Influence of patient factors on the efficacy of breathing system filters at preventing contamination of breathing systems

We measured the level of contamination in 207 breathing system filters of five different models. The median (IQR [range]) levels of contamination measured in relative light units on the machine side of the filters were: HMEF 750/S 27 (16–56 [4–13 615]); Ultipor BB25 26 (13–40 [9–66]); Humid-vent filter pedi 19 (15–34 [11–48]); Hygroboy 11 (7–19 [3–113]); and Hygrobaby 9 (6–14 [4–21]). A total of 41/138 (30%) of the HMEF 750/S (the most commonly used filter) had measured values > 50, indicating excessive contamination on the machine side of the filter. The incidence of coughing and duration of the case were significantly associated with the incidence of excessive contamination on the machine side (p = 0.034 and p = 0.024, respectively). Excessive contamination on the machine side of the filter could be from the patient or from the re-used breathing system and could result in cross-infection. The level of contamination may need to be checked routinely during each list