The risk of nosocomial pneumonia is not increased during partial liquid ventilation

Objective: To determine whether partial liquid ventilation (PLV) affects th e risk of nosocomial pneumonia. Study Design: To assess in vitro bacterial adhesion and viability after liq uid perfluorocarbon exposure and to assess bacterial recovery after partial liquid ventilation in vivo in rabbits. Setting: University animal research facility. Subjects: Thirty-six New Zealand White rabbits. Interventions: To assess adhesions, radiolabeled Escherichia coli were expo sed to perfluorocarbon, incubated against artificial biosurfaces, and compa red with nonexposed controls. Bacterial viability in vitro was assessed by exposing broth suspensions of Pasteurella multocida to perflubron for vario us times. Controls were run in parallel without exposure. Quantitative cult ures were performed to determine viability. We undertook short-term and rec overy in vivo investigations. The lungs of treated animals were filled with perflubron (similar to 18 mL/kg), and the control rabbits were ventilated without perflubron in an identical fashion. Cryopreserved aliquots of P. mu ltocida were administered via an endotracheal tube. The short-term study an imals were ventilated for 6 hrs before being killed. The recovery animals w ere ventilated for 2-4 hrs, extubated, and killed 20 hrs later. The lungs w ere removed, aseptically minced, and homogenized. Serial dilutions of the h omogenate were quantitatively cultured by manual counting of colonies on ag ar plates. The recovered organisms were typed for species by the clinical m icrobiology laboratory. Measurements and Main Results: The adhesion of bacteria to immobilized bron choalveolar lavage and human saliva, respectively, was reduced by 65% +/- 7 % and 66% +/- 1% (p < .05; n = 5) after exposure to perflubron and by 63% /- 9% and 68% +/- 6% after exposure to FC-77 (p < .05; n = 5); however, adh esion was not affected by exposure to Rimar. There was no difference in bac terial viability between the control and perflubron-exposed bacteria (n = 5 ). The in vivo study demonstrated a ten-fold or greater reduction in the nu mber of recovered bacteria in the partial liquid ventilated group compared with the control group. Conclusions: This study suggests that different per fluorocarbons affect adhesions differently. Perflubron and FC-77 appear to decrease bacterial adhesion, whereas Rimar does not. Rerflubron does not ha ve a direct bactericidal effect. Furthermore, PLV with perflubron decreased the number of viable bacteria per gram of tissue after an intentional inoc ulation of the airway, suggesting that the risk of nosocomial pneumonia is unlikely to be increased during PLV and may, in fact, he reduced in patient s supported with PLV.