Paolo Calzavacca

Introduction: Supra-clinical doses of clonidine appear beneficial in experimental sepsis, but there is limited understanding of the effects of clonidine at clinically relevant doses.Methods: In conscious sheep, with implanted renal and pulmonary artery flow probes, sepsis was induced by infusion of liveEscherichia coli. At 24 h, a high clinical dose of clonidine (HCDC) [1.0 μg/kg/h], a low clinical dose of clonidine (LCDC) [0.25 μg/kg/h] or vehicle, was infused for 8 h.Results: Animals developed hyperdynamic, hypotensive sepsis with acute kidney injury. The HCDC decreased heart rate (153 ± 6 to 119 ± 7 bpm) and cardiac output (5.6 ± 0.4 to 5.0 ± 0.4 L/min), with no reduction in mean arterial pressure (MAP). In contrast, LCDC increased cardiac output with peripheral vasodilatation. Both doses induced a large transient increase in urine output, an increase in plasma osmolality and, with the high dose, an increase in plasma arginine vasopressin. Sepsis increased plasma interleukin-6 (IL-6) and IL-10 and clonidine further increased IL-10 (1.6 ± 0.1 to 3.3 ± 0.7 ng/mL), but not IL-6. Clonidine reduced rectal temperature. During recovery from sepsis, MAP returned to baseline values more rapidly in the HCDC group (P < 0.001).Conclusions: In hyperdynamic, hypotensive sepsis, the effects of clonidine at clinically relevant doses are complex and dose dependent. HCDC attenuated sepsis-related increases in heart rate and cardiac output, with little effect on arterial pressure. It also induced a water diuresis, increased AVP, reduced body temperature, and had an anti-inflammatory action. Low-dose clonidine had similar but less pronounced effects, except that it induced moderate vasodilatation and increased cardiac output.

Purpose: The study aimed to investigate patients' characteristics, fluid and hemodynamic management, and outcomes according to the severity of cardiac surgery-associated acute kidney injury (CSA-AKI). Methods: In a single-center, prospective cohort study, we enrolled 282 adult cardiac surgical patients. In a secondary analysis, we assessed preoperative patients' characteristics, physiological variables, and medication for intra- and postoperative fluid and hemodynamic management and outcomes according to CSA-AKI stages by the Renal risk, Injury, Failure, Loss, End-stage renal disease (RIFLE) classification. Variables of fluid and hemodynamic management were further assessed with regard to the need for postoperative renal replacement therapy (RRT) and in-hospital mortality by the area under the curve for the receiver operating characteristic (AUC-ROC) and multivariate regression analysis. Results: Patients with worsening RIFLE stage, were significantly older, had lower estimated glomerular filtration rate and higher body mass index, more peripheral vascular and chronic obstructive pulmonary disease, atrial fibrillation, and prolonged duration of cardiopulmonary bypass (all p < 0.01). Patients with more severe AKI stage stayed longer in the intensive care and hospital, had higher in-hospital mortality, and requirement for RRT (all p < 0.001). Also, with worsening RIFLE stage, patients had lower intraoperative mean arterial pressure (MAP); p = 0.047, despite higher doses of norepinephrine (p < 0.001). The intraoperative MAP showed the best discriminatory ability (AUC-ROC: >0.8) for and was independently associated with RRT and in-hospital mortality. Moreover, with increasing AKI severity, patients received significantly more fluid infusion, and required higher dose of furosemide; nonetheless, they had increased postoperative fluid balance. Conclusions: In this cohort, reduced MAP and increased fluid balance were independently associated with increased mortality and need for RRT after cardiac surgery.

Vasoactive agents are used in critical care to optimize circulatory function, but their effects on renal tissue oxygenation in the absence of anesthesia remain largely unknown. Therefore, we assessed the effects of multiple vasoactive agents on regional kidney oxygenation in awake sheep. Sheep were surgically instrumented with pulmonary and renal artery flow probes, and combination fiber-optic probes, in the renal cortex and medulla, comprising a fluorescence optode to measure tissue Po₂ and a laser-Doppler probe to assess tissue perfusion. Carotid arterial and renal venous cannulas enabled measurement of arterial pressure and total renal oxygen delivery and consumption. Norepinephrine (0.1 or 0.8 μg·kg⁻¹·min⁻¹) dose-dependently reduced cortical and medullary laser Doppler flux (LDF) and Po₂ without significantly altering renal blood flow (RBF), or renal oxygen delivery or consumption. Angiotensin II (9.8 ± 2.1 μg/h) reduced RBF by 21%, renal oxygen delivery by 28%, oxygen consumption by 18%, and medullary Po₂ by 38%, but did not significantly alter cortical Po₂ or cortical or medullary LDF. Arginine vasopressin (3.3 ± 0.5 μg/h) caused similar decreases in RBF and renal oxygen delivery, but did not significantly alter renal oxygen consumption or cortical or medullary LDF or Po₂. Captopril had no observable effects on cortical or medullary LDF or Po₂, at a dose that increased renal oxygen delivery by 24%, but did not significantly alter renal oxygen consumption. We conclude that vasoactive agents have diverse effects on regional kidney oxygenation in awake sheep that are not predictable from their effects on LDF, RBF, or total renal oxygen delivery and consumption.

To determine whether there is a decrease in renal cortical or medullary perfusion and oxygenation in a conscious large animal model of hyperdynamic septic shock with acute kidney injury. Interventional animal study. University-affiliated research institute. Eight merino ewes. Sheep were surgically instrumented with pulmonary and renal artery flow probes in the renal cortex and medulla, combination fiber-optic probes comprising a fluorescence optode to measure tissue PO2, and a laser-Doppler probe to assess tissue perfusion. Sepsis was induced by infusion of live Escherichia coli for 24 hours followed by 24-hour recovery. In unanesthetized normal sheep, resting levels of cortical and medullary tissue PO2 were 29.5 ± 4.4 and 29.1 ± 4.3 mm Hg, respectively. During infusion of E. coli, hyperdynamic sepsis developed with hypotension, tachycardia, increased cardiac output, increased renal blood flow, oliguria, decreased creatinine clearance, and increased serum creatinine. Renal oxygen delivery increased while renal oxygen consumption was unchanged. During sepsis, cortical tissue PO2 increased from 29.4 ± 4.3 to 36.3 ± 3.5 mm Hg (p < 0.001), whereas medullary oxygenation decreased from 29.6 ± 4.7 to 13.1 ± 2.7 mm Hg (p < 0.001). Cortical perfusion was not significantly changed, but medullary perfusion decreased (671 BPU [500-900 BPU] to 480 BPU [349-661 BPU]; geometric mean [95% CI]; p < 0.001). In a large animal model of hyperdynamic sepsis, renal hyperemia was associated with preserved cortical oxygenation and perfusion, but decreased medullary oxygenation and perfusion. Medullary hypoxia due to intrarenal blood flow redistribution may be one of the factors causing acute kidney injury in sepsis.

The role of renal cortical and medullary hypoxia in the development of acute kidney injury is controversial, partly due to a lack of techniques for the long-term measurement of intrarenal oxygenation and perfusion in conscious animals. We have, therefore, developed a methodology to chronically implant combination probes to chronically measure renal cortical and medullary tissue perfusion and oxygen tension (tPo₂) in conscious sheep and evaluated their responsiveness and reliability. A transit-time flow probe and a vascular occluder were surgically implanted on the left renal artery. At the same operation, dual fiber-optic probes, comprising a fluorescence optode to measure tPo₂and a laser-Doppler probe to assess tissue perfusion, were inserted into the renal cortex and medulla. In recovered conscious sheep ( n = 8) breathing room air, mean 24-h cortical and medullary tPo₂were similar (31.4 ± 0.6 and 29.7 ± 0.7 mmHg, respectively). In the renal cortex and medulla, a 20% reduction in renal blood flow (RBF) decreased perfusion (14.6 ± 8.6 and 41.2 ± 8.5%, respectively) and oxygenation (48.1 ± 8.5 and 72.4 ± 8.5%, respectively), with greater decreases during a 50% reduction in RBF. At autopsy, minimal fibrosis was observed around the probes. In summary, we have developed a technique to chronically implant fiber-optic probes in the renal cortex and medulla for recording tissue perfusion and oxygenation over many days. In normal resting conscious sheep, cortical and medullary tPo₂were similar. The responses to and recovery from renal artery occlusion, together with the consistent measurements over a 24-h period, demonstrate the responsiveness and stability of the probes.

Background: Despite standardized definitions of acute kidney injury (AKI), there is wide variation in the reported rates of AKI and hospital mortality for patients with AKI. Variation could be due to actual differences in disease incidence, clinical course, or a function of data ascertainment and application of diagnostic criteria. Using standard criteria may help determine and compare the risk and outcomes of AKI across centers. Methods: In this cohort study of critically ill patients admitted to the intensive care units at six hospitals in four countries, we used KDIGO criteria to define AKI. The main outcomes were the occurrence of AKI and hospital mortality. Results: Of the 15,132 critically ill patients, 32% developed AKI based on serum creatinine criteria. After adjusting for differences in age, sex, and severity of illness, the odds ratio for AKI continued to vary across centers (odds ratio (OR), 2.57-6.04, p < 0.001). The overall, crude hospital mortality of patients with AKI was 27%, which also varied across centers after adjusting for KDIGO stage, differences in age, sex, and severity of illness (OR, 1.13-2.20, p < 0.001). The severity of AKI was associated with incremental mortality risk across centers. Conclusions: In this study, the absolute and severity-adjusted rates of AKI and hospital mortality rates for AKI varied across centers. Future studies should examine whether variation in the risk of AKI among centers is due to differences in clinical practice or process of care or residual confounding due to unmeasured factors.

Novel acute kidney injury (AKI) biomarkers offer promise of earlier diagnosis and risk stratification, but have yet to find widespread clinical application. We measured urinary α and π glutathione S-transferases (α-GST and π-GST), urinary l-type fatty acid-binding protein (l-FABP), urinary neutrophil gelatinase-associated lipocalin (NGAL), urinary hepcidin and serum cystatin c (CysC) before surgery, post-operatively and at 24 h after surgery in 93 high risk patient undergoing cardiopulmonary bypass (CPB) and assessed the ability of these biomarkers alone and in combination to predict RIFLE-R defined AKI in the first 5 post-operative days. Twenty-five patients developed AKI. π-GST (ROCAUC = 0.75), lower urine Hepcidin:Creatine ratio at 24 h (0.77), greater urine NGAL:Cr ratio post-op (0.73) and greater serum CysC at 24 h (0.72) best predicted AKI. Linear combinations with significant improvement in AUC were: Hepcidin:Cr 24 h + post-operative π-GST (AUC = 0.86, p = 0.01), Hepcidin:Cr 24 h + NGAL:Cr post-op (0.84, p = 0.03) and CysC 24 h + post-operative π-GST (0.83, p = 0.03), notably these significant biomarkers combinations all involved a tubular injury and a glomerular filtration biomarker. Despite statistical significance in receiver–operator characteristic (ROC) analysis, when assessed by ability to define patients to two groups at high and low risk of AKI, combinations failed to significantly improve classification of risk compared to the best single biomarkers. In an alternative approach using Classification and Regression Tree (CART) analysis a model involving NGAL:Cr measurement post-op followed by Hepcidin:Cr at 24 h was developed which identified high, intermediate and low risk groups for AKI. Regression tree analysis has the potential produce models with greater clinical utility than single combined scores.

Decreased renal blood flow (RBF) and vasoconstriction are considered major mechanisms of contrast-induced acute kidney injury (CIAKI). To understand the severity and duration of such putative effects, we measured systemic and renal hemodynamics after intra-arterial radiocontrast administration. The subjects were six Merino ewes. The setting was a university-affiliated research institute. This is a randomized cross-over experimental study. Transit-time flow probes were implanted on the pulmonary and left renal arteries 2 weeks before experimentation. We simulated percutaneous coronary intervention by administering five intra-arterial boluses of 0.5 mL/kg saline (control) or radiocontrast (iodixanol) to a total of 2.5 mL/kg over 1 h. Cardiac output (CO), heart rate, mean arterial pressure (MAP), RBF, renal vascular conductance (RVC), urine output (UO), creatinine clearance (CrCl), and fractional excretion of sodium (FENa) were measured. In the first 8 h after intra-arterial administration of radiocontrast, CO, total peripheral conductance (TPC), and heart rate (HR) increased compared with those after normal saline administration. Thereafter, CO and TPC were similar between the two groups, but HR remained higher with radiocontrast (p < 0.001). After a short (30 min) period of renal vasoconstriction with preserved RBF secondary to an associated increase in MAP, RBF and RVC showed an earlier and greater increase (vasodilatation) with radiocontrast (p < 0.001) and remained higher during the first 2 days. Radiocontrast initially increased urine output (p < 0.001) and FENa (p = 0.003). However, the overall daily urine output decreased in the radiocontrast-treated animals at 2 days (p < 0.001) and 3 days (p = 0.006). Creatinine clearance was not affected. In healthy animals, intra-arterial radiocontrast increased RBF, induced renal vasodilatation, and caused a delayed period of oliguria. Our findings suggest that sustained reduction in RBF and renal vasoconstriction may not occur in normal large mammals after intra-arterial radiocontrast administration.

Background: Contrast-enhanced ultrasonography (CEUS) is a novel imaging modality to estimate microvascular perfusion. We aimed to assess renal cortical microcirculatory changes by CEUS during pharmacologically or mechanically induced modifications of renal blood flow (RBF) in experimental animals. Methods: We implanted invasive transit-time Doppler flow probes and a vascular occluder around the renal artery in six Merino sheep. After induction of general anaesthesia, renal CEUS studies with destruction-replenishment sequences were performed at baseline and after different interventions aimed at modifying RBF. First, we administered angiotensin II (AngII) to achieve a 25% (AngII 25%) and 50% (AngII 50%) decrease in RBF. Then, we applied mechanical occlusion of the renal artery until RBF decreased by 25% (Occl 25%) and 50% (Occl 50%) of the baseline. Finally, a single dose of 25 mg of captopril was administered. CEUS sequences were analysed offline with dedicated software and perfusion indices (PI) calculated. Results: Pharmacological reduction of RBF with AngII was associated with a 62% (range: 68 decrease to 167 increase) increase (AngII 25%) and a 5% increase in PI (range: 92% decrease to 53% increase) (AngII 50%) in PI. Mechanical occlusion of the renal artery was associated with a 2% (range: 43% decrease to 2% increase) decrease (Occl 25%) and a 67% (range: 63% decrease to a 120% increase) increase (Occl 50%) in PI. The administration of captopril was associated with a 8% (range: 25% decrease to a 101% increase) decrease in PI. Pooled changes in PI failed to reach statistical significance. The study was limited by the difficulty to obtain high quality images. Conclusions: CEUS-derived parameters were highly heterogeneous in this sheep model. The current protocol and model did not allow the evaluation of the correlation between macro and microcirculation assessment by CEUS.

Introduction: Activation of the sympathetic nervous system has beneficial cardiovascular effects in sepsis, but there is also evidence that sympatholytics have beneficial actions in sepsis. We therefore determined the effect of selective β₁-adrenoceptor blockade on cardiac and renal function and cytokine release in ovine hyperdynamic sepsis. Methods: Hyperdynamic sepsis was induced by infusion of live E. coli for 24 hours in nine conscious sheep instrumented with flow probes on the pulmonary and left renal artery. Cardiovascular and renal function and levels of plasma cytokines were determined in a control group and during selective β1-adrenoceptor blockade with atenolol (10 mg intravenous bolus then 0.125 mg/kg/h) from 8 to 24 hours of sepsis. Results: Hyperdynamic sepsis was characterized by hypotension with increases in cardiac output (CO), heart rate (HR) and renal blood flow (RBF), and acute kidney injury. Atenolol caused sustained reductions in HR (P P 1-adrenoceptor blockade reduced CO, but not MAP. During sepsis, atenolol did not alter the development of acute kidney injury or the levels of pro-inflammatory cytokines, but enhanced the release of IL-10. Atenolol appears safe in sepsis, has no deleterious cardiovascular or renal effects, and has an anti-inflammatory effect.