If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
Comparison of number of airborne bacteria in operating rooms with turbulent mixing ventilation and unidirectional airflow when using reusable scrub suits and single-use scrub suits
Corresponding author. Address: Department of Infection Control and Hospital Hygiene, Region Stockholm, Jägargatan 20, Södersjukhuset, S-118 83, Stockholm, Sweden. Tel.: +46 8 123 134 57.
A low count of airborne bacteria in the operating room is a means to prevent surgical site infection.
Aim
To investigate levels of airborne bacteria during surgical procedures in two operating rooms with turbulent mixing ventilation (TMV) and unidirectional airflow (UDAF), both with an air supply of 2600 L/s, when staff used either reusable scrub suits made from a mixed material (dry penetration ≤300 cfu) or single-use scrub suits made from polypropylene (dry penetration ≤100 cfu).
Material and methods
In the TMV-room cfu/m3 air was measured during eight procedures with staff wearing reusable scrub suits and seven procedures with single-use scrub. In the UDAF-room cfu/m3 air was measured during seven procedures with staff wearing reusable scrub suits.
Findings
Mean values of cfu/m3 air were 1.3–10.8 in the TMV-room with staff dressed in reusable scrub suits and 0.8–4.0 with staff dressed in single-use scrub suits (P<0.01). Mean values of cfu/m3 air were 0.2–4.5 in the UDAF-room with staff dressed in reusable scrub suits. The difference obtained with reusable scrub suits in the two rooms was significant (P<0.01).
Conclusions
The mode of ventilation affects the cfu levels when staff are dressed in less occlusive scrub suits despite a high air supply. It is possible to decrease the cfu levels in a TMV-room by using scrub suits made from a tight material, thus reaching the same levels that are achieved by less protective scrub suits in a UDAF-room.
A low count of airborne bacteria in the operating room, measured as colony forming units (cfu) per m3 air, is a means to prevent deep surgical site infection (SSI) from occurring after orthopaedic prosthesis surgery [
Infection and sepsis after operations for total hip or knee-joint replacement: influence of ultraclean air, prophylactic antibiotics and other factors.
Comparison between mixed and laminar airflow systems in operating rooms and the influence of human factors: Experiences from a Swedish orthopedic center.
]. In this study we investigated the cfu levels achieved in two new-built operating rooms with turbulent mixing ventilation (TMV) and unidirectional airflow (UDAF) when all staff present used either reusable scrub suits or single-use scrub suits.
Methods
Setting
The operating rooms were situated at Karolinska University Hospital Huddinge, Stockholm County, Sweden (acute care hospital with about 500 beds) in a building constructed during 2016–2019 and put into operation in 2020.
The operating room with TMV had an area of 56.1 square meters. Dimensions were 7.1 m (w), 7.9 m (l), 3.2 m (h). The HEPA-filtered air was supplied through diffusers in the ceiling at a flow of 2600 L/s and evacuated through exhaust outlets at floor level (see Figure 1).
Figure 1Operating room with turbulent mixing ventilation (TMV).
The operating room with UDAF had an area of 55.2 square meters. Dimensions were 6.9 m (w), 8.0 m (l), 3.2 m (h). The HEPA-filtered air was supplied through a UDAF-ceiling with a protection zone of 9.5 square meters (2.8 m (w), 3.4 m (l)) situated above the operating table. The air flow was 2600 L/s, and the flow velocity was 0.25 m/s (see Figure 2).
Figure 2Operating room with unidirectional airflow (UDAF).
The reusable scrub suits were made of a mixed material (Mertex P-3477, HejMarAB, Borås, Sweden): 69% cotton, 30% polyester, and 1% carbon fibre; plain weave with warp 47 and weft 26 threads/cm; weight 150 g/m2; washed approximately 50 times. The material fulfils the requirements for “Resistance to microbial penetration – dry” for clean air suits in the standard EN 13795:2011 (penetration ≤300 cfu) but has not been tested according to the standard EN 13795-2:2019 [
EN 13795:2011 + A1:2013 Surgical drapes, gowns and clean air suits, used as medical devices for patients, clinical staff and equipment – General requirements for manufacturers, processors and products, test methods, performance requirements and performance levels.
European Committee for Standardization,
Brussels2013
The single-use scrub suits were made of Spunbond Meltblown Spunbond Polypropylene (Mölnlycke Health Care AB, Göteborg, Sweden); weight 35 g/m2 with a comfort layer of 70/30 Viscose/Polyester weight 30 g/m2. The material fulfils the requirements for “Microbial penetration – Dry” for clean air suit according to the standard EN 13795-2:2019 (penetration ≤100 cfu).
The requirement for dry microbial penetration for clean air suits is ≤300 cfu in the standard EN 13795:2011 and ≤100 cfu for clean air suits with “standard performance” in the standard EN 13795-2:2019.
Scrub suits made of the two materials had the same design, i.e., the trousers had cuffs at the lower end of the leg and the short-sleeved shirts had cuffs at the arm, bottom, and neckline. Sterile single-use surgical gowns of the same kind (Mölnlycke BARRIER®) were used by the sterile team during all operations. All persons present in the operating rooms wore single-use surgical masks IIR and single-use hoods (Mölnlycke BARRIER®) tucked down at the neckline during all procedures.
Air sampling
Air sampling was performed with an MD8 air sampler (Sartorius AG, Göttingen, Germany) with an inward flow of 100 L/min for periods of 10 min (total volume of air sampled 1.0 m3). Air was drawn over a sterile gelatine filter placed as close to the surgical wound as possible (about 20–50 cm). At each operation air was sampled for five to six periods of 10 min each. Every gelatine filter was placed on a sterile blood agar plate that was incubated at 35 °C for two days. The number of bacterial colonies on the plate was then counted and expressed as cfu/m3 air. From the samples a mean value of cfu/m3 air was calculated for each operation.
Surgical procedures
In the operating room with TMV air sampling took place during 15 orthopaedic surgical procedures performed in autumn 2021 (21st September to 18th October) and spring 2022 (26th April to 26th May). During the first set of eight operations, all attending staff wore reusable scrub suits made from the mixed material and during the second set of seven operations all staff wore single-use scrub suits made from polypropylene. In the operating room with UDAF, air sampling took place during seven urological procedures performed in autumn 2021 (6th September to 6th October) with all staff present wearing reusable scrub suits made from the mixed material.
The selection of surgical procedures was random and depended mainly on the availability of personnel who could perform the sample collection. All surgical procedures were performed as open surgery, i.e., not laparoscopic surgery.
Data analysis
Mann–Whitney U-test, two-sided, was used to compare the means of cfu/m3 air obtained from the two sets of operations in the operating room with TMV as well as the means of cfu/m3 air obtained with the reusable scrub suits in the two operating rooms. Software provided by Statistics Kingdom (http://www.statskingdom.com) was used for the analysis.
Results
In the operating room with TMV, the mean values of cfu/m3 air ranged from 1.3 to 10.8 in the eight orthopaedic operations with staff dressed in the less occlusive reusable scrub suits made from the mixed material, and from 0.8 to 4.0 in the seven orthopaedic operations with staff dressed in single-use scrub suits made from polypropylene (see Table I, Table II). The difference between mean values of cfu/m3 air with staff dressed in the two kinds of scrub suits in the operating room with TMV was significant (P<0.01).
Table IOperating room with turbulent mixing ventilation: procedures with staff dressed in reusable scrub suits made from mixed material
In the operating room with UDAF, the mean values of cfu/m3 air ranged from 0.2 to 4.5 in the seven urological operations with staff dressed in reusable scrub suits made from the mixed material (see Table III).
Table IIIOperating room with unidirectional airflow: procedures with staff dressed in reusable scrub suits made from mixed material
The difference between means of cfu/m3 air obtained with reusable scrub suits in the two operating rooms was significant (P<0.01).
Discussion
Modern operating rooms are often supplied with large volumes of air in the range of 2000–6000 L/s and the air supply is adapted to the size of the room [
Operating room ventilation and the risk of revision due to infection after total hip arthroplasty: assessment of validated data in the Norwegian Arthroplasty Register.
]. In theory, a powerful ventilation irrespective of using TMV or UDAF as distribution method should be able to keep a low level of air contaminants in the operating room even with a substantial number of persons present, which is often necessary in complicated surgery and when teaching students. A modern ventilation should also make the use of scrub suits made from tight materials such as polypropylene and polyester less necessary and make it possible to use less occlusive scrub suits made from mixed material as those often are perceived as more comfortable [
Both TMV and UDAF have advantages and disadvantages that are well known to experts in ventilation and thus should be taken into consideration when planning new operating rooms and choosing mode of ventilation and volume of air supply. In theory, TMV should secure that the level of cfu/m3 air is the same in the whole room. UDAF should result in a higher microbial cleanliness in the central part of the room, i.e., the area of the surgical wound, but the peripheral parts of the room where for example assistant tables are placed are at risk for higher contamination [
]. Irrespective of ventilation system the air flow could be disturbed by lamps, people and medical devices leading to an unequal distribution of air pollutants and an accumulation of air pollutants over and around the operating table [
Do surgeons and surgical facilities disturb the clean air distribution close to a surgical patient in an orthopedic operating room with laminar airflow?.
In our study, the operating rooms had a volume of around 177–180 m3. A supply of 2600 L air per second means that there were approximately 52 air changes per hour (ACH) which is far beyond the traditional 17–20 ACH in operating rooms [
]. This high level of ACH should secure low levels of cfu/m3 air in the area of the surgical wound, irrespective of TMV or UDAF. This study, however, shows that the mode of ventilation affects the cfu-levels as there was a significant difference between the results obtained from the two rooms with staff dressed in the reusable scrub suits. This is in accordance with results from Knudsen et al. [
Laminar airflow decreases microbial air contamination compared with turbulent ventilated operating theatres during live total joint arthroplasty: a nationwide survey.
]. Our study also shows that it is possible to decrease the levels of cfu/m3 air using scrub suits made from a tight material in a room with TMV reaching the same levels achieved by less protective scrub suits in a room with UDAF. In an earlier study, we compared the same kind of scrub suits in an older operating room with TMV and a supply of 845 L air per second and as in the present study found significantly lower cfu levels with the single-use scrub suits [
]. We had however expected that the difference between the two clothing systems would disappear when the air supply to the modern operating room was more than doubled. In hospitals where operating rooms have low air change rates the relative difference in air counts of cfu when using more or less occlusive scrub suits – reusable or single use – should be taken into consideration when improving patient safety.
The number of door openings should of course be as low as possible, preferably zero [
]. Our measuring of cfu was performed during real surgical procedures thus reflecting staff behaviour in everyday work. Organization of work and education of staff about the effect of door openings should continue, with the aim of improvement concerning this, but in our two sets of orthopaedic surgery with an average of 3.1 and 3.3 door openings per operation this did not affect the difference in levels of cfu/m3 air.
The mean levels of cfu/m3 air in the operating room with TMV and staff dressed in scrub suits made from mixed material resembled those obtained by Cao et al. (cases 4 and 5) in an operating room with TMV, i.e., 5–11 cfu/m3 air [
Can clothing systems and human activity in operating rooms with mixed flow ventilation systems help achieve the ultraclean air requirement (≤10 cfu/m3) during orthopaedic surgeries?.
]. It could of course be discussed whether this is sufficient as the commonly adopted value for ultraclean air (<10 cfu/m3 air) is reached. The definition of ultraclean air was, however, set by Lidwell et al. around the year 1980 [
] and our study shows that nowadays it is possible to achieve lower and more stable values of cfu/m3 air, either using scrub suits made from a tighter material or by installing UDAF ventilation when constructing new operating rooms. To us it seems reasonable to use modern technology to reach as low cfu values as possible.
This study concerned cfu levels in the operating room and how those are affected by ventilation and clothing but also included some information on staff behaviour. We hope that, in the future, studies will focus on cfu levels and how to reduce them by different means and not only refer to the technical solutions such as TMV versus UDAF without comparing the cfu levels that are reached with each kind of ventilation.
With regard to limitations, it would have been desirable that all surgical procedures performed in the two operating rooms were of the same kind, e.g., hip arthroplasty. This was however not possible as air-sampling took place during normal clinical activity in the surgical ward where it is decided in advance and dependent on the overall organization which kind of surgery should be performed in each room. In our opinion, this did not affect the results as the kind of surgery performed only affects the cfu levels to a lesser extent than the number of persons present and the number of door openings. It would also have been desirable to perform air-sampling in the operating room with UDAF with staff dressed in the single-use scrub suits. This was not performed as the low cfu counts achieved with staff dressed in the reusable scrub suits made from mixed material was regarded as sufficient to make decision on using this kind of scrub suit in operating rooms with UDAF.
Acknowledgements
The authors would like to thank Anna-Karin Ohlsson for skilful technical assistance in performing all the microbial analyses.
Conflict of interest statement
The authors have no conflict of interests to declare.
Funding sources
None.
References
Lidwell O.M.
Lowbury E.J.L.
Whyte W.
Blowers R.
Stanley S.J.
Lowe D.
Infection and sepsis after operations for total hip or knee-joint replacement: influence of ultraclean air, prophylactic antibiotics and other factors.
Comparison between mixed and laminar airflow systems in operating rooms and the influence of human factors: Experiences from a Swedish orthopedic center.
Surgical drapes, gowns and clean air suits, used as medical devices for patients, clinical staff and equipment – General requirements for manufacturers, processors and products, test methods, performance requirements and performance levels.
European Committee for Standardization,
Brussels2013
Operating room ventilation and the risk of revision due to infection after total hip arthroplasty: assessment of validated data in the Norwegian Arthroplasty Register.
Do surgeons and surgical facilities disturb the clean air distribution close to a surgical patient in an orthopedic operating room with laminar airflow?.
Laminar airflow decreases microbial air contamination compared with turbulent ventilated operating theatres during live total joint arthroplasty: a nationwide survey.
Can clothing systems and human activity in operating rooms with mixed flow ventilation systems help achieve the ultraclean air requirement (≤10 cfu/m3) during orthopaedic surgeries?.
00098-1&id=gr1.jpg){kind=link}
00098-1&id=gr2.jpg){kind=link}