The effect of bacterial superinfection on lung function after diffuse alveolar damage.

Although bacterial infection is very common in patients with adult respiratory distress syndrome (ARDS), the effects of infection on the clinical course of ARDS are unknown. We have studied the effects of gram-negative bacillary infections in 21 baboons during periods of prolonged anesthesia and ventilatory support. Sixteen animals received oleic acid, 0.04 to 0.06 ml/kg intravenously; 7 developed no infections, 5 developed nosocomial pneumonias, and 4 inadvertently received intravascular infusions of Serratia marcescens. Five uninjured animals were studied; all developed pneumonia. In the absence of infection, oleic-acid-induced lung injury was mild and all animals were successfully weaned. Uninjured animals that developed pneumonia demonstrated only mild abnormalities of lung function, but 4 of 5 died of complications of their infections. Gram-negative bacillary infections superimposed upon oleic acid injury produced rapid and marked deterioration of lung function. Acquired infection, either of the lung itself or at remote sites, may markedly worsen lung function in the presence of a previous lung injury.