Potential sources of operating room air contamination: a preliminary study (2022)


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Journal of Hospital Infection

Volume 113,

July 2021

, Pages 59-64

Author links open overlay panelJ.G.Brock-UtneEnvelopeJ.T.WardPersonEnvelopeR.A.Jaffe

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The Neptune® surgical suction system (NSSS) and the Bair Hugger® (BH) forced-air warmer both discharge filtered exhaust or heated air into the operating room (OR), often in close proximity to a surgical site.


To assess the effectiveness of this filtration, we examined the quantity and identity of microbial colonies emitted from their output ports compared with those obtained from circulating air entering the OR.


Air samples were collected from each device using industry-standard sampling devices in which a measured volume of air is impacted on to a blood agar plate at a controlled flow rate. Twelve ORs were studied. Sample plates were incubated for one week per study protocol, then interpreted for colony counts and sent for species identification.


The average colony count from the NSSS exhaust was not significantly different from that obtained from room air samples, however the average count from the BH output was significantly higher (P=0.0086) than room air. Genetic identification profiles revealed the presence of environmental or commensal organisms that differed depending on the source. High variability in colony counts from both devices suggests that certain NSSS and BH devices could be significant sources of OR air contamination.


Our study showed that the BH patient warming device could be a source of airborne microbial contamination in the OR and that individual BH and NSSS units exhibit a higher output of microbial cfu than would be expected compared with incoming room air. We make simple suggestions on ways to mitigate these risks.


Great lengths have been taken in previous decades to reduce the risk of surgical site infections (SSIs). Airborne pathogens have been recognized as a source of these infections to the extent that in the USA the Centers for Disease Control and Prevention (CDC) and Healthcare Infection Control Practices Advisory Committee (HICPAC) have made several recommendations related to the handling of operating room (OR) air which include the use of high-efficiency filtration [1]. Our study examined whether two common devices used in the OR may inadvertently be contributing to the burden of airborne microbes and thereby potentially increasing the risk of SSI.

The Neptune® surgical suction system (NSSS) (Stryker Worldwide, Kalamazoo, MI, USA) is a self-contained portable suction system employed widely in hospitals throughout the country, and it has replaced traditional wall suction-based systems in many ORs. It is considered by some to be a less hazardous and more efficient method of handling surgical suction waste [2]. The authors of this study have often observed multi-coloured deposits (possible microbial growth) on the inner walls of the NSSS collection canister that may persist for months despite adherence to the recommended cleaning protocols. Because fluid suctioned from a surgical site is often contaminated with antibiotics administered during surgery, these canisters have the potential to be reservoirs of antibiotic-resistant organisms which, if not properly isolated from the rest of the OR, could have important consequences for SSIs. This isolation depends entirely on the function of the confinement systems within the machine including a high-efficiency particulate air (HEPA) filter.

The Bair Hugger® (BH) forced-air warmer (3M® Company, Maplewood, MN, USA) has been a mainstay of temperature management in the OR for many years. The heated air this device produces is delivered in very close proximity to the patient and the surgical site, and because of this, it has been the subject of previous investigations as a potential source of SSIs. These studies, while not directly linking the device to infections, have shown that it can disrupt the air flow patterns employed in ORs to prevent SSIs [[3], [4], [5], [6], [7]]. The importance of this exhausted air being free of potential pathogens is essential, and to that end each BH contains a HEPA filter located at the air intake at the base of the machine.

The filters in use in both the NSSS and BH should, in theory, ensure that the output or exhaust from these devices is at least as clean as the filtered air entering the OR. HEPA filters are manufactured to a minimum efficiency of 99.97% for the removal of particles greater than 0.3μm, but both time and particulate loading tend to degrade that efficiency [8]. This is why manufacturers often recommend both interval-based and usage-based replacement schedules for every filter (e.g., 12 months or 500h of use). At some large institutions including ours, the interval-based replacement schedule presents less of a logistical challenge and is used for these devices.

To test the effectiveness of this filtration at eliminating airborne microbes, we sampled the exhaust air from 12 NSSS and 11 BH devices in 12 separate ORs. This was carried out to count and identify any colony forming units (cfu) they emitted, and then these data were compared with samples from the filtered room air entering the randomly selected ORs in which these devices were in use. We assumed that the HEPA-filtered air emitted from the NSSS and the BH devices would contain lower average colony counts compared with that found at the OR fresh air inlet.

Section snippets


Air samples were collected from a total of 12 randomly selected ORs following the completion of an open surgical procedure approximately 5–15min after the patient and surgical team had exited but prior to OR cleaning. ORs at our institution undergo at least 12–20 air exchanges per hour in compliance with State guidelines. In each room, samples were taken from the ceiling OR air inlet, the open NSSS exhaust port at the bottom of the machine and from the open end of the BH hose. These were


Sample data are shown in TableII. Using the unpaired two-sample Kolmogorov–Smirnoff test, average colony counts (adjusted to cfu/m3) from the NSSS exhaust (13.54 cfu/m3) were not significantly different from those obtained from room air (8.75 cfu/m3; P=0.69); however, the average number of colonies from the BH hose (26.04 cfu/m3) was significantly higher compared with room air (P=0.0086). This difference persisted when outlier data from OR 14 was excluded (P=0.022). A dot plot representation


Our results confirm that air samples from the BH outlet hose contain a larger number of bacteria on average than the air coming in through the OR ceiling inlets despite regularly scheduled maintenance and the use of high-efficiency filters. The potential risk of blowing air containing bacteria-laden particles in close proximity to the patient and surgical site should not be underestimated. Although the isolates were of low virulence, we feel it is the mechanism of contamination that is the more


Support for bacteriological testing and reporting was provided by Stryker® with the direct assistance of their Senior Principal Scientist in the Instrument Division, Rod Parker, Ph.D. Dr. Parker provided the industry standard microbial air samplers and helped with the collection of the samples.

Conflict of interest statement

The authors have no conflict to declare.

Funding sources

Support for bacteriological testing and reporting was provided by Stryker®. All other financial support and equipment was provided solely from institutional and/or departmental sources.

References (14)

  • C.E. Edmiston et al.Molecular epidemiology of microbial contamination in the operating roomenvironment: Is there a risk for infection?



  • M. Albrecht et al.Forced-air warming blowers: an evaluation of filtration adequacy and airborne contamination emissions in the operating room

    Am J Infect Control


  • L. Sehulster et al.

    Guidelines for environmental infection control in health-care facilities. Recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC)

    MMWR Recomm Rep

    (2003 Jun 06)

  • M. Horn et al.

    Traditional canister-based open waste management system versus closed system: Hazardous exposure prevention and operating theatre staff satisfaction


    (2016 Jun)

  • P.D. McGovern et al.

    Forced-air warming and ultra-clean ventilation do not mix: an investigation of theatre ventilation, patient warming and joint replacement infection in orthopaedics

    J Bone Joint Surg Br.


  • A.J. Legg et al.

    Do forced air patient-warming devices disrupt unidirectional downward airflow?

    JBone Joint Surg Br


  • K.B. Dasari et al.

    Effect of forced-air warming on the performance of operating theatre laminar flow ventilation



There are more references available in the full text version of this article.

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© 2021 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.

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What is the major source of contamination in the operating room? ›

It has been suggested that the main sources of contamination, especially in clean surgical procedures, are the patient's skin and airborne particles from operating room personnel [2, 3].

What are the 3 types of operating rooms? ›

Different Types of Operating Rooms: Hybrid, Integrated, Digital O.R. - Brainlab.

What is the most common source of infection during surgery? ›

Surgical site infections may be caused by endogenous or exogenous microorganisms. Most SSIs are caused by endogenous microorganisms present on the patient's skin when the surgical incision is made. Gram-positive bacteria such as Staphylococcus aureus are the most common causative skin-dwelling microorganisms.

What is the primary source of airborne bacteria in the operating room? ›

Non-woven fabric, widely used for surgical drapes, gowns, and hoods, is thought to be one of the major origins of airborne particles in the operating room.

Who is the most important person in the operating room? ›

The surgeon is your primary doctor and considered the leader in the operating room. It is the responsibility of the surgeon to ensure the operation goes smoothly, with minimal complications.

What is a Level 4 operating room? ›

Level 4. • Highly invasive procedure. • Blood loss greater than 1,500 cc. • Major risk to patient independent of anesthesia. Includes: Major orthopedic-spinal reconstruction, major reconstruction of the.

What temperature are operating rooms? ›

In the United States, an air temperature of 70 to 75°F. (21 to 24°C.) with 50 to 60% relative humidity provides a compromise between the requirements of the patients and those of the operators. In Britain, a temperature of 65 to 70°F.


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