Effect of partial liquid ventilation on bacterial clearance during Pseudomonas aeruginosa-induced lung injury in rats

Partial liquid ventilation (PLV) has been shown to exhibit anti-inflammatory properties during non-infectious models of acute lung injury. The aim of this experimental study was to assess the effects of PLV on bacterial clearance during Pseudomonas aeruginosa-induced pneumonia in rats.

The rats were assigned to four groups 4 h after bacterial challenge according to the kind of mechanical ventilation [gas ventilation (GV) or PLV, 6 ml/kg perflubron plus 2 ml/kg per h] and to the level of PEEP used (3 or 8 cm of water). Physiologic measures were recorded during anesthesia (arterial blood gases, airway and blood pressures) for 4 subsequent hours until sacrifice.

No improvement of oxygenation was demonstrated in any group. The bacterial counts were higher in PLV-PEEP 8 rats compared to GV-PEEP 8 rats: median, 1.7.10(4) cfu (25th-75th percentiles, 1.2.10(4)-1.8.10(4)) versus 1.1.10(4) (8.7.10(3)-1.3.10(4))/ml of BAL fluid and 4.0.10(6) cfu (2.0.10(6)-5.5.10(6)) versus 1.7.10(6) cfu (9.7.10(5)-3.2.10(6))/ml of lung homogenate, respectively ( P<0.05, n=8/10 surviving rats per group). PEEP 8 was associated with a significant decrease in neutrophil recruitment in BAL fluid compared to PEEP 3 in both GV and PLV groups. Additional in vitro experiments demonstrated that perflubron induced a decrease in phagocytosis of P. aeruginosa by alveolar neutrophils.

These results demonstrate that PLV is associated with an impaired bacterial clearance during early pneumonia in rats, which could have been favored by decreased bacterial phagocytosis by neutrophils.