- Email: [email protected]
Environmental controls in operating theatres
Journal of Hospital Infection (2002) 51: 79±84 doi:10.1053/jhin.2002.1217, available online at http://www.idealibrary.com on
REVIEW
Environmental controls in operating theatres S. Dharan and D. Pittet Infection Control Programme, Department of Internal Medicine, University of Geneva Hospitals, 1211 Geneva 14, Switzerland Summary: Surgical-site infection is the leading complication of surgery. Normal skin flora of patients or healthcare workers causes more than half all infections following clean surgery, but the importance of airborne bacteria in this setting remains controversial. Modern operating theatres have conventional plenum ventilation with filtered air where particles 5 mm are removed. For orthopaedic and other implant surgery, laminar-flow systems are used with high-efficiency particulate air (HEPA) filters where particles 0.3 mm are removed. The use of ultra-clean air has been shown to reduce infection rates significantly in orthopaedic implant surgery. Few countries have set bacterial threshold limits for conventionally ventilated operating rooms, although most recommend 20 air changes per hour to obtain 50±150 colony forming units/m3 of air. There are no standardized methods for bacterial air sampling or its frequency. With the use of HEPA filters in operating theatre ventilation, there is a tendency to apply cleanroom technology standards used in industry for hospitals. These are based on measuring the presence of particles of varying sizes and numbers, and are better suited than bacterial sampling. Environmental bacterial sampling in operating theatres should be limited to investigation of epidemics, validation of protocols, or changes made in materials which could influence the microbial content. & 2002 The Hospital Infection Society
Keywords: Surgical wound infection; operating rooms; environmental monitoring; quality control; reference standards; air microbiology.
Introduction Surgical-site infections are still a major problem in modern medicine. These infections may be deep or superficial. The superficial ones are easier to deal with, but the deep ones can be complicated, leading to re-operation, or even be life threatening. Factors causing surgical-site infection are multifarious; type of operation, surgeon's skill, insertion of foreign material or implants, appropriateness of surgical preparation, adequacy and timing of antimicrobial prophylaxis, the immune state of the patient and contamination of the inanimate environment. To reduce these infections, bacteriological management Author for correspondence: Professor Didier Pittet, Infection Control Programme, Department of Internal Medicine, University of Geneva Hospitals, 1211 Geneva 14, Switzerland; Tel. (office): 41-22/372 98 28; Fax: 41-22/372 39 87. E-mail: [email protected]
0195±6701/02/060079 1 06 $35.00/0
of operating theatres has been advocated. There is no international consensus on the methods, types of sampling and tolerable limits of bioburden in operating theatres. The main parameters associated with environmental biocontamination in operating theatres are discussed with a special emphasis on air quality and its control. Source and transport of organisms The control of surgical-site infection requires a knowledge of the source and transport of the causative organisms. In today's operating environment, more than half of clean surgical-site infection pathogens originate from normal skin flora of patients or staff.1±3 Bacteria on skin squames, lint and other dusts get into the air in the operating theatre and by turbulent air currents deposit on surfaces. They are also spread by direct contact between & 2002 The Hospital Infection Society
80
carrier and wound, but the importance of airborne bacteria as a source of infection remains a subject of debate among professionals in infection control.3±6 The inanimate environment is probably one of the factors that can be managed efficiently by the infection control team. Several studies, including experience at our institution, have shown a reduced number of infections when orthopaedic surgery is performed in operating theatres with ultra-clean air facilities.7±14 Thus, it can be assumed that for this type of surgery, higher bacterial counts in the air correlates with a higher risk for surgical site infection. To reduce prolonged morbidity and healthcare costs associated with these infections, airborne bacteria and other sources of contamination must be reduced to the minimum. This can be achieved by the choice of staff theatre dress, patient preparation and draping, education of personnel and design and controlled ventilation of operating theatres.15±23 The infection control team's role should be that of a consultant where expertise in materials and methods in asepsis are shared among the other professionals involved in the design, layout and functioning of operating theatres. Clothing and healthcare worker education Surgical drapes and the fronts and sleeves of surgical gowns should be impregnated with a fluid repellent and made of a non-woven or close-woven fabric.18 In the European Medical Devices Directive, these articles are considered as medical devices, and as such they should pose no infection risk for the user and the patient. The requirements for surgical drapes and gowns have been defined (resistance to bacterial penetration wet and dry, linting, tensile strength, etc.) and should be met by the manufacturers and distributors. Surgical staff should wear hoods and masks although the wearing of masks is controversial.19,21,24 Operating theatre dress made of non-woven fabric or impermeable material can be uncomfortable so climatic conditions in the operating theatre should compensate for this. Staff should be educated in the maintenance of sterility of instruments by no-touch behaviour, covering of sterile instruments with a sterile drape until use, and movement and number of persons in the operating theatre should be kept to the minimum.20,22
S. Dharan and D. Pittet
Ventilation Most modern operating theatres have conventional plenum ventilation with filtered air, using filters with an efficiency of 80±95% to remove airborne particles 5 mm [DOP test25]. Laminar air-flow systems with HEPA filters which remove airborne particles of 0.3 mm and above with 99.97% efficiency are generally used for orthopaedic and other implant surgery. HEPA-filtered laminar air-flow can be supplied to the operating area by ceiling-mounted (vertical flow) or wall-mounted (horizontal flow) units. Both systems have their inconveniences and the unidirectional flow of air can be disrupted. With the vertical flow system, heat generated by surgical lamps creates minor air turbulence. A horizontal laminar air-flow system was developed to overcome the problems associated with vertical air-flow. However, this system has a major inconvenience in that the operating team usually disrupts the unidirectional air-flow. Some studies have shown that vertical laminar air-flow generates less bacteria at the operating site.8,26 To overcome the problems associated with both horizontal and vertical flow systems, a combination of vertical and horizontal flow has been developed, known as exponential laminar airflow with the form of an upside-down trumpet.27,28 Few countries have set bacterial threshold limits in conventionally-ventilated operating theatres, although most recommend 20 air changes per hour in order to obtain 50±150 colony forming units (cfu)/m3 of air. In the United Kingdom, the limit is 35 cfu/m3 for an empty operating theatre and in activity it should not exceed 180 cfu/m3 for an average 5 min period. In an ultra-clean air operating theatre the limit is set at <10 cfu/m3 sampled within 30 cm of the wound using conventional clothing. The limit is set at <1 cfu/m3 of air when total body exhaust gowns are used (UK Department of Health document, Health Technical Memorandum 2025). These limits are not always easy to achieve during an operation as various factors influence the bioburden in the air during the surgical procedure. There are no standardized methods for air sampling in operating theatres or for its frequency. In addition, a variety of instruments are used in volumetric air sampling which renders correlation of results difficult due to variability. With the use of HEPA filters in operating theatre ventilation, there is a tendency to apply cleanroom technology standards used in industry for hospitals. Most of the industrialized countries have
Environmental controls in operating theatres
81
set their own standards, usually modifying the American Federal Standard 209E to their local needs (Table I).29 These standards are based on measuring the presence of particles of varying sizes and number [British standard 5295, Table II(a); German VDI 2083, Table II(b)].30,31 Many of these are presently being amended to align with the International Standards Organization (ISO) 14644 [Table II(c)].32 The European Standard, `Cleanroom technology', is presently in its draft form. This document covers methods of analysing and measuring aerobiocontamination in zones at risk, classified according to risk categories 1 to 4. This document does not set limits in bioburden or frequency in sampling; the decision is left to the individual institution. Systems (ultra-clean air) should be maintained to standards that will fulfil their desired functions. However, to measure these, controls have to be instituted. At present, there is no international consensus on the methods, types of samples (settle plates vs. volumetric air sampling), frequency of sampling, and tolerable limits of bioburden in operating theatres.26,33±38 Based on experience at our institution, we consider that a standard established on measured particle size and number, similar to the American Federal Standard 209E (Table I) would be better suited than bacterial sampling. It is less demanding, results are immediate, and it can be used for on-site teaching. The interval
between sampling should be decided by each institution based on the means available. We are not proponents of routine bacteriological surveillance of air and surfaces in conventionallyventilated operating theatres due to the fact that results obtained are valid only for the moment and location where they were obtained. Different factors influence the results and we cannot presume that results will be the same an hour or a day later. Furthermore, in a clinical setting not just the quantity of bacteria is important, but also its quality. Taking these factors into consideration, it would be a waste of resources to routinely take bacterial samples on a regular, i.e., monthly basis. Rather, we recommend annual maintenance of ventilation systems by the engineering department. Bacteriological sampling has its place in the investigation of epidemics, validation of changes in products and procedures in the maintenance of operating theatres (cleaning, disinfection, and ventilation) and education. Volumetric air sampling, either particle or bacterial counts, should be carried out in an empty operating theatre after any maintenance work carried out in the ventilation system and should meet previously set target limits. The limits set in Table III are not based on scientific evidence of the relation between contamination of the environment and surgical-site infection risk, but on local evaluation of contamination in empty operating theatres. When surgical techniques
Table I Limits of air particle contents according to standardized norms (adapted from FS209 E*) Superior limits in measured particle size (particle per volume unit) (equal to, or greater than stated size) y
0.1 mm volume unit
Class
0.2 mm volume unit
0.3 mm volume unit
0.5 mm volume unit
5 mm volume unit
FS 209
m3
ft3
m3
ft3
m3
ft3
m3
ft3
m3
ft3
M1 M1.5 1 M2 M2.5 10 M3 M3.5 100 M4 M4.5 1000 M5 M5.5 10 000 M6 M6.5 1 00 000 M7
350 1240 3500 12 400 35 000
9.91 35.0 99.1 350 991
75.7 265 757 2650 7570 26 500 75 700
2.14 7.50 21.4 75.0 214 750 2140
30.9 106 309 1060 3090 10 600 30 900
0.875 3.00 8.75 30.0 87.5 300 875
10 35.3 100 353 1000 3530 10 000 35 300 1 00 000 3 53 000 10 00 000 35 30 000 1 00 00 000
0.283 1.0 2.83 10.0 28.3 100 283 1000 2830 10 000 28 300 1 00 000 2 83 000
± ± ± ± ± ± ± 247 618 2470 6180 24 700 61 800
± ± ± ± ± ± ± 7.0 17.5 70 175 700 1750
SI
* Reference 29. Refers to the engineering classification of cleanrooms. SI: International system (metric); column 1 is the metric equivalent of the US standard FS209 (column 2).
y
82
S. Dharan and D. Pittet
Table II Limits of air particle contents according to different international standards (a) British Standard 5295*: classification and requirements of cleanrooms Superior limits in measured particle size per m3 (equal to, or greater than stated size) Classy C D E F G H J K L M
0.3 mm
0.5 mm
5 mm
10 mm
25 mm
100 1000 10 000 NS 1 00 000 NS NS NS NS NS
35 350 3500 3500 35 000 35 000 350 000 3 500 000 NS NS
0 0 0 0 200 200 2000 20 000 2 00 000 NS
NS NS NS NS 0 0 450 4500 45 000 4 50 000
NS NS NS NS NS NS 0 500 5000 50 000
NS Not specified. * Reference 30. y Refers to the engineering classification of cleanrooms.
(b) German VDI 2083*: classification and requirements of cleanrooms Superior limits in measured particle size per m3 (equal to, or greater than stated size) Classy x
0 1 2 3 4 5 6 7
0.1 mm 150 1500 15 000 ± ± ± ± ±
0.2 mm 33 330 3300 33 000 ± ± ± ±
0.3 mm
1.0 mmz
0.5 mm
14 140 1400 14 000 ± ± ± ±
5 mm
10 mm
300 3000 30 000 30 000
70 000
0
± 45 450 4500 45 000 4 50 000 45 00 000 ±
10 101 102 103 104 105 106 107
* Reference 31. Refers to the engineering classification of cleanrooms. z Size chosen for classification. x This class should be considered when cleanroom is unoccupied. y
(c) International norm (ISO 14644±1*: cleanrooms and associated controlled environments, classification and requirements) Superior limits in measured particle size per m3 (equal to, or greater than, stated size) Classy ISO 1 2 3 4 5 6 7 8 9
0.1 mm
0.2 mm
0.3 mm
0.5 mm
1.0 mm
5 mm
10 100 1000 10 000 100 000 10 00 000
2 24 237 2370 23 700 2 37 000
10 102 1020 10 200 1 02 000
4 35 352 3520 35 200 3 52 000 35 20 000 3 52 00 000
8 83 832 8320 83 200 8 32 000 83 20 000
29 293 2930 29 300 2 93 000
* Reference 32. Refers to the engineering classification of cleanrooms.
y
Environmental controls in operating theatres
83
Table III Classification of operating theatre zones according to risk categories and limits in airborne particles and bacteria*, University of Geneva Hospitals, Switzerland Particle size (Particles per m3) Class Level of risk 1. 2.
3.
4.
0.5 mm
Very high risk, within 10 laminar air-flow area with HEPA filtration High risk, exterior 353 laminar air-flow, but within the operating theatre Medium risk, 3 530 conventionally ventilated operating theatre with air filtered through terminal filters with an efficiency of 95% and above Low risk, areas with NS uncontrolled ventilation
5 mm
Bacterial counts (cfu/m3)
0
<1
10
5
25
25
NS
NS
* Sampling is performed in the operating theatre whilst at rest. cfu, Colony forming unit; NS, no specific limit.
or theatre dress are to be evaluated, both volumetric air sampling and settle plates may be used together. Plates should be placed as near as possible to the operating team and on the instrument trolley in order to obtain any meaningful results. However, this may create practical problems in some circumstances. Water supply Another area of environmental control in operating theatres is the bacteriological quality of water used for surgical handscrubs for which there are no standardized limits at present. Some institutions use sterile water for this procedure. At our institution, we use drinking quality water, <200 bacteria/mL, with bacterial counts carried out twice a year on these water outlets. Counts have never exceeded 400 bacteria/mL with most being below 100 (unpublished data). The exception to this was when a new operating theatre was built and warm water (30±35 C) was provided via a closed circuit for the comfort of surgeons. However, the problem was rapidly rectified by lowering the temperature to 20±25 C. Organisms recovered from these samples were mainly environmental, Gram-negative bacilli and atypical mycobacteria. Taking into account our
experience and the increasing use of alcohol-based solutions for surgical hand disinfection and doublegloving, we strongly believe that the use of sterile water for surgical hand disinfection is not a necessity. Conclusion There is presently no common standard method used to determine bacterial threshold limits in the operating theatre setting. In this situation, it is practically impossible to compare results between countries. We recommend the use of cleanroom technology standards based on the measurement of the presence of air particles as routine procedure. Our opinion is that environmental bacterial sampling should be restricted to the investigation of epidemics and validation of changes in products and maintenance procedure of the operating theatre. We suggest that there is a need to reach a consensus on the method of evaluation and also, to differentiate between cleanroom technology developed for industry and that used in hospitals.
Acknowledgement The authors thank Rosemary Sudan for editorial assistance. References 1. Bitkover CY, Marcusson E, Ransjo U. Spread of coagulase-negative staphylococci during cardiac operations in a modern operating room. Ann Thorac Surg 2000; 69: 1110±1115. 2. Whyte W, Hambraeus A, Laurell G, Hoborn J. The relative importance of routes and sources of wound contamination during general surgery. I. Nonairborne. J Hosp Infect 1991; 18: 93±107. 3. Whyte W, Hambraeus A, Laurell G, Hoborn J. The relative importance of routes and sources of wound contamination during general surgery. II. Airborne. J Hosp Infect 1992; 22: 41±54. 4. Whyte W, Hodgson R, Tinkler J. The importance of airborne contamination of wounds. J Hosp Infect 1982; 3: 123±135. 5. Ayliffe GAJ. Role of the environment of the operating suite in surgical wound infection. Rev Infect Dis 1991; 13 (Suppl. 10): S800±804. 6. Humphreys H. Infection control team in the operating room: separating aspiration from reality! J Hosp Infect 1999; 42: 265±267. 7. Charnley J, Eftekhar N. Postoperative infection in total prosthetic replacement arthroplasty of hip joint. Br J Surg 1969; 56: 641±649.
84 8. Lidwell OM, Lowbury EJL, Whyte W, Blowers R, Stanley SJ, Lowe D. The effect of ultraclean air in operating rooms on deep sepsis in the joint after hip or knee replacement: a randomised study. Br Med J 1982; 285: 10±14. 9. Gosden PE, MacGowan AP, Bannister GC. Importance of air quality and related factors in the prevention of infection in orthopaedic implant surgery. J Hosp Infect 1998; 39: 173±180. 10. Friberg B, Friberg S, Burman LG. Correlation between surface and air counts of particles carrying aerobic bacteria in operating rooms with turbulent ventilation: an experimental study. J Hosp Infect 1999; 42: 61±68. 11. Laufman H. Airflow effects in surgery. Arch Surg 1979; 114: 826±830. 12. Schwan A, Bengstsson S, Hambraeus A, Laurell G. Airborne contamination and post operative infection after total hip replacement. Acta Orthop Scand 1977; 48: 86±94. 13. Vasey H, Ducel G, Allgower D. Zones proteÂgeÂes en salle d'opeÂration. Evaluation d'une nouvelle enceinte de Charnley. Med Hyg 1987; 45; 1646±1651. 14. Lew DP, Pittet D, Waldvogel FA. Infections that complicate the insertion of prosthetic devices. In: Mayhall CG, Ed. Hospital Epidemiology and Infection Control. Baltimore: Williams and Wilkins 1995; 731±748. 15. Mitchell NJ, Evans DS, Kerr A. Reduction of skin bacteria in theatre air with comfortable, non-woven disposable clothing for operating theatre staff. Br Med J 1978; 1: 696±698. 16. Fitzgerald RH, Jr. Microbiological environment of the conventional operating room. Arch Surg 1979; 114: 772±775. 17. Ritter MA, Eitzen HE, Hart JB, French ML. The surgeon's garb. Clin Orthop 1980; 153: 204±209. 18. Berman BR, Hoborn J, Nachemson AL. Patient draping and staff clothing in the operating theatre: a microbiological study. Scand J Infect Dis 1985; 17: 421±426. 19. Hubble MJ, Weale AE, Perez JV, Bowker KE, MacGowan AP, Bannister GC. Clothing in laminarflow operating theatres. J Hosp Infect 1996; 32: 1±7. 20. Chosky SA, Modha D, Taylor GJ. Optimisation of ultraclean air. The role of instrument preparation. J Bone Joint Surg Br 1996; 78: 835±837. 21. Verkkala K, Eklund A, Ojajarvi J, Tiittanen L, Hoborn J, Makela P. The conventionally ventilated operating theatre and air contamination control during cardiac surgeryÐbacteriological and particulate matter control garment options for low level contamination. Eur J Cardiothor Surg 1998; 14: 206±210. 22. Pittet D, Ducel G. Infectious risk factors related to operating rooms. Infect Control Hosp Epidemiol 1994; 15: 456±462. È stensson R, Burman LG. 23. Friberg B, Friberg S, O Surgical area contaminationÐcomparable bacterial
S. Dharan and D. Pittet
24. 25.
26.
27.
28. 29. 30. 31. 32.
33. 34.
35.
36. 37.
38.
counts using disposable head and mask and helmet aspirator system, but dramatic increase upon omission of head-gear: an experimental study in horizontal laminar air-flow. J Hosp Infect 2001; 47: 110±115. Mitchell NJ, Hunt S. Surgical face masks in modern operating roomsÐa costly and unnecessary ritual? J Hosp Infect 1991; 18: 239±242. Military Standard 282. Military standard: filter units, protective clothing, gas-mask components and related productions: performance-test methods. United States Department of Defence, 1956. Whyte W, Lidwell OM, Lowbury EJ, Blower R. Suggested bacteriological standards for air in ultraclean operating rooms. J Hosp Infect 1983; 4: 133±139. Friberg BE, Friberg S, Burman LG. Zoned vertical ultraclean operating room ventilation. A novel concept making long side walls unnecessary. Acta Orthop Scand 1996; 6: 578±582. Johnston IDA, Hunter AR (Eds). The Design and Utilization of Operation Theatres. London: Edward Arnold 1984. Federal Standard 209E. Airborne particulate cleanliness classes in clean rooms and clean zones. United States General Service Administration 1992. British Standard 5295-1. Classification and requirements of cleanrooms. British Standards Institution 1989. Vereinigte Deutsche Ingenieure (VDI) 2083. ReinraumtechnikÐGrundlagen, Definitionen und Festlegungen der Reinheitsklassen 1995. ISO 14644-1. Cleanrooms and associated controlled environments, Part 1: Classification of air cleanliness. International Organization for Standardization Technical Committee (ISO TC 209) 1999. Whyte W. In support of settle plates. PDA J Pharm Sci Technol 1996; 50: 201±204. Gasper C, Calvente MJ, Fernandez C, Fereres J. Air microbiology monitoring in plenum-ventilated operating rooms. Proposed standards. Enferm Infecc Microbiol Clin 1997; 15: 250±254. Friberg B, Friberg S, Burman LG. Inconsistent correlation between aerobic bacterial surface and air counts in operating rooms with ultra clean laminar air-flows: proposal of a new bacteriological standard for surface contamination. J Hosp Infect 1999; 42: 287±293. Pasquarella C, Pitzurra O, Savino A. The index of microbial air contamination. J Hosp Infect 2000; 46: 241±256. Seal DV, Clark RP. Electronic particle counting for evaluating the quality of air in operating theatres: a potential basis for standards. J Appl Bacteriol 1990; 68: 225±230. Whyte W, Shaw BH, Barnes R. A bacteriological evaluation of laminar-flow systems for orthopaedic surgery. J Hyg Camb 1973; 71: 559±564.
REVIEW
Environmental controls in operating theatres S. Dharan and D. Pittet Infection Control Programme, Department of Internal Medicine, University of Geneva Hospitals, 1211 Geneva 14, Switzerland Summary: Surgical-site infection is the leading complication of surgery. Normal skin flora of patients or healthcare workers causes more than half all infections following clean surgery, but the importance of airborne bacteria in this setting remains controversial. Modern operating theatres have conventional plenum ventilation with filtered air where particles 5 mm are removed. For orthopaedic and other implant surgery, laminar-flow systems are used with high-efficiency particulate air (HEPA) filters where particles 0.3 mm are removed. The use of ultra-clean air has been shown to reduce infection rates significantly in orthopaedic implant surgery. Few countries have set bacterial threshold limits for conventionally ventilated operating rooms, although most recommend 20 air changes per hour to obtain 50±150 colony forming units/m3 of air. There are no standardized methods for bacterial air sampling or its frequency. With the use of HEPA filters in operating theatre ventilation, there is a tendency to apply cleanroom technology standards used in industry for hospitals. These are based on measuring the presence of particles of varying sizes and numbers, and are better suited than bacterial sampling. Environmental bacterial sampling in operating theatres should be limited to investigation of epidemics, validation of protocols, or changes made in materials which could influence the microbial content. & 2002 The Hospital Infection Society
Keywords: Surgical wound infection; operating rooms; environmental monitoring; quality control; reference standards; air microbiology.
Introduction Surgical-site infections are still a major problem in modern medicine. These infections may be deep or superficial. The superficial ones are easier to deal with, but the deep ones can be complicated, leading to re-operation, or even be life threatening. Factors causing surgical-site infection are multifarious; type of operation, surgeon's skill, insertion of foreign material or implants, appropriateness of surgical preparation, adequacy and timing of antimicrobial prophylaxis, the immune state of the patient and contamination of the inanimate environment. To reduce these infections, bacteriological management Author for correspondence: Professor Didier Pittet, Infection Control Programme, Department of Internal Medicine, University of Geneva Hospitals, 1211 Geneva 14, Switzerland; Tel. (office): 41-22/372 98 28; Fax: 41-22/372 39 87. E-mail: [email protected]
0195±6701/02/060079 1 06 $35.00/0
of operating theatres has been advocated. There is no international consensus on the methods, types of sampling and tolerable limits of bioburden in operating theatres. The main parameters associated with environmental biocontamination in operating theatres are discussed with a special emphasis on air quality and its control. Source and transport of organisms The control of surgical-site infection requires a knowledge of the source and transport of the causative organisms. In today's operating environment, more than half of clean surgical-site infection pathogens originate from normal skin flora of patients or staff.1±3 Bacteria on skin squames, lint and other dusts get into the air in the operating theatre and by turbulent air currents deposit on surfaces. They are also spread by direct contact between & 2002 The Hospital Infection Society
80
carrier and wound, but the importance of airborne bacteria as a source of infection remains a subject of debate among professionals in infection control.3±6 The inanimate environment is probably one of the factors that can be managed efficiently by the infection control team. Several studies, including experience at our institution, have shown a reduced number of infections when orthopaedic surgery is performed in operating theatres with ultra-clean air facilities.7±14 Thus, it can be assumed that for this type of surgery, higher bacterial counts in the air correlates with a higher risk for surgical site infection. To reduce prolonged morbidity and healthcare costs associated with these infections, airborne bacteria and other sources of contamination must be reduced to the minimum. This can be achieved by the choice of staff theatre dress, patient preparation and draping, education of personnel and design and controlled ventilation of operating theatres.15±23 The infection control team's role should be that of a consultant where expertise in materials and methods in asepsis are shared among the other professionals involved in the design, layout and functioning of operating theatres. Clothing and healthcare worker education Surgical drapes and the fronts and sleeves of surgical gowns should be impregnated with a fluid repellent and made of a non-woven or close-woven fabric.18 In the European Medical Devices Directive, these articles are considered as medical devices, and as such they should pose no infection risk for the user and the patient. The requirements for surgical drapes and gowns have been defined (resistance to bacterial penetration wet and dry, linting, tensile strength, etc.) and should be met by the manufacturers and distributors. Surgical staff should wear hoods and masks although the wearing of masks is controversial.19,21,24 Operating theatre dress made of non-woven fabric or impermeable material can be uncomfortable so climatic conditions in the operating theatre should compensate for this. Staff should be educated in the maintenance of sterility of instruments by no-touch behaviour, covering of sterile instruments with a sterile drape until use, and movement and number of persons in the operating theatre should be kept to the minimum.20,22
S. Dharan and D. Pittet
Ventilation Most modern operating theatres have conventional plenum ventilation with filtered air, using filters with an efficiency of 80±95% to remove airborne particles 5 mm [DOP test25]. Laminar air-flow systems with HEPA filters which remove airborne particles of 0.3 mm and above with 99.97% efficiency are generally used for orthopaedic and other implant surgery. HEPA-filtered laminar air-flow can be supplied to the operating area by ceiling-mounted (vertical flow) or wall-mounted (horizontal flow) units. Both systems have their inconveniences and the unidirectional flow of air can be disrupted. With the vertical flow system, heat generated by surgical lamps creates minor air turbulence. A horizontal laminar air-flow system was developed to overcome the problems associated with vertical air-flow. However, this system has a major inconvenience in that the operating team usually disrupts the unidirectional air-flow. Some studies have shown that vertical laminar air-flow generates less bacteria at the operating site.8,26 To overcome the problems associated with both horizontal and vertical flow systems, a combination of vertical and horizontal flow has been developed, known as exponential laminar airflow with the form of an upside-down trumpet.27,28 Few countries have set bacterial threshold limits in conventionally-ventilated operating theatres, although most recommend 20 air changes per hour in order to obtain 50±150 colony forming units (cfu)/m3 of air. In the United Kingdom, the limit is 35 cfu/m3 for an empty operating theatre and in activity it should not exceed 180 cfu/m3 for an average 5 min period. In an ultra-clean air operating theatre the limit is set at <10 cfu/m3 sampled within 30 cm of the wound using conventional clothing. The limit is set at <1 cfu/m3 of air when total body exhaust gowns are used (UK Department of Health document, Health Technical Memorandum 2025). These limits are not always easy to achieve during an operation as various factors influence the bioburden in the air during the surgical procedure. There are no standardized methods for air sampling in operating theatres or for its frequency. In addition, a variety of instruments are used in volumetric air sampling which renders correlation of results difficult due to variability. With the use of HEPA filters in operating theatre ventilation, there is a tendency to apply cleanroom technology standards used in industry for hospitals. Most of the industrialized countries have
Environmental controls in operating theatres
81
set their own standards, usually modifying the American Federal Standard 209E to their local needs (Table I).29 These standards are based on measuring the presence of particles of varying sizes and number [British standard 5295, Table II(a); German VDI 2083, Table II(b)].30,31 Many of these are presently being amended to align with the International Standards Organization (ISO) 14644 [Table II(c)].32 The European Standard, `Cleanroom technology', is presently in its draft form. This document covers methods of analysing and measuring aerobiocontamination in zones at risk, classified according to risk categories 1 to 4. This document does not set limits in bioburden or frequency in sampling; the decision is left to the individual institution. Systems (ultra-clean air) should be maintained to standards that will fulfil their desired functions. However, to measure these, controls have to be instituted. At present, there is no international consensus on the methods, types of samples (settle plates vs. volumetric air sampling), frequency of sampling, and tolerable limits of bioburden in operating theatres.26,33±38 Based on experience at our institution, we consider that a standard established on measured particle size and number, similar to the American Federal Standard 209E (Table I) would be better suited than bacterial sampling. It is less demanding, results are immediate, and it can be used for on-site teaching. The interval
between sampling should be decided by each institution based on the means available. We are not proponents of routine bacteriological surveillance of air and surfaces in conventionallyventilated operating theatres due to the fact that results obtained are valid only for the moment and location where they were obtained. Different factors influence the results and we cannot presume that results will be the same an hour or a day later. Furthermore, in a clinical setting not just the quantity of bacteria is important, but also its quality. Taking these factors into consideration, it would be a waste of resources to routinely take bacterial samples on a regular, i.e., monthly basis. Rather, we recommend annual maintenance of ventilation systems by the engineering department. Bacteriological sampling has its place in the investigation of epidemics, validation of changes in products and procedures in the maintenance of operating theatres (cleaning, disinfection, and ventilation) and education. Volumetric air sampling, either particle or bacterial counts, should be carried out in an empty operating theatre after any maintenance work carried out in the ventilation system and should meet previously set target limits. The limits set in Table III are not based on scientific evidence of the relation between contamination of the environment and surgical-site infection risk, but on local evaluation of contamination in empty operating theatres. When surgical techniques
Table I Limits of air particle contents according to standardized norms (adapted from FS209 E*) Superior limits in measured particle size (particle per volume unit) (equal to, or greater than stated size) y
0.1 mm volume unit
Class
0.2 mm volume unit
0.3 mm volume unit
0.5 mm volume unit
5 mm volume unit
FS 209
m3
ft3
m3
ft3
m3
ft3
m3
ft3
m3
ft3
M1 M1.5 1 M2 M2.5 10 M3 M3.5 100 M4 M4.5 1000 M5 M5.5 10 000 M6 M6.5 1 00 000 M7
350 1240 3500 12 400 35 000
9.91 35.0 99.1 350 991
75.7 265 757 2650 7570 26 500 75 700
2.14 7.50 21.4 75.0 214 750 2140
30.9 106 309 1060 3090 10 600 30 900
0.875 3.00 8.75 30.0 87.5 300 875
10 35.3 100 353 1000 3530 10 000 35 300 1 00 000 3 53 000 10 00 000 35 30 000 1 00 00 000
0.283 1.0 2.83 10.0 28.3 100 283 1000 2830 10 000 28 300 1 00 000 2 83 000
± ± ± ± ± ± ± 247 618 2470 6180 24 700 61 800
± ± ± ± ± ± ± 7.0 17.5 70 175 700 1750
SI
* Reference 29. Refers to the engineering classification of cleanrooms. SI: International system (metric); column 1 is the metric equivalent of the US standard FS209 (column 2).
y
82
S. Dharan and D. Pittet
Table II Limits of air particle contents according to different international standards (a) British Standard 5295*: classification and requirements of cleanrooms Superior limits in measured particle size per m3 (equal to, or greater than stated size) Classy C D E F G H J K L M
0.3 mm
0.5 mm
5 mm
10 mm
25 mm
100 1000 10 000 NS 1 00 000 NS NS NS NS NS
35 350 3500 3500 35 000 35 000 350 000 3 500 000 NS NS
0 0 0 0 200 200 2000 20 000 2 00 000 NS
NS NS NS NS 0 0 450 4500 45 000 4 50 000
NS NS NS NS NS NS 0 500 5000 50 000
NS Not specified. * Reference 30. y Refers to the engineering classification of cleanrooms.
(b) German VDI 2083*: classification and requirements of cleanrooms Superior limits in measured particle size per m3 (equal to, or greater than stated size) Classy x
0 1 2 3 4 5 6 7
0.1 mm 150 1500 15 000 ± ± ± ± ±
0.2 mm 33 330 3300 33 000 ± ± ± ±
0.3 mm
1.0 mmz
0.5 mm
14 140 1400 14 000 ± ± ± ±
5 mm
10 mm
300 3000 30 000 30 000
70 000
0
± 45 450 4500 45 000 4 50 000 45 00 000 ±
10 101 102 103 104 105 106 107
* Reference 31. Refers to the engineering classification of cleanrooms. z Size chosen for classification. x This class should be considered when cleanroom is unoccupied. y
(c) International norm (ISO 14644±1*: cleanrooms and associated controlled environments, classification and requirements) Superior limits in measured particle size per m3 (equal to, or greater than, stated size) Classy ISO 1 2 3 4 5 6 7 8 9
0.1 mm
0.2 mm
0.3 mm
0.5 mm
1.0 mm
5 mm
10 100 1000 10 000 100 000 10 00 000
2 24 237 2370 23 700 2 37 000
10 102 1020 10 200 1 02 000
4 35 352 3520 35 200 3 52 000 35 20 000 3 52 00 000
8 83 832 8320 83 200 8 32 000 83 20 000
29 293 2930 29 300 2 93 000
* Reference 32. Refers to the engineering classification of cleanrooms.
y
Environmental controls in operating theatres
83
Table III Classification of operating theatre zones according to risk categories and limits in airborne particles and bacteria*, University of Geneva Hospitals, Switzerland Particle size (Particles per m3) Class Level of risk 1. 2.
3.
4.
0.5 mm
Very high risk, within 10 laminar air-flow area with HEPA filtration High risk, exterior 353 laminar air-flow, but within the operating theatre Medium risk, 3 530 conventionally ventilated operating theatre with air filtered through terminal filters with an efficiency of 95% and above Low risk, areas with NS uncontrolled ventilation
5 mm
Bacterial counts (cfu/m3)
0
<1
10
5
25
25
NS
NS
* Sampling is performed in the operating theatre whilst at rest. cfu, Colony forming unit; NS, no specific limit.
or theatre dress are to be evaluated, both volumetric air sampling and settle plates may be used together. Plates should be placed as near as possible to the operating team and on the instrument trolley in order to obtain any meaningful results. However, this may create practical problems in some circumstances. Water supply Another area of environmental control in operating theatres is the bacteriological quality of water used for surgical handscrubs for which there are no standardized limits at present. Some institutions use sterile water for this procedure. At our institution, we use drinking quality water, <200 bacteria/mL, with bacterial counts carried out twice a year on these water outlets. Counts have never exceeded 400 bacteria/mL with most being below 100 (unpublished data). The exception to this was when a new operating theatre was built and warm water (30±35 C) was provided via a closed circuit for the comfort of surgeons. However, the problem was rapidly rectified by lowering the temperature to 20±25 C. Organisms recovered from these samples were mainly environmental, Gram-negative bacilli and atypical mycobacteria. Taking into account our
experience and the increasing use of alcohol-based solutions for surgical hand disinfection and doublegloving, we strongly believe that the use of sterile water for surgical hand disinfection is not a necessity. Conclusion There is presently no common standard method used to determine bacterial threshold limits in the operating theatre setting. In this situation, it is practically impossible to compare results between countries. We recommend the use of cleanroom technology standards based on the measurement of the presence of air particles as routine procedure. Our opinion is that environmental bacterial sampling should be restricted to the investigation of epidemics and validation of changes in products and maintenance procedure of the operating theatre. We suggest that there is a need to reach a consensus on the method of evaluation and also, to differentiate between cleanroom technology developed for industry and that used in hospitals.
Acknowledgement The authors thank Rosemary Sudan for editorial assistance. References 1. Bitkover CY, Marcusson E, Ransjo U. Spread of coagulase-negative staphylococci during cardiac operations in a modern operating room. Ann Thorac Surg 2000; 69: 1110±1115. 2. Whyte W, Hambraeus A, Laurell G, Hoborn J. The relative importance of routes and sources of wound contamination during general surgery. I. Nonairborne. J Hosp Infect 1991; 18: 93±107. 3. Whyte W, Hambraeus A, Laurell G, Hoborn J. The relative importance of routes and sources of wound contamination during general surgery. II. Airborne. J Hosp Infect 1992; 22: 41±54. 4. Whyte W, Hodgson R, Tinkler J. The importance of airborne contamination of wounds. J Hosp Infect 1982; 3: 123±135. 5. Ayliffe GAJ. Role of the environment of the operating suite in surgical wound infection. Rev Infect Dis 1991; 13 (Suppl. 10): S800±804. 6. Humphreys H. Infection control team in the operating room: separating aspiration from reality! J Hosp Infect 1999; 42: 265±267. 7. Charnley J, Eftekhar N. Postoperative infection in total prosthetic replacement arthroplasty of hip joint. Br J Surg 1969; 56: 641±649.
84 8. Lidwell OM, Lowbury EJL, Whyte W, Blowers R, Stanley SJ, Lowe D. The effect of ultraclean air in operating rooms on deep sepsis in the joint after hip or knee replacement: a randomised study. Br Med J 1982; 285: 10±14. 9. Gosden PE, MacGowan AP, Bannister GC. Importance of air quality and related factors in the prevention of infection in orthopaedic implant surgery. J Hosp Infect 1998; 39: 173±180. 10. Friberg B, Friberg S, Burman LG. Correlation between surface and air counts of particles carrying aerobic bacteria in operating rooms with turbulent ventilation: an experimental study. J Hosp Infect 1999; 42: 61±68. 11. Laufman H. Airflow effects in surgery. Arch Surg 1979; 114: 826±830. 12. Schwan A, Bengstsson S, Hambraeus A, Laurell G. Airborne contamination and post operative infection after total hip replacement. Acta Orthop Scand 1977; 48: 86±94. 13. Vasey H, Ducel G, Allgower D. Zones proteÂgeÂes en salle d'opeÂration. Evaluation d'une nouvelle enceinte de Charnley. Med Hyg 1987; 45; 1646±1651. 14. Lew DP, Pittet D, Waldvogel FA. Infections that complicate the insertion of prosthetic devices. In: Mayhall CG, Ed. Hospital Epidemiology and Infection Control. Baltimore: Williams and Wilkins 1995; 731±748. 15. Mitchell NJ, Evans DS, Kerr A. Reduction of skin bacteria in theatre air with comfortable, non-woven disposable clothing for operating theatre staff. Br Med J 1978; 1: 696±698. 16. Fitzgerald RH, Jr. Microbiological environment of the conventional operating room. Arch Surg 1979; 114: 772±775. 17. Ritter MA, Eitzen HE, Hart JB, French ML. The surgeon's garb. Clin Orthop 1980; 153: 204±209. 18. Berman BR, Hoborn J, Nachemson AL. Patient draping and staff clothing in the operating theatre: a microbiological study. Scand J Infect Dis 1985; 17: 421±426. 19. Hubble MJ, Weale AE, Perez JV, Bowker KE, MacGowan AP, Bannister GC. Clothing in laminarflow operating theatres. J Hosp Infect 1996; 32: 1±7. 20. Chosky SA, Modha D, Taylor GJ. Optimisation of ultraclean air. The role of instrument preparation. J Bone Joint Surg Br 1996; 78: 835±837. 21. Verkkala K, Eklund A, Ojajarvi J, Tiittanen L, Hoborn J, Makela P. The conventionally ventilated operating theatre and air contamination control during cardiac surgeryÐbacteriological and particulate matter control garment options for low level contamination. Eur J Cardiothor Surg 1998; 14: 206±210. 22. Pittet D, Ducel G. Infectious risk factors related to operating rooms. Infect Control Hosp Epidemiol 1994; 15: 456±462. È stensson R, Burman LG. 23. Friberg B, Friberg S, O Surgical area contaminationÐcomparable bacterial
S. Dharan and D. Pittet
24. 25.
26.
27.
28. 29. 30. 31. 32.
33. 34.
35.
36. 37.
38.
counts using disposable head and mask and helmet aspirator system, but dramatic increase upon omission of head-gear: an experimental study in horizontal laminar air-flow. J Hosp Infect 2001; 47: 110±115. Mitchell NJ, Hunt S. Surgical face masks in modern operating roomsÐa costly and unnecessary ritual? J Hosp Infect 1991; 18: 239±242. Military Standard 282. Military standard: filter units, protective clothing, gas-mask components and related productions: performance-test methods. United States Department of Defence, 1956. Whyte W, Lidwell OM, Lowbury EJ, Blower R. Suggested bacteriological standards for air in ultraclean operating rooms. J Hosp Infect 1983; 4: 133±139. Friberg BE, Friberg S, Burman LG. Zoned vertical ultraclean operating room ventilation. A novel concept making long side walls unnecessary. Acta Orthop Scand 1996; 6: 578±582. Johnston IDA, Hunter AR (Eds). The Design and Utilization of Operation Theatres. London: Edward Arnold 1984. Federal Standard 209E. Airborne particulate cleanliness classes in clean rooms and clean zones. United States General Service Administration 1992. British Standard 5295-1. Classification and requirements of cleanrooms. British Standards Institution 1989. Vereinigte Deutsche Ingenieure (VDI) 2083. ReinraumtechnikÐGrundlagen, Definitionen und Festlegungen der Reinheitsklassen 1995. ISO 14644-1. Cleanrooms and associated controlled environments, Part 1: Classification of air cleanliness. International Organization for Standardization Technical Committee (ISO TC 209) 1999. Whyte W. In support of settle plates. PDA J Pharm Sci Technol 1996; 50: 201±204. Gasper C, Calvente MJ, Fernandez C, Fereres J. Air microbiology monitoring in plenum-ventilated operating rooms. Proposed standards. Enferm Infecc Microbiol Clin 1997; 15: 250±254. Friberg B, Friberg S, Burman LG. Inconsistent correlation between aerobic bacterial surface and air counts in operating rooms with ultra clean laminar air-flows: proposal of a new bacteriological standard for surface contamination. J Hosp Infect 1999; 42: 287±293. Pasquarella C, Pitzurra O, Savino A. The index of microbial air contamination. J Hosp Infect 2000; 46: 241±256. Seal DV, Clark RP. Electronic particle counting for evaluating the quality of air in operating theatres: a potential basis for standards. J Appl Bacteriol 1990; 68: 225±230. Whyte W, Shaw BH, Barnes R. A bacteriological evaluation of laminar-flow systems for orthopaedic surgery. J Hyg Camb 1973; 71: 559±564.