Think locally: evaluation of the microcirculation in sepsis

ITGAM: A Pivotal Regulator in Macrophage Dynamics and Cardiac Function During Sepsis-Induced Cardiomyopathy

BACKGROUND

Sepsis-induced cardiomyopathy (SIC) is a critical complication arising from sepsis characterized by reversible myocardial dysfunction. Despite the increasing attention to SIC in research, the underlying molecular mechanisms remain poorly comprehended.

METHODS

In this study, we utilized bioinformatics to analyze RNA-sequencing (RNA-seq) and single-cell RNA-sequencing (scRNA-seq) data from the Gene Expression Omnibus (GEO) database to identify key immune cell populations and molecular markers associated with SIC. Our experimental approach combined in vitro and in vivo studies to investigate the roles of integrin alpha M (ITGAM) and intracellular adhesion molecule-1 (ICAM-1) in macrophage recruitment and phenotypic polarization, as well as their impact on cardiac function during SIC.

RESULTS

The bioinformatics analysis disclosed significant alterations in gene expression and immune cell composition within the cardiac tissue during SIC, where macrophages emerged as the predominant immune cell type. Notably, ITGAM was identified as a key regulatory molecule that modulates macrophage function, driving the pathogenesis of SIC through its influence on the recruitment and functional reprogramming of these cells. In vitro experiments revealed that lipopolysaccharide (LPS) stimulation triggered an upregulation of ITGAM in macrophages and ICAM-1 in endothelial cells, underscoring their critical roles in immune cell mobilization and intercellular communication. The strategic administration of ITGAM-neutralizing antibodies to SIC mice resulted in a marked decrease in macrophage infiltration within the cardiac tissue, which was initially associated with an improvement in cardiac function. However, this intervention paradoxically resulted in an increased mortality rate during the later phases of SIC, underscoring the complex and dualistic function of ITGAM.

CONCLUSION

This study provides new insights into the complex dynamics of immune cells within the cardiac environment during SIC, with a particular emphasis on the modulatory role of ITGAM in shaping macrophage behavior. The findings shed light on the reversible nature of myocardial dysfunction in SIC and emphasize the importance of targeted therapeutic strategies for the effective management of SIC.

Pathophysiology of sepsis-induced cardiomyopathy

Sepsis is the life-threatening organ dysfunction caused by a dysregulated host response to infection and is the leading cause of death in intensive care units. Cardiac dysfunction caused by sepsis, usually termed sepsis-induced cardiomyopathy, is common and has long been a subject of interest. In this Review, we explore the definition, epidemiology, diagnosis and pathophysiology of septic cardiomyopathy, with an emphasis on how best to interpret this condition in the clinical context. Advances in diagnostic techniques have increased the sensitivity of detection of myocardial abnormalities but have posed challenges in linking those abnormalities to therapeutic strategies and relevant clinical outcomes. Sophisticated methodologies have elucidated various pathophysiological mechanisms but the extent to which these are adaptive responses is yet to be definitively answered. Although the indications for monitoring and treating septic cardiomyopathy are clinical and directed towards restoring tissue perfusion, a better understanding of the course and implications of septic cardiomyopathy can help to optimize interventions and improve clinical outcomes.

Patterns of central venous oxygen saturation, lactate and veno-arterial CO2 difference in patients with septic shock

BACKGROUND AND AIMS

Tissue hypoperfusion is reflected by metabolic parameters such as lactate, central venous oxygen saturation (ScvO2) and the veno-arterial CO2 (vaCO2) difference. We studied the relation of these parameters over time and with outcome in patients with severe septic shock.

MATERIALS AND METHODS

In this single-center, prospective observational cohort study, adult patients (≥18 years) with circulatory shock were included. Echocardiography and simultaneous arterial and venous blood gases were done on enrolment (0 h) and at 24, 48 and 72 h. The partial pressure of CO2, lactate and ScvO2 were recorded from the central venous blood samples. The vaCO2 was calculated as the difference in CO2 between paired venous and arterial blood gas samples.

RESULTS

Of the 104 patients with circulatory shock, 79 patients (44 males) with septic shock aged 49.8 (standard deviation ± 14.6) years and with sequential organ failure assessment (SOFA) score of 11.0 ± 3.4 were included. 71 patients (89.9%) were ventilated (11.4 ± 12.3 ventilator-free days). The duration of hospitalization was 16.6 ± 12.8 days and hospital mortality 50.6%. Lactate significantly decreased over time with a greater decrement in survivors than nonsurvivors (-0.35 vs. -0.10, P < 0.001). For every l/min increase in cardiac output, vaCO2 decreased by 0.34 mmHg (P = 0.006). There was no association between ScvO2 and mortality (P = 0.930). 0 h SOFA and vaCO2 ≤6 mmHg were strongly associated (P = 0.005, P = 0.018, respectively) with higher odds of mortality. However, this association was evident only in those with ScvO2 >70% and not in ScvO2 ≤70%.

CONCLUSION

In septic shock, vaCO2 ≤6 mmHg is independently associated with mortality, particularly in those with normalized ScvO2 consistent with metabolic microcirculatory abnormalities in these patients.

Systemic and renal oxidative stress in the pathogenesis of hypertension: modulation of long-term control of arterial blood pressure by resveratrol

Hypertension affects over 25% of the global population and is associated with grave and often fatal complications that affect many organ systems. Although great advancements have been made in the clinical assessment and treatment of hypertension, the cause of hypertension in over 90% of these patients is unknown, which hampers the development of targeted and more effective treatment. The etiology of hypertension involves multiple pathological processes and organ systems, however one unifying feature of all of these contributing factors is oxidative stress. Once the body's natural anti-oxidant defense mechanisms are overwhelmed, reactive oxygen species (ROS) begin to accumulate in the tissues. ROS play important roles in normal regulation of many physiological processes, however in excess they are detrimental and cause widespread cell and tissue damage as well as derangements in many physiological processes. Thus, control of oxidative stress has become an attractive target for pharmacotherapy to prevent and manage hypertension. Resveratrol (trans-3,5,4'-Trihydroxystilbene) is a naturally occurring polyphenol which has anti-oxidant effects in vivo. Many studies have shown anti-hypertensive effects of resveratrol in different pre-clinical models of hypertension, via a multitude of mechanisms that include its function as an anti-oxidant. However, results have been mixed and in some cases resveratrol has no effect on blood pressure. This may be due to the heavy emphasis on peripheral vasodilator effects of resveratrol and virtually no investigation of its potential renal effects. This is particularly troubling in the arena of hypertension, where it is well known and accepted that the kidney plays an essential role in the long term regulation of arterial pressure and a vital role in the initiation, development and maintenance of chronic hypertension. It is thus the focus of this review to discuss the potential of resveratrol as an anti-hypertensive treatment via amelioration of oxidative stress within the framework of the fundamental physiological principles of long term regulation of arterial blood pressure.

Early neurovascular uncoupling in the brain during community acquired pneumonia

INTRODUCTION

Sepsis leads to microcirculatory dysfunction and therefore a disturbed neurovascular coupling in the brain. To investigate if the dysfunction is also present in less severe inflammatory diseases we studied the neurovascular coupling in patients suffering from community acquired pneumonia.

METHODS

Patients were investigated in the acute phase of pneumonia and after recovery. The neurovascular coupling was investigated with a simultaneous electroencephalogram (EEG)-Doppler technique applying a visual stimulation paradigm. Resting EEG frequencies, visual evoked potentials as well as resting and stimulated hemodynamic responses were obtained. Disease severity was characterized by laboratory and cognitive parameters as well as related scoring systems. Data were compared to a control group.

RESULTS

Whereas visually evoked potentials (VEP) remained stable a significant slowing and therefore uncoupling of the hemodynamic responses were found in the acute phase of pneumonia (Rate time: control group: 3.6 ± 2.5 vs. acute pneumonia: 1.6 ± 2.4 s; P < 0.0005). In the initial investigation, patients who deteriorated showed a decreased hemodynamic response as compared with those who recovered (gain: recovered: 15% ± 4% vs. deteriorated: 9% ± 3%, P < 0.05; control: 14% ± 5%). After recovery the coupling normalized.

CONCLUSIONS

Our study underlines the role of an early microcirculatory dysfunction in inflammatory syndromes that become evident in pre-septic conditions with a gradual decline according to disease severity.

Red blood cell transfusion affects microdialysis-assessed interstitial lactate/pyruvate ratio in critically ill patients with late sepsis

PURPOSE

The aim of this study was to explore the effect of red blood cell (RBC) transfusion on microdialysis-assessed interstitial fluid metabolic parameters in septic patients.

METHODS

We conducted a retrospective study of 37 patients with severe sepsis/septic shock requiring transfusion of one to two RBC units. Interstitial fluid metabolic alterations were monitored by a microdialysis catheter inserted in the subcutaneous adipose tissue. Samples were collected before (T0) and after transfusion at two time-points: T1a and T1b; median post-transfusion times of 120 [interquartile range (IQR); 45-180] and 360 (IQR; 285-320) min. Lactate, pyruvate, glycerol and glucose concentrations were measured with a bedside analyzer, and the lactate/pyruvate (LP) ratio was calculated automatically.

RESULTS

RBC transfusions decreased the LP ratio from (T0) 18.80 [interquartile range (IQR); 14.85-27.45] to (T1a) 17.80 (IQR; 14.35-25.20; P < 0.05) and (T1b) 17.90 (IQR; 14.45-22.75; P < 0.001), while there was also significant interindividual variation. Post-transfusion LP ratio changes at T1a [r = -0.42; 95 % confidence interval (CI), -0.66 to -0.098; P = 0.01] and T1b (r = -0.68; 95 % [CI], -0.82 to -0.44; P < 0.001) were significantly correlated with the pre-transfusion LP ratio, but not with baseline demographic characteristics, vital signs, severity scores, hemoglobin level and blood lactate. RBC storage time and leukocyte reduction had no influence on the tissue metabolic response to transfusion.

CONCLUSIONS

Tissue oxygenation is affected by RBC transfusion in critically ill septic patients. Monitoring of tissue LP ratio by microdialysis may represent a useful method for individual clinical management.

Review article: Part two: Goal-directed resuscitation--which goals? Perfusion targets

Haemodynamic targets, such as cardiac output, mean arterial blood pressure and central venous oxygen saturations, remain crude predictors of tissue perfusion and oxygen supply at a cellular level. Shocked patients may appear adequately resuscitated based on normalization of global vital signs, yet they are still experiencing occult hypoperfusion. If targeted resuscitation is employed, appropriate use of end-points is critical. In this review, we consider the value of directing resuscitation at the microcirculation or cellular level. Current technologies available include sublingual capnometry, video microscopy of the microcirculation and near-infrared spectroscopy providing a measure of tissue oxygenation, whereas base deficit and lactate potentially provide a surrogate measure of the adequacy of global perfusion. The methodology and evidence for these technologies guiding resuscitation are considered in this narrative review.

Resveratrol improves renal microcirculation, protects the tubular epithelium, and prolongs survival in a mouse model of sepsis-induced acute kidney injury

The mortality rate of patients who develop acute kidney injury during sepsis nearly doubles. The effectiveness of therapy is hampered because it is usually initiated only after the onset of symptoms. As renal microvascular failure during sepsis is correlated with the generation of reactive nitrogen species, the therapeutic potential of resveratrol, a polyphenol vasodilator that is also capable of scavenging reactive nitrogen species, was investigated using the cecal ligation and puncture (CLP) murine model of sepsis-induced acute kidney injury. Resveratrol when given at 5.5 h following CLP reversed the decline in cortical capillary perfusion, assessed by intravital microscopy, at 6 h in a dose-dependent manner. Resveratrol produced the greatest improvement in capillary perfusion and increased renal blood flow and the glomerular filtration rate without raising systemic pressure. A single dose at 6 h after CLP was unable to improve renal microcirculation assessed at 18 h; however, a second dose at 12 h significantly improved microcirculation and decreased the levels of reactive nitrogen species in tubules, while improving renal function. Moreover, resveratrol given at 6, 12, and 18 h significantly improved survival. Hence, resveratrol may have a dual mechanism of action to restore the renal microcirculation and scavenge reactive nitrogen species, thus protecting the tubular epithelium even when administered after the onset of sepsis.

Targeting the microcirculation in resuscitation of acutely unwell patients

PURPOSE OF REVIEW

The ultimate goals of hemodynamic therapy in acutely unwell patients are to restore effective tissue perfusion and oxygen delivery to maintain cellular metabolism. Optimization of systemic hemodynamics may improve the time course of microcirculatory dysfunction and eventually the patient's outcome. However, relationships between systemic hemodynamics and microcirculatory changes during resuscitation are complex and underperfused microcirculation may persist, despite restored macrohemodynamics. Thus, targeting the microcirculation is a logical goal to obtain an adequate resuscitation.

RECENT FINDINGS

The impact of systemic interventions such as fluid resuscitation, vasopressor therapy, and transfusion has been evaluated on microcirculatory perfusion in septic-shock patients. It demonstrated inconstant improvement according to time-course evolution of the underlying pathology with interindividual variability. Thus, therapy targeting the microcirculation should be adapted to individual microcirculatory monitoring. Specific therapy with nitroglycerin did not promote microcirculation in septic shock but was associated with microcirculatory improvement in cardiogenic shock.

SUMMARY

Microcirculatory hemodynamics have to be restored as soon as possible during the early phase of the management of acutely unwell patients. Future trials should test whether microcirculation-guided strategy could better improve organ dysfunction than global hemodynamic-guided strategy. An optimal resuscitation has to restore the systematic hemodynamics and make sure of the quality of the microcirculation.

Microdialysis-assessed interstitium alterations during sepsis: relationship to stage, infection, and pathogen

PURPOSE

More than a disorder of macrocirculation, sepsis is a disease affecting the microcirculation and the tissue metabolism. In vivo microdialysis (MD) is a bedside technique that can monitor tissue metabolic changes. We conducted this study aiming (1) to assess whether patients at different sepsis stages present with different MD-assessed tissue metabolic profiles and (2) to determine if different underlying types of infections and implicated pathogens are associated with dissimilar metabolic alterations.

METHODS

We studied 90 mechanically ventilated patients, 65 with septic shock and 25 with severe sepsis. An MD catheter was inserted in the subcutaneous adipose tissue of the upper thigh and interstitial fluid samples were collected along with arterial blood samples every 4 h for a maximum of 6 days. Lactate, pyruvate, glycerol, and glucose concentrations were measured.

RESULTS

During the study period, patients with septic shock had higher MD-assessed glycerol (P = 0.009), glycerol gradient (P = 0.016), and glucose (P = 0.004) than patients with severe sepsis, whereas tissue lactate, lactate gradient, and pyruvate dropped significantly with time (P = 0.007, <0.001, and <0.001, respectively) in both patient groups without any observed between-group difference. In addition, there was no between-group difference in their tissue lactate/pyruvate ratio on any day, nor did the ratio decrease significantly with time. Compared with pneumonia patients, and despite similar baseline clinical characteristics, those suffering from intra-abdominal infections showed a pattern of higher and progressively increasing tissue levels of glucose (P = 0.001) and glycerol (P = 0.001). Finally, patients harboring gram-positive infections had higher tissue levels of glycerol (P = 0.027) and glycerol gradient (P = 0.029) than patients with gram-negative infections.

CONCLUSIONS

MD can detect tissue metabolic abnormalities that differ in relation to the sepsis stage and the type of underlying infection or responsible pathogen. Some of the MD-assessed abnormalities are not reflected by conventional blood measurements and possess prognostic potential. It remains to be determined if this type of metabolic monitoring can find clinical applications in the wide population of septic critically ill patients.