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      Bench-to-bedside review: Sepsis is a disease of the microcirculation

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          Abstract

          Microcirculatory perfusion is disturbed in sepsis. Recent research has shown that maintaining systemic blood pressure is associated with inadequate perfusion of the microcirculation in sepsis. Microcirculatory perfusion is regulated by an intricate interplay of many neuroendocrine and paracrine pathways, which makes blood flow though this microvascular network a heterogeneous process. Owing to an increased microcirculatory resistance, a maldistribution of blood flow occurs with a decreased systemic vascular resistance due to shunting phenomena. Therapy in shock is aimed at the optimization of cardiac function, arterial hemoglobin saturation and tissue perfusion. This will mean the correction of hypovolemia and the restoration of an evenly distributed microcirculatory flow and adequate oxygen transport. A practical clinical score for the definition of shock is proposed and a novel technique for bedside visualization of the capillary network is discussed, including its possible implications for the treatment of septic shock patients with vasodilators to open the microcirculation.

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          Most cited references63

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          A trial of goal-oriented hemodynamic therapy in critically ill patients. SvO2 Collaborative Group.

          Hemodynamic therapy to raise the cardiac index and oxygen delivery to supranormal may improve outcomes in critically ill patients. We studied whether increasing the cardiac index to a supranormal level (cardiac-index group) or increasing mixed venous oxygen saturation to a normal level (oxygen-saturation group) would decrease morbidity and mortality among critically ill patients, as compared with a control group in which the target was a normal cardiac index. A total of 10,726 patients in 56 intensive care units were screened, among whom 762 patients belonging to predefined diagnostic categories with acute physiology scores of 11 or higher were randomly assigned to the three groups (252 to the control group, 253 to the cardiac-index group, and 257 to the oxygen-saturation group). The hemodynamic targets were reached by 94.3 percent of the control group, 44.9 percent of the cardiac-index group, and 66.7 percent of the oxygen-saturation group (P < 0.001). Mortality was 48.4, 48.6, and 52.1 percent, respectively (P = 0.638), up to the time of discharge from the intensive care unit and 62.3, 61.7, and 63.8 percent (P = 0.875) at six months. Among patients who survived, the number of dysfunctional organs and the length of the stay in the intensive care unit were similar in the three groups. No differences in mortality among the three groups were found for any diagnostic category. A subgroup analysis of the patients in whom hemodynamic targets were reached revealed similar mortality rates: 44.8, 40.4, and 39.0 percent, respectively (P = 0.478). Hemodynamic therapy aimed at achieving supranormal values for the cardiac index or normal values for mixed venous oxygen saturation does not reduce morbidity or mortality among critically ill patients.
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            The pathogenesis of sepsis.

            Sepsis and its sequelae (sepsis syndrome and septic shock) are increasingly common and are still potentially lethal diagnoses. Many mediators of the pathogenesis of sepsis have recently been described. These include tumor necrosis factor alpha (TNF alpha), interleukins, platelet activating factor, leukotrienes, thromboxane A2, and activators of the complement cascade. Neutrophil and platelet activation may also play a role. Other agents that may participate in the sepsis cascade include adhesion molecules, kinins, thrombin, myocardial depressant substance, beta-endorphin, and heat shock proteins. Endothelium-derived relaxing factor and endothelin-1 are released from the endothelium and seem to exert a regulatory effect, counterbalancing each other. A central mediator of sepsis does not seem to exist, although TNF alpha has been commonly proposed for this role. Animal studies are difficult to extrapolate to the clinical setting because of cross-species differences and variations in experimental design. Rather than being caused by any single pathogenic mechanism, it is more likely that sepsis is related to the state of activation of the target cell, the nearby presence of other mediators, and the ability of the target cell to release other mediators. Also important is the downregulation or negative feedback of these mediators or the generation of natural inflammation inhibitors, such as interleukin-4 and interleukin-8. Endothelial damage in sepsis probably results from persistent and repetitive inflammatory insults. Eventually, these insults produce sufficient damage that downregulation can no longer occur; this leads to a state of metabolic anarchy in which the body can no longer control its own inflammatory response.
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              Nitric oxide in the pathogenesis of vascular disease.

              Nitric oxide (NO) is synthesized by at least three distinct isoforms of NO synthase (NOS). Their substrate and cofactor requirements are very similar. All three isoforms have some implications, physiological or pathophysiological, in the cardiovascular system. The endothelial NOS III is physiologically important for vascular homeostasis, keeping the vasculature dilated, protecting the intima from platelet aggregates and leukocyte adhesion, and preventing smooth muscle proliferation. Central and peripheral neuronal NOS I may also contribute to blood pressure regulation. Vascular disease associated with hypercholesterolaemia, diabetes, and hypertension is characterized by endothelial dysfunction and reduced endothelium-mediated vasodilation. Oxidative stress and the inactivation of NO by superoxide anions play an important role in these disease states. Supplementation of the NOS substrate L-arginine can improve endothelial dysfunction in animals and man. Also, the addition of the NOS cofactor (6R)-5,6,7, 8-tetrahydrobiopterin improves endothelium-mediated vasodilation in certain disease states. In cerebrovascular stroke, neuronal NOS I and cytokine-inducible NOS II play a key role in neurodegeneration, whereas endothelial NOS III is important for maintaining cerebral blood flow and preventing neuronal injury. In sepsis, NOS II is induced in the vascular wall by bacterial endotoxin and/or cytokines. NOS II produces large amounts of NO, which is an important mediator of endotoxin-induced arteriolar vasodilatation, hypotension, and shock. Copyright 2000 John Wiley & Sons, Ltd.
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                Author and article information

                Journal
                Crit Care
                Critical Care
                BioMed Central (London )
                1364-8535
                1466-609X
                2004
                16 June 2004
                : 8
                : 6
                : 462-468
                Affiliations
                [1 ]Department of Intensive Care Medicine, Gelre ziekenhuizen, Apeldoorn, The Netherlands
                [2 ]Department of Physiology, Academic Medical Center, University of Amsterdam, The Netherlands
                [3 ]Department of Intensive Care Medicine, Onze Lieve Vrouwe Gasthuis, Amsterdam, The Netherlands
                Article
                cc2894
                10.1186/cc2894
                1065042
                15566617
                38ed5742-0f1e-46cc-b819-018176ec3236
                Copyright © 2004 BioMed Central Ltd
                History
                Categories
                Review

                Emergency medicine & Trauma
                microcirculation,shock,orthogonal polarization spectral imaging

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