Eur J Cardiothorac Surg 1998;14:206-210
© 1998 Elsevier Science NL
The conventionally ventilated operating theatre and air contamination control during cardiac surgery – bacteriological and particulate matter control garment options for low level contamination
Kalervo Verkkalaa,
Anne Eklunda,
Juhani Ojajärvic,
Leena Tiittanenb,
Jan Hobornd,
Paavo Mäkeläb
a Department of Thoracic and Cardiovascular Surgery, Helsinki University Central Hospital, P.O. Box 260, Haartmaninkatu 4, SF-00290 Helsinki, Finland
b Department of Infection Control, Helsinki University Central Hospital, Helsinki, Finland
c Department of Public Health, University of Helsinki, Helsinki, Finland
d Mölnlycke Health Care AB, Gothenburg, Sweden
Received 19 January 1998;
received in revised form 20 April 1998;
accepted 28 April 1998.
Corresponding author. Tel.: +358 9 4711; fax: +358 9 4714006; e-mail: anne.eklund@icon.fi
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Abstract
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Objective: The purpose of the study was to compare the usefulness of a conventional bacteriological technique with that of particle counting under lower air contamination and better aseptic conditions achieved with special staff garments and covering for the patient. Contamination levels were estimated with continuous on line air particle counting measurement, volumetric intermittent short period aerobic bacteriological cultures and wound surface contact cultures. Methods: In a series of 66 consecutive coronary artery bypass operations performed by the same team and in the same theatre using different types of patient and staff clothing, the impact of a reduced bacteriological and particulate contamination were assessed. The volumetric air contamination of particles 
5 µm and bacteria-carrying particles were monitored 30 cm above the sternal wound. The bacterial contamination and bacterial wound infections in the sternal and leg wounds were assessed as well. Results: With the alternative garment and textile system, the air counts fell from 25 colony-forming units (CFU)/m3 to 7 CFU/m3 (P<0.0038). The contamination of the sternal wound was reduced by 46% and that of the leg wound by >90%. In order to give continuous contamination feedback during the whole operation to the theatre staff, particle counts 5 µm were monitored and visualized. Air particle counts decreased rapidly from 850 particles/m3 and stabilized to approximately 50 particles/m3 when the alternative clothing system was used (P<0.001). Low particle counts 5 µm should offer the possibility to indirectly estimate air bacteria carrying particle counts during the entire operation. Less than 20% of the total count in this size group carries bacteria. The low air contamination was achieved even in an ordinary ventilated theatre when individual team members used clean air suits in combination with impermeable patient drapes. When air particle level 
50 particles/m3 is reached, the bacterial air contamination is in the order of that of orthopaedic hip operations. The staff must during the entire operation adjust their activity to air asepsis. Conclusions: The use of clean air suits and impermeable patient clothing results in a low exogenous contamination of air and wound. Continuous air particle monitoring is a good intraoperative method to monitor the air contamination longitudinally in an operating theatre.
Key Words: Cardiac surgery • Contamination • Clothing
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Introduction
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As post-operative infection after cardiac surgery is one of the most feared complications, demands on control of potential pathogenic micro-organisms during the surgical procedure are high
[1]
[2]
[3]
[4]. Possible air and contact routes of transfer have been outlined by Whyte and others
[5]. Traditionally, ultra-clean air has been achieved with the help of ventilation systems. These have been shown to be effective in orthopaedic surgery
[6]. Various air sampling methods, e.g. slit samplers, filter samplers and sedimentation plates, have been used to monitor microbial contamination. These techniques are cumbersome and the results are only available several days after the operation. Particulate contamination, on the other hand, may readily be continuously monitored on the spot. Seal et al. have reported on a technique to do that
[12]. The condition for using this technique is, however, to maintain very low particle counts. Hoborn, Bergman and Blomgren et al. have earlier shown, both in the laboratory and during surgery, that the use of specially designed working clothes, a polypropylene coverall, worn by all present in the theatre, maintains the proposed low level of microbial contamination in the theatre air during orthopaedic surgery
[7]
[8]
[9]
[10]. We have earlier shown that in cardiac surgery too, the use of a combined system of disposable gowns, drapes and staff clean air suits reduces bacterial air contamination
[11].
The aim of the present study was to assess continuous particulate contamination monitoring as a possible means to generate on-line information concerning air contamination during operation under the impact of the previously studied system of impervious clothing for both patient and staff on the microbial contamination of the operation wound, the operative site and the operating theatre air.
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Materials and methods
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The study includes 66 adult patients who underwent open, elective coronary artery bypass surgery. Mean patient age was 55 years (range 30–73 years). Preoperative whole body shower wash with 4% chlorhexidine emulsion was performed three times on consecutive days preoperatively by all patients. Before the operation, the skin of the patient was treated additionally three times in the operating theatre with 0.5% chlorhexidine in 80% v/v ethyl alcohol. The operations were carried out via a median sternotomy incision. Standard cardio-pulmonary bypass with a bubble oxygenator was used. Mild hypothermia and cold chemical cardioplegia were used for myocardial protection. The operative procedures were standardized as far as possible.
All operations were carried out in the same conventionally ventilated operating theatre with twenty changes of air per hour. The operating team consisted of 10±1 persons: always the same surgeon and mainly the same staff. Traffic inside the theatre and connecting with the outside was minimized. The procedures studied were always the first in the morning. All patients received cephamandol (Mandocef®, Lilly, USA) as a prophylactic antibiotic treatment for 2 days.
Clothing and draping
The patients were randomly allocated to two different systems of patient draping and staff clothing.
- Clean air suit group. All personnel working in the operating theatre wore polypropylene clean air suits, and the operating team also used non-woven operating gowns reinforced with plastic film in the front and lower parts of the sleeves (Mölnlycke Health Care AB). The patients were covered with plastic foil laminated impermeable drapes with self adhesive edges.
- Cotton group. The operating theatre personnel wore cotton shirts, trousers and conventional cotton operating gowns. The patient was covered with cotton drapes.
Head covers and masks in both groups were the disposable types. Operating gloves were consistently changed by the surgeon when the sternum had been opened. In all operations, the patient draping was supplemented by incision foil (Steridrape, 3M, St. Paul, MN).
Bacteriological sampling
Air
At 17 randomly selected operations in the two groups, volumetric air samples of 300 l were taken at the time of incision plus 1 and 2 h later from 30 cm above the sternal wound. A Sartorius filter sampler was used (Sartorius GmbH, Göttingen, Germany with a capacity of 30 l/min and equipped with 3 µm pore size gelatine filters. The filters were transferred immediately after sampling to blood agar plates for incubation aerobically for 48 h at 37°C. The colonies were then counted and typed using conventional clinical bacteriological techniques.
Wounds
Approximately 3 h after the incision, three pieces of sterile polyvinylalcohol (PVA) foam (Mölnlycke Health Care AB), 4x7.5 cm, were placed against the sternal wound surface; two pieces on the wall of the wound and one piece on the surface of the heart. Two pads were also placed against the inguinal wound (done for saphenous vein harvesting) surface. The pads were allowed to absorb to saturation and were then separately put into Ringer's solution to which had been added a ß-lactamase inactivator (Oxoid SR 113, Oxoid, Basingstoke, UK). They were immediately transported to the laboratory to be treated in a Stomacher homogenize (Seward Laboratories, London, UK). The eluates were spread onto blood agar plates, which were incubated at 37°C for 48 h after which the colonies were counted and typed.
Incision foil
Simultaneously with the wound sampling, the incision foil was sampled. A cardboard frame (aperture 50 cm2) was placed onto the foil between the wound and the surgeon (
Fig. 1
). The area in the aperture of the frame was rubbed with sterile lecithin–Tween solution (0.3 and 2.0%, respectively), on a sterile cotton swab. The specimen was placed in sterile 0.43% saline, modified according to Möller
[12]. At the laboratory, the swabs were treated with the same technique as the wound pads.
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Fig. 1. Layout of the operating theatre and the position of investigation sites. 1, particle analyzer; 2, incision foil.
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Particle counting
Particles (5 µm) were counted by means of a Climet 0208A Particle Analyzer (Climet, Redlands, CA) 30 cm above the wound for 4-min periods starting from the incision continually throughout the operation (
Fig. 1).
Statistical analysis
Statistical evaluation of differences was performed by means of the Wilcoxon two-sample test.
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Results
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The mean particulate contamination (5 µm) throughout the operations within the two-material systems is shown in
Fig. 2 . The results show that throughout the operation particle counts were lower in the clean air suit group. The counts in the cotton group stabilize after 160–180 min at approximately 800 particles 5 µm/m3 whereas the counts in the clean air suit group asymptotically approach zero.
The volumetric microbial air contamination is presented in Table 1. The contamination, in total and at the time of incision is 3.6 times higher in the cotton group than with the clean air suit.
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Table 1. Bacterial volumetric air contamination at wound site during operations (mean number of colonies counted (CFU/m3))
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The contamination on the incision foil surrounding the wound (Table 2) was found to be approximately 1/20 of that for cotton when the clean air suit system was used. The difference in the sternum wound was about 1/2, whereas in the leg wound no bacteria were grown in any of laminate operations but in three out of twelve (25%) in the cotton group (Table 3).
Table 3 shows the number of samples with growth from the incision foil and from the sternal wound, respectively. No significant difference was found in the sternal wound whereas four out of 32 (12.5%) of the foil samples gave growth in the clean air suit group and seven out of 34 (20.6%) in the cotton group. If only the operations showing simultaneous growth of bacteria from both sites are selected, the numbers are three for cotton and zero for the clean air suit. The differences in growth rates between the two material systems are, however, not statistically significant.
As the volumetric bacterial counts as well as the particle counts were partly performed simultaneously, it was possible to estimate the difference of the two parameters. Neither the total results nor the results associated with the first or second hour of operation showed any correlation. The low level of contamination in the clean air suit group was reached in 1 h and maintained steady through operation (
Fig. 2).
The aerobic bacteria cultured in the samples were mainly staphylococci epidermidis and a few staphylococci aureus.
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Discussion
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The seriousness of postoperative infections and the increased susceptibility of patients undergoing cardiac surgery increase the demands on the operating theatre asepsis to prevent even low infecting doses of bacteria from reaching the wound. Evidence is scarce of the prophylactic effects of different aseptic measures in different types of operations and mainly concerns endoprosthetic operations. Whyte has shown that a considerable amount of organisms carried by the air reaches the wound after having sedimented onto the sterile field
[5]. He has also presented a model to clarify the patterns of transfer.
Low bacterial contamination of the air has been shown to have an additional effect in preventing infections in orthopaedic surgery and this may be achieved by ventilation, special clothing and policy of staff behaviour
[13]. Whyte has proposed a maximum level of air contamination for orthopaedic surgery, 10 CFU/m3 measured 30 cm above the wound
[10]. The direct correlation between air contamination and wound infection has been shown in hip operations
[13]. Blomgren and co-workers have shown that if, in orthopaedic surgery, a zonal ventilation system was used in combination with body exhaust gowns, the contamination of the operative field could be brought to very low level
[9].
Due to the considerably larger wound area and longer operation time, increased cleanliness of the air should result in less wound contamination in cardiac surgery
[1]
[2].
Fig. 2 shows that use of the clean air suit system results in a significantly lower level of air particle counts at the beginning of the operation. A low level of total particles and corresponding bacteria carrying particle count would be an important possibility for individual operation air contamination follow-up.
When the level of air contamination is high, a poor correlation has been demonstrated between the number of particles between 5 and 7 µm and microbial contamination
[12]. The low level of particle counts, when achieved, would also mean low level of particles carrying bacteria. As part of total air particles size is 5 µm, the bacteria carrying particles demonstrate less than 20%. We have evaluated means to lower the initially high level of contamination and demonstrated the effect using continuous monitoring (
Fig. 2). We have earlier reported on the effect of experimental conditions on air cleanliness
[11]. Even if the air contamination here is low (25.2 CFU/m3), the effect of the clean air suit system is clear (7.0 CFU/m3). The difference then corresponds well with the lower degree of contamination observed on the incision foil, in the sternal wound and in the leg wound. The highest reduction was found on the incision foil, probably owing to both reduced sedimentation and a better barrier effect against the patient's own skin bacteria via contact transfer. The important result of this study is that when low levels of operative air contamination were achieved, continuous on-line air contamination information to the operating team throughout the operations could be generated.
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Conclusion
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Even in a conventionally ventilated operating theatre (20 changes of air/h), the use of impermeable patient and personnel clothing, a clean air suit which effectively lowers dispersal of organisms from the operating team, results in a low theatre air contamination and exogenous contamination of the operating wound. Continuous particle monitoring is a good intraoperative method to control the air contamination related to the theatre staff behaviour during individual operation. This increases further the possibility of studying the theatres, technical designs, materials and methods with a view towards lower contamination levels as well as the possibility of studying larger groups of patients regarding risk for wound infection.
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References
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Abstract
Introduction
