Reduction of the bacterial load by the silver-coated endotracheal tube (SCET),a laboratory investigation

Abstract

Microaspiration enabled by high-volume-low-pressure cuffed endotracheal tubes is the most likely explanation for ventilator-associated pneumonia. To decontaminate the secretion at the proximal end of the cuff we developed a silver-coated endotracheal tube (SCET). In an in vitro model we investigated the efficacy of SCET to lower the bacterial load of secretion and aspirate. We developed a continuously contaminated and mechanically ventilated oropharynx–larynx–lung model to investigate the reduction of the bacterial count by SCET compared to controls. The model was continuously contaminated via the oropharynx–larynx with Pseudomonas aeruginosa ATCC 27853. During the investigation period of 50 hours the bacterial count of oropharynx–larynx and lung was measured as colony-forming-units/ml. In addition, the characteristic curve of silver ion release of SCET was determined. SCET significantly reduced the bacterial count in oropharynx–larynx at all timepoints ( $\mathit{p}\mathrm{<}0.05$ ). In lung the bacterial count was significantly lower beginning with the 36th hour of recording ( $\mathit{p}\mathrm{<}0.05$ ). A reduction of greater than 2 log was found from 28 hours on in oropharynx–larynx and from 50 hours on in lung. The release of silver ions was very rapid and was described by a mono-exponential function with a time-constant τ of about 60 minutes and a saturation concentration of $200\pm 80\mathit{\mu }$ g/l. SCET showed a significant inhibition of growth of P. aeruginosa in the continuously contaminated and mechanically ventilated oropharynx–larynx–lung model. SCET by thus might be helpful in reducing ventilator-associated pneumonia.