Bacteriologic evaluation of the Servo 150 hygroscopic condenser-humidifier

The Servo 150 hygroscopic condenser-humidifier was evaluated during use to determine if the inner foam core became contaminated and if a bacteria-laden aerosol was produced during the inspiratory cycle of the patient's mechanical ventilator. Cultures from the core and of inspired gas were obtained from seven patients with known culture-positive sputum, after 4, 8, 12 and 24 h of humidifier use. In each case, the inner foam core was grossly contaminated after 4 h of use and colony counts increased during the 24-h testing period. The bacteria recovered were the same as those cultured from sputum. Despite the core's heavy bacterial growth, a bacteria-laden aerosol occurred in only 43% of the samples obtained during humidifier use. The Servo humidifier does not appear to increase the risk of airway exposure to airborne bacteria during mechanical ventilation.