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 1.4×10⁷ 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- 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- 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.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00134-003-2147-7This study was supported by a grant from Fondation pour la Recherche Médicale.