AA is the precursor of oxygenated metabolites called the eicosanoids, that are generated by the cyclooxygenase, lipoxygenase, or cytochrome P450 enzymatic pathways. The biologically active eicosanoids are labile, usually but not always, act near their site of synthesis, and are not stored in any tissue to any appreciable degree. In most tissues, there is a continuous low-level synthesis that is probably essential to normal function. Injury or surgical trauma can evoke a dramatic change in the quality and quantity of the metabolites. Pharmacologic manipulation of the pathways of AA metabolism, or alteration of the effects of AA metabolites, can significantly improve tissue perfusion in a variety of clinical situations. (See Figure 1 for a schematic summary of the pathways involved in arachidonic acid metabolites.