Circulation 84,122 • Volume 24, No. 1 • Spring 2009   Issue PDF

Cross-Contamination Via Anesthesia Equipment?

Pam Krueger, CRNA; Chuck Klos, CRNA, APNP; A. William Paulsen, MMSc, PhD, CCE, AAC; Gunnar Klauss, MD, MS; Randy Blessing, BMET; Steve Kimatian, MD; Robert Ponte, MD; Mark J. Shulkosky, MD

The APSF has received numerous questions regarding cross-contamination of one patient to another via the anesthetic machine and breathing circuit. They concern the need for and efficacy of various breathing circuit filters, their optimal location, the cleaning of the machine, and the reuse of disposable circuits and/or filters. These questions are interrelated and the Committee on Technology would like to address them in the next few issues of the Newsletter.

First, we’d like to refer the readership and question writers to a previous Dear SIRS column in the Spring 2007 issue of the Newsletter, pages 12-14, entitled “Can Soda Lime Canisters Spread MRSA?” ( Within that article are important references regarding filtration efficacy, filtration for M. tuberculosis, and the latest CDC recommendations for cleaning the anesthesia machine. Next, a few general issues surrounding contamination of the circle breathing system will be presented in this column, followed by specific questions and answers. Considerations of circuit re-use and specific manufacturer recommendations for cleaning the machine will be presented in a subsequent issue of the Newsletter.

The Committee on Technology was asked whether bacteria and/or viruses live through the highly alkaline pH of soda lime. In 1941 an overly simplistic model was proposed that bacteria became trapped in the breathing circuit and never reached the inspiratory limb, possibly due to the bactericidal action of soda lime (pH 11-14). Therefore, cross-contamination of patients was thought highly unlikely.1 When CO2 enters the reaction with soda lime, heat and water are released and soda lime forms a highly alkaline solution. This alkaline solution appears bactericidal for pathogens like Staphylococcus aureus and Pseudomonas aeruginosa but not for others, including Mycobacterium tuberculosis.2,3 Infectious particles aerosolized by patients have a wide range of particle size and mass which together with their velocity influences their ability to either 1) remain in the gas flow stream, 2) become trapped in the highly alkaline liquid surrounding the soda lime granules, or 3) deposit themselves on various surfaces.4 CO2 absorber canisters would see variable amounts of bacterial load dependent upon the fresh gas flow from the anesthesia machine, the inspiratory flow rate, and tidal volume of the delivered breath. For example, in the case of high fresh gas inflow, there would be redirection of exhaled gas outwards through the scavenger, and retrograde filling of the absorber with fresh gas, instead of recirculation of patient gas through the absorber. Conversely, in situations of low fresh gas flow and/or smaller CO2 canisters, there could theoretically be an increase in the pathogens eluted from the inspiratory limb. Soda lime is not a true barrier for bacteria or viruses.

One reason for so many conflicting studies regarding the cross-contamination of patients, relates to the large number of variables that contribute to transmission of virulent pathogens in sufficient numbers to the inspiratory limb of the breathing circuit, where they may be delivered to the next patient. Variables that are likely to influence this ability of pathogens to be transmitted include

  1. Number of organisms aerosolized
  2. Virulence of the organism
  3. Resistance of the organism
  4. Electrical charge of the organism and aerosol4
  5. Size and distribution of particles entering the breathing system4
  6. Fresh gas flow4
  7. Tidal volume, inspiratory flow rate, and I:E ratio
  8. Volume of the CO2 absorber canister
  9. Granule size of the CO2 absorbent
  10. Frequency of use of the machine5
  11. Time between cases5
  12. Immunity of the patient.

A single study that controls all of these variables is highly unlikely given the complexity of anesthesia care in a clinical setting. It must also be remembered that most studies are carried out under standardized conditions and can only approximate the clinical scenario of a busy operating room.

Q Dear Q&A,

Are filters a necessary precaution we need to use for the purpose of protecting patients, or are they not really performing any useful function? I am interested in the patient safety function of the filters and not the intent to re-use the circuit on another patient.

Pam Krueger, CRNA
Taylor, TX

A Dear Ms. Krueger,

Protecting patients from undesirable pathogens via the anesthesia circle breathing system has been the topic of many studies, often with divergent conclusions.1-3,5-10 Many of the contaminations found were non-pathogenic skin flora.9,11 Before a breathing circuit can serve as a vector for respiratory infections:

  1. A patient must aerosolize a sufficient number of pathogens to contaminate the anesthesia machine
  2. The pathogen must remain viable from one case to the next
  3. The pathogen must be eluted from the machine in sufficient numbers and with sufficient virulence to infect other patients.5

Infected patients can aerosolize large numbers of bacteria and efficiently transmit them to the anesthesia machine when intubated.5,6,12 These pathogens can reside in the anesthesia machine for prolonged periods of time.7 In particular, the mask, Y-piece, and breathing hoses, which can become readily contaminated with patient secretions, must be cleaned and subjected to high level disinfection, according to the Centers for Disease Control and Prevention,13,14 as well as the ASA Committee on Occupational Health of Operating Room Personnel as described in their Recommendations for Infection Control for the Practice of Anesthesiology.15 Many clinicians prefer single-use disposable breathing hoses instead. The low frequency of documented transmission of infections through use of the anesthesia equipment suggests that these policies are effective.6,16,17 There are, however, reports of cross- contamination despite such guidelines.18 Filters in the breathing circuit may be an approach to manage this complex situation; however, opinions regarding their use remain ambiguous.19,20 The current recommendations from the Centers for Disease Control and Prevention state that use of filters is an unresolved issue13,14 except in the case of patients with active tuberculosis.21 The ASA recommendations15 state that routine use of filters is not supported by current evidence, except in the prevention of transmission of M. Tuberculosis.

Filters bring their own set of potential dangers. Case reports described distal occlusion22 and filter obstruction from secretions,23 hypoxia,24 toxic metabolite production,25 increases in dead space for pediatric circuits,26 and undetectable changes in filter resistance leading to decreased tidal volumes, increased airway pressures25 and even bilateral pneumothoraces.27 These problems may not be immediately apparent and can lead to delay in diagnoses with dire consequences for patients.

Q Dear Q&A,

What is the current status on which limb of the anesthesia machine the viral filter of the circuit should attach? Expiration or inspiration limb of the machine? Any reasons?

Chuck Klos, CRNA, APNP
Menomonie, WI

A Dear Mr. Klos,

Breathing filters are assessed according to their bacterial filtration efficiency (BFE) and viral filtration efficiency (VFE). Protection of the anesthesia machine from the patient would suggest that a high efficiency filter be placed in the expiratory limb. Protecting the patient from the anesthesia machine suggests that a high efficiency filter be used on the inspiratory limb of the breathing circuit. Placing the breathing filter between the endotracheal tube and the Y-piece will protect the patient and the anesthesia machine from contamination,6,8,9,11,16,28-30 and is probably the most logical placement. The ASA recommends this location in cases of M. Tuberculosis.15 Interposition of a filter would lead some to suggest reuse of the breathing circuit tubing, thus saving the cost of a new circuit for each patient,31 but the issues related to reuse of single-use anesthesia equipment are complicated and will be discussed in a later issue of the Newsletter (see “On the Horizon” below).

In summary

Nosocomial pneumonia is one of the most costly hospital acquired infections. The magnitude of cross-contamination via the anesthesia machine or breathing circuit is very small in comparison to other modes of nosocomial infections. With the use of bacterial/viral filter devices this risk is further reduced and most experimental and clinical studies confirm the high efficiency of such devices. Viral filtration rate is most likely not as effective as bacterial filtration.6 Filters should be interposed between the endotracheal tube and the Y-piece. Thus, for cross-contamination to occur, a pathogen has to bridge a filter device twice, making the event even less likely. Routine filter use is currently not supported by CDC guidelines or ASA recommendations, except for M. Tuberculosis. Many advocates wish to use these filters in order to reuse breathing circuits and save costs. This practice, even though widespread in the US, Canada, and Europe, is not yet proven to be safe and is thus controversial.20

A. William Paulsen, MMSc, PhD, CCE, AAC
Vice-Chair, Committee on Technology
Gunnar Klauss, MD, MS
Resident, Department of Anesthesiology
Wake Forest University School of Medicine

On the Horizon: Questions Regarding Circuit Reuse and Filters

Dear Q&A,

We are trying to determine 1) a proper cleaning procedure for our machines, 2) the parts of these machines that are considered “reusable breathing components,” and 3) the necessity and costs associated with a routine disinfection protocol.

Randy Blessing, BMET
Augusta, GA

Q Dear Q&A,

We have been approached about using a filter device placed at the end of the Y-piece which supposedly allows you to protect the circuit from contamination and REUSE it! This is supposed to save costs and minimize storage and waste. Is this safe?

Steve Kimatian, MD
Hershey, PA

Our facility is considering the use of a filter that the manufacturer states can allow reuse of the circuit for the entire day. The filter is changed at the end of each day. The facility is strongly encouraging the use of this device. Are you aware of any independent data on these filters?

Robert Ponte, MD
Orange Park, FL

In an effort to decrease costs, the facility director of our ASC would like us to consider using filters on our anesthesia circuits, changing only masks between patients. Is this an acceptable practice? Any recommendations for what to look for in a filter? Can they be used for pediatric patients as well as adults? How often do the filters have to be changed? Other than resistance are there other patient risks? Infections? Do many other groups do this?

Mark J. Shulkosky, MD
Erie, PA


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  2. Dryden, GE. Risk of contamination from the anesthesia circle absorber: an evaluation. Anesth Analg 1969; 48: 939-934.
  3. Murphy PM, Fitzgeorge RB, Barrett RF. Viability and distribution of bacteria after passage through a circuit anaes-thetic system. Br J Anaesth 1991; 66: 300-304.
  4. Thiessen RJ. Filtration of respired gases: Theoretical aspects. Respir Care Clin 2006; 12: 183-201.
  5. Langevin PB, Rand KH, Layon AJ. The potential for dissemination of Mycobacterium tuberculosis through the anesthesia breathing circuit. Chest 1999; 115:1107-1114.
  6. Hartmann D, Jung M, Neubert TR, Susin C, Nonnenmacher C, Mutters R. Microbiological risk of anaesthetic breathing circuits after extended use. Acta Anaesthesiologica Scandinavica 2008; 52:432 – 436.
  7. Joseph JM. Disease transmission by inefficiently sanitized anesthesia apparatus. JAMA 1952; 149: 1196-1198.
  8. Leitjen D, Rejger V, Mouton R. Bacterial contamination and the effect of filters in anaesthetic circuits in a simulated patient model. J Hospital Infection 1992; 24: 51-60.
  9. Luttropp H, Berntmann NL. Bacterial filters protect anaesthetic equipment in a low flow system. Anaesthesia 1993; 48: 520-523.
  10. Stark DCC, Green CA, Pask EA. Anaesthetic machines and cross-infection. Anaesthesia 1962; 17: 12-20.
  11. Shiotani G, Nicholes P, Ballinger C, Shaw L. Prevention of contamination of the circle system and ventilators with a new disposable filter. Anesth Analg 1971; 50: 844-855.
  12. Cantanzaro A. Nosocomial tuberculosis. Am Rev Respir Dis 1982; 125: 559-562.
  13. CDC guideline for environmental infection control in health-care facilities, 2003.
  14. CDC guidelines for preventing health-care-associated pneumonia, 2003: recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee.
  15. American Society of Anesthesiologists Committee on Occupational Health of Operating Room Personnel. Recommendations for infection control for the practice of anesthesiology. 2nd ed. Park Ridge, IL: ASA, 1998.
  16. Berry AJ, Nolte FS. An alternative strategy for infection control of anesthesia breathing circuits: a laboratory assessment of the Pall HME filter. Anesth Analg 1991; 72: 651–5.
  17. DeMoulin GC, Saubermann AJ. The anesthesia machine and circle system are not likely to be sources of bacterial contamination. Anesthesiology 1977; 47: 353-358.
  18. Chant K, Kociuba K, Munro R, et al. Investigation of possible patient-to-patient transmission of Hepatis C in a hospital. New South Wales Public Health Bulletin 1994; 5: 47-51.
  19. Hogarth I. Anesthetic machine and breathng system contamination and the efficacy of bacterial/viral filters. Anaesth Intensive Care 1996; 24: 154-63.
  20. Lessard MR, Trepanier CA. Should we use breathing filters in anesthesia? Can J Anesth 2002; 49(2): 115-120.
  21. CDC Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings, 2005. MMWR 2005; 54 (RR-17), 1-147.
  22. Barton R. Detection of expiratory antibacterial filter occlusion. Anesth Analg 1993; 77: 197.
  23. Kopman A. Glaser L. Obstruction of bacterial filters by edema fluid. Anesthesiology 1976; 44: 169-170.
  24. Schwartz A, Howse J, Ellison N. The gasline filter: A cause for hypoxia. Anesth Analg 1980; 59: 617-618.
  25. Lawes EG. Hidden hazards and dangers associated with the use of HME/filters in breathing circuits. Their effect on toxic metabolite production, pulse oximetry and airway resistance. British Journal of Anaesthesia, 2003; 91: 249-264.
  26. Chau A, Kobe J, Kalyanaraman R, Reichert C, Ansermino M. Beware the airway filter: deadspace effect in children under 2 years. Pediatric Anesthesia 2006; 16: 932-38.
  27. Smith C, Otworth D, Kaluszyk P. Bilateral tension pneumothorax due to defective anaesthesia breathing circuit filters. J Clin Anaesth 1991; 3: 229-34.
  28. Gallagher J, Strangeways J, Allt-Graham J. Contamination control in long-term ventilation. Anaesthesia 1987; 42: 476-481.
  29. Vezina DP, Trepanier CA, Lessard MR, Gourdeau M, Tremblay C. Anesthesia breathing circuits protected by the DAR Barrierbac S® breathing filter have a low bacterial contamination rate. Can J Anesth 2001; 48: 748-754.
  30. Vezina DP, Trépanier CA, Lessard MR, Gourdeau M, Tremblay C, Guidoin R. An in vivo evaluation of the mycobacterial filtration efficacy of three breathing filters used in anesthesia. Anesthesiology 2004; 101: 104-9.
  31. Carter JA. The reuse of breathing systems in anesthesia. Respir Care Clin N Am 2006; 12: 275-86.


In order to access the referenced CDC Guidelines in PDF format please use the following convenient hyperlink:
The cited ASA Recommendations, also in PDF format, can be accessed through:

The information provided is for safety-related educational purposes only, and does not constitute medical or legal advice. Individual or group responses are only commentary, provided for purposes of education or discussion, and are neither statements of advice nor the opinions of APSF. It is not the intention of APSF to provide specific medical or legal advice or to endorse any specific views or recommendations in response to the inquiries posted. In no event shall APSF be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the reliance on any such information.