Pulmonary infection complicating intra-abdominal sepsis: clinical and experimental observations.

Pulmonary infection complicating intra-abdominal abscess is a major clinical problem. One hundred and forty-three patients with abdominal abscesses were reviewed; 41 had associated pneumonia by strictly defined criteria. The causative organisms for the pneumonia were Pseudomonas (35), Klebsiella (20), and Enterobacter (16), while abdominal infections were caused by Escherichia coli (22), Klebsiella (21), and Enterococcus (18). The temporal and bacteriologic relationship between the abdominal and pulmonary infection suggested that decreased pulmonary host defenses might be operative in the high incidence of pneumonia observed. An experimental model for intra-abdominal abscess was created using cecal ligation in the rat. Animals with an abdominal abscess had a marked depression of their ability to clear E. coli and Pseudomonas aeruginosa that were injected into the airway. Macrophages from infected animals did not differ in quantity or viability when compared with those in control animals. The ability to ingest bacteria appeared to be normal or enhanced in infected animals, but there was a significant decrease in the ability of the macrophage to kill the ingested organisms. Such macrophage defects may be partially responsible for the infected animals' inability to clear bacteria in a normal manner.