Pathophysiology of Systemic Inflammatory Response Syndrome

The signs of circulatory insufficiency in horses with a variety of gastrointestinal diseases have been linked with the term endotoxemia. This association between translocation of bacterial endotoxins (lipopolysaccharides) from the gastrointestinal tract into the circulation, and the subsequent development of clinical signs referable to endotoxemia, initially was based on the detection of lipopolysaccharides in the circulation of approximately 30–40% of horses presented to a variety of university veterinary clinics (Fessler et al., 1989; King & Gerring, 1988; Steverink et al., 1994). The strength of this association was increased by the results of experimental studies in which the cardiovascular effects of intravenous administration of purified lipopolysaccharides were noted to be similar to the derangements in cardiovascular function encountered in horses with gastrointestinal diseases characterized by loss of integrity of the intestinal wall (Barton et al., 1998; Moore & Morris, 1992; Morris et al., 1992). However, differences between experimentally induced endotoxemia and the clinical syndrome of endotoxemia have been recognized by veterinary clinicians. For example, the profound neutropenia and febrile responses classically reported to occur after intravenous administration of purified lipopolysaccharides were absent in many horses described as being endotoxemic. During the same time frame, a similarly confusing situation existed in human medicine, especially when the terms sepsis, septic shock, and sepsis syndrome were used interchangeably. As a result of this confusion, in the early 1990s the term “systemic inflammatory response syndrome”(SIRS …