An evaluation of the filtration performance of paediatric breathing system filters using sodium chloride particles at low flows

Abstract

Introduction: A minimum standard has yet to be set for paediatric breathing system filters. An evaluation of adult, paediatric and neonatal filters suggested that paediatric filters may have greater penetrance than adult filters at preset flows (1). Hence, it has been suggested that paediatric filters may be less efficient in the prevention of transmission of infective agents (2). While evaluations have been carried out at flows set by the British Standards Institution (3), concern has been expressed that these are not representative of the flows encountered in clinical practice. The use of more appropriate flows would allow the development of more reliable performance criteria. This study evaluated the pressure drop and penetrance of five filters at flows of 3 and 15 l·min‐1.Methods: The pressure drop across 15 unused samples of five different filters was measured at a flow of 15 l·min‐1 (RT‐200 Calibration Analyser, Timeter Corp, St Louis, USA). The penetration of sodium chloride particles through five samples of each filter was measured at a flow of 15 l·min‐1 using a ‘Moore's’ Test Rig (CEN Bench Rig, SFP Services, Christchurch, UK) (2). Subsequently, two groups of five of the same filters were tested in parallel using a flow of 15 l·min‐1, thus each filter was tested at a flow of 3 l·min‐1.Results: Filter type Pressure drop at 15 l·min‐1 (cmH2O) Penetrance (%) 15 l·min‐1 Parallel testing, equivalent to 3 l·min‐1 1st group 2nd group Hygroboy 1.3 (0.2) 1.9 (1.8–3.5) 0.3 0.2 Air safety MIDI 2.7 (0.9) 2.8 (2.4–2.9) 0.2 0.2 Intersurgical 1.9 (0.1) 3.2 (2.9–4.3) 0.4 0.4 Hygrobaby 3.0 (0.3) 3.0 (2.9–4.3) 0.6 0.4 Air safety Neonatal 1.4 (0.1) 10.3 (7.5–12.3) 1.8 1.6 Data are mean (SD) or median (range)Discussion and Conclusions: The filtration performance of paediatric filters when tested using sodium chloride particles and a gas flow of 3.l min‐1 is more efficient compared to their performance when tested at a gas flow of 15 l·min‐1. Coughing through a filter will produce much higher flows, at which the filters have yet to be evaluated. A minimum standard of performance is yet to be established for paediatric breathing system filters.References 1 Wilkes AR. An assessment of 104 breathing system filters. London: Medicines and Healthcare products Regulatory Agency. Evaluation 04005. March 2004.2 Bennett N, Bingham R. Association of Paediatric Anaesthetists of Great Britain and Ireland. Statement on Paediatric Filters and Breathing Systems. January 2005.3 British Standards Institution. Breathing system filters for anaesthetic and respiratory use – Part I: salt test method to assess filtration performance (BS EN 13328‐1:2001). Milton Keynes, UK: British Standards Institution, 2001.