Infectious and inflammatory dissemination are affected by ventilation strategy in rats with unilateral pneumonia

Objective. To evaluate the effect of V-T reduction and alveolar recruitment on systemic and contralateral dissemination of bacteria and inflammation during right-side pneumonia. Design. Interventional animal study. Setting. University hospital research laboratory. Subjects. A total of 54 male Wistar rats. Interventions. One day after right lung instillation of 1.4x10(7) Pseudomonas aeruginosa, rats were left unventilated or ventilated for 2 h at low V-T (6 ml/kg) with different strategies of alveolar recruitment: no PEEP, 8 cm H2O PEEP, 8 cm H2O PEEP in a left lateral position, 3 cm H2O PEEP with partial liquid ventilation, or high V-T (set such as end-inspiratory pressure was 30 cm H2O) without PEEP (ZEEP). After ventilation the lungs, spleen and liver were cultivated for bacterial counts. Global bacterial dissemination was scored considering the percentage of positive spleen, liver and left lung cultures. TNF-alpha was assayed in plasma before and after mechanical ventilation. Measurements and results. All rats had right-side pneumonia with similar bacterial counts. All mechanical ventilation strategies, with the exception of low V-T-PEEP 8, promoted contralateral lung dissemination. Overall bacterial dissemination was less in non-ventilated controls (22%) and low V-T-PEEP 8 (22%) than in high V-T-ZEEP (67%), low V-T-PEEP 8 in left lateral position (59%) and low V-T-ZEEP (56%) (p<0.05). Partial liquid ventilation prevented systemic bacterial translocation, but at the expense of contralateral bacterial seeding. Plasma TNF-alpha concentration increased significantly after mechanical ventilation with no PEEP at both high and low V-T. Conclusions. Our results suggest that PEEP might reduce the risk of ventilation-induced bacterial and inflammatory mediator dissemination during pneumonia.