Bench-to-bedside review: microvascular dysfunction in sepsis--hemodynamics, oxygen transport, and nitric oxide

Moderate exercise promotes human RBC-NOS activity, NO production and deformability through Akt kinase pathway

Background

Nitric oxide (NO) produced by nitric oxide synthase (NOS) in human red blood cells (RBCs) was shown to depend on shear stress and to exhibit important biological functions, such as inhibition of platelet activation. In the present study we hypothesized that exercise-induced shear stress stimulates RBC-NOS activation pathways, NO signaling, and deformability of human RBCs.

Methods/Findings

Fifteen male subjects conducted an exercise test with venous blood sampling before and after running on a treadmill for 1 hour. Immunohistochemical staining as well as western blot analysis were used to determine phosphorylation and thus activation of Akt kinase and RBC-NOS as well as accumulation of cyclic guanylyl monophosphate (cGMP) induced by the intervention. The data revealed that activation of NO upstream located enzyme Akt kinase was significantly increased after the test. Phosphorylation of RBC-NOSSer¹¹⁷⁷ was also significantly increased after exercise, indicating activation of RBC-NOS through Akt kinase. Total detectable RBC-NOS content and phosphorylation of RBC-NOSThr⁴⁹⁵ were not affected by the intervention. NO production by RBCs, determined by DAF fluorometry, and RBC deformability, measured via laser-assisted-optical-rotational red cell analyzer, were also significantly increased after the exercise test. The content of the NO downstream signaling molecule cGMP increased after the test. Pharmacological inhibition of phosphatidylinositol 3 (PI3)-kinase/Akt kinase pathway led to a decrease in RBC-NOS activation, NO production and RBC deformability.

Conclusion/Significance

This human in vivo study first-time provides strong evidence that exercise-induced shear stress stimuli activate RBC-NOS via the PI3-kinase/Akt kinase pathway. Actively RBC-NOS-produced NO in human RBCs is critical to maintain RBC deformability. Our data gain insights into human RBC-NOS regulation by exercise and, therefore, will stimulate new therapeutic exercise-based approaches for patients with microvascular disorders.

Normal-range blood lactate concentration in septic shock is prognostic and predictive

We hypothesized that lactate levels even within the normal range are prognostic and that low lactate levels predict a beneficial response to vasopressin infusion in septic shock. We conducted a retrospective analysis using the Vasopressin in Septic Shock Trial (VASST) as a derivation cohort (n = 665), then validated using another single-center septic shock cohort, St Paul's Hospital (SPH) cohort (n = 469). Lactate levels were divided into quartiles. The primary outcome variable was 28-day mortality in both cohorts. We used receiver operating characteristic (ROC) curve analysis to compare the prognostic value of lactate concentrations versus Acute Physiology and Chronic Health Evaluation II scores. We then explored whether lactate concentrations might predict beneficial response to vasopressin compared with noradrenaline in VASST. Normal lactate range is less than 2.3 mmol/L. At enrollment, patients in the second quartile (1.4 < lactate < 2.3 mmol/L) had significantly increased mortality and organ dysfunction compared with patients who had lactate ≤ 1.4 mmol/L (quartile 1) (P < 0.0001). Quartile 2 outcomes were as severe as quartile 3 (2.3 ≤ lactate < 4.4 mmol/L) outcomes. Baseline lactate values (ar ea under the ROC curve = 0.63, 0.66; VASST, SPH) were as good as Acute Physiology and Chronic Health Evaluation II scores (area under the ROC curve = 0.66, 0.73; VASST, SPH) as prognostic indicators of 28-day mortality. Lactate concentrations of 1.4 mmol/L or less predicted a beneficial response in those randomized to vasopressin compared with noradrenaline in VASST (P < 0.05). Lactate concentrations within the "normal" range can be a useful prognostic indicator in septic shock. Furthermore, patients whose lactate level is less than or equal to 1.4 mmol/L may benefit from vasopressin infusion.

Quantitative assessment of the microcirculation in healthy volunteers and in patients with septic shock

OBJECTIVE

The microcirculation of septic patients has been characterized only semiquantitatively. Our goal was to characterize the sublingual microcirculation in healthy volunteers and patients with septic shock quantitatively. Our hypotheses were that 1) hyperdynamic blood flow is absent in septic shock; 2) nonsurvivors show more severe alterations than survivors; and 3) quantitative and semiquantitative microcirculatory parameters have a similar performance.

DESIGN

Prospective, observational study.

SETTING

Teaching intensive care unit in a university-affiliated hospital.

SUBJECTS

Twenty-five normal volunteers and 25 patients with septic shock.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The sublingual microcirculation was evaluated by means of sidestream dark field imaging. Semiquantitative and quantitative microcirculatory parameters were determined through the use of applied software. Septic patients showed decreased perfused capillary density (13.2±4.4 mm/mm² vs. 16.6±1.6 mm/mm²), proportion of perfused capillaries (0.78±0.23 vs. 1.00±0.01), microvascular flow index (2.15±0.61 vs. 2.97±0.03), and red blood cell velocity (830±183 µm/sec vs. 1332±187 µm/sec) along with increased heterogeneity flow index (1.64±1.14 vs. 0.25±0.19) compared with controls. No differences were found in total capillary density (16.9±2.2 vs. 16.7±1.6). Only 4% of capillaries analyzed showed red blood cell velocities>75th percentile of the velocities of the normal volunteers. The nonsurvivors exhibited decreased perfused capillary density, proportion of perfused capillaries, and microvascular flow index along with increased heterogeneity flow index compared with the survivors. The correlations between microvascular flow index and proportion of perfused capillaries, total capillary density and number of grid-crossing capillaries, and red blood cell velocities and microvascular flow index gave high R values (0.92, 0.65, and 0.52, respectively; p<.0001 for all).

CONCLUSIONS

The main characteristics of sublingual microcirculation in patients with septic shock are hypoperfusion and increased flow heterogeneity. Hyperdynamic microvascular blood flow was not found. Nonsurvivors showed more severe alterations than survivors. Quantitative and semiquantitative microcirculatory variables displayed similar behaviors.

Oxygen blood transport during experimental sepsis: effect of hypothermia*

OBJECTIVES

The aim of this study was to highlight the link between induced hypothermia and increased survival duration as observed in the septic model developed by the laboratory. To reach this objective, survival duration and blood oxygen transport capacity were measured at two temperatures-38 °C (induced normothermia) and 34 °C (induced hypothermia)-in septic rats.

DESIGN

A prospective, randomized, experimental animal study.

SETTING

University laboratory.

SUBJECTS

Forty-four male Sprague-Dawley rats (median weight, 232 g; range, 200-303 g).

INTERVENTIONS

After anesthesia and obtention of the temperature goal, sepsis was induced by cecal ligation and perforation.

MEASUREMENTS AND MAIN RESULTS

Sepsis induction led to death 5 hrs 11 mins ± 0 hr 36 mins after cecal ligation and perforation at 38 °C. At this temperature, significant changes in blood oxygen transport capacity were observed in septic rats; Hill number decreased from 2.36 ± 0.10 (baseline group) to 1.99 ± 0.17 (septic group) (p = .008) and oxygen-hemoglobin affinity decreased and P50 increased from 41.40 ± 2.4 Torr (baseline group) to 51.17 ± 14.07 Torr (septic group). Furthermore, in normothermia, a significant increase of creatinine and albumin plasmatic concentrations was observed 4 hrs after sepsis induction. Survival duration was significantly higher in induced hypothermia (7 hrs 22 mins ± 0 hr 12 mins at 34 °C) compared with induced normothermia. At 34 °C, no significant change in blood oxygen transport capacity was observed. In the same way, exposure to 34 °C induced no change in measured plasmatic parameters except an increase in albumin concentration in septic rats compared with the baseline group.

CONCLUSIONS

Sepsis led to a decrease of both oxygen hemoglobin cooperativity and affinity at 38 °C. By contrast, no change in these parameters was observed when sepsis was induced during hypothermia. Taken together, these results could be interpreted in normothermia septic rats as an adaptive mechanism that could enhance the release of oxygen at the tissue level. Hypothermia by slowing down sepsis evolution could increase survival duration.

Pharmacological targets in the renal peritubular microenvironment: implications for therapy for sepsis-induced acute kidney injury

One of the most frequent and serious complications to develop in septic patients is acute kidney injury (AKI), a disorder characterized by a rapid failure of the kidneys to adequately filter the blood, regulate ion and water balance, and generate urine. AKI greatly worsens the already poor prognosis of sepsis and increases cost of care. To date, therapies have been mostly supportive; consequently there has been little change in the mortality rates over the last decade. This is due, at least in part, to the delay in establishing clinical evidence of an infection and the associated presence of the systemic inflammatory response syndrome and thus, a delay in initiating therapy. A second reason is a lack of understanding regarding the mechanisms leading to renal injury, which has hindered the development of more targeted therapies. In this review, we summarize recent studies, which have examined the development of renal injury during sepsis and propose how changes in the peritubular capillary microenvironment lead to and then perpetuate microcirculatory failure and tubular epithelial cell injury. We also discuss a number of potential therapeutic targets in the renal peritubular microenvironment, which may prevent or lessen injury and/or promote recovery.

Erythropoietin improves skeletal muscle microcirculation through the activation of eNOS in a mouse sepsis model

BACKGROUND

Sepsis and septic shock remain the major causes of morbidity and mortality in intensive care units. One mechanism that leads to organ failure is microcirculatory dysfunction. Erythropoietin (EPO) is a glycoprotein produced by the kidney that primarily regulates erythropoiesis, but it also can exert hemodynamic, anti-inflammatory, and tissue protective effects. We previously reported that administration of EPO to septic mice improves mouse skeletal muscle capillary perfusion and tissue bioenergetics. The objective of this study was to explore the potential mechanism(s) involved.

METHODS

Sepsis was induced by intraperitoneal (i.p.) injection of a fecal suspension (12.5 g in 0.5 saline/mouse) in mice. At 18 hours after sepsis induction, a single dose of rHuEPO (400 U/kg) was given to the mice. Mouse capillary perfusion density and nicotinamide adenine dinucleotide (NADH) fluorescence in skeletal muscle were observed using intravital microscopy. Endothelial cells derived from the skeletal muscle were treated with rHuEPO (5 U/mL) and endothelial nitric oxide synthase (eNOS) activation and activity were assessed.

RESULTS

Septic mice had decreased capillary perfusion density and increased tissue NADH fluorescence indicating impaired tissue bioenergetics, whereas animals treated with rHuEPO demonstrated an improvement in capillary perfusion density and decreased skeletal muscle NADH fluorescence. The beneficial effect of rHuEPO did not occur in septic mice treated with l-NAME (an NOS inhibitor, 20 mg/kg) or mice genetically deficient in eNOS. Treatment of endothelial cells with rHuEPO resulted in activation of eNOS as indicated by increased eNOS phosphorylation and NO production.

CONCLUSIONS

Our results suggest that eNOS plays an important role in mediating the beneficial effect of rHuEPO on microcirculation in this septic mouse model.

Physiopathology of shock

Shock syndromes are of three types: cardiogenic, hemorrhagic and inflammatory. Hemorrhagic shock has its initial deranged macro-hemodynamic variables in the blood volume and venous return. In cardiogenic shock there is a primary pump failure that has cardiac output/mean arterial pressure as initial deranged variables. In Inflammatory Shock it is the microcirculation that is mainly affected, while the initial deranged macrocirculation variable is the total peripheral resistance hit by systemic inflammatory response.

Arteriolar reactivity in lymphocyte-deficient mice

Mounting evidence suggests that lymphocytes have the capacity to contribute to the regulation of systemic circulatory control. We postulated that T and natural killer (NK) cells could modify basal microvascular activity under physiologically normal conditions. In situ intravital microscopy of mouse cremaster vasculature was used to evaluate arteriolar reactivities to the vasoconstrictors angiotensin II (ANG II) and phenylephrine (Phe) and the vasodilators acetylcholine (ACh) and adenosine (Ado) in normal [+/+; wild type (WT)] and genetically immunodeficient (T−B−NK+ or T−B−\NK−) C57BL/6 and BALB/c mice, strain backgrounds with differentially polarized T cell cytokine production. Immunodeficient mice tended to have smaller baseline and maximal diameters of third-order cremaster arterioles than their congenic WT partners. In C57BL/6, baseline diameters were similar in T-B− mice without or with NK cells; in BALB/c, baseline diameters were larger in T-B-NK− mice than in T−B−NK+ mice. Thus, at baseline, lymphocytes tended to promote vasodilation, except BALB/c NK cells, which mediated mild vasoconstriction. The presence of NK cells suppressed dilations to Ado in both strains, to ACh in the C57BL/6 strain, and dilatory responses to ANG II in C57BL/6 and to Phe in BALB/c. In the BALB/c strain, the presence of T and B cells promoted vasodilatory responses to Ado, attenuated dilations to low ACh concentrations, and exaggerated dilation and constriction responses to ANG II. Thus, under agonist challenge, NK cells generally promote constriction, whereas influences of T and B cells depend upon the stimulus. Therefore, lymphocytes or their products have physiological influences on microvascular arteriolar reactivity.

Sepsis-induced tissue hypoperfusion

The understanding of sepsis is continuously evolving. An overview of sepsis-induced tissue hypoperfusion has been provided herein. It is of critical importance that the clinician understands the pathophysiology of this emergent condition and is able to synthesize the available data in a rapid fashion so that tissue hypoperfusion is readily detected. Once detected, aggressive and endpoint-directed resuscitation should be implemented to reverse the hypoperfusion and to prevent further deterioration, organ dysfunction, and death.

Critical role for oxidative stress, platelets, and coagulation in capillary blood flow impairment in sepsis

Sepsis is a complex multifaceted response to a local infectious insult. One important facet is the circulatory system dysfunction, which includes capillary bed plugging. This review addresses the mechanisms of capillary plugging and highlights our recent discoveries on the roles of NO, ROS, and activated coagulation in platelet adhesion and blood flow stoppage in septic mouse capillaries. We show that sepsis increases platelet adhesion, fibrin deposition and flow stoppage in capillaries, and that NADPH oxidase-derived ROS, rather than NO, play a detrimental role in this adhesion/stoppage. P-selectin and activated coagulation are required for adhesion/stoppage. Further, platelet adhesion in capillaries (i) strongly predicts capillary flow stoppage, and (ii) may explain why severe sepsis is associated with a drop in platelet count in systemic blood. Significantly, we also show that a single bolus of the antioxidant ascorbate (injected intravenously at clinically relevant dose of 10 mg/kg) inhibits adhesion/stoppage. Our data suggest that eNOS-derived NO at the platelet-endothelial interface is anti-adhesive and required for the inhibitory effect of ascorbate. Because of the critical role of ROS in capillary plugging, ascorbate bolus administration may be beneficial to septic patients whose survival depends on restoring microvascular perfusion.

Spectral-profile-based algorithm for hemoglobin oxygen saturation determination from diffuse reflectance spectra

Variations of hemoglobin (Hb) oxygenation in tissue provide important indications concerning the physiological conditions of tissue, and the data related to these variations are of intense interest in medical research as well as in clinical care. In this study, we derived a new algorithm to estimate Hb oxygenation from diffuse reflectance spectra. The algorithm was developed based on the unique spectral profile differences between the extinction coefficient spectra of oxy-Hb and deoxy-Hb within the visible wavelength region. Using differential wavelet transformation, these differences were quantified using the locations of certain spectral features, and, then, they were related to the oxygenation saturation level of Hb. The applicability of the algorithm was evaluated using a set of diffuse reflectance spectra produced by a Monte Carlo simulation model of photon migration and by tissue phantoms experimentally. The algorithm was further applied to the diffuse reflectance spectra acquired from in vivo experiments to demonstrate its clinical utility. The validation and evaluation results concluded that the algorithm is applicable to various tissue types (i.e., scattering properties) and can be easily used in conjunction with a diverse range of probe geometries for real-time monitoring of Hb oxygenation.

Circulating endothelial and endothelial progenitor cells in patients with severe sepsis

Elevated circulating endothelial cell (CEC) and circulating endothelial progenitor cell (CEPC) counts may indicate vascular damage and disease status, but data on these cell populations in patients with severe sepsis are limited. This study compared CEC and CEPC counts in patients with and without severe sepsis following intensive care unit (ICU) admission. Venous blood samples were collected within 24 h, 48-72 h, and 120-144 h. Baseline demographics, 28-day mortality, ICU and hospital days, and Sequential Organ Failure Assessment (SOFA) scores were recorded. Patients with (n=18) and without (n=28) severe sepsis were balanced for mean age (63.7 and 61.3 years, respectively) and gender. There were no differences in 28-day mortality, ICU days, or hospital days. Baseline SOFA scores were higher in the sepsis group. At 48-72 h, patients with severe sepsis had significantly higher median CEC counts (51.5 vs. 28.0 cells/4 ml of blood, P=0.02). CEC values for all ICU patients were significantly (P<0.05) higher than in healthy volunteers. CEPC counts in both cohorts ranged from 0 to >21 colonies/4 ml blood (mean=1.13±2.25; median=0) without significant differences at any time point. This study demonstrates the ability to quantify CECs and CEPCs using consensus methodology. Understanding the relationship between CEC/CEPC counts and outcomes may provide insight into the mechanisms of endothelial cell changes in severe sepsis.

Adrenergic support in septic shock: a critical review

The definition of septic shock includes sepsis-induced hypotension despite adequate fluid resuscitation, along with the presence of organ perfusion abnormalities, and ultimately cell dysfunction. To restore adequate organ perfusion and cell homeostasis, cardiac output should be restored with volume infusion plus vasopressor agents as indicated. Appropriate arterial pressure for each individual patient and proper arterial oxygen content are key elements to restoring perfusion. Tissue perfusion can be monitored by markers of organ and mitochondrial function, namely urine output, level of consciousness, peripheral skin perfusion, central or mixed venous oxygen saturation, and lactate. The hemodynamic effects of the different vasopressor agents depend on the relative affinity to adrenergic receptors. Those with predominant alpha-agonist activity produce more vasoconstriction (inoconstrictors) while those with predominant beta-agonist stimulation increase cardiac performance (inodilators). The debate about whether one vasopressor agent is superior to another is still ongoing. The Surviving Sepsis Campaign guidelines refer to either norepinephrine or dopamine as the first-choice vasopressor agent to correct hypotension in septic shock. However, recent data from observational and controlled trials have challenged these recommendations concerning different adrenergic agents. As a result, our view on the prescription of vasopressors has changed from a probably oversimplified "one-size-fits-all" approach to a multimodal approach in vasopressor selection.

Red cell changes during storage

Red blood cells can be stored in liquid suspension in approved additive solutions for periods up to 6 weeks with 0.4% hemolysis, 84% 24-h in vivo recovery, and normal subsequent survival of the cells that persist in the circulation for at least 24h. However, while they are stored, the red cells undergo changes including the loss of adenosine triphosphate, diphosphoglycerate, and potassium, oxidative injury to proteins, lipids, and carbohydrates, loss of shape and membrane, increased adhesiveness, decreased flexibility, reduced capillary flow, and decreased oxygen delivery. Deaths have been reported related to the high potassium and lysophospholipids, but are rare.

[Microcirculatory alterations in critically ill patients: pathophysiology, monitoring and treatments]

Microcirculation represents a complex system devoted to provide optimal tissue substrates and oxygen. Therefore, pathophysiological and technological knowledge developments tailored for capillary circulation analysis should generate major advances for critically ill patients' management. In the future, microcirculatory monitoring in several critical care situations will allow recognition of macro-microcirculatory decoupling, and, hopefully, it will promote the use of treatments aimed at preserving tissue oxygenation and substrate delivery.

The microcirculation as a diagnostic and therapeutic target in sepsis

The microcirculation is defined as the smallest vessels where gas and nutrient exchange with tissues takes place. One of its primary functions is to ensure adequate oxygen delivery to meet the oxygen demands of tissue cells. Previous data from clinical and experimental studies and the recent development of new imaging modalities, such as Orthogonal Polarization Spectral videomicroscopy and Sidestream Dark Field imaging, have helped to identify the crucial role that microcirculation plays in sepsis. If not corrected, microcirculatory dysfunction can lead to respiratory distress in tissue cells and subsequent organ failure, even in the absence of global hemodynamic deficiency. In the present review, we will address past and recent developments regarding the role of the microcirculation as an important target in the pathogenesis of sepsis and its progression to multiple organ failure. Accordingly, we identify the microcirculation as an important diagnostic and therapeutic target for treatment in sepsis.

Erythropoietin enhances oxygenation in critically perfused tissue through modulation of nitric oxide synthase

The aim of this study was to investigate the effect of human recombinant erythropoietin (EPO) on the microcirculation and oxygenation of critically ischemic tissue and to elucidate the role of endothelial NO synthase in EPO-mediated tissue protection. Island flaps were dissected from the back skin of anesthetized male Syrian golden hamsters including a critically ischemic, hypoxic area that was perfused via a collateralized vasculature. Before ischemia, animals received an injection of epoetin beta at a dose of 5,000 U/kg body weight with (n = 7) or without (n = 7) blocking NO synthase by 30 mg/kg body weight L-NAME (Nomega-nitro-L-arginine methyl ester hydrochloride). Saline-treated animals served as control (n = 7). Ischemic tissue damage was characterized by severe hypoperfusion and inflammation, hypoxia, and accumulation of apoptotic cell nuclei after 5 h of collateralization. Erythropoietin pretreatment increased arteriolar and venular blood flow by 33% and 37%, respectively (P < 0.05), and attenuated leukocytic inflammation by approximately 75% (P < 0.05). Furthermore, partial tissue oxygen tension in the ischemic tissue increased from 8.2 to 15.8 mmHg (P < 0.05), which was paralleled by a 21% increased density of patent capillaries (P < 0.05) and a 50% reduced apoptotic cell count (P < 0.05). The improved microcirculation and oxygenation were associated with a 2.2-fold (P < 0.05) increase of endothelial NO synthase protein expression. Of interest, L-NAME completely abolished all the beneficial effects of EPO pretreatment. Our study demonstrates that, in critically ischemic and hypoxic collateralized tissue, EPO pretreatment improves tissue perfusion and oxygenation in vivo. This effect may be attributed to NO-dependent vasodilative effects and anti-inflammatory actions on the altered vascular endothelium.

Transfusion of stored red blood cells adhere in the rat microvasculature

BACKGROUND

Ex vivo storage of red blood cells (RBCS) for transfusions is associated with a "storage lesion," which decreases RBC deformability and increases RBC adhesiveness to vascular endothelium. This may impair microcirculatory flow with deleterious effects on oxygen delivery after transfusion. Previous studies have shown that human RBCs adhere to endothelial monolayers in vitro with prolonged storage and is reduced by prestorage leukoreduction (LR). The objective of this study was to determine whether duration of RBC storage and LR influence RBC adhesion in vivo in capillaries.

STUDY DESIGN AND METHODS

Rat RBCs were collected and stored in CPDA-1 under standard blood bank conditions. Three RBC products were compared: 1) fresh RBCs, less than 24 hours of storage (n = 6); 2) non leukoreduced (NLR) RBCs stored for 7 days (n = 6); and 3) prestorage LR RBCs stored for 7 days (n = 6). RBCs were labeled with fluorescein isothiocyanate (FITC) 24 hours before transfusion and reinjected in an isovolemic manner into healthy rats. The FITC-labeled RBCs were visualized in the extensor digitorum longus muscle using intravital video microscopy (20 x magnification). The number of RBCs adherent in capillaries was counted 1 hour after transfusion in 10 random fields and the median values were compared with one-way analysis of variance.

RESULTS

Stored RBCs showed increased levels of adherence in capillaries compared to their fresh counterparts (p < 0.05). Prestorage LR decreased RBC adherence to levels equivalent to those of fresh RBCs (p < 0.05 for stored LR vs. stored NLR).

CONCLUSION

Rat RBCs stored under conditions that closely mimicked clinical transfusion adhere in capillaries. The decreased RBC adherence with LR suggest a direct effect of white blood cells or their byproducts on RBC deformability and/or adhesiveness to microvascular endothelium. Further study will examine the mechanism of adherence and the impact it has on microcirculatory flow and oxygen delivery in the critically ill host.

[Sepsis as a cause of intrahepatic cholestasis]

INTRODUCTION

The causes of intrahepatic cholestasis include cholestatic viral hepatitis, primary biliary cirrhosis, benign recurrent cholestasis, primary sclerosing cholangitis and sepsis. During sepsis, proinflammatory cytokines and nitric oxide cause cholestasis by impairing hepatocellular and ductal bile formation.

CASE OUTLINE

We report a 48-year-old woman who was admitted to hospital due to malaise, jaundice, fever and pain in the neck. Physical examination revealed jaundice, tachycardia (pulse rate was 120/min), hypotension 90/60 mm Hg. Laboratory findings showed normocytic normochromic anaemia, inflammatory syndrome and abnormal liver function tests indicating cholestasis and hepatocellular necrosis. Abdominal ultrasonography detected hepatosplenomegaly. Chest computed tomography showed bronchopneumonic infiltrates. Percutaneous liver biopsy was performed using a Menghini needle of 1.4 mm. Pathohystological analysis of the liver tissue confirmed reactive, intrahepatic cholestasis. Blood cultures isolated Staphylococcus aureus. After the diagnosis was established the treatment with broad-spectrum antibiotics was carried out, resulting in the improvement of general condition of the patient, regression of inflammatory syndrome, disappearance of cholestasis and regression of pulmonary infiltrates. Abdominal ultrasonography after antibiotic treatment did not show hepatosplenomegaly.

CONCLUSION

Concerning patients with cholestasis of uncertain origin, we should always think of sepsis as a possible cause in order to start antibiotic treatment in time.

Invasive amebiasis: a microcirculatory disorder?

The two current models of invasive amebiasis both hold that direct contact of toxic molecules and amebas with tissue produces the necrotic areas characteristic of this disorder. Whereas one model characterizes these toxic molecules as amebic products (e.g., lectins, amebapores, cysteine proteinases and other proteolytic enzymes), the other describes them as products of the inflammatory response (e.g., cytokines, nitric oxide, reactive oxygen intermediates and cytotoxic granules). Both these models can account for necrotic areas with many amebas present and with acute inflammation, but not those with few or no amebas present or with scarce inflammation. A new model poses that an inadequate immune response leads to a continuous and prolonged activation of endothelial cells (ECs) by amebas, amebic molecules and cytokines, which triggers the mechanisms leading to necrosis. Other toxic molecules later contribute to EC activation: nitric oxide, reactive oxygen intermediates, the activated complement and proteases. Hyperactivated endothelial cells continuously express adhesion molecules (e.g., ICAM-1 and E-selectin), pro-coagulant molecules (e.g., tissue factor, von Willebrand factor, and the plasminogen activator inhibitor), resulting in ever greater inflammation and thrombosis, which eventually reduces or blocks blood flow in some vessels and starves certain tissue areas of an adequate oxygen and nutrient supply. When necrotic areas first develop, they are surrounded by inflammatory cells due to the acute inflammation at this stage. However, these cells are starved of oxygen and essential nutrients by the same microcirculatory dysfunction. The increasing concentration of nitric oxide during amebiasis eventually has an anti-inflammatory and vasodilating effect, creating a new mechanism for the microcirculatory dysfunction. This local microcirculatory dysfunction can explain necrotic areas in the presence of many, few, or no amebas, with abundant or scarce inflammation.

Exhaled nitric oxide in the diagnosis and management of asthma: clinical implications

Exhaled nitric oxide (eNO) used as an aid to the diagnosis and management of lung disease is receiving attention from pulmonary researchers and clinicians alike because it offers a noninvasive means to directly monitor airway inflammation. Research evidence suggests that eNO levels significantly increase in individuals with asthma before diagnosis, decrease with inhaled corticosteroid administration, and correlate with the number of eosinophils in induced sputum. These observations have been used to support an association between eNO levels and airway inflammation. This review presents an update on current opportunities regarding use of eNO in patient care, and more specifically on its potential usage for asthma diagnosis and monitoring. The review will also discuss factors that may complicate use of eNO as a diagnostic tool, including changes in disease severity, symptom response, and technical measurement issues. Regardless of the rapid, convenient, and noninvasive nature of this test, additional well-designed, long-term longitudinal studies are necessary to fully evaluate the clinical utility of eNO in asthma management.

Nitric oxide donors in sepsis: a systematic review of clinical and in vivo preclinical data

An abundant literature in the field of sepsis focuses on the role of NO. Inhibiting NO synthesis corrects certain hemodynamic parameters of septic shock but failed to improve outcome in patients. Conversely, administration of NO donors lowers blood pressure but restores microcirculatory flow in patients with sepsis. We undertook a systematic review of the literature to comprehensively summarize the results of studies exploring the effects of systemic NO donors in sepsis. We included both clinical and preclinical data. We described the details surrounding NO donor administration, and the results obtained in each study were regrouped in broad categories. In the case of animal research, we limited our data collection to in vivo protocols and described the sepsis model. Finally, we critically appraised all the studies included in the review. Overall, the reviewed publications aimed for physiopathological description rather than clinical relevance and did not meet the required criteria for extrapolation to clinical practice. With this reserve, NO donors usually improved the outcomes measured (e.g., mortality, pulmonary hypertension, tissue/organ perfusion, etc.) but also lowered blood pressure. We conclude that our findings warrant further animal experimentation designed to maximize clinical relevance.

Early increases in microcirculatory perfusion during protocol-directed resuscitation are associated with reduced multi-organ failure at 24 h in patients with sepsis

OBJECTIVE

Sepsis mortality is closely linked to multi-organ failure, and impaired microcirculatory blood flow is thought to be pivotal in the pathogenesis of sepsis-induced organ failure. We hypothesized that changes in microcirculatory flow during resuscitation are associated with changes in organ failure over the first 24 h of sepsis therapy.

DESIGN

Prospective observational study.

SETTING

Emergency Department and Intensive Care Unit.

PARTICIPANTS

Septic patients with systolic blood pressure <90 mmHg despite intravenous fluids or lactate >or=4.0 mM/L treated with early goal-directed therapy (EGDT).

MEASUREMENTS AND RESULTS

We performed Sidestream Dark Field (SDF) videomicroscopy of the sublingual microcirculation <3 h from EGDT initiation and again within a 3-6 h time window after initial. We imaged five sites and determined the mean microcirculatory flow index (MFI) (0 no flow to 3 normal) blinded to all clinical data. We calculated the Sequential Organ Failure Assessment (SOFA) score at 0 and 24 h, and defined improved SOFA a priori as a decrease >or=2 points. Of 33 subjects; 48% improved SOFA over 0-24 h. Age, APACHE II, and global hemodynamics did not differ significantly between organ failure groups. Among SOFA improvers, 88% increased MFI during EGDT, compared to 47% for non-improvers (P = 0.03). Median change in MFI was 0.23 for SOFA improvers versus -0.05 for non-improvers (P = 0.04).

CONCLUSIONS

Increased microcirculatory flow during resuscitation was associated with reduced organ failure at 24 h without substantial differences in global hemodynamics. These data support the hypothesis that targeting the microcirculation distinct from the macrocirculation could potentially improve organ failure in sepsis.

Year in review 2007: Critical Care--shock

The research papers on shock published in Critical Care throughout 2007 are related to three major subjects: the modulation of the macrocirculation and microcirculation during shock, focusing on arginine vasopressin, erythropoietin and nitric oxide; studies on metabolic homeostasis (acid–base status, energy expenditure and gastrointestinal motility); and basic supportive measures in critical illness (fluid resuscitation and sedation, and body-temperature management). The present review summarizes the key results of these studies and provides a brief discussion in the context of the relevant scientific and clinical background.

Septic impairment of capillary blood flow requires nicotinamide adenine dinucleotide phosphate oxidase but not nitric oxide synthase and is rapidly reversed by ascorbate through an endothelial nitric oxide synthase-dependent mechanism

OBJECTIVE

To determine the roles of nitric oxide synthase (NOS) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in the impairment of capillary blood flow in sepsis and in the reversal of this impairment by ascorbate.

DESIGN

Prospective, controlled laboratory study.

SETTING

Animal laboratory in research institute.

SUBJECTS

Adult male wild type (WT), neuronal nitric oxide synthase (nNOS)-/-, inducible NOS (iNOS)-/-, endothelial NOS (eNOS)-/-, and gp91phox-/- mice.

INTERVENTIONS

Sepsis was induced by feces injection into peritoneum (FIP). A bolus of ascorbate or NADPH oxidase inhibitor apocynin was injected intravenously at 6 hrs post-FIP. Alternatively, NOS cofactor (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4) or nitric oxide donor S-nitroso-N-acetylpenicillamine was superfused on the surface of the extensor digitorum longus muscle.

MEASUREMENTS AND MAIN RESULTS

Capillary blood flow impairment and NOS activity in the extensor digitorum longus muscle were measured by intravital microscopy and by enzymatic assay, respectively. Sepsis at 6 hrs impaired flow in WT mice. Apocynin, and knockout of gp91phox but not of any NOS isoforms, rescued this impairment. Constitutive NOS activity was unaffected by sepsis, but it was abolished by nNOS knockout (iNOS activity was negligible in all mice). Ascorbate rapidly (10 mins) rescued impaired flow in WT, nNOS-/-, iNOS-/- but not eNOS-/- mice. Ascorbate also improved survival of WT mice after FIP. BH4 and SNAP rescued flow in WT mice, while BH4 failed to rescue it in eNOS-/- mice.

CONCLUSION

Capillary blood flow impairment in septic skeletal muscle requires NADPH oxidase but not NOS, and it is rapidly reversed by ascorbate and BH4 through an eNOS-dependent mechanism.

Decreases in myocardial glucose and increases in pyruvate but not ischaemia are observed during porcine endotoxaemia

BACKGROUND

Myocardial dysfunction occurs commonly in septic shock. It is not known whether this is due to local ischaemia and metabolic disturbances. Our hypothesis was that endotoxaemic myocardial dysfunction may be associated with interstitial ischaemic and metabolic changes, measured using interstitial microdialysis (MD).

METHODS

Eighteen pigs were randomized to control (n=6) or endotoxin infusion (n=12). MD catheters were inserted into the myocardium for measurement of interstitial glucose, pyruvate and lactate concentrations. Plasma glucose and lactate concentrations and systemic haemodynamic parameters were measured simultaneously.

RESULTS

Compared with the control group, the endotoxaemic animals had significantly decreased left ventricular stroke work and venous oxygen saturation (SvO2), and increased mean pulmonary artery pressure and plasma lactate. In the endotoxaemic group, decreases in interstitial glucose were observed, occurring simultaneously with increases in interstitial pruvate. Interstitial lactate: pyruvate ratios decreased with time in all animals.

CONCLUSIONS

Despite severe systemic and pulmonary haemodynamic changes, interstitial MD measurements revealed no evidence of anaerobic metabolism in the myocardium of endotoxaemic pigs. There were, however, changes in glucose and pyruvate concentrations, suggesting local energy metabolic disturbances.

Microcirculation and oxidative stress

The microcirculation is a complex and integrated system, transporting oxygen and nutrients to the cells. The key component of this system is the endothelium, contributing to the local balance between pro and anti-inflammatory mediators, hemostatic balance, as well as vascular permeability and cell proliferation. A constant shear stress maintains vascular endothelium homeostasis while perturbed shear stress leads to changes in secretion of vasodilator and vasoconstrictor agents. Increased oxidative stress is a major pathogenetic mechanism of endothelial dysfunction by decreasing NO bioavailability, promoting inflammation and participating in activation of intracellular signals cascade, so influencing ion channels activation, signal transduction pathways, cytoskeleton remodelling, intercellular communication and ultimately gene expression. Targeting the microvascular inflammation and oxidative stress is a fascinating approach for novel therapies in order to decrease morbidity and mortality of chronic and acute diseases.

Platelet-derived exosomes induce endothelial cell apoptosis through peroxynitrite generation: experimental evidence for a novel mechanism of septic vascular dysfunction

Introduction

Several studies link hematological dysfunction to severity of sepsis. Previously we showed that platelet-derived microparticles from septic patients induce vascular cell apoptosis through the NADPH oxidase-dependent release of superoxide. We sought to further characterize the microparticle-dependent vascular injury pathway.

Methods

During septic shock there is increased generation of thrombin, TNF-α and nitric oxide (NO). Human platelets were exposed for 1 hour to the NO donor diethylamine-NONOate (0.5 μM), lipopolysaccharide (LPS; 100 ng/ml), TNF-α (40 ng/ml), or thrombin (5 IU/ml). Microparticles were recovered through filtration and ultracentrifugation and analyzed by electron microscopy, flow cytometry or Western blotting for protein identification. Redox activity was characterized by lucigenin (5 μM) or coelenterazine (5 μM) luminescence and by 4,5-diaminofluorescein (10 mM) and 2',7'-dichlorofluorescein (10 mM) fluorescence. Endothelial cell apoptosis was detected by phosphatidylserine exposure and by measurement of caspase-3 activity with an enzyme-linked immunoassay.

Results

Size, morphology, high exposure of the tetraspanins CD9, CD63, and CD81, together with low phosphatidylserine, showed that platelets exposed to NONOate and LPS, but not to TNF-α or thrombin, generate microparticles similar to those recovered from septic patients, and characterize them as exosomes. Luminescence and fluorescence studies, and the use of specific inhibitors, revealed concomitant superoxide and NO generation. Western blots showed the presence of NO synthase II (but not isoforms I or III) and of the NADPH oxidase subunits p22^phox, protein disulfide isomerase and Nox. Endothelial cells exposed to the exosomes underwent apoptosis and caspase-3 activation, which were inhibited by NO synthase inhibitors or by a superoxide dismutase mimetic and totally blocked by urate (1 mM), suggesting a role for the peroxynitrite radical. None of these redox properties and proapoptotic effects was evident in microparticles recovered from platelets exposed to thrombin or TNF-α.

Conclusion

We showed that, in sepsis, NO and bacterial elements are responsible for type-specific platelet-derived exosome generation. Those exosomes have an active role in vascular signaling as redox-active particles that can induce endothelial cell caspase-3 activation and apoptosis by generating superoxide, NO and peroxynitrite. Thus, exosomes must be considered for further developments in understanding and treating vascular dysfunction in sepsis.

Inflammation, endothelium, and coagulation in sepsis

Sepsis is a systemic response to infection, and symptoms are produced by host defense systems rather than by the invading pathogens. Amongst the most prominent features of sepsis, contributing significantly to its outcome, is activation of coagulation with concurrent down-regulation of anticoagulant systems and fibrinolysis. Inflammation-induced coagulation on its turn contributes to inflammation. Another important feature of sepsis, associated with key symptoms such as hypovolemia and hypotension, is endothelial dysfunction. Under normal conditions, the endothelium provides for an anticoagulant surface, a property that is lost in sepsis. In this review, data about the interplay between inflammation and coagulation in sepsis are summarized with a special focus on the influence of the endothelium on inflammation-induced coagulation and vice versa. Possible procoagulant properties of the endothelium are described, such as expression of tissue factor (TF) and von Willebrand factor and interaction with platelets. Possible procoagulant roles of microparticles, circulating endothelial cells and endothelial apoptosis, are also discussed. Moreover, the important roles of the endothelium in down-regulating the anticoagulants TF pathway inhibitor, antithrombin, and the protein C (PC) system and inhibition of fibrinolysis are discussed. The influence of coagulation on its turn on inflammation and the endothelium is described with a special focus on protease-activated receptors (PARs). We conclude that the relationship between endothelium and coagulation in sepsis is tight and that further research is needed, for example, to better understand the role of activated PC signaling via PAR-1, the role of the endothelial PC receptor herein, and the role of the glycocalyx.