Efficacy of HME filters used in children and factors responsible for contamination of breathing systems
Authors: Sinha V. , Dugani S. , Wilkes A.R. , Gildersleve C. 
Published: June 2009

Background:  Adenosine triphosphate (ATP) bioluminescence has been used to assess the efficacy and factors that increase the chance of cross‐contamination of HME (heat and moisture exchanging) filters in adults [1, 2]. This method is recommended for testing in hygiene monitoring [3]. The aim was to evaluate the efficacy of breathing system filters and ascertain potential factors responsible for contamination of breathing system used in children.

Method:  Breathing system filters were collected over 10 days from theatres and swabbed on both the patient and machine sides. The breathing system used in the anaesthetic rooms and theatres were swabbed twice daily. The contamination was assessed using the Bio trace Clean‐Trace® (3M Health Care Limited, Loughborough, UK). Data collected included age and weight of the patient, type of surgery, duration of use of the HME filter and breathing system, type of airway device and ventilation, position and episodes of cough at induction and extubation. Values of less than 50 relative light units (RLU) were considered as background contamination, >50 RLU as contamination [1]. Values >100 RLU are indicative of contamination in the food industry [3].

Results:  One hundred and nineteen breathing system filters (60 Dar Hygroboy®, 17 Dar Hygrobaby®, 33 Humid‐Vent® Filter Pedi, 5 Pall Ultipor®, 4 HMEF/750®) were tested. The age of the children ranged from 2 days to 15 years (mean 7.4 years). The median [IQR] {range} for duration of use of the filters in minutes were 40 [23–60] {8–330} respectively. On the patient side, the median [IQR] {range} RLU of the filters were 65 (30–125) {5–47006}. A total of 67 (56%) and 40 (34%) of these filters had RLU levels greater than 50 and 100 respectively. On the machine side, the median (IQR) [range] RLU of the filters were 12 (5–45) [2–202]. 27 (23%) and 7 (6%) of these filters had RLU levels greater than 50 and 100 respectively. Six of these seven filters were from patients either second or third on the list. There were mild associations between contamination on the patient and machine sides (Spearman's ρ = 0.26, P = 0.004) and duration and contamination on the patient side (ρ = 0.21, P = 0.022), but not between duration and contamination on the machine side (ρ = −0.02, P = 0.81). At start of the day, the median (IQR) [range] RLU of the breathing systems were 10 (6–30) [1–144]. 3 (12%) and 1 (4%) of these had RLU levels greater than 50 and 100 respectively. At the end of the day, the median [IQR] {range} RLU of the breathing systems were 84 (54–162) [14–331]. 16 (76%) and 8 (38%) of the breathing system had RLU levels greater than 50 and 100 respectively. Ten children (8.4%) coughed, this caused significant higher RLU on the patient side of the filter with median (IQR) [range] being 179 (107–400) [29–492]. However, RLU was 50 or less on the machine side in 90% of these filters.

Discussion:  HME filters are changed with every case, whereas change of breathing systems is variable from every list to every day to every week. Our results show that a majority of the breathing systems in the operating theatres were contaminated by the end of the day. We suggest using a bioluminescence test before reusing the breathing system for another list.

Acknowledgement:  3M Health Care Limited, Loughborough, UK for providing the Biotrace Clean‐Trace® equipment for this study.