Peritonitis: pathophysiology and local defense mechanisms

The peritoneal cavity can be divided in the supracolic infracolic and paracolic spaces, the lesser sack and the pelvis. The peritoneum is a semipermeable membrane which allows a flux of solutes into and from the peritoneal cavity. In addition, particles can be absorbed through the stomata of the diaphragmatic peritoneum. Secondary peritonitis is always a polymicrobial infection. The flora consists of aerobic enterobacteriaeceae and anaerobs mainly B. fragilis. These two groups of bacteria act synergistically. Besides unspecific defence mechanisms, i.e. the direct absorption of bacteria and the entrapment of bacteria in fibrin, the immunological defence mechanisms of the peritoneal cavity are triggered by endotoxin contained in the cell wall of the invading bacteria leading to the production of cytokines by macrophages, activation of complement and as a result the migration of granulocytes from the intervascular space into the peritoneal cavity.