Host response to intratracheally instilled bacteria in ventilated and nonventilated rats.
OBJECTIVE
Pneumonia occurs in approximately 7% of hospitalized patients. Susceptibility to certain bacteria such as Pseudomonas aeruginosa increases in critically ill patients, particularly those requiring mechanical ventilation. Previous studies investigating this susceptibility have used injurious modes of ventilation. The objective of this study was to evaluate the host's response to intratracheal instillation of P. aeruginosa in the setting of noninjurious mechanical ventilation and compare this with normal, spontaneously breathing animals receiving bacteria.


METHODS
Randomized, controlled in vivo animal study.


METHODS
Research laboratory at a university-affiliated institution.


METHODS
Adult male Sprague-Dawley rats.


METHODS
Rats were randomized into four groups: spontaneously breathing given saline, spontaneously breathing given bacteria, mechanically ventilated given saline, and mechanically ventilated given bacteria. The ventilation strategy used involved low stretch (tidal volume of 8 mL/kg) with a positive end-expiratory pressure of 5 cm H2O.


RESULTS
Lung compliance, bacterial recovery, surfactant, total cells, and cytokine concentrations in the lung lavage were analyzed after 4 hrs. Results showed that neither ventilation nor bacteria alone altered lung function, although the combination of ventilation and Pseudomonas significantly decreased arterial oxygenation and lung compliance. Increases in lavage cell counts, cytokines, and surfactant were observed in both groups administered bacteria compared with animals given saline. However, there were no significant differences in bacterial recovery, cell counts, cytokines, and surfactant measurements in the groups given bacteria.


CONCLUSIONS
These data suggest that bacterial instillation with low-stretch ventilation had a significant effect on lung function but did not alter the inflammatory response to a bacterial challenge over this time course compared with spontaneously breathing animals.
Brackenbury
Angela M
AM
Department of Medicine, St. Joseph's Health Care Centre, London, Ontario, Canada.
McCaig
Lynda A
LA
Yao
Li-Juan
LJ
Veldhuizen
Ruud A W
RA
Lewis
James F
JF
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D004195:Disease Models, Animal; D008297:Male; D018410:Pneumonia, Bacterial / Q000276:immunology* / Q000628:therapy; D011550:Pseudomonas aeruginosa; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D012121:Respiration, Artificial / Q000009:adverse effects; D012128:Respiratory Distress Syndrome / Q000209:etiology / Q000276:immunology*; D012129:Respiratory Function Tests; D012307:Risk Factors; D012680:Sensitivity and Specificity