Inflammatory mediators and their influence on haemostasis

Sepsis is the most important cause of mortality in the Intensive Care Units. At present, sepsis is understood to be the inflammatory response of the host to infection, rather than a direct effect of microbial aggression. From the clinical standpoint, this inflammatory response is known as systemic inflammatory response syndrome (SIRS). Pathophysiologically, SIRS is characterized by the activation of several groups of cell (monocytes/macrophages, PMNs, and endothelial cells) and by the release of inflammatory mediators (cytokines and others). Tumor necrosis factor (TNF) is the first cytokine released by endotoxin action over monocyte/macrophage. TNF secretion, modulated by interferon gamma (IFN gamma) and interleukin 10 (IL-10), is followed by release of other cytokines such as interleukins (IL) (IL-1, IL-6 and IL-8). These mediators are able to act over hemostasis activating the extrinsic pathway through tissue factor expression. The action of the mediators over endothelial cells induces an increase in plasminogen activator inhibitor type 1 (PAI-1) levels with inhibition of fibrinolysis. Both coagulation activation and fibrinolysis blockade result in fibrin deposit in the microvascular system. The complexity of the mechanisms implicated in systemic inflammatory response make a general rule so difficult to establish, because patient response is highly individualized and it is not possible to know which moment of this dynamic process is being analyzed.