Norepinephrine is the principal vasopressor used to restore blood pressure in sepsis, but its effects on intrarenal oxygenation are unknown. To clarify this, we examined renal cortical, medullary, and urinary oxygenation in ovine septic acute kidney injury and the response to resuscitation with norepinephrine. A renal artery flow probe and fiberoptic probes were placed in the cortex and medulla of sheep to measure tissue perfusion and oxygenation. A probe in the bladder catheter measured urinary oxygenation. Sepsis was induced in conscious sheep by infusion of Escherichia coli for 32 hours. At 24 to 30 hours of sepsis, either norepinephrine, to restore mean arterial pressure to preseptic levels or vehicle-saline was infused (8 sheep per group). Septic acute kidney injury was characterized by a reduction in blood pressure of ∼12 mm Hg, renal hyperperfusion, and oliguria. Sepsis reduced medullary perfusion (from an average of 1289 to 628 blood perfusion units), medullary oxygenation (from 32 to 16 mm Hg), and urinary oxygenation (from 36 to 24 mm Hg). Restoring blood pressure with norepinephrine further reduced medullary perfusion to an average of 331 blood perfusion units, medullary oxygenation to 8 mm Hg and urinary oxygenation to 18 mm Hg. Cortical perfusion and oxygenation were preserved. Thus, renal medullary hypoxia caused by intrarenal blood flow redistribution may contribute to the development of septic acute kidney injury, and resuscitation of blood pressure with norepinephrine exacerbates medullary hypoxia. The parallel changes in medullary and urinary oxygenation suggest that urinary oxygenation may be a useful real-time biomarker for risk of acute kidney injury.

In septic acute kidney injury, renal medullary and urinary hypoxia developed several hours before increases in currently used biomarkers. Angiotensin II transiently improved renal function without worsening medullary hypoxia. In septic acute kidney injury, angiotensin II appears to be a safe, effective therapy, and urinary PO2 may be used to detect medullary hypoxia.

Administration of clonidine during hypotensive sepsis reduced renal sympathetic nerve activity, restored vascular sensitivity to both phenylephrine and angiotensin II, and resulted in better preservation of arterial pressure. Considering these findings, a clinical trial for the use of clonidine in the treatment of persistent vasopressor-refractory hypotension in patients with septic shock would be worthwhile.

Background: Global and intra-renal perfusion and oxygenation may be affected by the choice of anaesthetic. We compared the effects of isoflurane with those of propofol and fentanyl on renal blood flow (RBF) and intra-renal perfusion and oxygenation, and assessed how these were associated with renal sympathetic nerve activity (RSNA). Methods: A renal artery flow probe and laser Doppler and oxygen-sensing probes were surgically implanted in the renal medulla and cortex in 20 Merino ewes. RSNA was measured in 12 additional ewes. We compared the effects of volatile or i.v. anaesthesia on global RBF, renal oxygen delivery (RDO 2), intra-renal perfusion, and RSNA with the non-anaesthetised state on postoperative day 3 as control reference. Results: Compared with a non-anaesthetised state, volatile anaesthesia reduced global RBF [e76 (82e68)%], RDO 2 [À76 (83e71)%], and cortical [e68 (74e54)%] and medullary [e76 (84e72)%] perfusion. I.V. anaesthesia reduced RBF [e55 (67e38)%], RDO 2 [e55 (65e44)%], and cortical [e27 (45e6)%] and medullary [e35 (48e30)%] perfusion, but to a lesser extent than volatile anaesthesia. Renal PO 2 was not influenced by anaesthesia, whilst RSNA was elevated during volatile, but not during i.v. anaesthesia. Conclusions: Volatile and i.v. general anaesthesia markedly reduced global RBF, RDO 2 , and regional kidney perfusion. These effects were greater with volatile anaesthesia, and were paralleled by an increase in RSNA. Our findings suggest a neurogenic modulatory effect of anaesthetics on renal perfusion and oxygenation.

Objectives: To examine the effects of fluid bolus therapy on systemic hemodynamics, renal blood flow, intrarenal perfusion and oxygenation, Po 2, renal function, and fluid balance in experimental early septic acute kidney injury. Design: Interventional study. Setting: Research institute. Subjects: Adult Merino ewes. Interventions: Implantation of flow probes on the pulmonary and renal arteries and laser Doppler oxygen-sensing probes in the renal cortex, medulla, and within a bladder catheter in sheep. Infusion of Escherichia coli to induce septic acute kidney injury (n = 8). After 24, 25, and 26 hours of sepsis, fluid bolus therapy (500 mL of Hartmann’s solution over 15 min) was administered. Measurements and Main Results: In conscious sheep, infusion of Escherichia coli decreased creatinine clearance and increased plasma creatinine, renal blood flow (+46% ± 6%) and cortical perfusion (+25% ± 4%), but medullary perfusion (–48% ± 5%), medullary Po 2 (–56% ± 4%), and urinary Po 2 (–54% ± 3%) decreased (p < 0.01). The first fluid bolus therapy increased blood pressure (+6% ± 1%), central venous pressure (+245% ± 65%), cardiac output (+11% ± 2%), medullary Po 2 (+280% ± 90%), urinary Po 2 (+164% ± 80%), and creatinine clearance (+120% ± 65%) at 30 minutes. The following two boluses had no beneficial effects on creatinine clearance. The improvement in medullary oxygenation dissipated following the third fluid bolus therapy. Study animals retained 69% of the total volume and 80% of sodium infused. Throughout the study, urinary Po 2 correlated significantly with medullary Po 2. Conclusions: In early experimental septic acute kidney injury, fluid bolus therapy transiently improved renal function and medullary Po 2, as also reflected by increased urinary Po 2. These initial effects of fluid bolus therapy dissipated within 4 hours, despite two additional fluid boluses, and resulted in significant volume retention.

The development of acute kidney injury (AKI) is both a significant and independent prognostic factor of mortality in patients with sepsis, but its pathophysiology remains unclear. Herein, we describe an ovine model of sepsis evoked by the administration of live Escherichia coli in which there is hypotension, peripheral vasodilatation with a large increase in cardiac output; a similar hyperdynamic state to that commonly reported in humans. Interestingly, in this sheep model of sepsis, despite an increase in global kidney blood flow, there is a progressive reduction in renal function. Although renal hyperperfusion develops, renal tissue hypoxia due to redistribution of intrarenal blood flow may contribute to the pathogenesis of septic AKI. We have, therefore, developed a novel methodology to chronically implant combination probes to monitor intrarenal tissue perfusion and oxygen tension during the development of septic AKI in conscious sheep with hyperdynamic sepsis.

Hemorrhagic shock and resuscitation induces pulmonary inflammation that leads to acute lung injury. Biliverdin, a metabolite of heme catabolism, has been shown to have potent cytoprotective, anti-inflammatory, and anti-oxidant effects. This study aimed to examine the effects of intravenous biliverdin administration on lung injury induced by hemorrhagic shock and resuscitation in rats. Biliverdin or vehicle was administered to the rats 1 h before sham or hemorrhagic shock-inducing surgery. The sham-operated rats underwent all surgical procedures except bleeding. To induce hemorrhagic shock, rats were bled to achieve a mean arterial pressure of 30 mmHg that was maintained for 60 min, followed by resuscitation with shed blood. Histopathological changes in the lungs were evaluated by histopathological scoring analysis. Inflammatory gene expression was determined by Northern blot analysis, and oxidative DNA damage was assessed by measuring 8-hydroxy-2′ deoxyguanosine levels in the lungs. Hemorrhagic shock and resuscitation resulted in prominent histopathological damage, including congestion, edema, cellular infiltration, and hemorrhage. Biliverdin administration prior to hemorrhagic shock and resuscitation significantly ameliorated these lung injuries as judged by histopathological improvement. After hemorrhagic shock and resuscitation, inflammatory gene expression of tumor necrosis factor-α and inducible nitric oxide synthase were increased by 18- and 8-fold, respectively. Inflammatory gene expression significantly decreased when biliverdin was administered prior to hemorrhagic shock and resuscitation. Moreover, after hemorrhagic shock and resuscitation, lung 8-hydroxy-2' deoxyguanosine levels in mitochondrial DNA expressed in the pulmonary interstitium increased by 1.5-fold. Biliverdin administration prior to hemorrhagic shock and resuscitation decreased mitochondrial 8-hydroxy-2' deoxyguanosine levels to almost the same level as that in the control animals. We also confirmed that biliverdin administration after hemorrhagic shock and resuscitation had protective effects on lung injury. Our findings suggest that biliverdin has a protective role, at least in part, against hemorrhagic shock and resuscitation-induced lung injury through anti-inflammatory and anti-oxidant mechanisms.

In models of experimental septic acute kidney injury in contemporary articles, acute tubular necrosis was relatively uncommon and, when present, reflected the presence of an associated low cardiac output or low renal blood flow syndrome. Tubular cell apoptosis seemed frequent in the few studies in which it was investigated. Nonspecific morphologic changes, however, were the most common histopathologic findings.