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

Blood platelets and sepsis pathophysiology: A new therapeutic prospect in critically [corrected] ill patients?

Beyond haemostasis, platelets have emerged as versatile effectors of the immune response. The contribution of platelets in inflammation, tissue integrity and defence against infections has considerably widened the spectrum of their role in health and disease. Here, we propose a narrative review that first describes these new platelet attributes. We then examine their relevance to microcirculatory alterations in multi-organ dysfunction, a major sepsis complication. Rapid progresses that are made on the knowledge of novel platelet functions should improve the understanding of thrombocytopenia, a common condition and a predictor of adverse outcome in sepsis, and may provide potential avenues for management and therapy.

Microcirculation and red cell transfusion in patients with sepsis

Early identification of sepsis followed by diagnostic blood cultures and prompt administration of appropriate intravenous antibiotics covering all likely pathogen remains the corner stone in the initial management of sepsis. Source control, obtained by harvesting microbiological cultures and removal or drainage of the infected foci, is mandatory. However, optimization of hemodynamically unstable patients including volume support supplemented with vasopressor, inotropic and transfusion of red blood cells (RBCs) in case of persistent hypoperfusion have the potential to reduce morbidity and mortality. Given the imbalance between the ability of the cardiovascular system to deliver enough oxygen to meet the oxygen demand, transfusion of RBCs should theoretically provide the ideal solution to the challenge. However, both changes in the septic patients' RBCs induced by endogenous factors as well as the storage lesion affecting transfused RBCs have negative effects on the microcirculation. RBC morphology, distribution of fatty acids on the membrane surface, RBC deformability needed for capillary circulation and the nitrogen oxide (NO) signaling systems are involved. Although these deteriorating effects develop during storage, transfusion of fresh RBCs has not proven to be beneficial, possibly due to limitations of the studies performed. Until better evidence exists, transfusion guidelines recommend a restrictive strategy of RBC transfusion i.e. transfuse when hemoglobin (Hb)<7g/dL in septic patients.

The Effect of Sepsis on the Erythrocyte

Sepsis induces a wide range of effects on the red blood cell (RBC). Some of the effects including altered metabolism and decreased 2,3-bisphosphoglycerate are preventable with appropriate treatment, whereas others, including decreased erythrocyte deformability and redistribution of membrane phospholipids, appear to be permanent, and factors in RBC clearance. Here, we review the effects of sepsis on the erythrocyte, including changes in RBC volume, metabolism and hemoglobin's affinity for oxygen, morphology, RBC deformability (an early indicator of sepsis), antioxidant status, intracellular Ca²⁺ homeostasis, membrane proteins, membrane phospholipid redistribution, clearance and RBC O₂-dependent adenosine triphosphate efflux (an RBC hypoxia signaling mechanism involved in microvascular autoregulation). We also consider the causes of these effects by host mediated oxidant stress and bacterial virulence factors. Additionally, we consider the altered erythrocyte microenvironment due to sepsis induced microvascular dysregulation and speculate on the possible effects of RBC autoxidation. In future, a better understanding of the mechanisms involved in sepsis induced erythrocyte pathophysiology and clearance may guide improved sepsis treatments. Evidence that small molecule antioxidants protect the erythrocyte from loss of deformability, and more importantly improve septic patient outcome suggest further research in this area is warranted. While not generally considered a critical factor in sepsis, erythrocytes (and especially a smaller subpopulation) appear to be highly susceptible to sepsis induced injury, provide an early warning signal of sepsis and are a factor in the microvascular dysfunction that has been associated with organ dysfunction.

Preadmission Use of Calcium Channel Blocking Agents Is Associated With Improved Outcomes in Patients With Sepsis: A Population-Based Propensity Score-Matched Cohort Study

OBJECTIVES

Use of calcium channel blockers has been found to improve sepsis outcomes in animal studies and one clinical study. This study determines whether the use of calcium channel blockers is associated with a decreased risk of mortality in patients with sepsis.

DESIGN

Population-based matched cohort study.

SETTING

National Health Insurance Research Database of Taiwan.

PATIENTS

Hospitalized severe sepsis patients identified from National Health Insurance Research Database by International Classification of Diseases, Ninth Revision, Clinical Modification codes.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The association between calcium channel blocker use and sepsis outcome was determined by multivariate-adjusted Cox proportional hazard models and propensity score analysis. To examine the influence of healthy user bias, beta-blocker was used as an active comparator. Our study identified 51,078 patients with sepsis, of which, 19,742 received calcium channel blocker treatments prior to the admission. Use of calcium channel blocker was associated with a reduced 30-day mortality after propensity score adjustment (hazard ratio, 0.94; 95% CI, 0.89-0.99), and the beneficial effect could extend to 90-day mortality (hazard ratio, 0.95; 95% CI, 0.89-1.00). In contrast, use of beta-blocker was not associated with an improved 30-day (hazard ratio, 1.06; 95% CI, 0.97-1.15) or 90-day mortality (hazard ratio, 1.00; 95% CI, 0.90-1.11). On subgroup analysis, calcium channel blockers tend to be more beneficial to patients with male gender, between 40 and 79 years old, with a low comorbidity burden, and to patients with cardiovascular diseases, diabetes, or renal diseases.

CONCLUSIONS

In this national cohort study, preadmission calcium channel blocker therapy before sepsis development was associated with a 6% reduction in mortality when compared with patients who have never received calcium channel blockers.

Real-time visualization of distinct nitric oxide generation of nitric oxide synthase isoforms in single cells

The members of the nitric oxide synthase (NOS) family, eNOS, nNOS and iNOS, are well-characterized enzymes. However, due to the lack of suitable direct NO sensors, little is known about the kinetic properties of cellular NO generation by the different nitric oxide synthase isoenzymes. Very recently, we developed a novel class of fluorescent protein-based NO-probes, the geNOps, which allow real-time measurement of cellular NO generation and fluctuation. By applying these genetic NO biosensors to nNOS-, eNOS- and iNOS-expressing HEK293 cells we were able to characterize the respective NO dynamics in single cells that exhibited identical Ca²⁺ signaling as comparable activator of nNOS and eNOS. Our data demonstrate that upon Ca²⁺ mobilization nNOS-derived NO signals occur instantly and strictly follow the Ca²⁺ elevation while NO release by eNOS occurs gradually and sustained. To detect high NO levels in cells expressing iNOS, a new ratiometric probe based on two fluorescent proteins was developed. This novel geNOp variant allows the measurement of the high NO levels in cells expressing iNOS. Moreover, we used this probe to study the L-arginine-dependency of NO generation by iNOS on the level of single cells. Our experiments highlight that the geNOps technology is suitable to detect obvious differences in the kinetics, amplitude and substrate-dependence of cellular NO signals-derived from all three nitric oxide synthase isoforms.

Muscle oxygenation as an indicator of shock severity in patients with suspected severe sepsis or septic shock

Purpose

The aim of this pilot study was to evaluate the potential of a new noninvasive optical measurement of muscle oxygenation (MOx) to identify shock severity in patients with suspected sepsis.

Methods

We enrolled 51 adult patients in the emergency department (ED) who presented with possible sepsis using traditional Systematic Inflammatory Response Syndrome criteria or who triggered a “Code Sepsis.” Noninvasive MOx measurements were made from the first dorsal interosseous muscles of the hand once potential sepsis/septic shock was identified, as soon as possible after admission to the ED. Shock severity was defined by concurrent systolic blood pressure, heart rate, and serum lactate levels. MOx was also measured in a control group of 17 healthy adults.

Results

Mean (± SD) MOx in the healthy control group was 91.0 ± 5.5% (n = 17). Patients with mild, moderate, and severe shock had mean MOx values of 79.4 ± 21.2%, 48.6 ± 28.6%, and 42.2 ± 4.7%, respectively. Mean MOx for the mild and moderate shock severity categories were statistically different from healthy controls and from each other based on two-sample t-tests (p < 0.05).

Conclusions

We demonstrate that noninvasive measurement of MOx was associated with clinical assessment of shock severity in suspected severe sepsis or septic shock. The ability of MOx to detect even mild septic shock has meaningful implications for emergency care, where decisions about triage and therapy must be made quickly and accurately. Future longitudinal studies may validate these findings and the value of MOx in monitoring patient status as treatment is administered.

Markers of nitric oxide are associated with sepsis severity: an observational study

Background

Nitric oxide (NO) regulates processes involved in sepsis progression, including vascular function and pathogen defense. Direct NO measurement in patients is unfeasible because of its short half-life. Surrogate markers for NO bioavailability are substrates of NO generating synthase (NOS): L-arginine (lArg) and homoarginine (hArg) together with the inhibitory competitive substrate asymmetric dimethylarginine (ADMA). In immune cells ADMA is cleaved by dimethylarginine-dimethylaminohydrolase-2 (DDAH2). The aim of this study was to investigate whether concentrations of surrogate markers for NO bioavailability are associated with sepsis severity.

Method

This single-center, prospective study involved 25 controls and 100 patients with surgical trauma (n = 20), sepsis (n = 63), or septic shock (n = 17) according to the Sepsis-3 definition. Plasma lArg, hArg, and ADMA concentrations were measured by mass spectrometry and peripheral blood mononuclear cells (PBMCs) were analyzed for DDAH2 expression.

Results

lArg concentrations did not differ between groups. Median (IQR) hArg concentrations were significantly lower in patient groups than controls, being 1.89 (1.30–2.29) μmol/L (P < 0.01), with the greatest difference in the septic shock group, being 0.74 (0.36–1.44) μmol/L. In contrast median ADMA concentrations were significantly higher in patient groups compared to controls, being 0.57 (0.46–0.65) μmol/L (P < 0.01), with the highest levels in the septic shock group, being 0.89 (0.56–1.39) μmol/L. The ratio of hArg:ADMA was inversely correlated with disease severity as determined by the Sequential Organ Failure Assessment (SOFA) score. Receiver-operating characteristic analysis for the presence or absence of septic shock revealed equally high sensitivity and specificity for the hArg:ADMA ratio compared to the SOFA score. DDAH2 expression was lower in patients than controls and lowest in the subgroup of patients with increasing SOFA.

Conclusions

In patients with sepsis, plasma hArg concentrations are decreased and ADMA concentrations are increased. Both metabolites affect NO metabolism and our findings suggest reduced NO bioavailability in sepsis. In addition, reduced expression of DDAH2 in immune cells was observed and may not only contribute to blunted NO signaling but also to subsequent impaired pathogen defense.

The optimum hematocrit

The hematocrit (Hct) determines the oxygen carrying capacity of blood, but also increases blood viscosity and thus flow resistance. From this dual role the concept of an optimum Hct for tissue oxygenation has been derived. Viscometric studies using the ratio Hct/blood viscosity at high shear rate showed an optimum Hct of 50-60% for red blood cell (RBC) suspensions in plasma. For the perfusion of an artificial microvascular network with 5-70μm channels the optimum Hct was 60-70% for high driving pressures. With lower shear rates or driving pressures the optimum Hct shifted towards lower values. In healthy, well trained athletes an increase of the Hct to supra-normal levels can increase exercise performance. These data with healthy individuals suggest that the optimum Hct for oxygen transport may be higher than the physiological range (35-40% in women, 39-50% in men). This is in contrast to clinical observations. Large clinical studies have repeatedly shown that a correction of anemia in a variety of disorders such as chronic kidney disease, heart failure, coronary syndrome, oncology, acute gastrointestinal bleeding, critical care, or surgery have better clinical outcomes when restrictive transfusion strategies are applied. Actual guidelines, therefore, recommend a transfusion threshold of 7-8 g/dL hemoglobin (Hct 20-24%) in stable, hospitalized patients. The discrepancy between the optimum Hct in health and disease may be due to factors such as decreased perfusion pressures (low cardiac output, vascular stenoses, change in vascular tone), endothelial cell dysfunction, leukocyte adhesion and others.

Intravenous Fluids and Acute Kidney Injury

Over 50% of the human body is comprised of fluids that are distributed in defined compartments. Although compartmentalized, these fluids are dynamically connected. Fluids, electrolytes, and acid-base balance in each compartment are tightly regulated, mostly in an energy-dependent manner to achieve their designed functions. For over a century, our understanding of the microvascular fluid homeostasis has evolved from hypothesized Ernest Starling principle to evidence-based and the revised Starling principle, incorporating the functional endothelial surface layer. The kidney is a highly vascular and encapsulated organ that is exquisitely sensitive to inadequate (insufficient or excess) blood flow. The kidney is particularly sensitive to venous congestion, and studies show that reduced venous return triggers a greater degree of kidney damage than that from lacking arterial flow. Thus, fluid overload can induce severe and sustained kidney injury. In the setting of established acute kidney injury, fluid management can be challenging. Impaired capacity of urine output and urine concentration and dilution should be taken into consideration when designing fluid therapy. Video Journal Club 'Cappuccino with Claudio Ronco' at http://www.karger.com/?doi=452702.

Clogging of microfluidic systems

The transport of suspensions of microparticles in confined environments is associated with complex phenomena at the interface of fluid mechanics and soft matter. Indeed, the deposition and assembly of particles under flow involve hydrodynamic, steric and colloidal forces, and can lead to the clogging of microchannels. The formation of clogs dramatically alters the performance of both natural and engineered systems, effectively limiting the use of microfluidic technology. While the fouling of porous filters has been studied at the macroscopic level, it is only recently that the formation of clogs has been considered at the pore-scale, using microfluidic devices. In this review, we present the clogging mechanisms recently reported for suspension flows of colloidal particles and for biofluids in microfluidic channels, including sieving, bridging and aggregation of particles. We discuss the technological implications of the clogging of microchannels and the schemes that leverage the formation of clogs. We finally consider some of the outstanding challenges involving clogging in human health, which could be tackled with microfluidic methods.

Effects of volume resuscitation on the microcirculation in animal models of lipopolysaccharide sepsis: a systematic review

Background

Recent research has identified an increased rate of mortality associated with fluid bolus therapy for severe sepsis and septic shock, but the mechanisms are still not well understood. Fluid resuscitation therapy administered for sepsis and septic shock targets restoration of the macro-circulation, but the pathogenesis of sepsis is complex and includes microcirculatory dysfunction.

Objective

The objective of the study is to systematically review data comparing the effects of different types of fluid resuscitation on the microcirculation in clinically relevant animal models of lipopolysaccharide-induced sepsis.

Methods

A structured search of PubMed/MEDLINE and EMBASE for relevant publications from 1 January 1990 to 31 December 2015 was performed, in accordance with PRISMA guidelines.

Results

The number of published papers on sepsis and the microcirculation has increased steadily over the last 25 years. We identified 11 experimental animal studies comparing the effects of different fluid resuscitation regimens on the microcirculation. Heterogeneity precluded any meta-analysis.

Conclusions

Few animal model studies have been published comparing the microcirculatory effects of different types of fluid resuscitation for sepsis and septic shock. Biologically relevant animal model studies remain necessary to enhance understanding regarding the mechanisms by which fluid resuscitation affects the microcirculation and to facilitate the transfer of basic science discoveries to clinical applications.

Hemodynamic coherence in sepsis

Microvascular alterations are a hallmark of sepsis and play a crucial role in its pathophysiology. Such alterations are the result of overwhelming inflammation, which negatively affects all the components of the microcirculation. As the severity of microvascular alterations is associated with organ dysfunction and mortality, several strategies have been tested for improving microcirculation. Nevertheless, they are mainly based on the conventional manipulation of systemic hemodynamics to increase the total flow to the organs and tissues. Other therapeutic interventions are still being investigated. In this review, we discuss the pathophysiology of septic microcirculatory dysfunction and its implications for possible treatments.

Similar Microcirculatory Alterations in Patients with Normodynamic and Hyperdynamic Septic Shock

RATIONALE

In normodynamic septic shock, the quantitative assessment of sublingual microcirculation has shown decreases in perfused vascular density and red blood cell velocity. However, no studies have been performed in hyperdynamic septic shock.

OBJECTIVES

To characterize the microcirculatory patterns and rule out the presence of fast red blood cell velocity in patients with hyperdynamic septic shock.

METHODS

We prospectively evaluated the sublingual microcirculation in healthy volunteers (n = 20) and in patients with hyperdynamic (n = 20) and normodynamic (n = 20) septic shock. Hyperdynamic septic shock was defined by a cardiac index >4.0 L/min/m(2). The microcirculation was assessed with sidestream dark field imaging and AVA 3.0 software.

MEASUREMENTS AND MAIN RESULTS

There were no differences in perfused vascular density, proportion of perfused vessels, or microvascular flow index between patients with hyperdynamic and normodynamic septic shock, but these variables were reduced compared with those of healthy volunteers, A similar pattern was observed in red blood cell velocity (912 ± 291, 968 ± 204, and 1303 ± 120 μm/s, respectively; P < 0.0001) and its coefficient of variation. In both types of septic shock, no microvessel had a red blood cell velocity higher than the 100th percentile value for healthy volunteers.

CONCLUSIONS

Patients with hyperdynamic septic shock showed microcirculatory alterations similar to those of patients with normal cardiac output. Both groups of patients had reduced perfused vascular density and red blood cell velocity and increased flow heterogeneity compared with that of healthy subjects. Fast red blood cell velocity was not found, even in patients with high cardiac output. These results support the conclusion that microcirculatory function is frequently dissociated from systemic hemodynamic derangements in septic shock.

Nuclear Countermeasure Activity of TP508 Linked to Restoration of Endothelial Function and Acceleration of DNA Repair

There is increasing evidence that radiation-induced damage to endothelial cells and loss of endothelial function may contribute to both acute radiation syndromes and long-term effects of whole-body nuclear irradiation. Therefore, several drugs are being developed to mitigate the effects of nuclear radiation, most of these drugs will target and protect or regenerate leukocytes and platelets. Our laboratory has demonstrated that TP508, a 23-amino acid thrombin peptide, activates endothelial cells and stem cells to revascularize and regenerate tissues. We now show that TP508 can mitigate radiation-induced damage to endothelial cells in vitro and in vivo. Our in vitro results demonstrate that human endothelial cells irradiation attenuates nitric oxide (NO) signaling, disrupts tube formation and induces DNA double-strand breaks (DSB). TP508 treatment reverses radiation effects on NO signaling, restores tube formation and accelerates the repair of radiation-induced DSB. The radiation-mitigating effects of TP508 on endothelial cells were also seen in CD-1 mice where systemic injection of TP508 stimulated endothelial cell sprouting from aortic explants after 8 Gy irradiation. Systemic doses of TP508 that mitigated radiation-induced endothelial cell damage, also significantly increased survival of CD-1 mice when injected 24 h after 8.5 Gy exposure. These data suggest that increased survival observed with TP508 treatment may be due to its effects on vascular and microvascular endothelial cells. Our study supports the usage of a regenerative drug such as TP508 to activate endothelial cells as a countermeasure for mitigating the effects of nuclear radiation.

Microcirculatory dysfunction in sepsis: pathophysiology, clinical monitoring, and potential therapies

Abnormal microvascular perfusion, including decreased functional capillary density and increased blood flow heterogeneity, is observed in early stages of the systemic inflammatory response to infection and appears to have prognostic significance in human sepsis. It is known that improvements in systemic hemodynamics are weakly correlated with the correction of microcirculatory parameters, despite an appropriate treatment of macrohemodynamic abnormalities. Furthermore, conventional hemodynamic monitoring systems available in clinical practice fail to detect microcirculatory parameter changes and responses to treatments, as they do not evaluate intrinsic events that occur in the microcirculation. Fortunately, some bedside diagnostic methods and therapeutic options are specifically directed to the assessment and treatment of microcirculatory changes. In the present review we discuss fundamental aspects of septic microcirculatory abnormalities, including pathophysiology, clinical monitoring, and potential therapies.

Impact of Incremental Perfusion Loss on Oxygen Transport in a Capillary Network Mathematical Model

OBJECTIVES

To quantify how incremental capillary PL, such as that seen in experimental models of sepsis, affects tissue oxygenation using a computation model of oxygen transport.

METHODS

A computational model was applied to capillary networks with dimensions 84 × 168 × 342 (NI) and 70 × 157 × 268 (NII) μm, reconstructed in vivo from rat skeletal muscle. FCD loss was applied incrementally up to ~40% and combined with high tissue oxygen consumption to simulate severe sepsis.

RESULTS

A loss of ~40% FCD loss decreased median tissue PO2 to 22.9 and 20.1 mmHg in NI and NII compared to 28.1 and 27.5 mmHg under resting conditions. Increasing RBC SR to baseline levels returned tissue PO2 to within 5% of baseline. HC combined with a 40% FCD loss, resulted in tissue anoxia in both network volumes and median tissue PO2 of 11.5 and 8.9 mmHg in NI and NII respectively; median tissue PO2 was recovered to baseline levels by increasing total SR 3-4 fold.

CONCLUSIONS

These results suggest a substantial increase in total SR is required in order to compensate for impaired oxygen delivery as a result of loss of capillary perfusion and increased oxygen consumption during sepsis.

Impaired microcirculatory perfusion in a rat model of cardiopulmonary bypass: the role of hemodilution

Although hemodilution is attributed as the main cause of microcirculatory impairment during cardiopulmonary bypass (CPB), this relationship has never been investigated. We investigated the distinct effects of hemodilution with or without CPB on microvascular perfusion and subsequent renal tissue injury in a rat model. Male Wistar rats (375–425 g) were anesthetized, prepared for cremaster muscle intravital microscopy, and subjected to CPB ( n = 9), hemodilution alone ( n = 9), or a sham procedure ( n = 6). Microcirculatory recordings were performed at multiple time points and analyzed for perfusion characteristics. Kidney and lung tissue were investigated for mRNA expression for genes regulating inflammation and endothelial adhesion molecule expression. Renal injury was assessed with immunohistochemistry. Hematocrit levels dropped to 0.24 ± 0.03 l/l and 0.22 ± 0.02 l/l after onset of hemodilution with or without CPB. Microcirculatory perfusion remained unaltered in sham rats. Hemodilution alone induced a 13% decrease in perfused capillaries, after which recovery was observed. Onset of CPB reduced the perfused capillaries by 40% (9.2 ± 0.9 to 5.5 ± 1.5 perfused capillaries per microscope field; P < 0.001), and this reduction persisted throughout the experiment. Endothelial and inflammatory activation and renal histological injury were increased after CPB compared with hemodilution or sham procedure. Hemodilution leads to minor and transient disturbances in microcirculatory perfusion, which cannot fully explain impaired microcirculation following cardiopulmonary bypass. CPB led to increased renal injury and endothelial adhesion molecule expression in the kidney and lung compared with hemodilution. Our findings suggest that microcirculatory impairment during CPB may play a role in the development of kidney injury.

Basic concepts of hemorheology in microvascular hemodynamics

Blood rheology, or hemorheology, involves the flow and deformation behavior of blood and its formed elements (ie, erythrocytes, leukocytes, platelets). The adequacy of blood flow to meet metabolic demands through large circulatory vessels depends highly on vascular control mechanisms. However, the extent to which rheologic properties of blood contribute to vascular flow resistance, particularly in the microcirculation, is becoming more appreciated. Current evidence suggests that microvascular blood flow is determined by local vessel resistance and hemorheologic factors such as blood viscosity, erythrocyte deformability, and erythrocyte aggregation. Such knowledge will aid clinicians caring for patients with hemodynamic alterations.

Microcirculatory alterations in shock states

Functional components of the microcirculation provide oxygen and nutrients and remove waste products from the tissue beds of the body's organs. Shock states overwhelmingly stress functional capacity of the microcirculation, resulting in microcirculatory failure. In septic shock, inflammatory mediators contribute to hemodynamic instability. In nonseptic shock states, the microcirculation is better able to compensate for alterations in vascular resistance, cardiac output, and blood pressure. Therefore, global hemodynamic and oxygen delivery parameters are appropriate for assessing, monitoring, and guiding therapy in hypovolemic and cardiogenic shock but, alone, are inadequate for septic shock.

What is microcirculatory shock?

PURPOSE OF REVIEW

Microcirculatory shock is a condition defined by the presence of tissue hypoperfusion despite the normalization of systemic and regional blood flow. In this article, we discuss the characteristics of the microcirculation in septic shock, the main form of microcirculatory shock, along with its interaction with systemic hemodynamics, and the response to different therapies.

RECENT FINDINGS

In septic shock, microcirculatory abnormalities are common, and more severe in nonsurvivors. In addition, the microcirculation shows a behavior that is frequently dissociated from that of systemic hemodynamics. Therefore, microcirculatory alterations may persist despite correction of systemic hemodynamic variables. Sublingual and intestinal microcirculation might also display divergent behaviors. Moreover, microvascular alterations may improve in response to hemodynamic resuscitation, but the response might depend on the underlying microcirculatory alterations. Particularly, the response to fluids seems to be related to both its basal state and the magnitude of the increase in cardiac output.

SUMMARY

The optimal treatment of microcirculatory shock might require monitoring and therapeutic goals targeted on the microcirculation, more than in systemic variables. The clinical benefits of this approach should be demonstrated in clinical trials.

Sepsis impairs microvascular autoregulation and delays capillary response within hypoxic capillaries

Introduction

The microcirculation supplies oxygen (O₂) and nutrients to all cells with the red blood cell (RBC) acting as both a deliverer and sensor of O₂. In sepsis, a proinflammatory disease with microvascular complications, small blood vessel alterations are associated with multi-organ dysfunction and poor septic patient outcome. We hypothesized that microvascular autoregulation—existing at three levels: over the entire capillary network, within a capillary and within the erythrocyte—was impaired during onset of sepsis. This study had three objectives: 1) measure capillary response time within hypoxic capillaries, 2) test the null hypothesis that RBC O₂-dependent adenosine triphosphate (ATP) efflux was not altered by sepsis and 3) develop a framework of a pathophysiological model.

Methods

This was an animal study, comparing sepsis with control, set in a university laboratory. Acute hypotensive sepsis was studied using cecal ligation and perforation (CLP) with a 6-hour end-point. Rat hindlimb skeletal muscle microcirculation was imaged, and capillary RBC supply rate (SR = RBC/s), RBC hemoglobin O₂ saturation (SO₂) and O₂ supply rate (qO₂ = pLO₂/s) were quantified. Arterial NOx (nitrite + nitrate) and RBC O₂-dependent ATP efflux were measured using a nitric oxide (NO) analyzer and gas exchanger, respectively.

Results

Sepsis increased capillary stopped-flow (p = 0.001) and increased plasma lactate (p < 0.001). Increased plasma NOx (p < 0.001) was related to increased capillary RBC supply rate (p = 0.027). Analysis of 30-second SR–SO₂–qO₂ profiles revealed a shift towards decreased (p < 0.05) O₂ supply rates in some capillaries. Moreover, we detected a three- to fourfold increase (p < 0.05) in capillary response time within hypoxic capillaries (capillary flow states where RBC SO₂ < 20 %). Additionally, sepsis decreased the erythrocyte’s ability to respond to hypoxic environments, as normalized RBC O₂-dependent ATP efflux decreased by 62.5 % (p < 0.001).

Conclusions

Sepsis impaired microvascular autoregulation at both the individual capillary and erythrocyte level, seemingly uncoupling the RBC acting as an “O₂ sensor” from microvascular autoregulation. Impaired microvascular autoregulation was manifested by increased capillary stopped-flow, increased capillary response time within hypoxic capillaries, decreased capillary O₂ supply rate and decreased RBC O₂-dependent ATP efflux. This loss of local microvascular control was partially off-set by increased capillary RBC supply rate, which correlated with increased plasma NOx.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1102-7) contains supplementary material, which is available to authorized users.

Investigation on oxidative stress of nitric oxide synthase interacting protein from Clonorchis sinensis

Numerous evidences indicate that excretory-secretory products (ESPs) from liver flukes trigger the generation of free radicals that are associated with the initial pathophysiological responses in host cells. In this study, we first constructed a Clonorchis sinensis (C. sinensis, Cs)-infected BALB/c mouse model and examined relative results respectively at 3, 5, 7, and 9 weeks postinfection (p.i.). Quantitative reverse transcription (RT)-PCR indicated that the transcriptional level of both endothelial nitric oxide synthase (eNOS) and superoxide dismutase (SOD) gradually decreased with lastingness of infection, while the transcriptional level of inducible NOS (iNOS) significantly increased. The level of malondialdehyde (MDA) in sera of infected mouse significantly increased versus the healthy control group. These results showed that the liver of C. sinensis-infected mouse was in a state with elevated levels of oxidation stress. Previously, C. sinensis NOS interacting protein coding gene (named CsNOSIP) has been isolated and recombinant CsNOSIP (rCsNOSIP) has been expressed in Escherichia coli, which has been confirmed to be a component present in CsESPs and confirmed to play important roles in immune regulation of the host. In the present paper, we investigated the effects of rCsNOSIP on the lipopolysaccharide (LPS)-induced activated RAW264.7, a murine macrophage cell line. We found that endotoxin-free rCsNOSIP significantly promoted the levels of nitric oxide (NO) and reactive oxygen species (ROS) after pretreated with rCsNOSIP, while the level of SOD decreased. Furthermore, rCsNOSIP could also increase the level of lipid peroxidation MDA. Taken together, these results suggested that CsNOSIP was a key molecule which was involved in the production of nitric oxide (NO) and its reactive intermediates, and played an important role in oxidative stress during C. sinensis infection.

Microvascular reactivity and clinical outcomes in cardiac surgery

Introduction

Microvascular reactivity is decreased in patients with septic shock; this is associated with worse clinical outcomes. The objectives of the present study were to investigate microvascular reactivity in cardiac surgery patients and to assess any association with clinical outcomes.

Methods

We retrospectively analyzed a prospectively collected registry. In total, 254 consecutive adult patients undergoing cardiac and thoracic aortic surgeries from January 2013 through May 2014 were analyzed. We performed a vascular occlusion test (VOT) by using near-infrared spectroscopy to measure microvascular reactivity. VOT was performed three times per patient: prior to the induction of anesthesia, at the end of surgery, and on postoperative day 1. The primary endpoint was a composite of major adverse complications, including death, myocardial infarction, acute kidney injury, acute respiratory distress syndrome, and persistent cardiogenic shock.

Results

VOT recovery slope decreased during the surgery. VOT recovery slope on postoperative day 1 was significantly lower in patients with composite complications than those without (3.1 ± 1.6 versus 4.0 ± 1.5 %/s, P = 0.001), although conventional hemodynamic values, such as cardiac output and blood pressure, did not differ between the groups. On multivariable regression and linear analyses, low VOT recovery slope on postoperative day 1 was associated with increases of composite complications (odds ratio 0.742; 95 % confidence interval (CI) 0.584 to 0.943; P = 0.015) and hospital length of stay (regression coefficient (B) −1.276; 95 % CI −2.440 to −0.112; P = 0.032).

Conclusion

Microvascular reactivity largely recovered on postoperative day 1 in the patients without composite complications, but this restoration was attenuated in patients with composite complications.

Trial registration

ClinicalTrials.gov NCT01713192. Registered 22 October 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1025-3) contains supplementary material, which is available to authorized users.

Plasma free hemoglobin and microcirculatory response to fresh or old blood transfusions in sepsis

BACKGROUND

Free hemoglobin (fHb) may induce vasoconstriction by scavenging nitric oxide. It may increase in older blood units due to storage lesions. This study evaluated whether old red blood cell transfusion increases plasma fHb in sepsis and how the microvascular response may be affected.

METHODS

This is a secondary analysis of a randomized study. Twenty adult septic patients received either fresh or old (<10 or >15 days storage, respectively) RBC transfusions. fHb was measured in RBC units and in the plasma before and 1 hour after transfusion. Simultaneously, the sublingual microcirculation was assessed with sidestream-dark field imaging. The perfused boundary region was calculated as an index of glycocalyx damage. Tissue oxygen saturation (StO2) and Hb index (THI) were measured with near-infrared spectroscopy and a vascular occlusion test was performed.

RESULTS

Similar fHb levels were found in the supernatant of fresh and old RBC units. Despite this, plasma fHb increased in the old RBC group after transfusion (from 0.125 [0.098-0.219] mg/mL to 0.238 [0.163-0.369] mg/mL, p = 0.006). The sublingual microcirculation was unaltered in both groups, while THI increased. The change in plasma fHb was inversely correlated with the changes in total vessel density (r = -0.57 [95% confidence interval -0.82, -0.16], p = 0.008), De Backer score (r = -0.63 [95% confidence interval -0.84, -0.25], p = 0.003) and THI (r = -0.72 [95% confidence interval -0.88, -0.39], p = 0.0003).

CONCLUSIONS

Old RBC transfusion was associated with an increase in plasma fHb in septic patients. Increasing plasma fHb levels were associated with decreased microvascular density.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01584999.

Clinical significance of circulating endothelial cells in patients with severe sepsis or septic shock

BACKGROUND

Endothelial damage developing in severe sepsis or septic shock results in multiorgan dysfunction. An increased circulating endothelial cell (CEC) count represents a novel marker of endothelial damage, which has been reported in cases of severe sepsis or septic shock. The aim of this study was to evaluate the clinical significance of CECs in patients with severe sepsis or septic shock.

METHODS

CECs were evaluated and quantified by flow cytometry using plasma collected from patients with severe sepsis or septic shock who were admitted to a medical intensive care unit from February 2011 to August 2011.

RESULTS

During the study period, 77 patients were enrolled. The median CEC count was 350 cells/ml (range 0-15 984 cells/ml). There was no significant difference between cases of severe sepsis and septic shock [163 cells/ml (0-15 984 cells/ml) vs 363 cells/ml (0-7884 cells/ml), p = 0.507]. There were no correlations between the number of CECs and inflammatory markers. CEC counts were significantly increased in non-survivors compared to survivors [588.5 cells/ml (1-15 984 cells/ml) vs 292 cells/ml (0-12 882 cells/ml), p = 0.044] within 28 days. The sequential-related organ failure assessment score, CEC counts ≥ 500 cells/ml and blood lactate levels were significantly associated with 28 day mortality.

CONCLUSIONS

CEC counts were higher in non-survivors of severe sepsis or septic shock and could be used as a biomarker to predict the prognosis in these patients.

Nociceptin/orphanin FQ-NOP receptor system in inflammatory and immune-mediated diseases

The neuropeptide nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand of the G-protein-coupled receptor NOP. Cells from the immune system express the precursor preproN/OFQ and the NOP receptor, as well as secrete N/OFQ. The activation of the N/OFQ-NOP pathway can regulate inflammatory and immune responses. Several immune activities, including leukocyte migration, cytokine and chemokine production, and lymphocytes proliferation are influenced by NOP activation. It was demonstrated that cytokines and other stimuli such as Toll-like receptor agonist (e.g., lipopolysaccharide) induce N/OFQ production by cells from innate and adaptive immune response. In this context, N/OFQ could modulate the outcome of inflammatory diseases, such as sepsis and immune-mediated pathologies by mechanisms not clearly elucidated. In fact, clinical studies revealed increased levels of N/OFQ under sepsis, arthritis, and Parkinson's disease. Preclinical and clinical studies pointed to the blockade of NOP receptor signaling as successful strategy for the treatment of inflammatory diseases. This review is focused on experimental and clinical data that suggest the participation of N/OFQ-NOP receptor activation in the modulation of the immune response, highlighting the immunomodulatory potential of NOP antagonists in the inflammatory and immunological disturbances.

Overexpression of GTP cyclohydrolase 1 feedback regulatory protein is protective in a murine model of septic shock

Overproduction of nitric oxide (NO) by inducible NO synthase contributes toward refractory hypotension, impaired microvascular perfusion, and end-organ damage in septic shock patients. Tetrahydrobiopterin (BH4) is an essential NOS cofactor. GTP cyclohydrolase 1 (GCH1) is the rate-limiting enzyme for BH4 biosynthesis. Under inflammatory conditions, GCH1 activity and hence BH4 levels are increased, supporting pathological NOS activity. GCH1 activity can be controlled through allosteric interactions with GCH1 feedback regulatory protein (GFRP). We investigated whether overexpression of GFRP can regulate BH4 and NO production and attenuate cardiovascular dysfunction in sepsis. Sepsis was induced in mice conditionally overexpressing GFRP and wild-type littermates by cecal ligation and puncture. Blood pressure was monitored by radiotelemetry, and mesenteric blood flow was quantified by laser speckle contrast imaging. Blood biochemistry data were obtained using an iSTAT analyzer, and BH4 levels were measured in plasma and tissues by high-performance liquid chromatography. Increased BH4 and NO production and hypotension were observed in all mice, but the extents of these pathophysiological changes were attenuated in GFRP OE mice. Perturbations in blood biochemistry were similarly attenuated in GFRP OE compared with wild-type controls. These results suggest that GFRP overexpression regulates GCH1 activity during septic shock, which in turn limits BH4 bioavailability for iNOS. We conclude that the GCH1-GFRP axis is a critical regulator of BH4 and NO production and the cardiovascular derangements that occur in septic shock.

Methods to study the tumor microenvironment under controlled oxygen conditions

The tumor microenvironment (TME) is a complex heterogeneous assembly composed of a variety of cell types and physical features. One such feature, hypoxia, is associated with metabolic reprogramming, the epithelial-mesenchymal transition, and therapeutic resistance. Many questions remain regarding the effects of hypoxia on these outcomes; however, only a few experimental methods enable both precise control over oxygen concentration and real-time imaging of cell behavior. Recent efforts with microfluidic platforms offer a promising solution to these limitations. In this review, we discuss conventional methods and tools used to control oxygen concentration for cell studies, and then highlight recent advances in microfluidic-based approaches for controlling oxygen in engineered platforms.

Photoacoustic microscopy and computed tomography: from bench to bedside

Photoacoustic imaging (PAI) of biological tissue has seen immense growth in the past decade, providing unprecedented spatial resolution and functional information at depths in the optical diffusive regime. PAI uniquely combines the advantages of optical excitation and those of acoustic detection. The hybrid imaging modality features high sensitivity to optical absorption and wide scalability of spatial resolution with the desired imaging depth. Here we first summarize the fundamental principles underpinning the technology, then highlight its practical implementation, and finally discuss recent advances toward clinical translation.

Microcirculatory oxygen transport and utilization

The cardiovascular system (macrocirculation) circulates blood throughout the body, but the microcirculation is responsible for modifying tissue perfusion and adapting it to metabolic demand. Hemodynamic assessment and monitoring of the critically ill patient is typically focused on global measures of oxygen transport and utilization, which do not evaluate the status of the microcirculation. Despite achievement and maintenance of global hemodynamic and oxygenation goals, patients may develop microcirculatory dysfunction with associated organ failure. A thorough understanding of the microcirculatory system under physiologic conditions will assist the clinician in early recognition of microcirculatory dysfunction in impending and actual disease states.

The renal microcirculation in sepsis

Despite identification of several cellular mechanisms being thought to underlie the development of septic acute kidney injury (AKI), the pathophysiology of the occurrence of AKI is still poorly understood. It is clear, however, that instead of a single mechanism being responsible for its aetiology, an orchestra of cellular mechanisms failing is associated with AKI. The integrative physiological compartment where these mechanisms come together and exert their integrative deleterious action is the renal microcirculation (MC). This is why it is opportune to review the response of the renal MC to sepsis and discuss the determinants of its (dys)function and how it contributes to the pathogenesis of renal failure. A main determinant of adequate organ function is the adequate supply and utilization of oxygen at the microcirculatory and cellular level to perform organ function. The highly complex architecture of the renal microvasculature, the need to meet a high energy demand and the fact that the kidney is borderline ischaemic makes the kidney a highly vulnerable organ to hypoxaemic injury. Under normal, steady-state conditions, oxygen (O2) supply to the renal tissues is well regulated; however, under septic conditions the delicate balance of oxygen supply versus demand is disturbed due to renal microvasculature dysfunction. This dysfunction is largely due to the interaction of renal oxygen handling, nitric oxide metabolism and radical formation. Renal tissue oxygenation is highly heterogeneous not only between the cortex and medulla but also within these renal compartments. Integrative evaluation of the different determinants of tissue oxygen in sepsis models has identified the deterioration of microcirculatory oxygenation as a key component in the development AKI. It is becoming clear that resuscitation of the failing kidney needs to integratively correct the homeostasis between oxygen, and reactive oxygen and nitrogen species. Several experimental therapeutic modalities have been found to be effective in restoring microcirculatory oxygenation in parallel to improving renal function following septic AKI. However, these have to be verified in clinical studies. The development of clinical physiological biomarkers of AKI specifically aimed at the MC should form a valuable contribution to monitoring such new therapeutic modalities.

Outer membrane vesicles alter inflammation and coagulation mediators

INTRODUCTION

Outer membrane vesicles (OMVs) were previously shown to be capable of initiating the inflammatory response seen in the transition of an infection to sepsis. However, another tenet of sepsis is the development of a hypercoagulable state and the role of OMVs in the development of this hypercoagulability has not been evaluated. The objective of this study was to evaluate the ability of OMVs to elicit endothelial mediators of coagulation and inflammation and induce platelet activation.

METHODS

Human umbilical vein endothelial cells (HUVECs) were incubated with OMVs and were analyzed for the expression of tissue factor (TF), thrombomodulin, and the adhesion molecules P-selectin and E-selectin. Supernatants of OMV-treated HUVECs were mixed with whole blood and assessed for prothrombotic monocyte-platelet aggregates (MPA).

RESULTS

OMVs induce significantly increased expression of TF, E-selectin, and P-selectin, whereas, the expression of thrombomodulin by HUVECs is significantly decreased (P < 0.05). The lipopolysaccharide inhibitor clearly inhibited the expression of E-selectin following incubation with OMVs, although its impact on TF and thrombomodulin expression was nominal. Incubation of whole blood with supernatant from HUVECs exposed to OVMs resulted in increased MPAs.

CONCLUSIONS

This study demonstrates that, at the cellular level, OMVs from pathogenic bacteria play a complex role in endothelial activation. Although OMV-bound lipopolysaccharide modulates inflammatory proteins, including E-selectin, it has a negligible effect on the tested coagulation mediators. Additionally, endothelial activation by OMVs facilitates platelet activation as indicated by increased MPAs. By influencing the inflammatory and coagulation cascades, OMVs may contribute to the hypercoagulable response seen in sepsis.

Gold nanoparticle modifies nitric oxide release and vasodilation in rat aorta

Nitric oxide (NO) plays an important role on several biological functions. Recently, it has been reported the possibility of modifying the NO release profile from the NO donors through its coupling to gold nanoparticles (AuNPs). Thus, AuNPs were synthesized and they were exposed to the NO donor ruthenium complex Cis-[Ru(bpy)2(NO)(4PySH)].(PF6)3 termed (Ru-4PySH)-forming AuNPs-{Ru-4PySH}n cluster. Our results indicate that AuNPs do not modify the maximum effect (ME) and potency (pD2) in the vasodilation induced by Ru-4PySH. Both complexes induce similar vascular relaxation in concentration-dependent way. However, the NO released from the complex AuNPs-{Ru-4PySH}n is lower than Ru-4PySH. Both complexes release only NO(0) specie, but AuNPs-{Ru-4PySH}n releases NO in constant way and exclusively in the extracellular medium. In time-course, Ru-4Py-SH was faster than AuNPs-{Ru-4PySH}n in inducing the maximum vasodilation. Inhibition of soluble guanylyl cyclase (sGC) abolished the vasodilation induced by Ru-4PYSH, but not by AuNPs-{Ru-4PySH}n. Non-selective potassium (K(+)) channel blocker TEA had no effect on the vasodilation induced by AuNPs-{Ru-4PySH}n, but it reduced the potency to Ru-4PySH. In conclusion, our results suggest that AuNPs can reduce the permeability of NO donor Ru-4PySH due to AuNPs-{Ru-4PySH}n cluster formation. AuNPs reduce NO release, but they do not impair the vasodilator effect induced by the NO donor. Ru-4PySH induces vasodilation by sGC and K(+) channels activation, while AuNPs-{Ru-4PySH}n activates mainly sGC. Taken together, these findings represent a new pharmacological strategy to control the NO release which could activate selective biological targets.

Dual blockade of endothelin action exacerbates up-regulated VEGF angiogenic signaling in the heart of lipopolysaccharide-induced endotoxemic rat model

AIMS

Sepsis is a cluster of heterogeneous syndromes associated with progressive endotoxemic developments, ultimately leading to damage of multiple organs, including the heart. However, the pathogenesis of sepsis-induced myocardial dysfunction is still not fully understood. The present study is the first to examine alterations in expression of key angiogenic signaling system mediated by vascular endothelial growth factor (VEGF) in septic heart and the effects of endothelin dual blocker (ETDB) on it.

MAIN METHODS

Normal Wistar rats were either administered with: a) vehicle only (control group), b) lipopolysaccharide only (LPS: 15 mg/kg) and then sacrificed at different time points (1 h, 3 h, 6 h and 10 h), and c) the last group was co-administered with LPS and ETDB (SB-209670, 1 mg/kg body weight) for 6 h and then sacrificed.

KEY FINDINGS

Administration of LPS resulted in increases in levels of: a) serum tumor necrosis factor (TNF)-α, b) serum VEGF and c) serum endothelin (ET)-1 levels accompanied by up-regulation of cardiac VEGF and its downstream angiogenic signaling molecules. While cardiac TNF-α level was unchanged among experimental groups, cardiac ET-1 level was significantly higher in LPS-administered group.

SIGNIFICANCE

We conclude that elevation in VEGF angiogenic signaling may be triggered by diminished oxygenation in the myocardium following LPS administration as a consequence of sepsis-induced microvascular dysfunction. Because of this cardiac dysfunction, oxygen supply may be inadequate at microregional level to support the normal heart metabolism and function. ETDB at 6 h further increased the elevated levels of VEGF angiogenic signaling in endotoxemic heart.

The microcirculation is preserved in emergency department low-acuity sepsis patients without hypotension

OBJECTIVES

Microcirculatory dysfunction plays an important role in sepsis pathophysiology. Previous studies using sidestream dark-field (SDF) imaging have demonstrated microcirculatory flow abnormalities in patients with septic shock; however, the microcirculation is relatively unstudied in lower-acuity sepsis patients. The hypothesis was that patients with sepsis, but without hypotension, will demonstrate signs of flow abnormalities compared to noninfected control patients.

METHODS

This was a prospective, observational study in a convenience sample of patients with sepsis and noninfected controls, conducted in three urban, tertiary care emergency departments (EDs) in the United States. Sepsis was defined as suspected infection plus two or more systemic inflammatory response syndrome (SIRS) criteria; those with hypotension were excluded. Noninfected controls were ED patients without infection and without SIRS criteria. SDF imaging was obtained in all study patients during ED evaluation. Recommended microcirculatory flow parameters were measured, and the difference in these measures between sepsis patients and noninfected controls were calculated. The authors also correlated microcirculatory flow parameters with patient variables, including serum lactate.

RESULTS

A total of 106 patients were enrolled: 63 with sepsis and 43 noninfected controls. There were no differences in microcirculatory flow scores between sepsis patients and noninfected controls. Median microvascular flow index (MFI; with interquartile range [IQR] was 3.00 (IQR = 2.73 to 3.00) in sepsis patients versus 2.93 (IQR = 2.73 to 3.00) in control patients (p = 0.33), and mean proportion of perfused small vessels (PPV) was 91.5% (95% CI = 89.7% to 93.3%) versus 91.8% (95% CI = 89.7% to 93.9%), with a mean difference of 0.3% (95% CI = -2.5% to 3.1%; p = 0.84). Similarly, there were no significant differences in total vessel density, perfused vessel density, or heterogeneity index (HI). In the subset of infected patients for whom serum lactates were obtained (n % 37), MFI and PPV were negatively correlated with elevated serum lactate values: r = -0.32, p = 0.04; and r = -0.44, p < 0.01, respectively.

CONCLUSIONS

Measureable microcirculatory flow abnormalities were not observed in patients with early sepsis in the absence of hypotension. However, microcirculatory abnormalities were correlated with elevated serum lactate in normotensive sepsis patients, supporting the notion that impaired microcirculatory flow is coupled with cellular distress.

Fluid management in the critically ill child

Fluid management has a major impact on the duration, severity and outcome of critical illness. The overall strategy for the acutely ill child should be biphasic. Aggressive volume expansion to support tissue oxygen delivery as part of early goal-directed resuscitation algorithms for shock--especially septic shock--has been associated with dramatic improvements in outcome. Recent data suggest that the cost-benefit of aggressive fluid resuscitation may be more complex than previously thought, and may depend on case-mix and the availability of intensive care. After the resuscitation phase, critically ill children tend to retain free water while having reduced insensible losses. Fluid regimens that limit or avoid positive fluid balance are associated with a reduced length of hospital stay and fewer complications. Identifying the point at which patients change from the 'early shock' pattern to the later 'chronic critical illness' pattern remains a major challenge. Very little data are available on the choice of fluids, and most of the information that is available arises from studies of critically ill adults. There is therefore an urgent need for high-quality trials of both resuscitation and maintenance fluid regimens in critically ill children.

Near-infrared spectroscopy StO2 monitoring to assess the therapeutic effect of drotrecogin alfa (activated) on microcirculation in patients with severe sepsis or septic shock

Background

Sepsis is a leading cause of death despite appropriate management. There is increasing evidence that microcirculatory alterations might persist independently from macrohemodynamic improvement and are related to clinical evolution. Future efforts need to be directed towards microperfusion monitoring and treatment. This study explored the utility of thenar muscle oxygen saturation (StO₂) and its changes during a transient vascular occlusion test (VOT) to measure the microcirculatory response to drotrecogin alfa (activated) (DrotAA) in septic patients.

Methods

A prospective, observational study was performed in three general intensive care units at three university hospitals. We studied 58 patients with recent onset of severe sepsis or septic shock and at least two organ dysfunctions. Thirty-two patients were treated with DrotAA and 26 were not treated because of formal contraindication. StO₂ was monitored using near-infrared spectroscopy (NIRS), and VOT was performed to obtain deoxygenation (DeOx) and reoxygenation (ReOx) slopes. Measurements were obtained before DrotAA was started and were repeated daily for a 96-hour period.

Results

Patients’ characteristics, outcome, severity, and baseline values of StO₂, DeOx, and ReOx did not differ between groups. Treated patients significantly improved DeOx and ReOx values over time, whereas control patients did not. In treated patients, ReOx improvements were correlated to norepinephrine dose reductions. Early clinical response (SOFA improvement after 48 hours of treatment) was not associated to changes in VOT-derived slopes. In the treated group, the relative improvement of DeOx within 48 hours was able to predict mortality (AUC 0.91, p < 0.01).

Conclusions

In patients with severe sepsis or septic shock, DrotAA infusion was associated with improvement in regional tissue oxygenation. The degree of DeOx amelioration after 2 days in treated patients predicted mortality with high sensitivity and specificity. Thus, StO₂ derived variables might be useful to evaluate the microcirculatory response to treatment of septic shock.

Correlation between different Chinese medicine syndromes and changes in microcirculation in septic shock patients

OBJECTIVE

To investigate the correlation between different Chinese medicine (CM) syndromes and variations in microcirculation in septic shock patients.

METHODS

seventy Septic shock patients were divided into four groups: heat damaging qi-yin group (HDQY, 23 cases); yin exhaustion and yang collapse group (YEYC, 26 cases); excessive heat in Fu organ group (EHFO, 10 cases); and heat damaging nutrient-blood group (HDNB, 11 cases). Sublingual microcirculation parameters were observed by sidestream dark-field (SDF) imaging and scored by Acute Physiology and Chronic Health Evaluation II (APACHE II) and the Sequential Organ Failure Assessment (SOFA), and parameters of microcirculation perfusion variations and prognoses were analyzed.

RESULTS

Compared with those with qi-yin heat damage, perfused vessel density (PVD) in other groups decreased dramatically (P<0.05), and APACHE II scores increased significantly (P<0.05). In addition, the recovery time was prolonged substantially (P<0.05), and the mixed venous oxygen saturation (SVO2) decreased (P<0.05). Blood lactic acid increased significantly (P<0.05), and the mixed SVO decreased (P<0.05), in the YEYC group. Compared with the thermal injury camp blood group, sublingual microcirculation parameter variations showed no obvious difference in the YEYC and EHFO groups (P>0.05). There were significant positive correlations between CM syndromes and APACHE II scoring in different groups (r=0.512, P<0.05). There were negative correlations between PVD and APACHE II scoring (r=-0.378, P=0.043), the proportion of perfused vessels (PPV) and APACHE II scoring (r=-0.472, P=0.008), as well as between the microvascular flow index (MFI) and APACHE II scoring (r=-0.424, P=0.023) in different patients.

CONCLUSION

Sublingual microcirculation may serve as a clinical diagnostic parameter of the patient condition, as well as being a prognostic indicator.

From macrohemodynamic to the microcirculation

ICU patients need a prompt normalization of macrohemodynamic parameters. Unfortunately, this optimization sometimes does not protect patients from organ failure development. Prevention or treatment of organ failure needs another target to be pursued: the microcirculatory restoration. Microcirculation is the ensemble of vessels of maximum 100 μm in diameter. Nowadays the Sidestream Dark Field (SDF) imaging technique allows its bedside investigation and a recent round-table conference established the criteria for its evaluation. First, microcirculatory derangements have been studied in sepsis: they are mainly characterized by a reduction of vessel density, an alteration of flow, and a heterogeneous distribution of perfusion. Endothelial malfunction and glycocalyx rupture were proved to be the main reasons for the observed microthrombi, capillary leakage, leukocyte rolling, and rouleaux phenomenon, even if further studies are necessary for a better explanation. Therapeutic approaches targeting microcirculation are under investigation. Microcirculatory alterations have been recently demonstrated in other diseases such as hypovolemia and cardiac failure but this issue still needs to be explored. The aim of this paper is to gather the already known information, focus the reader's attention on the importance of microvascular physiopathology in critical illness, and prompt him to actively participate to achieve a more comprehensive understanding of the issue.

RBC-NOS-dependent S-nitrosylation of cytoskeletal proteins improves RBC deformability

Background

Red blood cells (RBC) possess a nitric oxide synthase (RBC-NOS) whose activation depends on the PI3-kinase/Akt kinase pathway. RBC-NOS-produced NO exhibits important biological functions like maintaining RBC deformability. Until now, the cellular target structure for NO, to exert its influence on RBC deformability, remains unknown. In the present study we analyzed the modification of RBC-NOS activity by pharmacological treatments, the resulting influence on RBC deformability and provide first evidence for possible target proteins of RBC-NOS-produced NO in the RBC cytoskeletal scaffold.

Methods/Findings

Blood from fifteen male subjects was incubated with the NOS substrate L-arginine to directly stimulate enzyme activity. Direct inhibition of enzyme activity was induced by L-N5-(1-Iminoethyl)-ornithin (L-NIO). Indirect stimulation and inhibition of RBC-NOS were achieved by applying insulin and wortmannin, respectively, substances known to affect PI3-kinase/Akt kinase pathway. The NO donor sodium nitroprusside (SNP) and the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) were additionally applied as NO positive and negative controls, respectively. Immunohistochemical staining was used to determine phosphorylation and thus activation of RBC-NOS. As a marker for NO synthesis nitrite was measured in plasma and RBCs using chemiluminescence detection. S-nitrosylation of erythrocyte proteins was determined by biotin switch assay and modified proteins were identified using LC-MS. RBC deformability was determined by ektacytometry. The data reveal that activated RBC-NOS leads to increased NO production, S-nitrosylation of RBC proteins and RBC deformability, whereas RBC-NOS inhibition resulted in contrary effects.

Conclusion/Significance

This study first-time provides strong evidence that RBC-NOS-produced NO modifies RBC deformability through direct S-nitrosylation of cytoskeleton proteins, most likely α- and β-spectrins. Our data, therefore, gain novel insights into biological functions of RBC-NOS by connecting impaired RBC deformability abilities to specific posttranslational modifications of RBC proteins. By identifying likely NO-target proteins in RBC, our results will stimulate new therapeutic approaches for patients with microvascular disorders.

An automated method for analysis of microcirculation videos for accurate assessment of tissue perfusion

Background

Imaging of the human microcirculation in real-time has the potential to detect injuries and illnesses that disturb the microcirculation at earlier stages and may improve the efficacy of resuscitation. Despite advanced imaging techniques to monitor the microcirculation, there are currently no tools for the near real-time analysis of the videos produced by these imaging systems. An automated system tool that can extract microvasculature information and monitor changes in tissue perfusion quantitatively might be invaluable as a diagnostic and therapeutic endpoint for resuscitation.

Methods

The experimental algorithm automatically extracts microvascular network and quantitatively measures changes in the microcirculation. There are two main parts in the algorithm: video processing and vessel segmentation. Microcirculatory videos are first stabilized in a video processing step to remove motion artifacts. In the vessel segmentation process, the microvascular network is extracted using multiple level thresholding and pixel verification techniques. Threshold levels are selected using histogram information of a set of training video recordings. Pixel-by-pixel differences are calculated throughout the frames to identify active blood vessels and capillaries with flow.

Results

Sublingual microcirculatory videos are recorded from anesthetized swine at baseline and during hemorrhage using a hand-held Side-stream Dark Field (SDF) imaging device to track changes in the microvasculature during hemorrhage. Automatically segmented vessels in the recordings are analyzed visually and the functional capillary density (FCD) values calculated by the algorithm are compared for both health baseline and hemorrhagic conditions. These results were compared to independently made FCD measurements using a well-known semi-automated method. Results of the fully automated algorithm demonstrated a significant decrease of FCD values. Similar, but more variable FCD values were calculated using a commercially available software program requiring manual editing.

Conclusions

An entirely automated system for analyzing microcirculation videos to reduce human interaction and computation time is developed. The algorithm successfully stabilizes video recordings, segments blood vessels, identifies vessels without flow and calculates FCD in a fully automated process. The automated process provides an equal or better separation between healthy and hemorrhagic FCD values compared to currently available semi-automatic techniques. The proposed method shows promise for the quantitative measurement of changes occurring in microcirculation during injury.

Enoxaparin sodium prevents intestinal microcirculatory dysfunction in endotoxemic rats

Introduction

During severe sepsis or septic shock, activation of the inflammatory and coagulatory systems can result in microcirculatory dysfunction as well as microvascular thrombosis, culminating in multiple organ dysfunction and death. Enoxaparin can inhibit factor Xa and attenuate endothelial damage. The primary purpose of this study was to investigate the effect of enoxaparin on intestinal microcirculation in endotoxemic rats.

Methods

Thirty male Wistar rats were divided into the following three groups: sham operated (OP); lipopolysaccharide (LPS); and LPS + Enoxaparin group. The rats received a midline laparotomy to exteriorize a segment of terminal ileum for microcirculation examination by full-field laser perfusion imager and sidestream dark field video microscope on mucosa, muscle, and Peyer's patch. In the LPS and LPS + Enoxaparin groups, 15 mg/kg LPS was administered intravenously to induce endotoxemia, and 400 IU/kg enoxaparin sodium was also administered in the LPS + Enoxaparin group.

Results

At 240 minutes, the mean arterial pressure was higher in the LPS + Enoxaparin group than in the LPS group (93 ± 9 versus 64 ± 16 mm Hg, P < 0.001). Microcirculatory blood flow intensity was higher in the LPS + Enoxaparin group than in the LPS group as follows: mucosa (1085 ± 215 versus 617 ± 214 perfusion unit [PU], P < 0.001); muscle (760 ± 202 versus 416 ± 223 PU, P = 0.001); and Peyer's patch (1,116 ± 245 versus 570 ± 280 PU, P < 0.001). Enoxaparin inhibited LPS-induced reduction in perfused small vessel density and increase in heterogeneity of microcirculation.

Conclusions

Enoxaparin can prevent intestinal microcirculatory dysfunction in endotoxemic rats by preventing microvascular thrombosis formation and maintaining normal mean arterial pressure.

Angiopoietin-1 variant reduces LPS-induced microvascular dysfunction in a murine model of sepsis

Introduction

Severe sepsis is characterised by intravascular or extravascular infection with microbial agents, systemic inflammation and microcirculatory dysfunction, leading to tissue damage, organ failure and death. The growth factor angiopoietin (Ang-1) has therapeutic potential but recombinant Ang-1 tends to aggregate and has a short half-life in vivo. This study aimed to investigate the acute effects of the more stable Ang-1 variant matrilin-1-angiopoietin-1 (MAT.Ang-1) on the function of the microcirculation in an experimental model of sepsis, and whether any protection by MAT-Ang-1 was associated with modulation of inflammatory cytokines, angiogenic factors or the endothelial nitric oxide synthase (eNOS)-Akt and vascular endothelial (VE)-cadherin pathways.

Methods

Aluminium window chambers were implanted into the dorsal skinfold of male C3H/HeN mice (7 to 10 weeks old) to expose the striated muscle microcirculation. Endotoxemia was induced by intraperitoneal injection of lipopolysaccharide (LPS, 1 mg/kg at 0 and 19 hours). MAT.Ang-1 was administered intravenously 20 hours after the onset of sepsis. Microcirculatory function was evaluated by intravital microscopy and Doppler fluximetry.

Results

Endotoxemia resulted in macromolecular leak, which was ameliorated by MAT.Ang-1 post-treatment. LPS induced a dramatic reduction in tissue perfusion, which was improved by MAT.Ang-1. Proteome profiler array analysis of skeletal muscle also demonstrated increased inflammatory and reduced angiogenic factors during endotoxemia. MAT.Ang-1 post-treatment reduced the level of IL-1β but did not significantly induce the expression of angiogenic factors. MAT.Ang-1 alone did not induce leak or increase angiogenic factors but did reduce vascular endothelial growth factor expression in controls.

Conclusion

Administration of MAT.Ang-1 after the onset of sepsis protects the microcirculation from endotoxemia-induced vascular dysfunction through reducing inflammation but without pro-angiogenic actions, thus representing a novel, potential pharmacotherapeutic agent for the treatment of sepsis.