I am being asked to consider reusable anesthesia breathing circuits with Pall filters. Searching the APSF Newsletter, I found several questions regarding this topic in the Spring 09 issue. Some of those questions were printed under the “On the Horizon” title. I haven’t found any follow-up since. What is the status of this debate?
R. Mauricio Gonzalez MD
Clinical Assistant Professor of Anesthesiology
Boston University School of Medicine
Vice Chairman of Clinical Affairs
Department of Anesthesiology
Boston Medical Center
Dear Dr. Gonzalez:
It has become increasingly common to use anesthesia breathing circuit filters in an effort to decrease infectious risk from diseases such as HIV, hepatitis C, tuberculosis, SARS, vCJD, and H1N1 influenza.1 This trend may also be fueled, in part, by liability concerns regarding the possibility of transmitting such dangerous infections in health care.1 When the SARS pandemic hit in Canada, 50% of the deaths were health care workers, including 3 anesthesiologists.2 Once it was better understood how the infection was being spread, the Ontario Ministry of Health mandated the use of pleated hydrophobic submicron filters.2
There are several reports in the literature of contamination potentially spreading through anesthesia machines. In 2 instances, a seemingly unlikely pathogen, HCV, (Hepatitis C Virus) spread from patient to patient via the anesthesia breathing circle system.3 Studies have shown that anesthesia machines can become contaminated, and ventilators have been shown to spread infections from patient to patient.4,5 If an anesthesia machine is used in caring for a patient who is recognized as being colonized or infected, it should be decontaminated. Too often, however, decontamination consists of merely wiping the machine with a disinfectant. This does little or nothing to protect subsequent patients from organisms that may be residing in the machine or soda lime canister.
The anesthesia environment presents a difficult challenge for a filter or a heat and moisture exchange filter (HMEF). High levels of moisture may negatively affect filtration efficiency. Filters that test well in a dry environment may be less effective in the relatively moist environment found in the anesthesia setting.6 Vulnerable patients may be suffering from preexisting infections, may be immunocompromised, intubated, and placed in an environment that is warm and moist, resulting in considerable risk for infection.
There are 2 basic types of filters, mechanical (pleated hydrophobic) and electrostatic. Electrostatic filters have an applied charge on the media. This applied charge will attract aerosolized particles of the opposite charge, and hold them on the media. Mechanical filters have no applied charge. Instead, they filter primarily by having smaller interstices in the media, and they are often pleated to increase the surface area in order to keep resistance to a minimum.7
Electrostatic filters may perform well in the dry environment during testing, but not as well in the more humid environment associated with anesthesia delivery.8 It is important to keep patient respiratory secretions from entering the media, which may facilitate infectious contamination. Several studies have shown that many filters are penetrated by fluid even when low pressures are applied.6,9,10 The pressure needed to drive the fluid through the filter media is often below those pressures commonly used to deliver anesthetic gases to patients. It has been shown that pleated hydrophobic HMEF require substantially higher pressures to force fluid into the media.11 The entry of fluid into filter media is particularly problematic for electrostatic filters that may lose much of their efficacy when they become wet.10 Should the HMEFs or filters be breached, the anesthesia circuit may become contaminated.12
The International Organization for Standardization (ISO) has addressed breathing system filters for anesthetic and respiratory use and promulgated a standard, ISO 23328-1.13 A key point is that this international standard requires filter validation by means of a standardized test using a 0.3 micron particle challenge. It also mandates specific tidal volumes and flow rates to be used to insure consistency and accuracy of testing. This type of standardization provides a more consistent and scientifically objective method for judging the effectiveness of a filter and should be used along with studies that evaluate filtration performance in a moist environment.
We have known for a long time that anesthesia machines and circuits may become contaminated.14,15 The discussion of filtration use has, however, gradually moved from answering the question: “Can filters contribute to decreasing machine and circuit contamination?” to “Are filters a safe alternative to the individual replacement of breathing circuits and can we extend circuit life?”16
From the standpoint of infection control and circuit reuse it is important to think of the circuits as a part of the machine, rather than a separate entity. The entire circle system may become contaminated, including the soda lime, and the machine.17,18 Bernards et al. found infectious contamination by Acinetobacter baumannii in critical care unit ventilators. Critical care ventilators are similar enough to anesthesia machines to raise concern that the latter may serve as vehicles for infection as well.19
In the United States it is becoming more common for circuits to be reused between patients, when an HMEF is being used at the patient wye. This practice is much more widespread in Europe, where anesthesia caregivers are especially aware of the issues associated with disposable plastics and the environment. The Association of Anaesthetists of Great Britain and Ireland supports circuit reuse for multiple patients when using an effective HMEF.20 A recent German Anesthesia and Infection Control Associations (DGKH/DGAI) statement allows for anesthesia circuits to be reused for multiple patients according to the circuit labeling, when employing an HMEF with an efficiency of >99% measured according to ISO 23328-1, with an important caveat relating to liquid penetration values.21
An earlier Dear SIRS column posed a question about a company (Pall Corporation) that has had a 510(k) for circuit reuse since 2002.22 This company’s HMEF (Pall Ultipor™ 25 filter) uses a pleated ceramic, hydrophobic sub-micron media, which has performed at the highest levels, irrespective of testing methodology. These filters work equally well in a dry or moist environment and have been shown to prevent contamination of the circuit in clinical use for 24 hours.23,24 This particular HMEF has also been used,
in vivo, on a standard anesthesia breathing circuit over a 72-hour period with a new filter being utilized for each patient. No patient contamination of the circuit occurred.25
If a hospital chooses to reuse its circuits for multiple patients, in the interests of cost savings and the environment, it is extremely important to be certain that the HMEFs have been properly validated against organisms, resistance, and fluid penetration and that the circuit is labeled specifically to permit reuse for multiple patients. If a hospital chooses to go “off label,” using a circuit that is labeled “Single Patient Use,” effective filtration may not be assured and risks of cross contamination and infection may exist. Therefore, it is important that products be selected which are intended for and support multiple patient use.
James M. Maguire, PhD, RCP, FCCP
Senior Scientist/Lecturer, Pall Life Sciences
Senior Consultant, Respiratory Care
- Kamming D, Gardam M, Chung F. Anaesthesia and SARS. Br J Anaesth 2003;90:715-8
- Directive 03-06(R). SARS Provincial Operations Centre. Directives to all Ontario acute care hospitals for high-risk procedures involving SARS patients critical care areas. Available at: http://sars.medtau.org/revisedhighrisk.pdf. Accessed July 22, 2010
- Heinsen A, Bendtsen F, Fomsgaard A. A phylogenetic analysis elucidating a case of patient-to-patient transmission of hepatitis C virus during surgery. J Hosp Infect 2000;46:309-13.
- Langevin PB, Rand KH, Layon AJ. The potential for dissemination of Mycobacterium tuberculosis through the anesthesia breathing circuit. Chest 1999;115:1107-14.
- Centers for Disease Control and Prevention (CDC). Tuberculosis outbreak in a community hospital—District of Columbia, 2002. MMWR Morb Mortal Wkly Rep 2004;53:214-6.
- Hedley RM, Allt-Graham J. A comparison of the filtration properties of heat and moisture exchangers. Anaesthesia 1992;47:414-20.
- Turnbull D, Fisher PC, Mills GH, Morgan-Hughes NJ. Performance of breathing filters under wet conditions: a laboratory evaluation. Br J Anaesth 2005;94:675-82.
- Wilkes AR. Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 1—history, principles and efficiency. Anaesthesia 2011;66:31-9.
- Vezina DP, Trépanier CA, Lessard MR, et al. An in vivo evaluation of the mycobacterial filtration efficacy of three breathing filters used in anesthesia. Anesthesiology 2004;101:104-9.
- Lee MG, Ford JL, Hunt PB, et al. Bacterial retention properties of heat and moisture exchange filters. Br J Anaesth 1992;69:522-5.
- Vijayakumar M, Morton W, Zuchner K, et al.. Pressure required to force water through breathing system filters—a laboratory study. Eur J Anaesthesiol 2010;27:237 (Abstract 17AP3-10)
- Cann C, Hampson MA, Wilkes AR, et al. The pressure required to force liquid through breathing system filters. Anaesthesia 2006;61:492-7.
- International Organization for Standardization. Anaesthetic and respiratory equipment (ISO 23328). Available at: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=35330. Accessed July 22, 2011.
- Magath TB. Method for preventing cross-infection with gas machines. Anaesth Analg 1938;17:215-7.
- Gross GL. Decontamination of anesthesia apparatus. Anesthesiology 1955;16:903-9.
- Egger Halbeis CB, Macario A, Brock-Utne JG. The reuse of anesthesia breathing systems: another difference of opinion and practice between the United States and Europe. J Clin Anesth 2008;20:81-3.
- Body SC, Philip JH. Gram-negative rod contamination of an Ohmeda anesthesia machine. Anesthesiology 2000;92:911.
- Brooks JHJ, Gupta B, Baker D. Anesthesia machine contamination (abstract). Anesthesiology 1991;75(3A):A874.
- Bernards AT, Harinck HI, Dijkshoorn L, et al. Persistent Acinetobacter baumannii? Look inside your medical equipment. Infect Control Hosp Epidemiol 2004;25:1002-4.
- Association of Anaesthetists of Great Britain and Ireland. Infection control in anaesthesia. Anaesthesia 2008;63:1027-36.
- Kramer A, Kranabetter R, Rathgeber J, et al. 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). GMS Krankenhhyg Interdiszip 2010;5(2).
- 510(k) Summary. Pall Medical, East Hills, NY. Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf/k013093.pdf. Accessed July 22, 2011.
- Tischler JM, et al. Determining the effectiveness of the Pall BB25A HME filter as a bidirectional barrier to the transmission of bacteria during inhalational anesthesia. (abstract) AANA J 1997;65(5):507.
- Imai N, Nishimura C, Ikeno S, et al. Clinical utility of a breathing circuit filter during general anesthesia of long duration. Available at: http://www.asaabstracts.com/strands/asaabstracts/searchArticle.htm;jsessionid=
0&bold=true&italic=false. Accessed July 22, 2011.
- Hanover JJ et al. The effectiveness of the Pall BB25A HME filter during extended use of an anesthesia circuit. (abstract) AANA J 1999;67(5):448.