Assessing the efficacy of HME filters at preventing contamination of breathing systems*

Abstract

SummaryBreathing system filters are intended to prevent cross-infection during anaesthesia. However, there is a lack of information on whether filters prevent contamination of the breathing system by the patient. We measured the contamination of 235 used filters of four different types obtained from operating theatres: two pleated hydrophobic (BB25M and BB22 ⁄ 15M, Pall Medical, Portsmouth, UK) used for adult patients and two electrostatic (355 ⁄ 5430 Hygroboy and 355 ⁄ 5427 Hygrobaby, Tyco Healthcare, Gosport, UK) used for paediatric patients. The filters were swabbed over their internal surfaces on both the patient and the machine sides and these were assessed with the use of adenosine triphosphate bioluminescence. Contamination was present on the machine side of 20 (9%) filters. Current standards for testing of filters has no set 'pass' level and is performed in the laboratory setting. Bioluminescence may be used in the clinical setting to elucidate factors that might increase the chance of cross-contamination between patients.

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

“…However, comparison of results from the HMEF 750 ⁄ S from main theatres in this study with results from the BB25 from the study by Rees et al [4] (carried out in the same theatres) showed a significant difference in contamination on the machine side between the two filters (Table 5): there was a greater incidence of excessive contamination (RLU > 50) with the HMEF 750 ⁄ S filter compared with the BB25. Cost was the factor that led to a change in the type of filter used.…”

“…Other factors may include the type of airway device, depth of anaesthesia, position of the filter, smoking, medical history of asthma, current chest infection and patient position. These factors were not recorded in the study by Rees et al [4].…”

“…Only two operators were involved (SD and AK), both of whom had been trained in the use of ATP bioluminescence. Contamination was considered excessive if the RLU was > 50 [4]; levels below this were considered as background contamination by the manufacturer of the Biotrace equipment.…”

“…The Biotrace Clean-Trace Ò (3M Health Care Limited, Loughborough, UK) system was used to assess the level of contamination in the filters on the patient and machine sides [4]. The test consists of a swab device containing a Dacron bud, premoistened with a cationic agent to release ATP from microbial cells or organic material.…”

“…Work by Rees et al [4] revealed that 9% (20 ⁄ 235) of filters randomly collected from theatres were excessively contaminated on the machine side as assessed by adenosine triphosphate (ATP) bioluminescence. Contamination was expressed in relative light units (RLUs) and the authors defined excessive contamination as RLU > 50; RLU < 50 were considered to be background (insignificant) levels of contamination.…”