Critical care : the official journal of the Critical Care Forum
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Sepsis and shock result in disturbances in microcirculatory perfusion and tissue oxygen utilisation that may not be reflected in global measures of haemodynamics. Near-infrared spectroscopy enables measurement of tissue oxygen saturation (StO2) and provides information on local microvascular and mitochondrial function. This measure could be incorporated with existing targets of goal-directed therapy to provide an integrated approach to haemodynamic resuscitation of both the macro- and microcirculation in various shock states. However, key methodological factors must be addressed before widespread clinical application.
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Cardiac-related failure of weaning from mechanical ventilation is an important reason for prolonged mechanical ventilation, intensive care unit treatment, and increased morbidity and mortality. When transthoracic echocardiography (TTE) is routinely performed before a weaning trial, patients at high risk of cardiac-related failure can be detected by low left ventricular (LV) ejection fraction, diastolic dysfunction, and elevated LV filling pressure. During the weaning trial, a further increase of LV filling pressure and progression of diastolic failure can be observed by repeated TTE. Owing to certain limitations concerning patients and methodology, TTE cannot be employed in every patient and invasive hemodynamic monitoring is still mandatory in selected patients with repetitive weaning failure.
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Crystalloid and colloid solutions are used for resuscitation of the critically ill. One set of options, widely used today, are different preparations of hydroxyethyl starch (HES). However, the safety of HES regarding impairment of blood coagulation remains incompletely elucidated, a circumstance that limits its clinical use. Understanding mechanisms and potential differences between low-molecular and low-substituted HES and other HES solutions seems clinically relevant.
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The interesting study by Davis and colleagues in the current issue of Critical Care expands on the increasingly recognized role of angiopoietins in human sepsis but raises a number of questions, which are discussed in this commentary. The authors describe an association between elevated angiopoietin (ang)-2 levels and impaired vascular reactivity, measured by the partly nitric oxide-dependent finger hyperemic response to forearm vascular occlusion, in patients with sepsis. This suggests that the ang-1/2-Tie2 system is involved in a number of pathophysiologic, phenotypic and perhaps prognostic alterations in human sepsis, on top of the effect on pulmonary endothelial barrier function. The novel inflammatory route may be a target for future therapeutic studies in human sepsis and acute lung injury, including those with activated protein C.
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The hypothalamic-pituitary-adrenal (HPA) axis response in sepsis remains to be elucidated. Apart from corticotropin-releasing hormone, adrenocorticotropic hormone, and cortisol, many other neuroendocrine factors participate in the regulation of HPA stress response. ⋯ All of these add to the complexity of the concept of 'relative adrenal insufficiency' and may account for the difficulty of clinical diagnosis and for the conflicting results of corticosteroid replacement therapy in severe sepsis/septic shock. The study by Lesur and colleagues expands our understanding of the mechanism, and further study of HPA stress response is warranted.