI. In this review, we outline the recent progress on each of these fronts.

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

Background

Acute kidney injury (AKI) occurs frequently after liver transplantation and is associated with the development of chronic kidney disease and increased mortality. There is a lack of data on renal blood flow (RBF), oxygen consumption, glomerular filtration rate (GFR) and renal oxygenation, i.e. the renal oxygen supply/demand relationship, early after liver transplantation. Increased insight into the renal pathophysiology after liver transplantation is needed to improve the prevention and treatment of postoperative AKI. We have therefore studied renal hemodynamics, function and oxygenation early after liver transplantation in humans.

Methods

Systemic hemodynamic and renal variables were measured during two 30-min periods in liver transplant recipients (n = 12) and post-cardiac surgery patients (controls, n = 73). RBF and GFR were measured by the renal vein retrograde thermodilution technique and by renal extraction of Cr-EDTA (= filtration fraction), respectively. Renal oxygenation was estimated from the renal oxygen extraction.

Results

In the liver transplant group, GFR decreased by 40% (p < 0.05), compared to the preoperative value. Cardiac index and systemic vascular resistance index were 65% higher (p < 0.001) and 36% lower (p < 0.001), respectively, in the liver transplant recipients compared to the control group. GFR was 27% (p < 0.05) and filtration fraction 40% (p < 0.01) lower in the liver transplant group. Renal vascular resistance was 15% lower (p < 0.05) and RBF was 18% higher (p < 0.05) in liver transplant recipients, but the ratio between RBF and cardiac index was 27% lower (p < 0.001) among the liver-transplanted patients compared to the control group. Renal oxygen consumption and extraction were both higher in the liver transplants, 44% (p < 0.01) and 24% (p < 0.05) respectively.

Conclusions

Despite the hyperdynamic systemic circulation and renal vasodilation, there is a severe decline in renal function directly after liver transplantation. This decline is accompanied by an impaired renal oxygenation, as the pronounced elevation of renal oxygen consumption is not met by a proportional increase in renal oxygen delivery. This information may provide new insights into renal pathophysiology as a basis for future strategies to prevent/treat AKI after liver transplantation.

Trial registration

ClinicalTrials.gov, NCT02455115. Registered on 23 April 2015.

Risk factors for continuous renal replacement therapy after surgical repair of type A aortic dissection

BACKGROUND

To identify the risk factors for continuous renal replacement therapy (CRRT) following surgical repair of type A aortic dissection (TAAD) using the total arch replacement and frozen elephant trunk (TAR + FET) technique.

METHODS

The study included 330 patients with TAAD repaired using TAR + FET between January 2014 and April 2015. Mean age was 47.1±10.2 years (range, 18-73 years) and 242 were male (73.3%). Univariate and multivariate analyses were used to identify the risk factors for CRRT.

RESULTS

Postoperative CRRT was required in 38 patients (mean age 50.7±10.0 years; 27 males). Operative death occurred in 12 patients (3.6%, 12/330). The mortality rate was 23.7% (9/38) in patients with CRRT and 1.0% (3/292) in those without CRRT (P<0.001). Factors associated with CRRT were age (50.7±10.0 vs. 46.7±10.2 years, P=0.023), preoperative serum creatinine (sCr) (135.0±154.2 vs. 85.7±37.0 µmol/L, P<0.001), emergency operation (89.5% vs. 73.3%, P=0.030), cardiopulmonary bypass (CPB) time (265.2±98.8 vs. 199.7±44.2 minutes, P<0.001), cross-clamp time (144.6±54.8 vs. 116.3±33.2 minutes, P<0.001), the amount of red blood cell (8.0±5.2 vs. 3.7±3.3 unit, P<0.001) and fresh frozen plasma (507.8±350.3 vs. 784.2±488.5 mL, P<0.001) transfused intraoperatively, preoperative D-dimmer level (11,361.0 vs. 2,856.7 mg/L, P<0.001) and reexploration for bleeding (15.8% vs. 2.4%, P<0.001). In multivariate analysis, risk factors for CRRT were CPB time (minute) [odds ratio (OR) 1.018; 95% confidence interval (CI), 1.007-1.029; P=0.002], preoperative sCr level (µmol/L) (OR, 1.008; 95% CI, 1.000-1.015; P=0.040), and the amount of red blood cell transfused intraoperatively (unit) (OR, 1.206; 95% CI, 1.077-1.350; P<0.001).

CONCLUSIONS

In this series of patients with TAAD, the time of CPB (minute), sCr level (µmol/L) and the amount of red blood cell transfused intraoperatively (unit) were risk factors for CRRT after TAR + FET.

The role of levosimendan in acute heart failure complicating acute coronary syndrome: A review and expert consensus opinion

Acute heart failure and/or cardiogenic shock are frequently triggered by ischemic coronary events. Yet, there is a paucity of randomized data on the management of patients with heart failure complicating acute coronary syndrome, as acute coronary syndrome and cardiogenic shock have frequently been defined as exclusion criteria in trials and registries. As a consequence, guideline recommendations are mostly driven by observational studies, even though these patients have a particularly poor prognosis compared to heart failure patients without signs of coronary artery disease. In acute heart failure, and especially in cardiogenic shock related to ischemic conditions, vasopressors and inotropes are used. However, both pathophysiological considerations and available clinical data suggest that these treatments may have disadvantageous effects. The inodilator levosimendan offers potential benefits due to a range of distinct effects including positive inotropy, restoration of ventriculo-arterial coupling, increases in tissue perfusion, and anti-stunning and anti-inflammatory effects. In clinical trials levosimendan improves symptoms, cardiac function, hemodynamics, and end-organ function. Adverse effects are generally less common than with other inotropic and vasoactive therapies, with the notable exception of hypotension. The decision to use levosimendan, in terms of timing and dosing, is influenced by the presence of pulmonary congestion, and blood pressure measurements. Levosimendan should be preferred over adrenergic inotropes as a first line therapy for all ACS-AHF patients who are under beta-blockade and/or when urinary output is insufficient after diuretics. Levosimendan can be used alone or in combination with other inotropic or vasopressor agents, but requires monitoring due to the risk of hypotension.

Renal effects of added low-dose dopamine in acute heart failure patients with diuretic resistance to natriuretic peptide

Worsening renal function during the early phase of hospitalization is related to adverse outcomes in acute heart failure (AHF). This study aimed to clarify whether added low-dose dopamine (DA) is clinically beneficial for AHF patients with diuretic resistance to human atrial natriuretic peptide (hANP). Twenty-four AHF patients, who did not have adequate diuresis by 4 hours after administration of hANP, were randomized to a low dose of DA (1-3 μg·kg·min, n = 12) or a low dose of furosemide (10-30 mg injection, n = 12). The significant increase in mean hourly urine volume from baseline (265% ± 204% with hANP + DA; 187% ± 118% with hANP + furosemide) and improvement of dyspnea were similarly observed in both groups. Significant decreases in serum creatinine levels were observed by -14.0% ± 14.2% in the hANP + DA group compared with the hANP + furosemide group (4.5% ± 9.6%, P = 0.0011) without increases in the renotubular and myocardial markers. The incidence of worsening renal function defined as a rise in serum creatinine of >0.3 mg/dL was not observed within 3 days of admission in both groups. Added low-dose DA might not have a harmful effect on renal function and effects of diuresis and symptom relief without a significant increase in troponin-T in AHF patients with diuretic resistance to hANP.

Renal effects of levosimendan: a consensus report

Renal dysfunction is common in clinical settings in which cardiac function is compromised such as heart failure, cardiac surgery or sepsis, and is associated with high morbidity and mortality. Levosimendan is a calcium sensitizer and potassium channel opener used in the treatment of acute heart failure. This review describes the effects of the inodilator levosimendan on renal function. A panel of 25 scientists and clinicians from 15 European countries (Austria, Finland, France, Hungary, Germany, Greece, Italy, Portugal, the Netherlands, Slovenia, Spain, Sweden, Turkey, the United Kingdom, and Ukraine) convened and reached a consensus on the current interpretation of the renal effects of levosimendan described both in non-clinical research and in clinical study reports. Most reports on the effect of levosimendan indicate an improvement of renal function in heart failure, sepsis and cardiac surgery settings. However, caution should be applied as study designs differed from randomized, controlled studies to uncontrolled ones. Importantly, in the largest HF study (REVIVE I and II) no significant changes in the renal function were detected. As it regards the mechanism of action, the opening of mitochondrial KATP channels by levosimendan is involved through a preconditioning effect. There is a strong rationale for randomized controlled trials seeking beneficial renal effects of levosimendan. As an example, a study is shortly to commence to assess the role of levosimendan for the prevention of acute organ dysfunction in sepsis (LeoPARDS).

Effects of levosimendan on glomerular filtration rate, renal blood flow, and renal oxygenation after cardiac surgery with cardiopulmonary bypass: a randomized placebo-controlled study

OBJECTIVES

Acute kidney injury develops in a large proportion of patients after cardiac surgery because of the low cardiac output syndrome. The inodilator levosimendan increases cardiac output after cardiac surgery with cardiopulmonary bypass, but a detailed analysis of its effects on renal perfusion, glomerular filtration, and renal oxygenation in this group of patients is lacking. We therefore evaluated the effects of levosimendan on renal blood flow, glomerular filtration rate, renal oxygen consumption, and renal oxygen demand/supply relationship, i.e., renal oxygen extraction, early after cardiac surgery with cardiopulmonary bypass.

DESIGN

Prospective, placebo-controlled, and randomized trial.

SETTING

Cardiothoracic ICU of a tertiary center.

PATIENTS

Postcardiac surgery patients (n=30).

INTERVENTIONS

The patients were randomized to receive levosimendan, 0.1 µg/kg/min after a loading dose of 12 µg/kg (n=15), or placebo (n=15).

MEASUREMENTS AND MAIN RESULTS

The experimental procedure started 4-6 hours after surgery in the ICU during propofol sedation and mechanical ventilation. Systemic hemodynamic were evaluated by a pulmonary artery thermodilution catheter. Renal blood flow and glomerular filtration rate were measured by the renal vein retrograde thermodilution technique and by renal extraction of Cr-EDTA, respectively. Central venous pressure was kept constant by colloid/crystalloid infusion. Compared to placebo, levosimendan increased cardiac index (22%), stroke volume index (15%), and heart rate (7%) and decreased systemic vascular resistance index (21%), whereas mean arterial pressure was not affected. Levosimendan induced significant increases in renal blood flow (12%, p<0.05) and glomerular filtration rate (21%, p<0.05), decreased renal vascular resistance (18%, p<0.05) but caused no significant changes in filtration fraction, renal oxygen consumption, or renal oxygen extraction, compared to placebo.

CONCLUSIONS

After cardiac surgery with cardiopulmonary bypass, levosimendan induces a vasodilation, preferentially of preglomerular resistance vessels, increasing both renal blood flow and glomerular filtration rate without jeopardizing renal oxygenation. Due to its pharmacodynamic profile, levosimendan might be an interesting alternative for treatment of postoperative heart failure complicated by acute kidney injury in postcardiac surgery patients.

Renal oxygenation and haemodynamics in acute kidney injury and chronic kidney disease

Acute kidney injury (AKI) is a major burden on health systems and may arise from multiple initiating insults, including ischaemia-reperfusion injury, cardiovascular surgery, radiocontrast administration and sepsis. Similarly, the incidence and prevalence of chronic kidney disease (CKD) continues to increase, with significant morbidity and mortality. Moreover, an increasing number of AKI patients survive to develop CKD and end-stage renal disease. Although the mechanisms for the development of AKI and progression to CKD remain poorly understood, initial impairment of oxygen balance likely constitutes a common pathway, causing renal tissue hypoxia and ATP starvation that, in turn, induce extracellular matrix production, collagen deposition and fibrosis. Thus, possible future strategies for one or both conditions may involve dopamine, loop diuretics, atrial natriuretic peptide and inhibitors of inducible nitric oxide synthase, substances that target kidney oxygen consumption and regulators of renal oxygenation, such as nitric oxide and heme oxygenase-1.

Neurohormonal interactions on the renal oxygen delivery and consumption in haemorrhagic shock-induced acute kidney injury

Haemorrhagic shock is a common cause of acute kidney injury (AKI), which is a major risk factor for developing chronic kidney disease. The mechanism is superficially straightforward. An arterial pressure below the kidney's autoregulatory region leads to a direct reduction in filtration pressure and perfusion, which in turn cause renal failure with reduced glomerular filtration rate and AKI because of hypoxia. However, the kidney's situation is further worsened by the hormonal and neural reactions to reduced perfusion pressure. There are three major systems working to maintain arterial pressure in shock: sympathetic signalling, the renin-angiotensin system and vasopressin. These work to retain electrolytes and water and to increase peripheral resistance and cardiac output. In the kidney, the increased electrolyte reabsorption consumes oxygen. At the same time, at the signalling level seen in shock, all of these hormones reduce renal perfusion and thereby oxygen delivery. This creates an exaggerated hypoxic situation that is liable to worsen the AKI. The present review will examine this mechanistic background and identify a number of areas that require further studies. At this time, the ideal treatment of haemorrhagic shock appears to be slow fluid resuscitation, possibly with hyperosmolar sodium, low chloride and no artificial colloids. From the standpoint of the kidney, renin-angiotensin system inhibitors appear fruitful for further study.

Contrast-enhanced ultrasound to evaluate changes in renal cortical perfusion around cardiac surgery: a pilot study

Introduction

Contrast-enhanced ultrasound (CEUS) is a new technique that might enable portable and non-invasive organ perfusion quantification at the bedside. However, it has not yet been tested in critically ill patients. We sought to establish CEUS's feasibility, safety, reproducibility and potential diagnostic value in the assessment of renal cortical perfusion in the peri-operative period in cardiac surgery patients.

Methods

We recruited twelve patients deemed at risk of acute kidney injury (AKI) planned for elective cardiac surgery. We performed renal CEUS with destruction-replenishment sequences before the operation, on ICU arrival and the day following the admission. Enhancement was obtained with Sonovue^® (Bracco, Milano, Italy) at an infusion rate of 1 ml/min. We collected hemodynamic parameters before, during and after contrast agent infusion. At each study time, we obtained five video sequences, which were analysed using dedicated software by two independent radiologists blinded to patient and time. The main output was a perfusion index (PI), corresponding to the ratio of relative blood volume (RBV) over mean transit time (mTT).

Results

All 36 renal CEUS studies, including 24 in the immediate post-operative period could be performed and were well tolerated. Correlation between readers for PI was excellent (R² = 0.96, P < 0.0001). Compared with baseline, there was no overall difference in median PI's on ICU admission. However, the day after surgery, median PI's had decreased by 50% (P < 0.01) (22% decrease in RBV (P = 0.09); 48% increase in mTT (P = 0.04), both suggestive of decreased perfusion). These differences persisted after correction for haemoglobin; vasopressors use and mean arterial pressure. Four patients developed AKI in the post-operative period.

Conclusions

CEUS appears feasible and well-tolerated in patients undergoing cardiac surgery even immediately after ICU admission. CEUS derived-parameters suggest a decrease in renal perfusion occurring within 24 hours of surgery.

Mannitol increases renal blood flow and maintains filtration fraction and oxygenation in postoperative acute kidney injury: a prospective interventional study

Introduction

Acute kidney injury (AKI), which is a major complication after cardiovascular surgery, is associated with significant morbidity and mortality. Diuretic agents are frequently used to improve urine output and to facilitate fluid management in these patients. Mannitol, an osmotic diuretic, is used in the perioperative setting in the belief that it exerts reno-protective properties. In a recent study on uncomplicated postcardiac-surgery patients with normal renal function, mannitol increased glomerular filtration rate (GFR), possibly by a deswelling effect on tubular cells. Furthermore, experimental studies have previously shown that renal ischemia causes an endothelial cell injury and dysfunction followed by endothelial cell edema. We studied the effects of mannitol on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO₂), and extraction (RO₂Ex) in early, ischemic AKI after cardiac surgery.

Methods

Eleven patients with AKI were studied during propofol sedation and mechanical ventilation 2 to 6 days after complicated cardiac surgery. All patients had severe heart failure treated with one (100%) or two (73%) inotropic agents and intraaortic balloon pump (36%). Systemic hemodynamics were measured with a pulmonary artery catheter. RBF and renal filtration fraction (FF) were measured by the renal vein thermo-dilution technique and by renal extraction of chromium-51-ethylenediaminetetraacetic acid (⁵¹Cr-EDTA), respectively. GFR was calculated as the product of FF and renal plasma flow RBF × (1-hematocrit). RVO₂ and RO₂Ex were calculated from arterial and renal vein blood samples according to standard formulae. After control measurements, a bolus dose of mannitol, 225 mg/kg, was given, followed by an infusion at a rate of 75 mg/kg/h for two 30-minute periods.

Results

Mannitol did not affect cardiac index or cardiac filling pressures. Mannitol increased urine flow by 61% (P < 0.001). This was accompanied by a 12% increase in RBF (P < 0.05) and a 13% decrease in renal vascular resistance (P < 0.05). Mannitol increased the RBF/cardiac output (CO) relation (P = 0.040). Mannitol caused no significant changes in RO₂Ext or renal FF.

Conclusions

Mannitol treatment of postoperative AKI induces a renal vasodilation and redistributes systemic blood flow to the kidneys. Mannitol does not affect filtration fraction or renal oxygenation, suggestive of balanced increases in perfusion/filtration and oxygen demand/supply.

Cystatin C in diabetics as a marker of mild renal insufficiency after CABG

PURPOSE

The purpose of this study was to evaluate the accuracy of plasma cystatin C in acute impairment in renal function; plasma cystatin C was compared to plasma creatinine in two hundred patients undergoing elective CABG surgery.

METHODS

We performed a prospective clinical study of two hundred patients undergoing coronary bypass surgery. Plasma creatinine and cystatin C were measured preoperatively and on the first and fourth days after surgery. Estimated glomerular filtration rate (GFR) was calculated using one creatinine-based and two cystatin C-based equations.

RESULTS

There were 144 non-diabetic and 56 diabetic patients. The need for furosemide was more common among diabetics (80.4% of the patients vs. 53.9%, p = 0.024). Changes in cystatin C-based GFR with both equations were significantly greater in the group of diabetics (-14.3 ± 28.0 and -11.2 ± 19.3 ml/min/1.73 m(2) vs. -4.3 ± 26.9 and -3.1 ± 20.5 ml/min/1.73 m(2), p = 0.025 and 0.016, respectively). Changes in creatinine-based GFR did not differ between the diabetics and the non-diabetics.

CONCLUSION

Cystatin C and cystatin C-based estimation of GFR may be useful and more sensitive than creatinine in detecting mild acute renal insufficiency in diabetic patients.

Unloading therapy by intravenous diuretic in chronic heart failure: a double-edged weapon?

A well established part of therapeutic approaches applying to cases of chronic heart failure (CHF) with extreme fluid retention is represented by intensive intravenous (i.v.) therapy with loop diuretics. This kind of therapy, if appropriately modulated according to the individual clinical picture and biohumoral pattern, is able to decrease the abnormally high ventricular filling pressures, thereby relieving the breathlessness while being able to retrieve a suitable urine output, so as to propitiate regression or disappearance of edema without unfavorable influences on renal clearance of nitrogenous compounds. Nevertheless, the intensive i.v. diuretic therapy should be tailored on the basis of a close assessment of baseline hemodynamic data and hemodynamic response to the medications, in addition to the careful diuretic dose titration and cautious evaluation of risk/benefit ratio. Actually, by using this kind of therapy, there is a risk that a tubular or glomerular injury can be generated and that a frequently preexisting renal dysfunction can be aggravated, especially when excessive doses of loop diuretics are being erroneously administered, so as to cause hypotension, hypoperfusion and/or relative dehydration in patients with decompensated CHF who could have expressly benefitted from intensive unloading therapy. Recently, the genesis of CHF-related progressive renal deterioration has been highlighted by affirming that a major role may be played rather by neurovegetative disorders, that is, by increase in sympathetic tone and abnormalities in kidney's vasomotility than by cardiac inotropism deficiency. The measures, thought to be able to prevent renal arterial constriction and to impede deterioration of glomerular filtration rate (GFR) due to the ischemic-necrotic tubular injury, as occurring in the set of intensive unloading therapy with i.v. furosemide or other loop diuretic, are represented by application of inotropic and renal vasodilator support by dopamine i.v. infusion at low doses or by other inotropic agents provided with recognized renal vasodilator properties and/or by addition to i.v. furosemide of osmotic agents able to expand the hematic volume, so counteracting or minimizing the reflex renal vasoconstriction induced by furosemide-related reduction in intravascular circulating volume: i.v. infusion of small volumes of hypertonic saline solution, as well as administration of albumin, mannitol and/or plasma expanders. Because renal impairment, as developing in the setting of CHF, has proven to represent a very important indicator of adverse outcome, every effort should be addressed to prevent any significant (>25% of basal value) rise in serum creatinine consequent to diuretic unloading therapy or to other procedures (paracentesis of tense ascites, ultrafiltration) aimed at rapid fluid removal in edematous or ascitic CHF or cardiogenetic anasarca. Ultrafiltration, even though a promising technique highly valued for its acknowledged property to obtain a more rapid fluid and weight loss in CHF patients with marked fluid retention, has been demonstrated so far to produce neurohumoral activation, creatinine abnormalities and symptomatic hypotensions similar to those due to i.v. loop diuretics; thus, the hypothesized advantages of this technique remain to be further clarified and confirmed, with regard to its safety profile and cost-effectiveness.

Acute renal failure is NOT an "acute renal success"--a clinical study on the renal oxygen supply/demand relationship in acute kidney injury

OBJECTIVES

Acute kidney injury occurs frequently after cardiac or major vascular surgery and is believed to be predominantly a consequence of impaired renal oxygenation. However, in patients with acute kidney injury, data on renal oxygen consumption (RVO2), renal blood flow, glomerular filtration, and renal oxygenation, i.e., the renal oxygen supply/demand relationship, are lacking and current views on renal oxygenation in the clinical situation of acute kidney injury are presumptive and largely based on experimental studies.

DESIGN

Prospective, two-group comparative study.

SETTING

Cardiothoracic intensive care unit of a tertiary center.

PATIENTS

Postcardiac surgery patients with (n = 12) and without (n = 37) acute kidney injury were compared with respect to renal blood flow, glomerular filtration, RVO2, and renal oxygenation.

INTERVENTIONS

None

MEASUREMENTS AND MAIN RESULTS

Data on systemic hemodynamics (pulmonary artery catheter) and renal variables were obtained during two 30-min periods. Renal blood flow was measured using two independent techniques: the renal vein thermodilution technique and the infusion clearance of paraaminohippuric acid, corrected for renal extraction of paraaminohippuric acid. The filtration fraction was measured by the renal extraction of Cr-EDTA and the renal sodium resorption was measured as the difference between filtered and excreted sodium. Renal oxygenation was estimated from the renal oxygen extraction. Cardiac index and mean arterial pressure did not differ between the two groups. In the acute kidney injury group, glomerular filtration (-57%), renal blood flow (-40%), filtration fraction (-26%), and sodium resorption (-59%) were lower, renal vascular resistance (52%) and renal oxygen extraction (68%) were higher, whereas there was no difference in renal oxygen consumption between groups. Renal oxygen consumption for one unit of reabsorbed sodium was 2.4 times higher in acute kidney injury.

CONCLUSIONS

Renal oxygenation is severely impaired in acute kidney injury after cardiac surgery, despite the decrease in glomerular filtration and tubular workload. This was caused by a combination of renal vasoconstriction and tubular sodium resorption at a high oxygen demand.