Chapter 42: Intra-Abdominal Infections

INTRODUCTION

• Intra-abdominal infections are those contained within the peritoneum or retroperitoneal space. Two general types of intra-abdominal infections are discussed throughout this chapter: peritonitis and abscess.

• Peritonitis is defined as the acute, inflammatory response of peritoneal lining to microorganisms, chemicals, irradiation, or foreign body injury. It may be classified as either primary or secondary. With primary peritonitis, an intra-abdominal focus of disease may not be evident. In secondary peritonitis, a focal disease process is evident within the abdomen.

• An abscess is a purulent collection of fluid separated from surrounding tissue by a wall consisting of inflammatory cells and adjacent organs. It usually contains necrotic debris, bacteria, and inflammatory cells.

PATHOPHYSIOLOGY

• Table 42–1 summarizes many of the potential causes of bacterial peritonitis. Appendicitis is the most frequent cause of abscess. Intra-abdominal infection results from entry of bacteria into the peritoneal or retroperitoneal spaces or from bacterial collections within intra-abdominal organs. When peritonitis results from peritoneal dialysis, skin surface flora are introduced via the peritoneal catheter.

• In primary peritonitis, bacteria may enter the abdomen via the bloodstream or the lymphatic system, by transmigration through the bowel wall, through an indwelling peritoneal dialysis catheter, or via the fallopian tubes in female patients.

• In secondary peritonitis, bacteria most often enter the peritoneum or retroperitoneum as a result of disruption of the integrity of the gastrointestinal (GI) tract caused by diseases or traumatic injuries.

• When bacteria become dispersed throughout the peritoneum, the inflammatory process involves the majority of the peritoneal lining. Fluid and protein shift into the abdomen (called “third spacing”) may decrease circulating blood volume and cause shock.

• Peritonitis often results in death because of the effects on major organ systems. Fluid shifts and endotoxins may cause hypotension and shock.

• An abscess begins by the combined action of inflammatory cells (eg, neutrophils), bacteria, fibrin, and other inflammatory components. Within the abscess, oxygen tension is low, and anaerobic bacteria thrive.

MICROBIOLOGY

• Primary bacterial peritonitis is often caused by a single organism. In children, the pathogen is usually group A Streptococcus, Escherichia coli, Streptococcus pneumoniae, or Bacteroides species. When peritonitis occurs in association with cirrhotic ascites, E. coli is isolated most frequently.

• Peritonitis in patients undergoing peritoneal ...