Effect of lung-protective ventilation on severe Pseudomonas aeruginosa pneumonia and sepsis in rats.

Pneumonia caused by Pseudomonas aeruginosa carries a high rate of morbidity and mortality. A lung-protective strategy using low tidal volume (V(T)) ventilation for acute lung injury improves patient outcomes. The goal of this study was to determine whether low V(T) ventilation has similar utility in severe P. aeruginosa infection. A cytotoxic P. aeruginosa strain, PA103, was instilled into the left lung of rats anesthetized with pentobarbital. The lung-protective effect of low V(T) (6 ml/kg) with or without high positive end-expiratory pressure (PEEP, 10 or 3 cmH(2)O) was then compared with high V(T) with low PEEP ventilation (V(T) 12 ml/kg, PEEP 3 cmH(2)O). Severe lung injury and septic shock was induced. Although ventilatory mode had little effect on the involved lung or septic physiology, injury to noninvolved regions was attenuated by low V(T) ventilation as indicated by the wet-to-dry weight ratio (W/D; 6.13 +/- 0.78 vs. 3.78 +/- 0.26, respectively) and confirmed by histopathological examinations. High PEEP did not yield a significant protective effect (W/D, 4.03 +/- 0.32) but, rather, caused overdistension of noninvolved lungs. Bronchoalveolar lavage revealed higher concentrations of TNF-alpha in the fluid of noninvolved lung undergoing high V(T) ventilation compared with those animals receiving low V(T). We conclude that low V(T) ventilation is protective in noninvolved regions and that the application of high PEEP attenuated the beneficial effects of low V(T) ventilation, at least short term. Furthermore, low V(T) ventilation cannot protect the involved lung, and high PEEP did not significantly alter lung injury over a short time course.