In an investigation of infection control methods for respirator systems in 89 randomly selected German intensive care units as a part of the NIDEP study (Nosocomial Infections in Germany--Surveillance and Prevention), it was found that respirator systems were exchanged daily in about 50% of the intensive care units. However, Craven et al. found that changing circuits (including tubing and exhalation valve and the attached humidifier) every 24 h rather than every 48 h was independently associated with the occurrence of nosocomial pneumonia. On the basis of these results and recent studies, the current situation in the literature was analyzed in order to make recommendations for exchanging ventilator circuits.
Methods: Based on the extensive analysis of the literature by the Hospital Infection Control Practices Advisory Committee (HICPAC), we could limit our investigation to the years after 1994. A MEDLINE search was done, and abstracts from congresses of the past few years were considered. The main focus of the analysis was the development of pneumonia and not the contamination of the breathing circuit. The following methodological factors were analyzed for the most important published studies: design, applied definitions of pneumonia, sample size, comparability of study groups, inclusion and exclusion criteria. The results of the different studies were compared considering the potential bias factors.
Results and discussion: There were nine prospective controlled studies on this topic. In all studies, the authors tried to investigate whether a longer interval between ventilator circuit exchange (more than 48 h) is safe or whether it is possible to leave the circuits unchanged (without using breathing filters). The design and results of the available studies were analyzed. The three most important studies were compared very carefully (Table 1 and 2), and a recommendation for infection control measures for ventilator circuits was made as a modification of the HICPAC guidelines. In addition, the device-associated pneumonia rates of ventilated intensive care patients in the NIDEP study were analyzed separately according to a daily or a 48-h or longer interval of ventilator circuit exchange. For patients with daily exchange, we found a device-associated rate of 17.4 per 1000 ventilator days and for those with longer intervals a rate of 7.9 per 1000 ventilator days. Only considering those patients without heat and moisture filters, the figures were 14.8 versus 6.1. These differences were not significant because of the small number of patients investigated.
Conclusion: The available studies show clear advantages of not routinely exchanging the ventilator circuit, including tubing, exhalation valve and the attached humidifier, more often then every 7 days for an individual patient. Based on these findings, the current practice in most German intensive care units should be reevaluated.