Clinics in chest medicine
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Clinics in chest medicine · Dec 2008
ReviewThe heterogeneity of the microcirculation in critical illness.
Microcirculation, a complex and specialized facet of organ architecture, has characteristics that vary according to the function of the tissue it supplies. Bedside technology that can directly observe microcirculation in patients, such as orthogonal polarization spectral imaging and sidestream dark field imaging, has opened the way to investigating this network and its components, especially in critical illness and surgery. These investigations have underscored the central role of microcirculation in perioperative disease states. ⋯ This review focuses on studies conducted to date on the microcirculatory beds of critically ill patients. The functional anatomy of microcirculation networks and the role of these networks in the pathogenesis of critical illness are discussed. The morphology of microvascular beds that have been visualized during surgery and intensive care at the bedside are also described, including those of the brain, sublingual region, skin, intestine, and eyes.
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Hyperglycemia is common during the course of critical illness and is associated with adverse clinical outcomes. Randomized controlled trials and large observational trials of insulin therapy titrated to achieve glucose values approximating the normal range (80 to 110 mg/dL) demonstrate improved morbidity and mortality in heterogeneous populations and have led to recommendations for improved glucose control. Patients who have septic shock, however, appear to be at higher risk for hypoglycemia, and a recent randomized trial focusing exclusively on patients who had severe sepsis did not show benefit. The recent Surviving Sepsis consensus statement recommends insulin therapy using validated protocols to lower glucose (less than 150 mg/dL) pending the results of adequately powered trials to determine if normalization (less than 110 mg/dL) of glucose is needed to optimize outcomes in patients who have severe sepsis.
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Sepsis is often associated with systemic intravascular activation of coagulation, potentially leading to widespread microvascular deposits of fibrin, and thereby contributing to multiple organ dysfunction. A complex interaction exists between activation of inflammatory systems and the initiating and regulating pathways of coagulation. A diagnosis of sepsis-associated disseminated intravascular coagulation can be made by a combination of routinely available laboratory tests, for which simple diagnostic algorithms have become available. Strategies to inhibit coagulation activation may theoretically be justified and are being evaluated in clinical studies.
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Definitions have been considered important in all fields of medicine, both at a patient level to facilitate accurate diagnosis and treatment, and at a research level to clarify patient inclusion criteria and interpretation of study results. Although there is agreement that sepsis refers to the host response to infection, the complexity of this response and of the patient groups affected, however, has meant that establishing accepted definitions of sepsis has been difficult. Recent consensus has provided global definitions of sepsis and infection, but further work is necessary to provide a means of more completely characterizing the sepsis response in individual patients, such that new interventions can be targeted better as physicians strive to decrease the still high mortality rates associated with this condition.
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Key links in the chain of survival for the management of severe sepsis and septic shock are early identification and comprehensive resuscitation of high-risk patients. Multiple studies have shown that the first 6 hours of early sepsis management are especially important from a diagnostic, pathogenic, and therapeutic perspective, and that steps taken during this period can have a significant impact on outcome. The recognition of this critical time period and the robust outcome benefit realized in previous studies provides the rationale for adopting early resuscitation as a distinct intervention. Sepsis joins trauma, stroke, and acute myocardial infarction in having "golden hours," representing a critical opportunity early on in the course of disease for actions that offer the most benefit.