Activity of a silver-coated endotracheal tube in preclinical models of ventilator-associated pneumonia and a study after extubation

Objective: To elucidate the mechanism of action of the silver-coated endotracheal tube in models of the early pathogenesis of ventilator-associated pneumonia. Design: Open-labeled, prospective, controlled, sequentially conducted, preclinical studies, and in vitro assessment of tubes from patients. Setting: Microbiology laboratory of a device manufacturer, animal research facility of a university, and a tertiary medical center. Interventions: Endotracheal tubes were similar except for the silver coating. In the 21-day in vitro elution model, tube samples were incubated in saline solution at 37.8°C. In the in vitro adherence model, coated and uncoated tubes were exposed to 21 respiratory isolates of radiolabeled microorganisms for 2-4 hrs. In the animal model, 12 healthy white rabbits were intubated for 16 hrs with noncuffed silver-coated or uncoated tubes and challenged with buccal administration of Pseudomonas aeruginosa. In the in vitro assessment, tubes from 16 patients underwent quantitative culture assessment and qualitative confocal laser scanning microscopy. Measurements and Main Results: After in vitro incubation, the mean residual silver concentration was 2.6 μg/cm, confirming that the coating was not entirely depleted. In vitro adherence to the silver-coated endotracheal tube was less than that of the uncoated tube for 12 of 21 isolates and equivalent for seven. For example, adherence to the silver-coated endotracheal tube was reduced >90% for all five isolates of P. aeruginosa (p <.05). In rabbits, P. aeruginosa colonization on the silver-coated endotracheal tube was reduced 99.9% compared with that on the uncoated tube (p <.0001); colonization in the tracheal and lung tissue was reduced >99% (p <.05). In the in vitro assessment, pathogens were detected on none of nine silver-coated tubes from patients and three of seven control tubes (p >.05). Conclusions: The collective findings of this series of studies demonstrated that the silver-coated endotracheal tube was active in models designed to mimic the early pathogenesis of ventilator-associated pneumonia.