Current concepts in clinical therapeutics: intra-abdominal infections.

The etiology, pathophysiology, clinical presentation, and treatment of the two major types of intra-abdominal infections--peritonitis and abscesses--are described. Peritonitis of infectious origin is the acute response of the peritoneum to microorganisms; it is classified as primary (when the source of bacteria is not apparent) or secondary (usually involving perforation of a hollow structure of the GI tract with subsequent release of microbes). Peritonitis results in mortality because of fluid shifts and endotoxins that may cause hypovolemia and shock. Abscesses, purulent collections of fluid physically separated from the surrounding tissues, are the result of chronic inflammation following failure of the body to eradicate a pathogen completely. Secondary intra-abdominal infections are often polymicrobial because of the diversity of organisms in the GI tract. The size of bacterial inocula and the number and types of species present substantially affect patient outcome. The patient with peritonitis usually presents in acute distress, with generalized abdominal pain and faint bowel sounds. The presentation of the patient with intra-abdominal abscess is more variable and less dramatic; pain and fever may be present. The treatment of these infections requires the coordinated use of prompt surgical intervention, support of vital functions, and appropriate antimicrobial therapy. Surgical procedures are used to stop continuing bacterial contamination of the peritoneum, remove foreign material from the abdomen, and drain purulent collections; it is the foundation of treating most types of intra-abdominal infections. Aggressive fluid therapy is required to assure adequate intravascular volumes in most patients. Generally, antimicrobial coverage for both aerobes and anaerobes must be started before culture results are available. Antimicrobial therapy for specific types of infections is given in the article. Surgical procedures are the foundation of treatment of most intra-abdominal infections; antimicrobial agents active against aerobic gram-negative bacilli and anaerobes are important adjuncts.