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

To determine whether partial liquid ventilation (PLV) affects the risk of nosocomial pneumonia.

To assess in vitro bacterial adhesion and viability after liquid perfluorocarbon exposure and to assess bacterial recovery after partial liquid ventilation in vivo in rabbits.

University animal research facility.

Thirty-six New Zealand White rabbits.

To assess adhesions, radiolabeled Escherichia coli were exposed to perfluorocarbon, incubated against artificial biosurfaces, and compared with nonexposed controls. Bacterial viability in vitro was assessed by exposing broth suspensions of Pasteurella multocida to perflubron for various times. Controls were run in parallel without exposure. Quantitative cultures were performed to determine viability. We undertook short-term and recovery in vivo investigations. The lungs of treated animals were filled with perflubron (approximately 18 mL/kg), and the control rabbits were ventilated without perflubron in an identical fashion. Cryopreserved aliquots of P. multocida were administered via an endotracheal tube. The short-term study animals were ventilated for 6 hrs before being killed. The recovery animals were ventilated for 2-4 hrs, extubated, and killed 20 hrs later. The lungs were removed, aseptically minced, and homogenized. Serial dilutions of the homogenate were quantitatively cultured by manual counting of colonies on agar plates. The recovered organisms were typed for species by the clinical microbiology laboratory.

The adhesion of bacteria to immobilized bronchoalveolar 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, adhesion was not affected by exposure to Rimar. There was no difference in bacterial viability between the control and perflubron-exposed bacteria (n = 5). The in vivo study demonstrated a ten-fold or greater reduction in the number of recovered bacteria in the partial liquid ventilated group compared with the control group.

This study suggests that different perfluorocarbons affect adhesions differently. Perflubron and FC-77 appear to decrease bacterial adhesion, whereas Rimar does not. Rerflubron does not have a direct bactericidal effect. Furthermore, PLV with perflubron decreased the number of viable bacteria per gram of tissue after an intentional inoculation of the airway, suggesting that the risk of nosocomial pneumonia is unlikely to be increased during PLV and may, in fact, be reduced in patients supported with PLV.