10 BACTERIAL/VIRAL FILTERS IN PULMONARY FUNCTION …

1 BG-10 bacterial FILTERS 6/8/07 20:55 Page 144. 10 BACTERIAL/VIRAL FILTERS IN PULMONARY FUNCTION DEPARTMENTS. 144 THE BUYERS' GUIDE TO RESPIRATORY CARE PRODUCTS. BG-10 bacterial FILTERS 6/8/07 20:55 Page 145. BACTERIAL/VIRAL FILTERS IN PULMONARY FUNCTION DEPARTMENTS 10. Correspondence D. Cramer, S. Ward Lung FUNCTION Unit Royal Brompton Hospital Fulham Road London SW3 6HP. UK. E-mail: BACTERIAL/VIRAL FILTERS . IN PULMONARY FUNCTION . DEPARTMENTS. D. Cramer and S. Ward Routine PULMONARY FUNCTION tests inhale these infective droplets may require patients to perform during the forced inspiratory phase. maximal inspiratory and expiratory Very few bacteria are required to breathing manoeuvres.

2 They may facilitate the infectious process of be asked to rebreathe via the some diseases, such as tuberculosis, breathing circuits and equipment, and therefore the potential risk of which may be difficult to disinfect cross-infection using this particular between patients. Infection can be type of equipment may be transmitted by direct or indirect comparatively high [1]. contact via mouthpieces and immediate proximal surfaces of the In order to essentially eliminate any valves or tubing within the potential risk of cross-infection, a equipment, and possibly by aerosol BACTERIAL/VIRAL filter can be placed droplet formation. between the patient's mouth and the test equipment.

3 It is common Patients performing PULMONARY practice to use BACTERIAL/VIRAL FILTERS FUNCTION tests may generate flows when patients are known to be (peak expiratory flows) as high as infectious or immunocompromised. 12 L s-1 (720 L min-1). Infective However, as the infectious status of droplets may be expelled during many patients is unknown, it may these forced expirations, which be prudent to presuppose that any could contaminate the PULMONARY patient performing the tests could FUNCTION equipment. A subsequent be infectious. Using a single-use patient carrying out the same BACTERIAL/VIRAL filter for all patients manoeuvre on this equipment could overcomes this issue.

4 THE BUYERS' GUIDE TO RESPIRATORY CARE PRODUCTS 145. BG-10 bacterial FILTERS 6/8/07 20:55 Page 146. 10 BACTERIAL/VIRAL FILTERS IN PULMONARY FUNCTION DEPARTMENTS. What are BACTERIAL/VIRAL the likelihood that they will collide FILTERS ? And how do they with the filter material [2]. work? FILTERS used in PULMONARY FUNCTION Issues for consideration laboratories are consumable items when making a choice of used for trapping bacteria and FILTERS viruses, ensuring prevention of any cross-contamination. The FILTERS There are several factors to consider generally consist of a flat wad of prior to purchasing BACTERIAL/VIRAL electrostatically charged fibres or FILTERS . pleats formed from a wad of fibres.

5 These FILTERS may/should have bacterial removal efficiency (BRE). hydrophobic properties. A system has been developed at the The electrostatically charged fibres Centre for Emergency Preparedness are of two types: fibrillated or and Response (Porton Down, UK). tribocharged. Fibrillated fibres are enabling the efficiencies of many made by splitting sheets of types of microbial FILTERS to be electrostatically charged assessed, including FILTERS used with polypropylene. Tribocharged fibres PULMONARY FUNCTION equipment. are created by rubbing two types of fibre together (polypropylene and An apparatus developed originally modified acrylic) [1]. In the first by HENDERSON [3] and DRUETT [4] to instance, bacteria and viruses are study experimental airborne trapped as they pass through the infection is used.

6 A suspension of interlocking fibres of the filter micro-organisms in aqueous material. They are further attracted solution is nebulised by a three-jet to these fibres by the positive and collision spray forming a fine negative electrostatic charges on the aerosol containing viable microbes. fibres. It is designed to deliver a challenge of >107 Bacillus subtilis spores in The pleated FILTERS , also known as aerosol at a relative humidity of mechanical FILTERS , achieve their 96% at 30 L min-1. efficiency by making use of tightly packed layers of mixed strands of The efficiencies of the FILTERS are fibres that physically prevent calculated by determining the bacteria and viruses from passing airborne concentration of viable through.

7 These fibres have a micro-organisms upstream and hydrophobic coating that repels any downstream of the filter using water droplets containing bacteria suitable aerosol sampling or viruses thus preventing the techniques and microbial assay passage of these organisms. methods. The efficiency of filtration depends More recently, an alternative system on the density of the fibres, the for assessing BRE was developed at depth of the filter layer and the the National Institute for velocity of the gas to be filtered. Occupational Safety and Health Direct interception or filtration (Atlanta, GA, USA) [5]. An aerosol removes large particles (>1 m) of sodium chloride particles with a whose diameter is greater than that median diameter of m is of the pores of the filter membrane.

8 Generated from a 2% sodium Inertial impaction results in the chloride solution. Samples of air are removal of smaller particles ( drawn from the upstream m in diameter) by collision within (challenge) and downstream the filter material. Diffusional (penetration) sides of the filter interception removes very small through two laser photometers. particles (< m) due to their These photometers measure the Brownian motion, which increases concentration (mass of sodium 146 THE BUYERS' GUIDE TO RESPIRATORY CARE PRODUCTS. BG-10 bacterial FILTERS 6/8/07 20:55 Page 147. BACTERIAL/VIRAL FILTERS IN PULMONARY FUNCTION DEPARTMENTS 10. 'SpiroSafe' filter shown with Paediatric adaptor and mouthpiece Infection Control efficient bacterial / viral filter Designed to stop moisture droplets passing to and from the spirometer Protects both patient and spirometer Should be used when an inspiratory manoeuvre is performed or when testing patients who pose a health risk to others Micro Medical Ltd PO Box 6, Rochester, Kent ME1 2AZ, United Kingdom Tel +44 (0) 1634 893500.)

9 Fax +44 (0) 1634 893600. chloride particles per unit volume measurement of airway resistance of air) in the challenge and in the using a plethysmograph, the air that passes through the filter [6]. resistance of the filter in the circuit Manufacturers can currently offer should be established. With most FILTERS with efficiency levels of modern software, the additional > resistance offered by the filter should be taken into account when Resistance carrying out the calculations. If FILTERS are used during PULMONARY A filter must have maximal FUNCTION tests , when calibrating efficiency in trapping and pneumotachograph devices for removing bacteria and viruses, but volume it is essential to place a it should also have a low resistance filter between the calibration to airflow.

10 Depending on the type syringe and the instrument, as the of breathing manoeuvre being added resistance of the filter will performed, resistance must be affect pressure changes across the checked at the appropriate flow pneumotachograph. rates (peaking >12 L s-1, 720 L min-1. in some subjects). The American It appears that the FILTERS with the Thoracic Society criteria for lowest resistances to flow are those PULMONARY FUNCTION testing state with the poorest BRE, implying that that the resistance of the BRE may be sacrificed for a low respiratory circuit (including the resistance. If the resistance of the BACTERIAL/VIRAL filter ) must not respiratory circuit is too high, there exceed cmH2O L-1 s-1 for flows may be clinically significant effects up to 14 L s-1 [7].