Hypotension due to diffuse vasodilation is the most severe expression of circulatory dysfunction in sepsis. It is probably an unintended consequence of the release of vasoactive mediators, whose purpose is to improve metabolic autoregulation (the process that matches oxygen availability to changing tissue oxygen needs) by inducing appropriate vasodilation. Mediators include the vasodilators prostacyclin and nitric oxide (NO), which are produced by endothelial cells.