Norepinephrine to increase blood pressure in endotoxaemic pigs is associated with improved hepatic mitochondrial respiration

Norepinephrine Infusion and the Central Venous Waveform in a Porcine Model of Endotoxemic Hypotension with Resuscitation: A Large Animal Study

BACKGROUND

Venous waveform analysis is an emerging technique to estimate intravascular fluid status by fast Fourier transform deconvolution. Fluid status has been shown proportional to f0, the amplitude of the fundamental frequency of the waveform's cardiac wave upon deconvolution. Using a porcine model of distributive shock and fluid resuscitation, we sought to determine the influence of norepinephrine on f0 of the central venous waveform.

METHODS

Eight pigs were anesthetized, catheterized and treated with norepinephrine after precipitation of endotoxemic hypotension, and subsequent fluid resuscitation to mimic sepsis physiology. Hemodynamic parameters and central venous waveforms were continually transduced throughout the protocol for post-hoc analysis. Central venous waveform f0 before, during and after norepinephrine administration were determined using Fourier analysis.

RESULTS

Heart rate increased, while central venous pressure, pulmonary capillary wedge pressure and stroke volume decreased throughout norepinephrine administration (p < 0.05). Mean f0 at pre-norepinephrine, and doses 0.05, 0.10, 0.15, 0.20 and 0.25 mcg/kg/min, were 2.5, 1.4, 1.7, 1.7, 1.6 and 1.4 mmHg2, respectively (repeated measures ANOVA; p < 0.001). On post-hoc comparison to pre-norepinephrine, f0 at 0.05 mcg/kg/min was decreased (p = 0.04).

CONCLUSIONS

As the performance of f0 was previously characterized during fluid administration, these data offer novel insight into the performance of f0 during vasopressor delivery. Central venous waveform f0 is a decreased with norepinephrine, in concordance with pulmonary capillary wedge pressure. This allows contextualization of the novel, venous-derived signal f0 during vasopressor administration, a finding that must be understood prior to clinical translation.

The role of hormones in sepsis: an integrated overview with a focus on mitochondrial and immune cell dysfunction

Sepsis is a dysregulated host response to infection that results in life-threatening organ dysfunction. Virtually every body system can be affected by this syndrome to greater or lesser extents. Gene transcription and downstream pathways are either up- or downregulated, albeit with considerable fluctuation over the course of the patient's illness. This multi-system complexity contributes to a pathophysiology that remains to be fully elucidated. Consequentially, little progress has been made to date in developing new outcome-improving therapeutics. Endocrine alterations are well characterised in sepsis with variations in circulating blood levels and/or receptor resistance. However, little attention has been paid to an integrated view of how these hormonal changes impact upon the development of organ dysfunction and recovery. Here, we present a narrative review describing the impact of the altered endocrine system on mitochondrial dysfunction and immune suppression, two interlinked and key aspects of sepsis pathophysiology.

Association between acute kidney injury and norepinephrine use following cardiac surgery: a retrospective propensity score-weighted analysis

BACKGROUND

Excess exposure to norepinephrine can compromise microcirculation and organ function. We aimed to assess the association between norepinephrine exposure and acute kidney injury (AKI) and intensive care unit (ICU) mortality after cardiac surgery.

METHODS

This retrospective observational study included adult patients who underwent cardiac surgery under cardiopulmonary bypass from January 1, 2008, to December 31, 2017, at the Amiens University Hospital in France. The primary exposure variable was postoperative norepinephrine during the ICU stay and the primary endpoint was the presence of AKI. The secondary endpoint was in-ICU mortality. As the cohort was nonrandom, inverse probability weighting (IPW) derived from propensity scores was used to reduce imbalances in the pre- and intra-operative characteristics.

RESULTS

Among a population of 5053 patients, 1605 (32%) were exposed to norepinephrine following cardiac surgery. Before weighting, the prevalence of AKI was 25% and ICU mortality 10% for patients exposed to norepinephrine. Exposure to norepinephrine was estimated to be significantly associated with AKI by a factor of 1.95 (95% confidence interval, 1.63-2.34%; P < 0.001) in the IPW cohort and with in-ICU mortality by a factor of 1.54 (95% confidence interval, 1.19-1.99%; P < 0.001).

CONCLUSION

Norepinephrine was associated with AKI and in-ICU mortality following cardiac surgery. While these results discourage norepinephrine use for vasoplegic syndrome in cardiac surgery, prospective investigations are needed to substantiate findings and to suggest alternative strategies for organ protection.

Endothelial Activation and Microcirculatory Disorders in Sepsis

The vascular endothelium is crucial for the maintenance of vascular homeostasis. Moreover, in sepsis, endothelial cells can acquire new properties and actively participate in the host's response. If endothelial activation is mostly necessary and efficient in eliminating a pathogen, an exaggerated and maladaptive reaction leads to severe microcirculatory damage. The microcirculatory disorders in sepsis are well known to be associated with poor outcome. Better recognition of microcirculatory alteration is therefore essential to identify patients with the worse outcomes and to guide therapeutic interventions. In this review, we will discuss the main features of endothelial activation and dysfunction in sepsis, its assessment at the bedside, and the main advances in microcirculatory resuscitation.

Pathological Impact of the Interaction of NO and CO with Mitochondria in Critical Care Diseases

The outcome of patients with critical care diseases (CCD) such as sepsis, hemorrhagic shock, or trauma is often associated with mitochondrial dysfunction. In turn, mitochondrial dysfunction is frequently induced upon interaction with nitric oxide (NO) and carbon monoxide (CO), two gaseous messengers formed in the body by NO synthase (NOS) and heme oxygenase (HO), respectively. Both, NOS and HO are upregulated in the majority of CCD. A multitude of factors that are associated with the pathology of CCD exert a potential to interfere with mitochondrial function or the effects of the gaseous messengers. From these, four major factors can be identified that directly influence the effects of NO and CO on mitochondria and which are defined by (i) local concentration of NO and/or CO, (ii) tissue oxygenation, (iii) redox status of cells in terms of facilitating or inhibiting reactive oxygen species formation, and (iv) the degree of tissue acidosis. The combination of these four factors in specific pathological situations defines whether effects of NO and CO are beneficial or deleterious.

Skeletal Muscle and Lymphocyte Mitochondrial Dysfunctions in Septic Shock Trigger ICU-Acquired Weakness and Sepsis-Induced Immunoparalysis

Fundamental events driving the pathological processes of septic shock-induced multiorgan failure (MOF) at the cellular and subcellular levels remain debated. Emerging data implicate mitochondrial dysfunction as a critical factor in the pathogenesis of sepsis-associated MOF. If macrocirculatory and microcirculatory dysfunctions undoubtedly participate in organ dysfunction at the early stage of septic shock, an intrinsic bioenergetic failure, sometimes called "cytopathic hypoxia," perpetuates cellular dysfunction. Short-term failure of vital organs immediately threatens patient survival but long-term recovery is also severely hindered by persistent dysfunction of organs traditionally described as nonvital, such as skeletal muscle and peripheral blood mononuclear cells (PBMCs). In this review, we will stress how and why a persistent mitochondrial dysfunction in skeletal muscles and PBMC could impair survival in patients who overcome the first acute phase of their septic episode. First, muscle wasting protracts weaning from mechanical ventilation, increases the risk of mechanical ventilator-associated pneumonia, and creates a state of ICU-acquired muscle weakness, compelling the patient to bed. Second, failure of the immune system ("immunoparalysis") translates into its inability to clear infectious foci and predisposes the patient to recurrent nosocomial infections. We will finally emphasize how mitochondrial-targeted therapies could represent a realistic strategy to promote long-term recovery after sepsis.

Gentisic acid sodium salt, a phenolic compound, is superior to norepinephrine in reversing cardiovascular collapse, hepatic mitochondrial dysfunction and lactic acidemia in Pseudomonas aeruginosa septic shock in dogs

BACKGROUND

The development of lactic acidemia (LA) in septic shock (SS) is associated with an ominous prognosis. We previously showed that the mechanism of LA in SS may relate to impaired hepatic uptake of lactate, but the mechanism was not clear. Uptake of lactate by the liver occurs by a membrane-associated, pH-dependent, antiport system known as the monocarboxylate transporter. In the hepatocyte, lactate can then be metabolized by oxidative phosphorylation or converted to glucose in the cytosol. In the present study, we examined (1) whether hepatic mitochondrial dysfunction accounted for decreased uptake of lactate in a canine model of Pseudomonas aeruginosa SS, (2) whether norepinephrine (NE) treatment by increasing mean arterial pressure (MAP) could improve mitochondrial dysfunction and LA in this model, and (3) whether gentisic acid sodium salt (GSS), a novel phenolic compound, was superior to NE in these effects.

METHODS

In anesthetized/ventilated dogs, we infused the bacteria over ~10 h and measured hemodynamics in various treatment groups (see below). We then euthanized the animal and isolated the hepatic mitochondria. We measured hepatic mitochondrial oxygen consumption rates using the novel Seahorse XF24 analyzer under conditions that included: basal respiration, after the addition of adenosine- diphosphate to produce coupled respiration, and after the addition of a protonophore to produce maximal respiration.

RESULTS

We found that in the septic control group, mean arterial pressure decreased over the course of the study, and that mitochondrial dysfunction developed in which there was a reduction in maximal respiration. Whereas both NE and GSS treatments reversed the reduction in mean arterial pressure and increased maximal respiration to similar extents in respective groups, only in the GSS group was there a reduction in LA.

CONCLUSIONS

Hepatic mitochondrial dysfunction occurs in SS, but does not appear to be required for the development of LA in SS, since NE improved mitochondrial dysfunction without reversing LA. GSS, a phenolic compound restored mean arterial pressure, mitochondrial dysfunction, and LA in SS. This reduction in LA may be independent of its effect on improving hepatic mitochondrial function.

The effect of plasma from septic ICU patients on healthy rat muscle mitochondria

Background

Although sepsis-induced organ failure is a major cause of death in ICU worldwide, the associated mitochondrial dysfunction is not fully characterized and there is presently no evidence of causality. In this study, we examined whether a central factor in septic plasma could directly affect respiratory function of healthy rat muscle mitochondria.

Methods

ICU patients with severe sepsis or septic shock were recruited within 24 h of admission together with age-matched controls. Blood samples were centrifuged and immediately frozen. Two trials were performed, and mitochondrial respiration was analyzed using an Oxygraph chamber with a Clark-electrode. (1) Isolated mitochondria from the rat skeletal muscle were divided and incubated for 30 min with plasma from patients or postoperative controls (n = 10). Respiration was normalized for citrate synthase activity. (2) Permeabilized muscle fibers from rats were divided and incubated with plasma from patients or healthy controls, for 30 and 120 min, and analyzed for mitochondrial respiration (n = 10). Respiration was normalized for wet weight. Primary outcome was state 3 respiration, corresponding to the maximal respiration initiated by ADP and energy substrates (malate and pyruvate). T test was used for statistical comparison.

Results

No differences in respiratory function of the mitochondria were seen between the groups in either of the experiments. (1) State 3 respiration of isolated mitochondria were 19.9 ± 6.7 vs. 20.2 ± 8.8 nmol O₂ × U CS⁻¹ × min⁻¹ for sepsis vs. control, respectively. (2) State 3 respiration for fibers incubated with septic and control plasma were after 30 min 2.6 ± 0.3 vs. 2.4 ± 0.7 and after 120 min 2.5 ± 0.4 vs. 2.5 ± 0.6 nmol O₂ × mg × w.w⁻¹ × min⁻¹. Respiratory control ratios were good in all experiments (8.8–11.2), ensuring functioning mitochondria.

Conclusions

These findings indicate that muscle mitochondria are not directly influenced by a factor in plasma of septic patients. The effects seen in mitochondrial function in sepsis may rather be a result of intracellular processes and signaling, such as e.g., production of reactive oxygen species.

Impairment of exogenous lactate clearance in experimental hyperdynamic septic shock is not related to total liver hypoperfusion

Introduction

Although the prognostic value of persistent hyperlactatemia in septic shock is unequivocal, its physiological determinants are controversial. Particularly, the role of impaired hepatic clearance has been underestimated and is only considered relevant in patients with liver ischemia or cirrhosis. Our objectives were to establish whether endotoxemia impairs whole body net lactate clearance, and to explore a potential role for total liver hypoperfusion during the early phase of septic shock.

Methods

After anesthesia, 12 sheep were subjected to hemodynamic/perfusion monitoring including hepatic and portal catheterization, and a hepatic ultrasound flow probe. After stabilization (point A), sheep were alternatively assigned to lipopolysaccharide (LPS) (5 mcg/kg bolus followed by 4 mcg/kg/h) or sham for a three-hour study period. After 60 minutes of shock, animals were fluid resuscitated to normalize mean arterial pressure. Repeated series of measurements were performed immediately after fluid resuscitation (point B), and one (point C) and two hours later (point D). Monitoring included systemic and regional hemodynamics, blood gases and lactate measurements, and ex-vivo hepatic mitochondrial respiration at point D. Parallel exogenous lactate and sorbitol clearances were performed at points B and D. Both groups included an intravenous bolus followed by serial blood sampling to draw a curve using the least squares method.

Results

Significant hyperlactatemia was already present in LPS as compared to sham animals at point B (4.7 (3.1 to 6.7) versus 1.8 (1.5 to 3.7) mmol/L), increasing to 10.2 (7.8 to 12.3) mmol/L at point D. A significant increase in portal and hepatic lactate levels in LPS animals was also observed. No within-group difference in hepatic DO₂, VO₂ or O₂ extraction, total hepatic blood flow (point D: 915 (773 to 1,046) versus 655 (593 to 1,175) ml/min), mitochondrial respiration, liver enzymes or sorbitol clearance was found. However, there was a highly significant decrease in lactate clearance in LPS animals (point B: 46 (30 to 180) versus 1,212 (743 to 2,116) ml/min, P <0.01; point D: 113 (65 to 322) versus 944 (363 to 1,235) ml/min, P <0.01).

Conclusions

Endotoxemia induces an early and severe impairment in lactate clearance that is not related to total liver hypoperfusion.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0928-3) contains supplementary material, which is available to authorized users.

Effects of glycemic control on glucose utilization and mitochondrial respiration during resuscitated murine septic shock

Background

This study aims to test the hypothesis whether lowering glycemia improves mitochondrial function and thereby attenuates apoptotic cell death during resuscitated murine septic shock.

Methods

Immediately and 6 h after cecal ligation and puncture (CLP), mice randomly received either vehicle or the anti-diabetic drug EMD008 (100 μg · g^-1). At 15 h post CLP, mice were anesthetized, mechanically ventilated, instrumented and rendered normo- or hyperglycemic (target glycemia 100 ± 20 and 180 ± 50 mg · dL^-1, respectively) by infusing stable, non-radioactive isotope-labeled ¹³C₆-glucose. Target hemodynamics was achieved by colloid fluid resuscitation and continuous i.v. noradrenaline, and mechanical ventilation was titrated according to blood gases and pulmonary compliance measurements. Gluconeogenesis and glucose oxidation were derived from blood and expiratory glucose and ¹³CO₂ isotope enrichments, respectively; mathematical modeling allowed analyzing isotope data for glucose uptake as a function of glycemia. Postmortem liver tissue was analyzed for HO-1, AMPK, caspase-3, and Bax (western blotting) expression as well as for mitochondrial respiratory activity (high-resolution respirometry).

Results

Hyperglycemia lowered mitochondrial respiratory capacity; EMD008 treatment was associated with increased mitochondrial respiration. Hyperglycemia decreased AMPK phosphorylation, and EMD008 attenuated both this effect as well as the expression of activated caspase-3 and Bax. During hyperglycemia EMD008 increased HO-1 expression. During hyperglycemia, maximal mitochondrial oxidative phosphorylation rate was directly related to HO-1 expression, while it was unrelated to AMPK activation. According to the mathematical modeling, EMD008 increased the slope of glucose uptake plotted as a function of glycemia.

Conclusions

During resuscitated, polymicrobial, murine septic shock, glycemic control either by reducing glucose infusion rates or EMD008 improved glucose uptake and thereby liver tissue mitochondrial respiratory activity. EMD008 effects were more pronounced during hyperglycemia and coincided with attenuated markers of apoptosis. The effects of glucose control were at least in part due to the up-regulation of HO-1 and activation of AMPK.

Electronic supplementary material

The online version of this article (doi:10.1186/2197-425X-2-19) contains supplementary material, which is available to authorized users.

Mitochondrial function in sepsis

BACKGROUND

The relevance of mitochondrial dysfunction as to pathogenesis of multiple organ dysfunction and failure in sepsis is controversial. This focused review evaluates the evidence for impaired mitochondrial function in sepsis.

DESIGN

Review of original studies in experimental sepsis animal models and clinical studies on mitochondrial function in sepsis. In vitro studies solely on cells and tissues were excluded. PubMed was searched for articles published between 1964 and July 2012.

RESULTS

Data from animal experiments (rodents and pigs) and from clinical studies of septic critically ill patients and human volunteers were included. A clear pattern of sepsis-related changes in mitochondrial function is missing in all species. The wide range of sepsis models, length of experiments, presence or absence of fluid resuscitation and methods to measure mitochondrial function may contribute to the contradictory findings. A consistent finding was the high variability of mitochondrial function also in control conditions and between organs.

CONCLUSION

Mitochondrial function in sepsis is highly variable, organ specific and changes over the course of sepsis. Patients who will die from sepsis may be more affected than survivors. Nevertheless, the current data from mostly young and otherwise healthy animals does not support the view that mitochondrial dysfunction is the general denominator for multiple organ failure in severe sepsis and septic shock. Whether this is true if underlying comorbidities are present, especially in older patients, should be addressed in further studies.

Increasing mean arterial blood pressure in sepsis: effects on fluid balance, vasopressor load and renal function

Introduction

The objective of this study was to evaluate the effects of two different mean arterial blood pressure (MAP) targets on needs for resuscitation, organ dysfunction, mitochondrial respiration and inflammatory response in a long-term model of fecal peritonitis.

Methods

Twenty-four anesthetized and mechanically ventilated pigs were randomly assigned (n = 8/group) to a septic control group (septic-CG) without resuscitation until death or one of two groups with resuscitation performed after 12 hours of untreated sepsis for 48 hours, targeting MAP 50-60 mmHg (low-MAP) or 75-85 mmHg (high-MAP).

Results

MAP at the end of resuscitation was 56 ± 13 mmHg (mean ± SD) and 76 ± 17 mmHg respectively, for low-MAP and high-MAP groups. One animal each in high- and low-MAP groups, and all animals in septic-CG died (median survival time: 21.8 hours, inter-quartile range: 16.3-27.5 hours). Norepinephrine was administered to all animals of the high-MAP group (0.38 (0.21-0.56) mcg/kg/min), and to three animals of the low-MAP group (0.00 (0.00-0.25) mcg/kg/min; P = 0.009). The high-MAP group had a more positive fluid balance (3.3 ± 1.0 mL/kg/h vs. 2.3 ± 0.7 mL/kg/h; P = 0.001). Inflammatory markers, skeletal muscle ATP content and hemodynamics other than MAP did not differ between low- and high-MAP groups. The incidence of acute kidney injury (AKI) after 12 hours of untreated sepsis was, respectively for low- and high-MAP groups, 50% (4/8) and 38% (3/8), and in the end of the study 57% (4/7) and 0% (P = 0.026). In septic-CG, maximal isolated skeletal muscle mitochondrial Complex I, State 3 respiration increased from 1357 ± 149 pmol/s/mg to 1822 ± 385 pmol/s/mg, (P = 0.020). In high- and low-MAP groups, permeabilized skeletal muscle fibers Complex IV-state 3 respiration increased during resuscitation (P = 0.003).

Conclusions

The MAP targets during resuscitation did not alter the inflammatory response, nor affected skeletal muscle ATP content and mitochondrial respiration. While targeting a lower MAP was associated with increased incidence of AKI, targeting a higher MAP resulted in increased net positive fluid balance and vasopressor load during resuscitation. The long-term effects of different MAP targets need to be evaluated in further studies.

Use of inotropes and vasopressor agents in critically ill patients

Inotropes and vasopressors are biologically and clinically important compounds that originate from different pharmacological groups and act at some of the most fundamental receptor and signal transduction systems in the body. More than 20 such agents are in common clinical use, yet few reviews of their pharmacology exist outside of physiology and pharmacology textbooks. Despite widespread use in critically ill patients, understanding of the clinical effects of these drugs in pathological states is poor. The purpose of this article is to describe the pharmacology and clinical applications of inotropic and vasopressor agents in critically ill patients.

Bioenergetic failure of human peripheral blood monocytes in patients with septic shock is mediated by reduced F1Fo adenosine-5'-triphosphate synthase activity

OBJECTIVE

Increasing evidence points to the role of mitochondrial dysfunction in the pathogenesis of sepsis. Previous data indicate that mitochondrial function is affected in monocytes from septic patients, but the underlying mechanisms and the impact of these changes on the patients' outcome are unknown. We aimed to determine the mechanisms involved in mitochondrial dysfunction in peripheral blood mononuclear cells from patients with septic shock.

DESIGN

A cohort of patients with septic shock to study peripheral blood mononuclear cell mitochondrial respiration by high-resolution respirometry analyses and to compare with cells from control subjects.

SETTING

Three intensive care units and an academic research laboratory.

SUBJECTS

Twenty patients with septic shock and a control group composed of 18 postoperative patients without sepsis or shock.

INTERVENTIONS

Ex vivo measurements of mitochondrial oxygen consumption were carried out in digitonin-permeabilized peripheral blood mononuclear cells from 20 patients with septic shock taken during the first 48 hrs after intensive care unit admission as well as in peripheral blood mononuclear cells from control subjects. Clinical parameters such as hospital outcome and sepsis severity were also analyzed and the relationship between these parameters and the oxygen consumption pattern was investigated.

MEASUREMENTS AND MAIN RESULTS

We observed a significant reduction in the respiration specifically associated with adenosine-5'-triphosphate synthesis (state 3) compared with the control group (5.60 vs. 9.89 nmol O2/min/10(7) cells, respectively, p < .01). Reduction of state 3 respiration in patients with septic shock was seen with increased prevalence of organ failure (r = -0.46, p = .005). Nonsurviving patients with septic shock presented significantly lower adenosine diphosphate-stimulated respiration when compared with the control group (4.56 vs. 10.27 nmol O2/min/10(7) cells, respectively; p = .004). Finally, the presence of the functional F1Fo adenosine-5'-triphosphate synthase complex (0.51 vs. 1.00 ng oligo/mL/10(6) cells, p = .02), but not the adenine nucleotide translocator, was significantly lower in patients with septic shock compared with control cells.

CONCLUSION

Mitochondrial dysfunction is present in immune cells from patients with septic shock and is characterized as a reduced respiration associated to adenosine-5'-triphosphate synthesis. The molecular basis of this phenotype involve a reduction of F1Fo adenosine-5'-triphosphate synthase activity, which may contribute to the energetic failure found in sepsis.

Effects of catecholamines on hepatic and skeletal muscle mitochondrial respiration after prolonged exposure to faecal peritonitis in pigs

Use of norepinephrine to increase blood pressure in septic animals has been associated with increased efficiency of hepatic mitochondrial respiration. The aim of this study was to evaluate whether the same effect could be reproduced in isolated hepatic mitochondria after prolonged in vivo exposure to faecal peritonitis. Eighteen pigs were randomized to 27 h of faecal peritonitis and to a control condition (n = 9 each group). At the end, hepatic mitochondria were isolated and incubated for one hour with either norepinephrine or placebo, with and without pretreatment with the specific receptor antagonists prazosin and yohimbine. Mitochondrial state 3 and state 4 respiration were measured for respiratory chain complexes I and II, and state 3 for complex IV using high-resolution respirometry, and respiratory control ratios were calculated. Additionally, skeletal muscle mitochondrial respiration was evaluated after incubation with norepinephrine and dobutamine with and without the respective antagonists (atenolol, propranolol and phentolamine for dobutamine). Faecal peritonitis was characterized by decreasing blood pressure and stroke volume, and maintained systemic oxygen consumption. Neither faecal peritonitis nor any of the drugs or drug combinations had measurable effects on hepatic or skeletal muscle mitochondrial respiration. Norepinephrine did not improve the efficiency of complex I- and complex II-dependent isolated hepatic mitochondrial respiration [respiratory control ratio (RCR) complex I: 5.6 ± 5.3 (placebo) vs. 5.4 ± 4.6 (norepinephrine) in controls and 2.7 ± 2.1 (placebo) vs. 2.9 ± 1.5 (norepinephrine) in septic animals; RCR complex II: 3.5 ± 2.0 (placebo) vs. 3.5 ± 1.8 (norepinephrine) in controls; 2.3 ± 1.6 (placebo) vs. 2.2 ± 1.1 (norepinephrine) in septic animals]. Prolonged faecal peritonitis did not affect either hepatic or skeletal muscle mitochondrial respiration. Subsequent incubation of isolated mitochondria with norepinephrine and dobutamine did not significantly influence their respiration.

The impact of resuscitated fecal peritonitis on the expression of the hepatic bile salt transporters in a porcine model

Sepsis is often associated with cholestatic liver dysfunction caused by changes in the expression profile of hepatic bile salt transporters. However, in rodent endotoxin models, the role of ischemic hepatitis caused by liver hypoperfusion cannot be delineated. We hypothesized that hepatocytes change their expression pattern of bile salt transporters during early severe sepsis despite adequate resuscitation. Fifteen anesthetized and instrumented pigs were randomized to either fecal peritonitis (n = 8) or control (n = 7). Resuscitation was performed by hydroxyethyl starch and norepinephrine infusion. Hemodynamic parameters and markers of cholestatic and ischemic hepatic dysfunction were recorded. At baseline and after 21 h, messenger RNA (mRNA) and protein expression of bile salt transporters was determined by quantitative real-time polymerase chain reaction and immunohistochemistry, respectively, on in vivo liver biopsies. All resuscitated septic pigs developed a normotensive hyperdynamic circulation with increased portal flow. After 21 h of peritonitis, no signs of biochemical or histological cholestasis were present. Na-taurocholate cotransporting polypeptide and bile salt export pump mRNA were downregulated by 83% (P = 0.001) and 67% (P = 0.001), respectively, in comparison with controls, whereas multidrug resistance-associated protein 4 (MRP4) mRNA was upregulated by 85% (P = 0.02). Bile salt export pump and MRP2 staining were downregulated in septic pigs. During early porcine fluid-resuscitated sepsis, hepatic basolateral influx (Na-taurocholate cotransporting polypeptide) and canalicular efflux (bile salt export pump) of bile salts were downregulated without hemodynamic signs of hepatic hypoperfusion or biochemical signs of cholestasis. In parallel, the basolateral escape transport (MRP4) was markedly upregulated, possibly as an early adaptive response to counteract hepatocellular accumulation of toxic bile acids.

Critical care "normality": individualized versus protocolized care

Patients with critical illness are heterogeneous, with differing physiologic requirements over time. Goal-directed therapy in the emergency room demonstrates that protocolized care could result in improved outcomes. Subsequent studies have confirmed benefit with such a "bundle-based approach" in the emergency room and in preoperative and postoperative scenarios. However, this cannot be necessarily extrapolated to the medium-term and long-term care pathway of the critically ill patient. It is likely that the development of mitochondrial dysfunction could result in goal-directed types of approaches being detrimental. Equally, arterial pressure aims are likely to be considerably different as the patient's physiology moves toward "hibernation." The agents we utilize as sedative and pressor agents have considerable effects on immune function and the inflammatory profile, and should be considered as part of the total clinical picture. The role of gut failure in driving inflammation is considerable, and the drive to feed enterally, regardless of aspirate volume, may be detrimental in those with degrees of ileus, which is often a difficult diagnosis in the critically ill. The pathogenesis of liver dysfunction may be, at least in part, related to venous engorgement that will contribute toward portal hypertension and gut edema. This, in association with loss of the hepatosplanchnic buffer response, it is likely to contribute to venous pooling in the abdominal cavity, impaired venous return, and decreased central blood volumes. Therapies such as those used in "small-for-size syndrome" may have a role in the chronic stages of septic vascular failure.

Alterations of mitochondrial function in sepsis and critical illness

PURPOSE OF REVIEW

Septic shock is the consequence of a conflict between a pathogenic agent and the immune system of the host. This conflict induces an immune-mediated cytokine storm, with a whole-body inflammatory response often leading to multiple organ failure. Although extensively studied, the pathophysiology of sepsis-associated multiorgan failure remains unknown. One postulated mechanism is changes in mitochondrial function with an inhibition of mitochondrial respiratory chain and a decrease of oxygen utilization.

RECENT FINDINGS

Mitochondrion is a key organelle in supplying energy to the cell according to its metabolic need. Hypoxia and a number of the mediators implicated in sepsis and in the associated systemic inflammatory response have been demonstrated to directly impair mitochondrial function. A large body of evidence supports a key role of the peroxynitrite, which can react with most of the components of the electron transport chain, in the mitochondrial dysfunction.

SUMMARY

A pivotal role is suggested for mitochondrial dysfunction during the occurrence of multiorgan failure. Understanding the precise effect of sepsis on the mitochondrial function and the involvement of mitochondria in the development of multiple organ failure is fundamental. More human studies are thus necessary to clarify the mitochondrial dysfunction in the various phases of sepsis (early and late phase) before testing therapeutic strategies targeting mitochondria.

Microcirculation and mitochondria in sepsis: getting out of breath

PURPOSE OF REVIEW

To present the recent findings obtained in clinical and experimental studies examining microcirculatory alterations in sepsis, their link to mitochondrial dysfunction, and current knowledge regarding the impact of these alterations on the outcome of septic patients.

RECENT FINDINGS

Interlinked by a mutual cascade effect and driven by the host-pathogen interaction, microcirculatory and mitochondrial functions are impaired during sepsis. Mitochondrial respiration seems to evolve during the course of sepsis, demonstrating a change from reversible to irreversible inhibition. The spatiotemporal heterogeneity of microcirculatory and mitochondrial dysfunction suggests that these processes may be compartmentalized. Although a causal relationship between mitochondrial and microcirculatory dysfunction and organ failure in sepsis is supported by an increasing number of studies, adaptive processes have also emerged as part of microcirculatory and mitochondrial alterations. Treatments for improving or preserving microcirculatory, mitochondrial function, or both seem to yield a better outcome in patients.

SUMMARY

Even though there is evidence that microcirculatory and mitochondrial dysfunction plays a role in the development of sepsis-induced organ failure, their interaction and respective contribution to the disease remains poorly understood. Future research is necessary to better define such relationships in order to identify therapeutic targets and refine treatment strategies.

Comparison of cardiac, hepatic, and renal effects of arginine vasopressin and noradrenaline during porcine fecal peritonitis: a randomized controlled trial

Introduction

Infusing arginine vasopressin (AVP) in vasodilatory shock usually decreases cardiac output and thus systemic oxygen transport. It is still a matter of debate whether this vasoconstriction impedes visceral organ blood flow and thereby causes organ dysfunction and injury. Therefore, we tested the hypothesis whether low-dose AVP is safe with respect to liver, kidney, and heart function and organ injury during resuscitated septic shock.

Methods

After intraperitoneal inoculation of autologous feces, 24 anesthetized, mechanically ventilated, and instrumented pigs were randomly assigned to noradrenaline alone (increments of 0.05 μg/kg/min until maximal heart rate of 160 beats/min; n = 12) or AVP (1 to 5 ng/kg/min; supplemented by noradrenaline if the maximal AVP dosage failed to maintain mean blood pressure; n = 12) to treat sepsis-associated hypotension. Parameters of systemic and regional hemodynamics (ultrasound flow probes on the portal vein and hepatic artery), oxygen transport, metabolism (endogenous glucose production and whole body glucose oxidation derived from blood glucose isotope and expiratory ¹³CO₂/¹²CO₂ enrichment during 1,2,3,4,5,6-¹³C₆-glucose infusion), visceral organ function (blood transaminase activities, bilirubin and creatinine concentrations, creatinine clearance, fractional Na⁺ excretion), nitric oxide (exhaled NO and blood nitrate + nitrite levels) and cytokine production (interleukin-6 and tumor necrosis factor-α blood levels), and myocardial function (left ventricular dp/dt_max and dp/dt_min) and injury (troponin I blood levels) were measured before and 12, 18, and 24 hours after peritonitis induction. Immediate post mortem liver and kidney biopsies were analysed for histomorphology (hematoxylin eosin staining) and apoptosis (TUNEL staining).

Results

AVP decreased heart rate and cardiac output without otherwise affecting heart function and significantly decreased troponin I blood levels. AVP increased the rate of direct, aerobic glucose oxidation and reduced hyperlactatemia, which coincided with less severe kidney dysfunction and liver injury, attenuated systemic inflammation, and decreased kidney tubular apoptosis.

Conclusions

During well-resuscitated septic shock low-dose AVP appears to be safe with respect to myocardial function and heart injury and reduces kidney and liver damage. It remains to be elucidated whether this is due to the treatment per se and/or to the decreased exogenous catecholamine requirements.

Increasing arterial blood pressure with norepinephrine does not improve microcirculatory blood flow: a prospective study

Introduction

Our goal was to assess the effects of titration of a norepinephrine infusion to increasing levels of mean arterial pressure (MAP) on sublingual microcirculation.

Methods

Twenty septic shock patients were prospectively studied in two teaching intensive care units. The patients were mechanically ventilated and required norepinephrine to maintain a mean arterial pressure (MAP) of 65 mmHg. We measured systemic hemodynamics, oxygen transport and consumption (DO₂ and VO₂), lactate, albumin-corrected anion gap, and gastric intramucosal-arterial PCO₂ difference (ΔPCO₂). Sublingual microcirculation was evaluated by sidestream darkfield (SDF) imaging. After basal measurements at a MAP of 65 mmHg, norepinephrine was titrated to reach a MAP of 75 mmHg, and then to 85 mmHg. Data were analyzed using repeated measurements ANOVA and Dunnett test. Linear trends between the different variables and increasing levels of MAP were calculated.

Results

Increasing doses of norepinephrine reached the target values of MAP. The cardiac index, pulmonary pressures, systemic vascular resistance, and left and right ventricular stroke work indexes increased as norepinephrine infusion was augmented. Heart rate, DO₂ and VO₂, lactate, albumin-corrected anion gap, and ΔPCO₂ remained unchanged. There were no changes in sublingual capillary microvascular flow index (2.1 ± 0.7, 2.2 ± 0.7, 2.0 ± 0.8) and the percent of perfused capillaries (72 ± 26, 71 ± 27, 67 ± 32%) for MAP values of 65, 75, and 85 mmHg, respectively. There was, however, a trend to decreased capillary perfused density (18 ± 10,17 ± 10,14 ± 2 vessels/mm², respectively, ANOVA P = 0.09, linear trend P = 0.045). In addition, the changes of perfused capillary density at increasing MAP were inversely correlated with the basal perfused capillary density (R² = 0.95, P < 0.0001).

Conclusions

Patients with septic shock showed severe sublingual microcirculatory alterations that failed to improve with the increases in MAP with norepinephrine. Nevertheless, there was a considerable interindividual variation. Our results suggest that the increase in MAP above 65 mmHg is not an adequate approach to improve microcirculatory perfusion and might be harmful in some patients.

Sepsis therapy: what's the best for the mitochondria?

It is suspected that mitochondrial dysfunction is a major cause of organ failure in sepsis and septic shock. A study presented in this issue of Critical Care revealed that liver mitochondria from pigs treated with norepinephrine during endotoxaemia exhibit greater in vitro respiratory activity. The investigators provide an elegant demonstration of how therapeutic interventions in sepsis may profoundly influence mitochondrial respiration, but many aspects of mitochondrial function in sepsis remain to be clarified.