NOSOCOMIAL RESPIRATORY TRACT INFECTIONS ASSOCIATED WITH THE USE OF VENTILATORY SUPPORT SYSTEMS: EPIDEMIOLOGICAL AND BACTERIOLOGICAL STUDY OF THE EFFECT OF CHANGING BREATHING CIRCUITS AT 24 OR 48 HOURS

Currently, it is recommended that breathing circuits on ventilators be changed every 24 hours. To determine whether circuits could be changed safely at 48 hours, patients without respiratory tract infection were randomized to receive ventilator circuit changes at 24 hours (Group I) or 48 hours (Group II). The patients were studied epidemiologically and microbiologically. Patients were evaluated for occurrence of pneumonia and tracheobronchitis by two pulmonary physicians. Cultures were taken from each circuit as it was discontinued and daily sputum specimens from each patient were cultured. Of 211 evaluable patients, 116 persons were in Group I and 95 persons were in Group II. There were 35 cases of pneumonia (16.6%) and 118 cases of tracheobronchitis (56.0%). The rate of pneumonia in Group I (13%) was not significantly different from the rate in Group II (21.1%) (p = 0.14). Risk factors for pneumonia included long duration of ventilation, not having received antibiotics during controlled ventilation and having had a chest injury and administration of pancuronium. The only risk factor identified for tracheobronchitis was long duration of ventilation. Ten thousand and ten cultures were obtained from 1,247 breathing circuits. One or more species of microorganisms was recovered from 56.5% of the cultures. Ten and seven-tenths percent of all cultures taken yielded a pathogen. The great majority of these cultures yielded Gram-negative bacilli. Cultures of circuits from Group I patients who were on controlled ventilation for less than 48 hours were significantly less likely to be positive than cultures of circuits of Group I patients who were on ventilatory support for 48 or more hours. The rate of positive cultures from the breathing circuits of Group I patients were not significantly different from the rate of positive cultures from breathing circuits of Group II patients. It can be concluded from my study that changing breathing circuits of patients on ventilatory support at 48 hours poses no greater risk of infection to patients than when these circuits are changed at 24 hours. It can also be concluded that the most important risk factor for ventilator-associated pneumonia is prolonged duration of ventilation.