RESUMEN
To identify the onset time of bacterial proliferation in mechanical ventilator circuits in a pediatric intensive care unit (PICU) and the colonizing agents involved, as well to verify any possible pre-use contamination, we conducted a prospective microbiological analysis of the circuits of 30 patients, with a total of 342 cultures. Bacterial colonization of the mechanical ventilator circuits in the studied PICU was confirmed. Microorganisms were present in 39% of expiratory branch cultures: K. pneumoniae (77%), A. baumannii (65%), and S. aureus (42%). The inspiratory branch registered a smaller number of positive culture: A. baumannii (51%), S. aureus, coagulase-negative (38%) and K. pneumoniae (32%). As to the colonization onset time, 23% of the cultures collected on the 1st day from the inspiratory branch were positive, versus 30% of those collected from the expiratory branch, which lead us to conclude that bacteria can be present within the first hours of use. The sequential analysis of bacterial colonization over the course of circuit usage and the observation that the number of positive cultures becomes progressively higher on the 5th, 6th and 7th days in the expiratory branch both suggest that the systems should be replaced more often.