gms | German Medical Science

GMS Hygiene and Infection Control

Deutsche Gesellschaft für Krankenhaushygiene (DGKH)

ISSN 2196-5226

Infection prevention during anaesthesia ventilation by the use of breathing system filters (BSF): Joint recommendation by German Society of Hospital Hygiene (DGKH) and German Society for Anaesthesiology and Intensive Care (DGAI)

Recommendation

  • corresponding author Axel Kramer - Institute for Hygiene and Environmental Medicine, University Greifswald, Germany
  • Rainer Kranabetter - Clinical Centre Nuremberg, Germany
  • Jörg Rathgeber - Anaesthesiology and Operative Intensive Care Medicine, Albertinen-Hospital Hamburg, Germany
  • Klaus Züchner - Medical-Technical Service, University Medicine Göttingen, Germany
  • Ojan Assadian - Institute for Hygiene and Environmental Medicine, University Greifswald, Germany
  • Georg Daeschlein - Institute for Hygiene and Environmental Medicine, University Greifswald, Germany
  • Nils-Olaf Hübner - Institute for Hygiene and Environmental Medicine, University Greifswald, Germany
  • Edeltrut Dietlein - Institute for Hygiene and Public Health, University Bonn, Germany
  • Martin Exner - Institute for Hygiene and Public Health, University Bonn, Germany
  • Matthias Gründling - Clinic and Policlinic for Anaesthesiology and Intensive Care Medicine, University Greifswald, Germany
  • Christian Lehmann - Clinic and Policlinic for Anaesthesiology and Intensive Care Medicine, University Greifswald, Germany
  • Michael Wendt - Clinic and Policlinic for Anaesthesiology and Intensive Care Medicine, University Greifswald, Germany
  • Bernhard Martin Graf - Clinic for Anaesthesiology, University Regensburg, Germany
  • Dietmar Holst - Clinic for Anaesthesia and Intensive Care Medicine, Clinic GmbH Hamburg, Germany
  • Lutz Jatzwauk - Hospital Hygiene, University Clinic Dresden, Germany
  • Birgit Puhlmann - Clinic and Policlinic for Anaesthesiology and Intensive Care Medicine, Charité Berlin, Germany
  • Thomas Welte - Clinic for Pneumology, Medical University Hanover, Germany
  • Antony R. Wilkes - Cardiff University, Cardiff, United Kingdom

GMS Krankenhaushyg Interdiszip 2010;5(2):Doc13

doi: 10.3205/dgkh000156, urn:nbn:de:0183-dgkh0001561

This is the English version of the article.
The German version can be found at: http://www.egms.de/de/journals/dgkh/2010-5/dgkh000156.shtml

Published: September 21, 2010

© 2010 Kramer et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Abstract

An interdisciplinary working group from the German Society of Hospital Hygiene (DGKH) and the German Society for Anaesthesiology and Intensive Care (DGAI) worked out the following recommendations for infection prevention during anaesthesia by using breathing system filters (BSF). The BSF shall be changed after each patient. The filter retention efficiency for airborne particles is recommended to be >99% (II). The retention performance of BSF for liquids is recommended to be at pressures of at least 60 hPa (=60 mbar) or 20 hPa above the selected maximum ventilation pressure in the anaesthetic system.

The anaesthesia breathing system may be used for a period of up to 7 days provided that the functional requirements of the system remain unchanged and the manufacturer states this in the instructions for use.

The breathing system and the manual ventilation bag are changed immediately after the respective anaesthesia if the following situation has occurred or it is suspected to have occurred: Notifiable infectious disease involving the risk of transmission via the breathing system and the manual bag, e.g. tuberculosis, acute viral hepatitis, measles, influenza virus, infection and/or colonisation with a multi-resistant pathogen or upper or lower respiratory tract infections.

In case of visible contamination e.g. by blood or in case of defect, it is required that the BSF and also the anaesthesia breathing system is changed and the breathing gas conducting parts of the anaesthesia ventilator are hygienically reprocessed.

Observing of the appropriate hand disinfection is very important. All surfaces of the anaesthesia equipment exposed to hand contact must be disinfected after each case.

Keywords: requirements for breathing system filters, changing of anaesthesia breathing system, disinfection, hand contact surfaces


Preamble

Under the responsibility of the German Society of Hospital Hygiene (DGKH) and the German Society for Anaesthesiology and Intensive Care (DGAI) an interdisciplinary working group was established to work out recommendations for infection prevention during anaesthesia by using breathing system filters (BSF). Dr. A. R. Wilkes, Cardiff, UK served as an external advisor.

Members of the working group: Prof. Dr. med. A. Kramer* (Institute for Hygiene and Environmental Medicine, University Greifswald), R. Kranabetter** (Clinical Centre Nuremberg), Prof. Dr. med. J. Rathgeber** (Anaesthesiology and Operative Intensive Care Medicine, Albertinen-Hospital Hamburg) und Dr. rer. nat. K. Züchner** (Medical-Technical Service, University Medicine Göttingen) (Red.)

Prof. Dr.med. O. Assadian*, Dr. med. G. Daeschlein* and Dr. med. N.-O. Hübner* (Institute for Hygiene and Environmental Medicine, University Greifswald), Dr. med. E. Dietlein*, Prof. Dr. med. M. Exner* (Institute for Hygiene and Public Health, University Bonn), Dr. med. M. Gründling**, Prof. Dr. med. Ch. Lehmann** and Prof. Dr. med. M. Wendt** (Clinic and Policlinic for Anaesthesiology and Intensive Care Medicine, University Greifswald), Prof. B. M. Graf** (Clinic for Anaesthesiology, University Regensburg), PD Dr. med. D. Holst** (Clinic for Anaesthesia and Intensive Care Medicine, Clinic GmbH Hamburg), Dr. med. L. Jatzwauk* (Hospital Hygiene, University Clinic Dresden), Dr. med. B. Puhlmann** (Clinic and Policlinic for Anaesthesiology and Intensive Care Medicine, Charité Berlin), Dr. med. T. Welte** (Clinic for Pneumology, Medical University Hanover) und Dr. A. R. Wilkes***, PhD (Cardiff University, Cardiff).

*DGKH **DGAI ***external consultant

Categorisation of the recommendations: The respective evidence of the recommendations is made clear by means of categorisation in accordance with the directive of the Commission for hospital hygiene and infection prevention (state of April 2004), published by the Robert Koch-Institut Berlin. The categories are as follows:

Category I: Strong recommendation. IA: The recommendations are based on well-designed experimental or epidemiological studies, IB: The recommendations are considered to be effective by experts and by virtue of a consensus resolution by the working group, and they are based on well-founded indications as to their effectiveness. A classification is also possible even if there have not been any studies yet.

Category II: Restricted recommendation. The recommendations are based partly on indicative clinical or epidemiological studies, partly on comprehensible theoretical explanations or studies.

Category III: No recommendation or unresolved issue: Measures supported with insufficient evidence about their efficiency or without consensus on this.

Category IV: Legislative provisions.


Objective

Due to frequent patient changes at the anaesthesia workstation, anaesthesia ventilation is characterised by the risk of cross-contamination and subsequent infection. As the entire complex of prevention measures regarding nosocomial pneumonia is concerned [1] both in the CDC Guidelines [2] and in the recommendations by the commission for hospital hygiene and infection prevention at the Robert-Koch-Institute (RKI), the present recommendations are limited to the evaluation of the literature published in the meantime on the application of breathing system filters (BSF) as an alternative to the change of the anaesthesia breathing system after each patient, and on the hygienic reprocessing of the breathing gas conducting systems of the anaesthesia ventilator. The requirements for BSF and their potential applications are derived from this objective of filter use. Further prevention measures are only emphasized if they can be considered as a prerequisite for the safe use of BSF without changing the anaesthesia breathing system.


Recommendations on the application of breathing system filters (BSF)

The use of suitable BSF between tracheal tube and anaesthetic system and the adherence to appropriate disinfection measures at all contact points of the anaesthetic equipment represent, if used together, a safe and cost-effective alternative to the use of a new or individually cleaned breathing system and to the reprocessing of the breathing gas conducting parts of the anaesthesia ventilator after each patient (IB), and they contribute to the process optimisation.

Principles

  • The BSF shall be changed after each patient (IB, IV). Operating time according to manufacturer's instructions must be followed (IV).
  • The filter retention efficiency for airborne particles, measured according to ISO 23328-1, is recommended to be >99% (II).
  • The retention performance of BSF for liquids [3] is recommended to be at pressures of at least 60 hPa (=60 mbar) or 20 hPa above the selected maximum ventilation pressure in the anaesthetic system (II). This value may be changed according to the minimum performance value defined in an international standard.
  • Side stream breathing gas monitoring and/or airway pressure measurement shall be performed on machine side of the BSF (II).
  • During anaesthesia respiration, an adequate breathing gas humidification is to be ensured; BSF alone do not guarantee this as a rule. Breathing gas humidification during anaesthesia ventilation may be ensured by keeping the fresh gas flow as low as possible [4], [5] (IB).
  • In paediatrics or neonatology, respectively, breathing gas humidification must be observed particularly carefully. When tidal volumes are small, it is not sufficient to reduce the fresh gas flow for this, humidification must therefore be ensured with other methods, e.g. with appropriate HME, which, however, have possibly no or only limited filtration and liquid retention characteristics. Moreover, to avoid CO2-rebreathing, the dead space must be very small for these patients; in neonatology each additional dead space is often out of the question anyway. In this dilemma, breathing gas humidification with HME, possibly by an insert in the tracheal tube adapter, shall be given priority, and the hygienic protection of the patient shall be ensured by using a new or individually cleaned breathing system respectively (II).
  • The filter’s respiratory resistance should be as low as possible, (specific values obtained acc. to ISO 9360-1 [6] or EN ISO 23328-2 [7]). In this context it must be considered that according to ISO 8835-2 [8], the respiratory resistance to be adhered to in the entire breathing system including BSF is ≤6 hPa/l/s (≤6 mbar/l/s).
  • The dead space volume shall be as small as possible (specific values obtained acc. to ISO 9360-1 [6] or EN ISO 23328-2 [7]). As no standard exists on the determination of the dead space volume of BSF and HME for tidal volumes <250 ml, the BSF must be approved by the manufacturer for the intended use in this area (IV).
  • The use of sterile BSF is not required (II). Manufacturing under clean room conditions acc. ISO EN DIN 14644-1 is sufficient.
  • If a surgery takes several hours (more than 2–3 h approximately), it makes sense to apply water traps (II).
  • All surfaces of the anaesthesia workstation exposed to hand contact must be disinfected in accordance with the requirements for the treatment of medical products of the semi-critical category A [9] (IB).
  • In case of visible contamination e.g. by blood or in case of defect, it is required that the BSF and also the anaesthesia breathing system is changed and the breathing gas conducting parts of the anaesthesia ventilator are hygienically reprocessed in accordance with manufacturers’ instructions (IB).
  • To rule out any risk of transmission during anaesthesia ventilation, the principles of hand hygiene summarised in the table must be strictly followed (Table 1 [Tab. 1]).

Application notes

Changing the BSF

The BSF shall be changed after each patient (IB, IV). Operating time according to manufacturer's instructions must be followed (IV).

The BSF can be used during patient transport and for subsequent ventilation in intensive care. For the duration of use of the BSF for subsequent ventilation without rebreathing, e.g. in the recovery room or in intensive care, it must be borne in mind that BSF do normally not have good heat and moisture exchanging characteristics. If post operative ventilation takes longer, an appropriate breathing gas humidification must be ensured, e.g. with HME or active humidifiers.

Changing the breathing system

The breathing system and the manual ventilation bag are changed immediately after the respective anaesthesia if the following situation has occurred or it is suspected to have occurred:

  • Notifiable infectious disease as per § 6 of the Infectious Disease Control Act (IfSG) involving the risk of transmission via the breathing system and the manual bag, e.g. tuberculosis, acute viral hepatitis, measles, influenza virus (IB)
  • Infection and/or colonisation with a multi-resistant pathogen required to be documented as per § 23 IfSG, e.g. MRSA, VRE, ESBL (II)
  • Upper or lower respiratory tract infections (II)

Respective patients should be operated – if possible – at the end of the operation list; the breathing system and the manual bag are changed after that.

Complying with these measures allows the use of anaesthesia breathing systems for a period of up to 7 days based on the latest state of knowledge, provided that the system continues to meet functional requirements such as air tightness (IB) and if stated by the manufacturer in the instructions for use. Moreover, the recommendations for preventing nosocomial pneumonia shall apply in full [2].

Reprocessing of the anaesthesia apparatus

If no BSF is used or the above-mentioned principles are not observed, the anaesthesia breathing system must be changed after each patient and the anaesthesia circle system (breathing circle system) must be processed in accordance with the manufacturers‘ instructions (IV).

Otherwise, if a BSF is used it is unnecessary to sanitize the interior of the device (breathing circle system); exception: repairs that require opening of the machine’s interior (IB) [1].


Explanation report

1 Risks of infection during anaesthesia ventilation

1.1 Exogenous
Release of droplet nuclei or aerosols

Pathogens can be released directly from the patient to the environment or transmitted via the staff. After use on the patient, all breathing gas conducting parts of the anaesthetic system can therefore be contaminated with pathogens, with the greatest levels of contamination being detectable close to the patient [10], [11], [12], [13]. After inhalation anaesthesia without BSF, the contamination rate of the anaesthesia breathing system and circle system amounted to 8–13% [14], [15], [16], [17], however, showing pulmonary pathogens only rarely enter the breathing system [16]. The risk of viral transmission is considered to be comparatively low [1], [2].

In the era of insufficient processing of breathing gas conducting parts of the anaesthetic system, particularly of the tracheal tubes and of the anaesthesia breathing system, infections or outbreaks due to contaminated systems were reported sporadically [12], [18], [19], [20], [21].

Dust (e.g. soda lime, wear, debris), with its often aggressive properties, can be transported with the anaesthesia ventilation gases, and has an inflammatory effect, which may weaken the mucosal barriers and increase the risk of infection [22]. Measurements of aerosol particles (Fraunhofer Institut Neuherberg) in the anaesthesia breathing system have shown a low contamination with aerosol particles of <0.5/cm3 in the presence of dry and cold soda lime [23]. This contamination can be minimised with BSF.

Liquid-borne infection

Pathogen-rich or potentially pathogen-containing bodily fluids such as saliva, blood, sputum etc. can be introduced into the anaesthesia breathing system by the patient during anaesthesia ventilation [10], [17], [18], unless appropriate BSF are used. This may be enhanced by patient positioning, increased secretion production and blood release due to illness as well as errors and trauma during intubation. Furthermore, CO2-absorption in the rebreathing anaesthesia ventilation system leads to the release of humidity, which condenses over the course of the operation. Approximately 15–20 ml water per hour accumulate in an unheated breathing system [24]; which, depending on the fresh gas flow, may remain in the system where it gathers primarily in the lower bends of the breathing systems.

1.2 Endogenous

Aspiration: During anaesthesia, pathogen-containing saliva, tracheal secretion and, eventually, blood may gather thus posing a risk of aspiration.

2 Application of breathing system filters (BSF)

During mechanical ventilation both inspiration and expiration gases pass through the junction between tracheal tube and anaesthesia breathing system. Consequently this is the suitable interface at which the application of BSF can effectively block the transport of microbial and particulate contamination within the breathing gas conducting components of the breathing system in each direction of flow. BSF are designed to prevent the passage of air borne and liquid borne pathogens in both directions, without increasing the air flow resistance and dead space to non physiological levels, and to contribute to the breathing gas humidification.

2.1 Design and function of breathing system filters

BSF are designed for the retention of aerosols from the ventilation gases. The filter medium is constructed as a three-dimensional depth filter. It is enclosed by a gas-tight housing, which has standardised conical connectors for connection to the patient’s tracheal tube on one side, and the breathing system on the other side. Clinically relevant characteristics of BSF are dead space and gas flow resistance, which are defined in accordance with ISO 23328-2 [7]. Additional heat and moisture exchanging components may be integrated in the filter housing to improve breathing gas humidification; this combination is called a Heat and Moisture Exchanging Filter (HME-F). Breathing systems are nowadays used for up to 7 days on the same anaesthesia ventilator [25]. By reducing the fresh gas flow, part of the expiration gas is conducted to the CO2-absorber, where heat and water are released according to the gross reaction formula CO2 + Ca(OH)2 → CaCO3 + H2O. Modern CO2-absorbers can be used until the soda lime is completely exhausted. It is therefore not unlikely that large amounts of liquid will gather in the breathing system, where exhaled bacteria may even proliferate; viruses do not have this capability. In order to evaluate the suitability of BSF therefore both air-borne and liquid-borne transport processes must be considered.

Air-borne filtration

Aerosols are a suspension of liquid or solid particles in a gas. Their typically polydisperse distribution may extend over a wide range of sizes. Liquid particles are usually spherical; their diameter is determined by the surface tension of the liquid and the partial vapour pressure in the environment. Due to evaporation or condensation of the fluid, the size of liquid particles is variable; a droplet may also contain different numbers of microorganisms. Solid particles can take very different irregular shapes. Filtration of aerosols is based on the interaction of different mechanisms [26] if the diameter of the particle is sufficiently large, the particle may be retained close to the surface of the filter medium already (direct interception). Due to their mass, smaller particles cannot always follow the changes of direction in the carrier gas surrounding the filter fibres. During their passage through the filter medium they are adsorbed deeper inside the filter medium (inertial impaction). Even smaller particles, e.g. in the size range of viruses, are subject to Brownian motion. This increases their virtual diameter, which in turn brings them into contact with the filter medium, where they are adsorbed as well (diffusion filtration). These mechanisms characterise the so-called mechanical filters. In suitable filter materials the filtration performance can be additionally increased by applying electrical charge, which attracts and binds particles with opposite charge (electret filters). The spatial effect of these charges allows, at a similar air-borne retention performance, a more open structure of these filter media in comparison with mechanical filters. The filtration characteristics of electret filters enhanced by electrostatic forces are destroyed by gamma sterilisation [27]. The different filtration mechanisms described above add up to a filtration performance, which is very high for both small and large particles but which shows a minimum at around 0.1–0.3 µm, being referred to as the filtration gap. Aerosol particles with a diameter of this size, which is called the Most Penetrating Particle Size (MPPS), can pass the filter medium more easily. Consequently, the air-borne filtration performance of BSF must be determined with uncharged test particles of this size. The results of such tests are therefore considered as “worst case” situation and are representative for the retention performance for microorganisms. EN ISO 23328-1 [28] describes the test method of applying NaCl particles of 0.1–0.3 µm in order to determine the filtration performance. Already in 1995, the National Institute for Occupational Safety and Health (NIOSH) categorised the results for respirator masks obtained with this method [29]: N95 filters retain at least 95%, N99 filters at least 99% and N100 filters at least 99.97% of the MPPS particles applied. Wilkes [30] examined 33 different BSF models using this method at a flow appropriate to anaesthesia (30 L/min) and obtained the following results: 14 of 24 electret filters did not comply with N95, 8 complied with N95, 2 complied with N99 and none complied with the N100 category. 4 of 9 mechanical filters complied with N99 and 5 with the N100 category.

Liquid retention

In contrast to the passage of gas, the passage of liquids through a BSF causes irreversible damage to the filter medium, which destroys its hygienic barrier function between patient and ventilation system. With the liquid, microorganisms contained therein pass the damaged filter medium regardless of their size or other properties. The passage of liquid through a BSF happens according to the all-or-nothing principle and must be prevented in anaesthesia ventilation practice [31]. If the entire filter surface is covered by liquid, the ventilation pressure applied by the anaesthesia ventilator on this liquid can cause the passage through the filter medium. Consequently, an appropriate filter must be used which does not allow the passage of liquid at the pressures generated during ventilation. These are typically max. 20–30 hPa (=20–30 mbar), which can be preset as pressure limits on the ventilator. To date there is no international standard for measuring the pressure limit up to which the liquid retention of a BSF is guaranteed. Cann et al. [3] have determined for different BSF the pressure at which water passed through the filter medium. Electret filters showed liquid passage at pressures between 3 and 14 hPa, whereas water break through was observed in mechanical filters at pressures between 20 and 133 hPa only. These are substantially discrete values, which do not overlap in their range.

2.2 Justification for specific values

The misleading term “hydrophobic” is often used to characterise and categorise the filter medium. This often means that the filters have high liquid retention values. However, as both of the terms “hydrophobic” and “mechanical” do not include defined retention rates for airborne particles or retention values for potentially contaminated liquids, these terms should only be used in conjunction with the specific values of the BSF.

Air-borne retention rate

There is no international consensus on the lowest required retention efficiency of BSF for pathogens. A retention performance of 99.95% or more is mentioned in some manufacturers’ data. Lumley et al. [32] even recommend 99.997%, and the French Society for Anaesthesiology and Intensive Care Medicine [33] even 99.9999%. As the MPPS has not been considered in this work, these specifications and requirements cannot be used.

An air-borne retention efficiency of >99% (2 log) recommended by the working group is insofar justified as on the patient side of the filter a maximum of only 30 cfu was detectable after anaesthesia ventilation [13]. This shows that only a fraction of the pathogens contained in the sputum is transported by air, since in the event of tuberculosis for example, a bacterial content of 5–6 log can be reached in the tracheal secretion or sputum respectively, and 8 log/ml can be reached in case of respiratory infections in total [34]. In order to reach the next patient, the microorganisms deposited in the circuit have to be mobilised again and pass through the entire circle system including CO2-absorber and BSF towards the patient. In view of these data, the recommended retention rate of 2 log, i.e. 4 log in total, ensures adequate safety.

Anaesthesia ventilation of patients with notifiable infectious diseases as per § 6 of the Infectious Disease Control Act (IfSG) requires that the breathing system be changed for legal reasons.

If anaesthesia ventilation is performed on patients with infectious diseases required to be documented as per § 23 or on patients with upper or lower respiratory tract infections, the anaesthesia breathing system should be exchanged as well in order to rule out any risk of transmission.

Liquid retention

An appropriate filter must be used, which does not allow the passage of liquids at the pressures generated during ventilation. In order to achieve adequate safety, liquids should be retained at pressures ranging up to about 10–20 hPa (=10–20 mbar) above the pressure limit preset on the ventilator.

According to Cann et al. [3], the use of electret filters is not recommended in anaesthesia ventilation when copious condensate formation occurs.

2.3 Breathing gas humidification

Within just a short period of time, ventilation with dry breathing gases leads to dehydration and cooling of the mucosa and, consequently, to a decrease in secretion viscosity and to an impairment of the mucociliary clearance and a reduced barrier function, unless adequate measures for the humidification and heating of the breathing gases are taken [4], [5], [35], [36], [37]. The humidification properties of BSF alone are normally not sufficient to adequately humidify the dry breathing gases from a central gas supply system or from pressurised gas cylinders. By reducing the fresh gas flow, part of the expiration gas is conducted over the CO2-absorber. The lower the fresh gas flow, the higher is the level of formation of water and the breathing gas humidification [4], [5], [38].

2.4 Special features in paediatrics and neonatology

During anaesthesia ventilation of children and newborns, potential injury of the respiratory tract due to exceedingly dry breathing gases is even more significant, particularly as humidification by the rebreathing system is virtually ruled out in these cases. Furthermore, the dead space of the selected BSF must be taken into account during ventilation to avoid undesirable CO2-rebreathing. Suitable mechanical filters for tidal volumes below 250 ml are available – if at all – only to a very limited extent. Breathing gas humidification must be given priority at this point, for example with HME or active humidifiers. In these cases the required hygienic protection can only be guaranteed by using a new, unused breathing system for each patient.

Some of the HMEs or catheter mounts used in paediatrics have a monitoring port on the patient side. Monitoring lines for airway pressure or side stream CO2-measurements are connected to this port. The respiratory tract is thus connected with potentially contaminated devices without the hygienic barrier of the BSF. This must be taken into account either by using a fresh monitoring line or by attaching the monitoring line on the machine side.

2.5 Biocompatibility

It has not been examined whether residuals from the materials used are accumulated in the inspiration air during the passage through the BSF and the anaesthesia breathing system. Correspondingly, the verification of this feature has not taken place so far.

2.6 Product life of the breathing system and treatment of the anaesthesia circle system when using a BSF

Up until now it has been recommended to change the breathing system after a maximum of 24 h when a BSF has been used [1], [14]. As there is no internal contamination of the anaesthesia breathing system downstream of the BSF, the same degree of safety is given even after a 7 d period of use [13]. The postoperative pneumonia rate at a weekly change is not different from the rate at a daily change policy [39]. However, the functionality e.g. with respect to air tightness etc. must be guaranteed according to the DGAI guidelines on the basis of

  • Check for proper condition and operability before planned operation (system check A)
  • Check for proper condition and operability at patient change (system check W).

When the BSF is used as intended, the treatment of the ventilation system’s interior (breathing system, circle system) is not required. Repair situations, which require that the system is opened is considered as an exception, as there is normally no complete control over the prevention of potential contamination.

2.7 Environmental contamination

The anaesthesia breathing system must be changed when visible contamination e.g. with blood occurs. When visibly contaminated, the breathing bag must be cleaned and disinfected or changed [13], [40]. At the end of the operation list, all surfaces of the anaesthesia working station with hand contact must be disinfected (IB). When using disinfectants the manufacturers’ instructions have to be followed (IV).

3 International recommendations on the use of breathing system filters

Netherlands: In 1991, in view of the emerging AIDS pandemic, the Dutch Werkgroep Infectie Preventie [41] recommended the use of mechanical hydrophobic filters (retention >5 log) as an alternative to the change of anaesthesia tubes for each patient.

Great Britain and Ireland: The working group “Blood born viruses and anaesthesia” of the Association of Anaesthetists of Great Britain and Ireland has critically examined the common practice at that time of leaving breathing systems for all patients on one operation list after a debatable cross-infection with hepatitis C had occurred in the mid-nineties [18]. As a result they recommended that anaesthesiologists wear (non-sterile) disposable gloves and that either the anaesthesia breathing system be changed after each patient or mechanical BSF be used [42].

France: In 1997 the French Society for Anaesthesiology and Intensive Care Medicine recommended bacterial and viral filters for anaesthesia ventilation [33]. 3 years later this recommendation was specified in such a way that a hydrophobic mechanical HME filter be applied, which at least withstands a hydrostatic pressure of a 50 cm water column [43].

USA: The Centers for Disease Control and Prevention (CDC) recommend the use of filters in anaesthesia for patients with known TB infection [44], [45], [46]. The filters recommended by the CDC are hydrophobic and validated for the retention of Mycobacterium tuberculosis. In 2003, when giving recommendations concerning the containment of SARS infections, the CDC pointed to the guidelines on the treatment of TB patients in the absence of clear findings about this new lung disease [47].

Canada: The health ministry of the region of Ontario decided for all patients suffering from SARS or suspected of suffering from SARS that a mechanical breathing system filter be placed between patient and ventilator [48].

Taiwan: The Respiratory Society expressly recommends the use of a mechanical filter for the ventilation of SARS patients [49].


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