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Reduction of Airborne Bacterial Burden in the OR by Installation of Unidirectional Displacement Airflow (UDF) Systems

Reduction of Airborne Bacterial Burden in the OR by Installation of Unidirectional Displacement... MEDICAL TECHNOLOGY e-ISSN 1643-3750 © Med Sci Monit, 2015; 21: 2367-2374 DOI: 10.12659/MSM.894251 Received: 2015.03.27 Reduction of Airborne Bacterial Burden in Accepted: 2015.05.04 Published: 2015.08.13 the OR by Installation of Unidirectional Displacement Airflow (UDF) Systems Authors’ Contrib ution: ACDEF 1 Sebastian Fischer 1 Department of Hand, Plastic, and Reconstructive Surgery, Burn Center, BG Trauma Study Design A Center Ludwigshafen, University of Heidelberg, Ludwigshafen, Germany ADF 2 Martin Thieves Data Collection B 2 Division of Hospital Hygiene, Darmstadt Clinic, Darmstadt, Germany ADE 3 Tobias Hirsch Statistical Analysis C 3 Department of Plastic and Reconstructive Surgery, Burn Centre, BG University Data Interpr etation D DE 1 Klaus-Dieter Fischer Hospital Bergmannsheil, Ruhr University Bochum, Bochum, Germany Manuscript Preparation E 4 Department of Hygiene, University of Applied Science, Giessen-Friedberg, ABCD 4 Helmine Hubert Literature Search F Germany ABD 4 Steffen Bepler Funds Collection G ACDEF 4 Hans-Martin Seipp Corresponding Author: Hans-Martin Seipp, e-mail: Hans-Martin.Seipp@tg.fh-giessen.de Source of support: Departmental sources Background: Intraoperative bacterial contamination is a major risk factor for postoperative wound infections. This study in- vestigated the influence of type of ventilation system on intraoperative airborne bacterial burden before and after installation of unidirectional displacement air flow systems. Material/Methods: We microbiologically monitored 1286 surgeries performed by a single surgical team that moved from operat- ing rooms (ORs) equipped with turbulent mixing ventilation (TMV, according to standard DIN-1946-4 [1999], ORs 1, 2, and 3) to ORs with unidirectional displacement airflow (UDF, according to standard DIN-1946-4, an - nex D [2008], ORs 7 and 8). The airborne bacteria were collected intraoperatively with sedimentation plates. After incubation for 48 h, we analyzed the average number of bacteria per h, peak values, and correlation to surgery duration. In addition, we compared the last 138 surgeries in ORs 1-3 with the first 138 surgeries in ORs 7 and 8. Results: Intraoperative airborne bacterial burden was 5.4 CFU/h, 5.5 CFU/h, and 6.1 CFU/h in ORs 1, 2, and 3, respective- ly. Peak values of burden were 10.7 CFU/h, 11.1 CFU/h, and 11.0 CFU/h in ORs 1, 2, and 3, respectively). With the UDF system, the intraoperative airborne bacterial burden was reduced to 0.21 CFU/h (OR 7) and 0.35 CFU/h (OR 8) on average (p<0.01). Accordingly, peak values decreased to 0.9 CFU/h and 1.0 CFU/h in ORs 7 and 8, re- spectively (p<0.01). Airborne bacterial burden increased linearly with surgery duration in ORs 1–3, but the UDF system in ORs 7 and 8 kept bacterial levels constantly low (<3 CFU/h). A comparison of the last 138 surgeries before with the first 138 surgeries after changing ORs revealed a 94% reduction in average airborne bacterial burden (5 CFU/h vs. 0.29 CFU/h, p<0.01). Conclusions: The unidirectional displacement airflow, which fulfills the requirements of standard DIN-1946-4 annex D of 2008, is an effective ventilation system that reduces airborne bacterial burden under real clinical conditions by more than 90%. Although decreased postoperative wound infection incidence was not specifically assessed, it is clear that airborne microbiological burden contributes to surgical infections. MeSH Keywords: Environment, Controlled • Operating Rooms • Ventilation Full-text PDF: http://www.medscimonit.com/abstract/index/idArt/894251 2743 4 4 19 Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Background In our previous study, we demonstrated that bacterial con- tamination of the surgical field under real clinical conditions Postoperative wound infections are one of the most common is significantly lower with unidirectional displacement airflow complications after surgery. In Germany, 225 000 postoper- (UDF) compared to turbulent mixing ventilation (TMV) sys- ative wound infections are recorded annually, representing tems [10]. However, ORs included in the study were each sit- 1.8% of all performed surgeries [1]. Besides a prolonged heal- uated in different hospitals, leading to differences in the OR ing process, extended in-patient hospital stay, and addition- team as well as their surgical approach and spectrum, and, al surgeries, wound infections can lead to serious complica- thus, are factors that can significantly influence intraoperative tions such as sepsis or even death. Although their origin is not bacterial contamination. clearly defined, wound infections are most likely due to multi - ple causes. The systemic distribution of microbial pathogens The purpose of this study was to assess the intraoperative air- and intraoperative bacterial contamination are highly suspect- borne bacterial burden in surgeries performed by a single sur- ed to be the main factors causing surgical infections. Whether gical team that initially utilized ORs ventilated by turbulent airborne or attached to skin particles of the OR team, these mixing ventilation systems and subsequently switched to ORs pathogens directly or indirectly reach the surgical field during with ventilation systems according to the principle of unidirec- surgery [2]. Cecsey et al. showed that a square centimeter of tional displacement airflow. As there were no other changes, skin carries 2300 microorganisms on average, and that a per- except of the ventilation system, the effects shown are only son loses about 10 000 dead skin scales per day [3]. Although based on this technical change. To the best of our knowledge, these data were not assessed in an intraoperative setting, they no study thus far has compared has these 2 ventilation sys- provide a reference value for the expected OR team-related tems in such a controlled setting. bacterial burden in the surgical field. Contamination of the surgical field occurs not only direct - Material and Methods ly, but also indirectly, for example, through instruments or gloves. However, indirect contamination depends on air qual- Theatres ity as well. Chosky et al. demonstrated that sterilized OR in- strument are contaminated to a higher extent depending on The following ORs were included in this study: the ventilation system [4]. Therefore, a lower bacterial burden in the air of the OR should reduce direct and indirect contam- ORs 1–3 were equipped with air canopies with supported noz- ination of the surgical field. zles in a special turbulent mixing ventilation (TMV) system, ac- cording to DIN-Standard 1946-4 (1999) [11]. Each TMV system Two types of OR ventilation systems are currently available: was installed 3.1 m above the floor. The supply air volume was 3 3 turbulent mixing ventilation (TMV) and laminar airflow (LAF). 2200 m /h in OR 1 and OR 2 and 1600 m /h in OR 3. ORs 1–3 While the former (TMV) reduces bacterial concentration by had an ambient volume of 103 m each. streaming sterile and filtered inlet air into the surgical field and thereby provokes turbulent mixing with contaminated air, After construction of the new surgical wing of the hospi- laminar airflow (LAF) follows the opposite principle [5,6] with tal, 2 ORs with new ventilation systems were created (ORs 7 sterile filtered inlet air flowing with low turbulence from the and 8), which functioned according to the principle of unidi- ceiling, displacing the contaminated air without cross-con- rectional displacement airflow (DIN-Standard 1946-4, annex tamination [7]. In contrast, LAF systems with very low turbu- D 2008) [9]. The size of the each ceiling was 3.2×3.2 m and lence (<5%) are established for cleanrooms, and a compara- supply air volume was 9000m /h. In both ORs, flow stabiliz - ble ventilation system is available for ORs – the unidirectional ers were installed at the ceiling 2.1 m above floor level. OR 7 displacement airflow (UDF) systems. Although UDF has high - had an ambient volume of 94 m and OR 8 had an ambient er turbulence (5–20%) compared to LAF, they are still able to volume of 112 m and both were connected to vestibules. OR achieve an airborne bacterial burden of less than 1 CFU/m equipment, including medical devices, clothes, supplies, and in- under experimental conditions [8,9. However, the extent of struments, remained the same after moving into the new ORs. pathogen reduction compared to other OR ventilation sys- tems and under real clinical conditions is hard to evaluate. According to DIN 1946-4, each ventilation system involved in The type of surgery, the number of attending staff, and the this study was maintained on a regular basis (every 3 years) individual approach to performing surgery differ significantly by means of particle number measurements as well as inspec- among hospitals, making valid comparison of evaluated bac- tions of tightness of fit and integrity of all filter components terial numbers difficult. to warranty optimal performance, efficacy, and safety, and to facilitate comparison over the entire study period. Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 1. Overview of operating room (OR). Turbulent mixing ventilation Unidirectional displacement airflow System (TMV) (UDF) Name OR-1 OR-2 OR-3 OR-7 OR-8 Ceiling size [m ] – 3.2×3.2 3.2×3.2 Supply air [m /h] 2.200 2.200 1.600 9.000 9.000 Ambient volume [m ] 103 103 103 94 112 Number of surgeries 243 465 440 62 76 Mean value [min] 77 102 92 114 88 IC- Standard deviation 68 81 73 80 68 time Variation coefficient 88% 79% 80% 70% 78% TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time. Sedimentation ORs with their respective ventilation systems: short (<35 min), middle (36–75 min), and long (>75 min) IC time. Variance compar- Sterile sedimentation plates (ICR plates, item number: 03075e ison was verified by Levene test (F-test). Mean value discrepan - Heipha Dr. Müller GmbH Co., Eppelheim, Germany) were ex- cies were then tested for statistical signic fi ance by t test; p<0.05 posed on the instrument table. Scrub nurses positioned and was defined as significant and p<0.005 as highly significant. opened the plates in the sterile area. Plates were opened at the beginning of surgical incision and were closed at the To increase comparability of the situation before and after end of suturing (sedimentation period = incision-to-closure switching ORs, the last 138 surgeries in ORs 1–3 were com- time [IC time]) in accordance with the objectives of the stan- pared to the first 138 surgeries in ORs 7 and 8. Thereby, the dards DIN-1946-4 [9] and ISO-14698-1 [12]. The cover plates airborne bacterial burden in each OR and each surgery was were affixed with tape and labeled immediately after surgery. calculated and correlated to the IC time. Accompanying data sheets included the documentation of pa- tient information, duration of surgery (IC time), surgical pro- cedures, and plate numbers. Results For 48 h, ICR plates were incubated at a temperature of 37°C For the comparison of both ventilation systems, we performed (Incubator type B12, Heraeus Holding GmbH Co., Hanau, measurements in 5 ORs over a period of 6 years in the same Germany). The colonies grown were then counted numerical- hospital. A total of 1286 surgeries were performed and a cor- ly as colony-forming units (CFUs). responding number of sedimentation plates were used (1 plate for each surgery). The mean value of IC time was 94.6 min and Statistics varied between 77 min (OR 1) and 114 min (OR 7) (Table 1). The primary result parameter of the CFUs was matched to the Bacterial contamination analyzed ORs. The calculation of mean value, median, varia- tion coefficient, and standard deviation was completed. The Turbulent mixing ventilation (TMV) determination of the trimmed mean value (percentile range 85–95%) was used to eliminate outliers. IC time was harmo- In ORs 1, 2, and 3, we analyzed 243, 465, and 440 surgeries, nized to 60 min and the bacterial count was calculated (CFU/h) respectively. IC time ranged from 77 min (OR 1) to 102 min in accordance with the objective of the standard DIN-1946 (an- (OR 2) on average. Mean bacterial burdens were 6.5, 8.1, and nex F) to compare the airborne bacterial burden (in CFUs) be- 7.5 CFU in ORs 1, 2, and 3, respectively, and reached a maxi- tween the various ORs. The t test was used for pairwise com- mum of 121 CFU (OR 2). Trimmed mean values were 16.6, 18.5, parison of harmonized CFUs. and 17.1 CFU in ORs 1, 2, and 3, respectively. Detailed results are given in Table 2. Comparing ORs 1–3 with each other, no Three groups were created, based on different IC times and for statistically significant differences in airborne bacterial bur - comparison of the intraoperative bacterial transmission of the 5 den or harmonized bacterial burden were detectable (p>0.05). Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 2. System comparison of ventilation systems. Turbulent mixing ventilation Unidirectional displacement airflow system (TMV) (UDF) Name OR-1 OR-2 OR-3 OR-7 OR-8 Mean IC-time [min] 77 102 92 114 88 Mean value 6.5 8.1 7.5 0.3 0.4 Standard deviation 7.0 9.3 7.8 0.6 0.6 Median 4 5 5 0 0 CFU Minimum 0 0 0 0 0 Maximum 36 121 58 2 2 Trimmed SD (0.85–0.95) 16.6 18.5 17.1 1.0 1.0 Mean value 5.4 5.5 6.1 0.2 0.4 Standard deviation 4.3 6.3 9.2 0.4 0.9 Median 4 4 4 0 0 CFU/h Minimum 0 0 0 0 0 Maximum 23 101 96 1.7 6.7 Trimmed SD (0.85–0.95) 10.7 11.1 11.0 0.9 1.0 TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time; CFU – colony- forming units. Unidirectional displacement airflow (UDF) In OR 7, 62 surgeries were performed, with a mean IC time of 114 min. In OR 8, the 76 surgeries performed had an average IC time of 88 min. Therefore, mean airborne bacterial burdens were 0.3 and 0.4 CFU for OR 7 and 8, respectively, reaching a maximum of 2 CFU in both ORs 7 and 8. Trimmed mean value was 1 CFU for both ORs 7 and 8. Detailed results are shown in Table 2. In contrast, both OR 7 and OR 8 had no statistical- ly significant differences in airborne bacterial burden or har - monized bacterial burden (p>0.05). Comparison of ventilation systems OR-1 OR-2 OR-3 OR-7 OR-8 IC time was harmonized to 60 min and a calculation of the cor- responding bacterial count was performed to compare the 2 different ventilation systems. For turbulent mixing ventilation Figure 1. Comparison of bacterial burden in ORs 1–3 (turbulent mixing ventilation) with ORs 7 and 8 (unidirectional (TMV), bacterial burdens harmonized to 1 h were 5.4, 5.5, and displacement airflow). Brackets indicate statistical 6.1 CFU/h for ORs 1, 2, and 3, respectively, and reached maxima significance (p<0.05). of 23, 101, and 96 CFU/h, respectively. Trimmed mean values of harmonized airborne bacterial burden were 10.7, 11.1, and 11 CFU/h for ORs 1, 2, and 3, respectively. In contrast, airborne 1 CFU/h in ORs 7 and 8, respectively. Detailed results are pre- bacterial burden of ORs with unidirectional displacement air- sented in Table 2. Each OR with turbulent mixing ventilation flow (UDF) varied from 0.2 CFU/h in OR 7 to 0.4 CFU/h in OR 8, (ORs 1–3) demonstrated a statistically significant (p<0.005) and reached a maximum of 6.7 CFU/h in OR 8. Trimmed mean higher bacterial burden per hour compared to both ORs with values of harmonized airborne bacterial burden were 0.9 and unidirectional displacement airflow (ORs 7 and 8, Figure 1). Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU/h Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 3. Comparison of the last 138 surgeries in ORs 1–3 with the first 138 surgeries in OR 7 and 8. system Turbulent mixing ventilation (TMV) Unidirectional displacement airflow (UDF) Name OR1–3 OR7+8 Number of surgeries 138 138 Mean [min] 89 100 IC-time Standard deviation 74 75 Mean value 6.1 0.4 Standard deviation 5.7 0.6 Median 4.3 0 CFU Minimum 0 0 Maximum 26.3 2 Trimmed SD (0.85–0.95) 13.6 1 Mean value 5 0.3 Standard deviation 5.3 0.7 Median 3.8 0 CFU/h Minimum 0 0 Maximum 31.9 6.7 Trimmed SD (0.85–0.95) 10.8 1 TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time; CFU – colony-forming units; SD – standard deviation. Importantly, the large differences in maximum values of air - Last 138 vs. first 138 surgeries borne bacterial burden per h within the same study group were based on outliers. To increase reliability of comparing the 2 ventilation systems, the last 138 surgeries of ORs 1-3 (group A) were compared to the first 138 surgeries of ORs 7 and 8 (group B). Thereby, mean IC times were 89 min and 100 min for groups A and B, respectively. Mean airborne bacterial burden in group A was 6.1 CFU, ranging from 0 to 26.3 CFU and a trimmed value of 4 13.6 CFU. For group B, mean airborne bacterial burden was 0.35, with a minimum of 0 CFU and a maximum of 2 CFU, and a trimmed value of 1. Mean bacterial burden harmonized to 1 h was 5 CFU/h and 0.29 CFU/h for groups A and B, respec- OR1–3 OR7–8 tively. Detailed results are presented in Table 3. Comparing the 2 groups, group A had a significantly higher (p<0.005) air - borne bacterial burden than group B (Figure 2). Figure 2. Comparison of bacterial transmission of the last 138 surgeries in ORs 1–3 with the first 138 surgeries in ORs 7 and 8. Brackets indicate statistical significance Impact of surgical procedure duration (IC) on bacterial (p<0.05). burden The gathered data were analyzed. Surgical procedure duration to increased IC time, the bacterial burden constantly rose in (IC time) was divided into 3 groups: short (<35 min), middle ORs with turbulent mixing ventilation (ORs 1–3), whereas bac- (35–75 min), and long (>75 min) surgical procedures (Table 4). terial burden in ORs with unidirectional displacement airflow These groups were compared with the data collected. In relation (ORs 7 and 8) remained low over the study period (Figures 3, 4). Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU/h Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 4. System comparison with respect to surgery durations. Turbulent mixing ventilation Unidirectional displacement System (TMV) airflow (UDF) Name OR-1 OR-2 OR-3 OR-7 OR-8 Number of surgeries 61 73 88 7 13 Mean value IC-time [min] 26 26 25 21 21 Short IC-time Standard deviation IC-time 6 7 8 8 8 (<35 min.) Mean value CFU 2.5 2.8 3.5 0 0.3 Standard deviation CFU 1.9 2.2 5 0 0.6 Number of surgeries 115 160 149 17 26 Mean value IC-time [min] 56 56 55 54 52 Middle IC-time Standard deviation IC-time 11 12 12 9 11 (36 to 75 min.) Mean value CFU 4.9 5.7 4.7 0.4 0.3 Standard deviation CFU 4.4 10 3.9 0.6 0.5 Number of surgeries 66 220 191 38 37 Mean value IC-time [min] 143 162 151 159 137 Long IC-time Standard deviation IC-time 80 79 73 71 68 (>75 min.) Mean value CFU 12.9 11.8 11.8 0.4 0.4 Standard deviation CFU 9 8.9 9.2 0.6 0.6 TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time; CFU – colony- forming units. Discussion Turbulent mixing ventilation It is obvious that bacterial contamination of surgical wounds (TMV), ORs 1–3 Unidirectional displacement should be avoided as much as possible. As postulated by airflow (UDF), ORs 78 Soots et al. 30 years ago, 98% of bacteria found in wound in- fections originated directly or indirectly from airborne con- tamination [13]. In this context, Fitzgerald and Washington reported that the degree of airborne contamination depends on the number of persons and the physical activity of the OR team [14]. Strong physical activity during surgery leads to lib- eration of about 10 000 particles per min and 10% of these bacteria persist in the air longer than half an hour. According to Salvigni et al., presence of humans in the OR is without dis- 0 020406080100 120 140160 pute the biggest source of contamination [15]. Reducing the IC-time (min) number of medical personnel in the OR is difficult, so optimi - zation of ventilation systems is the best option to reduce bac- terial contamination in the OR. In our latest study we also used Figure 3. Comparison of turbulent mixing airflow systems (mean values of ORs 1–3) with unidirectional displacement sedimentation plates according to national and internation- airflow systems (mean values of ORs 7 and 8) in als standards [9,12] and demonstrated that unidirectional dis- correlation to surgery durations. IC-time – incision-to- placement airflow (UDF) significantly reduces bacterial burden closure time, CFU – colony-forming units. in the OR compared to other ventilation systems [10]. Besides having the lowest bacterial counts per h, the UDF system was Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Figure 4. Comparison of turbulent mixing airflow in ORs 1–3 with unidirectional displacement airflow in ORs 7 and 8, both in correlation to surgery durations. IC-time – incision-to-closure time, CFU – colony-forming units. 20 OR 7 OR 8 OR 1 OR 2 OR 3 04 1005 200 300 00 00 IC-time (min) able to constantly maintain airborne bacterial burden inde- the bacteria become airborne and induce drafts that are un- pendent of surgery duration. Furthermore, in agreement with comfortable for the OR team [17]. The dependence of TMV sys- the results of Thomas and Meierhans, we found the highest tems on the room volume is also disadvantageous because in- airborne bacterial burden in ORs equipped with a window- flow of sterile filtered air aims to reduce of bacterial burden, based ventilation system without filters or prevention of tur - not to replace contaminated air [18]. bulence [16]. Although our results showed the superiority of UDF, some limitations were seen retrospectively. Because in- To confirm compliance with the current standard for TMV vestigations were simultaneously performed in different ORs systems, a 99% reduction in airborne bacterial burden in ORs and, especially, with different OR teams, reduction of bacterial must be achieved within 25 min (recovery time). In contrast, burden cannot be attributed solely to the ventilation system. the same reduction is obtained by UDF systems in less than 8 s by a flow velocity of 25 cm/s out of the ceiling [19]. The aim of the present study was to determine the impact of ventilation system type on bacterial burden by comparison We demonstrated that UDF significantly reduces airborne bac - under similar conditions. Therefore, we performed investiga- terial contamination of the surgical site in comparison to TMV tions in the same institution involving the same OR team be- (0.29 vs. 4.98 CFU/h). Whereas TMV leads to linear increase fore and after switching from ORs with turbulent mixing ven- over time, UDF was able to maintain airborne bacterial burden tilation (TMV) to ORs with unidirectional displacement airflow at constantly low levels. Considering the conditions of mea- ventilation systems (UDF). Thereby, the surgical spectrum and surement (identical surgical spectrum, equipment, and staff), procedures remained identical and reduction of airborne con- this effect results mainly from the installation of the UDF ven - tamination was solely attributed to the ventilation system. tilation system. The main principle of UDF is to replace contaminated air by Limitations of this study include lack of specification regarding discharging sterile filtered air coming from the ceiling into the bacterial pathogenicity and relevance for the clinical outcome protection zone (PZ) [7]. The PZ is defined as the area beneath after surgery. The significant reduction of bacterial contami - the ceiling in which the surgical procedure is performed, in- nation might be clinically irrelevant because obvious wound cluding personnel and instrument table. Discharge occurs with infections probably do not depend on bacterial counts in the low velocity to avoid turbulence and to replace the potentially surgical field, but rather on concomitant diseases or the gen - contaminated air without mixture and without cross-contam- eral condition of the patient. OR wound infections only oc- ination. The latter is the main difference from turbulent mix - cur at a certain threshold of bacterial counts in the surgical ing ventilation systems (TMV), which have been the criterion field, which is not achieved by TMV or UDF ventilation sys - standard in ORs for several decades. Directly streaming ster- tems. Therefore, further studies are necessary to evaluate the ile filtered air via outlets into the surgical field (with different effect of ventilation systems on postoperative wound infec - types depending on the manufacturer, e.g., iron pipes) is the tions. Investigations in the literature have not accounted for only way to reduce bacterial burden by TMV [6]. A reduction co-morbidities, limiting the usefulness of results. of bacterial burden is thus required by mixing sterile filtered air with contaminated air. To provide the maximum mixture, Nevertheless, the results of the present study clearly show the TMV systems create turbulences by streaming with high ve- significant impact of ventilation systems on airborne bacteri - locity out of the supply air. High turbulences, however, make al burden during surgery. Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Conclusions postoperative wound infections, it is clear that microbiologi- cal contamination causes these infections. The unidirectional displacement airflow, which fulfills the re - quirements of standard DIN-1946-4 annex D of 2008, is an Conflict of interest effective ventilation system that reduces the airborne bac - terial burden under real clinical conditions by more than The authors state no conflict of interest. 90%. Although we did not specifically assess the incidence of References: 1. 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V., Berlin. Beuth Verlag GmbH, 10772 68–70 Berlin, Germany 19. ISO 14644 Part 3, March 2006: Cleanrooms and associated controlled envi- 10. Hirsch T, Hubert H, Fischer S et al: Bacterial burden in the operating room: ronments, Test methods. DIN Deutsches Institut für Normung e. V., Berlin. impact of airflow systems. Am J Infect Control, 2012; 40(7): e228–32 Beuth Verlag GmbH, 10772 Berlin, Germany Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Medical Science Monitor : International Medical Journal of Experimental and Clinical Research Pubmed Central

Reduction of Airborne Bacterial Burden in the OR by Installation of Unidirectional Displacement Airflow (UDF) Systems

Medical Science Monitor : International Medical Journal of Experimental and Clinical Research , Volume 21 – Aug 13, 2015

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Abstract

MEDICAL TECHNOLOGY e-ISSN 1643-3750 © Med Sci Monit, 2015; 21: 2367-2374 DOI: 10.12659/MSM.894251 Received: 2015.03.27 Reduction of Airborne Bacterial Burden in Accepted: 2015.05.04 Published: 2015.08.13 the OR by Installation of Unidirectional Displacement Airflow (UDF) Systems Authors’ Contrib ution: ACDEF 1 Sebastian Fischer 1 Department of Hand, Plastic, and Reconstructive Surgery, Burn Center, BG Trauma Study Design A Center Ludwigshafen, University of Heidelberg, Ludwigshafen, Germany ADF 2 Martin Thieves Data Collection B 2 Division of Hospital Hygiene, Darmstadt Clinic, Darmstadt, Germany ADE 3 Tobias Hirsch Statistical Analysis C 3 Department of Plastic and Reconstructive Surgery, Burn Centre, BG University Data Interpr etation D DE 1 Klaus-Dieter Fischer Hospital Bergmannsheil, Ruhr University Bochum, Bochum, Germany Manuscript Preparation E 4 Department of Hygiene, University of Applied Science, Giessen-Friedberg, ABCD 4 Helmine Hubert Literature Search F Germany ABD 4 Steffen Bepler Funds Collection G ACDEF 4 Hans-Martin Seipp Corresponding Author: Hans-Martin Seipp, e-mail: Hans-Martin.Seipp@tg.fh-giessen.de Source of support: Departmental sources Background: Intraoperative bacterial contamination is a major risk factor for postoperative wound infections. This study in- vestigated the influence of type of ventilation system on intraoperative airborne bacterial burden before and after installation of unidirectional displacement air flow systems. Material/Methods: We microbiologically monitored 1286 surgeries performed by a single surgical team that moved from operat- ing rooms (ORs) equipped with turbulent mixing ventilation (TMV, according to standard DIN-1946-4 [1999], ORs 1, 2, and 3) to ORs with unidirectional displacement airflow (UDF, according to standard DIN-1946-4, an - nex D [2008], ORs 7 and 8). The airborne bacteria were collected intraoperatively with sedimentation plates. After incubation for 48 h, we analyzed the average number of bacteria per h, peak values, and correlation to surgery duration. In addition, we compared the last 138 surgeries in ORs 1-3 with the first 138 surgeries in ORs 7 and 8. Results: Intraoperative airborne bacterial burden was 5.4 CFU/h, 5.5 CFU/h, and 6.1 CFU/h in ORs 1, 2, and 3, respective- ly. Peak values of burden were 10.7 CFU/h, 11.1 CFU/h, and 11.0 CFU/h in ORs 1, 2, and 3, respectively). With the UDF system, the intraoperative airborne bacterial burden was reduced to 0.21 CFU/h (OR 7) and 0.35 CFU/h (OR 8) on average (p<0.01). Accordingly, peak values decreased to 0.9 CFU/h and 1.0 CFU/h in ORs 7 and 8, re- spectively (p<0.01). Airborne bacterial burden increased linearly with surgery duration in ORs 1–3, but the UDF system in ORs 7 and 8 kept bacterial levels constantly low (<3 CFU/h). A comparison of the last 138 surgeries before with the first 138 surgeries after changing ORs revealed a 94% reduction in average airborne bacterial burden (5 CFU/h vs. 0.29 CFU/h, p<0.01). Conclusions: The unidirectional displacement airflow, which fulfills the requirements of standard DIN-1946-4 annex D of 2008, is an effective ventilation system that reduces airborne bacterial burden under real clinical conditions by more than 90%. Although decreased postoperative wound infection incidence was not specifically assessed, it is clear that airborne microbiological burden contributes to surgical infections. MeSH Keywords: Environment, Controlled • Operating Rooms • Ventilation Full-text PDF: http://www.medscimonit.com/abstract/index/idArt/894251 2743 4 4 19 Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Background In our previous study, we demonstrated that bacterial con- tamination of the surgical field under real clinical conditions Postoperative wound infections are one of the most common is significantly lower with unidirectional displacement airflow complications after surgery. In Germany, 225 000 postoper- (UDF) compared to turbulent mixing ventilation (TMV) sys- ative wound infections are recorded annually, representing tems [10]. However, ORs included in the study were each sit- 1.8% of all performed surgeries [1]. Besides a prolonged heal- uated in different hospitals, leading to differences in the OR ing process, extended in-patient hospital stay, and addition- team as well as their surgical approach and spectrum, and, al surgeries, wound infections can lead to serious complica- thus, are factors that can significantly influence intraoperative tions such as sepsis or even death. Although their origin is not bacterial contamination. clearly defined, wound infections are most likely due to multi - ple causes. The systemic distribution of microbial pathogens The purpose of this study was to assess the intraoperative air- and intraoperative bacterial contamination are highly suspect- borne bacterial burden in surgeries performed by a single sur- ed to be the main factors causing surgical infections. Whether gical team that initially utilized ORs ventilated by turbulent airborne or attached to skin particles of the OR team, these mixing ventilation systems and subsequently switched to ORs pathogens directly or indirectly reach the surgical field during with ventilation systems according to the principle of unidirec- surgery [2]. Cecsey et al. showed that a square centimeter of tional displacement airflow. As there were no other changes, skin carries 2300 microorganisms on average, and that a per- except of the ventilation system, the effects shown are only son loses about 10 000 dead skin scales per day [3]. Although based on this technical change. To the best of our knowledge, these data were not assessed in an intraoperative setting, they no study thus far has compared has these 2 ventilation sys- provide a reference value for the expected OR team-related tems in such a controlled setting. bacterial burden in the surgical field. Contamination of the surgical field occurs not only direct - Material and Methods ly, but also indirectly, for example, through instruments or gloves. However, indirect contamination depends on air qual- Theatres ity as well. Chosky et al. demonstrated that sterilized OR in- strument are contaminated to a higher extent depending on The following ORs were included in this study: the ventilation system [4]. Therefore, a lower bacterial burden in the air of the OR should reduce direct and indirect contam- ORs 1–3 were equipped with air canopies with supported noz- ination of the surgical field. zles in a special turbulent mixing ventilation (TMV) system, ac- cording to DIN-Standard 1946-4 (1999) [11]. Each TMV system Two types of OR ventilation systems are currently available: was installed 3.1 m above the floor. The supply air volume was 3 3 turbulent mixing ventilation (TMV) and laminar airflow (LAF). 2200 m /h in OR 1 and OR 2 and 1600 m /h in OR 3. ORs 1–3 While the former (TMV) reduces bacterial concentration by had an ambient volume of 103 m each. streaming sterile and filtered inlet air into the surgical field and thereby provokes turbulent mixing with contaminated air, After construction of the new surgical wing of the hospi- laminar airflow (LAF) follows the opposite principle [5,6] with tal, 2 ORs with new ventilation systems were created (ORs 7 sterile filtered inlet air flowing with low turbulence from the and 8), which functioned according to the principle of unidi- ceiling, displacing the contaminated air without cross-con- rectional displacement airflow (DIN-Standard 1946-4, annex tamination [7]. In contrast, LAF systems with very low turbu- D 2008) [9]. The size of the each ceiling was 3.2×3.2 m and lence (<5%) are established for cleanrooms, and a compara- supply air volume was 9000m /h. In both ORs, flow stabiliz - ble ventilation system is available for ORs – the unidirectional ers were installed at the ceiling 2.1 m above floor level. OR 7 displacement airflow (UDF) systems. Although UDF has high - had an ambient volume of 94 m and OR 8 had an ambient er turbulence (5–20%) compared to LAF, they are still able to volume of 112 m and both were connected to vestibules. OR achieve an airborne bacterial burden of less than 1 CFU/m equipment, including medical devices, clothes, supplies, and in- under experimental conditions [8,9. However, the extent of struments, remained the same after moving into the new ORs. pathogen reduction compared to other OR ventilation sys- tems and under real clinical conditions is hard to evaluate. According to DIN 1946-4, each ventilation system involved in The type of surgery, the number of attending staff, and the this study was maintained on a regular basis (every 3 years) individual approach to performing surgery differ significantly by means of particle number measurements as well as inspec- among hospitals, making valid comparison of evaluated bac- tions of tightness of fit and integrity of all filter components terial numbers difficult. to warranty optimal performance, efficacy, and safety, and to facilitate comparison over the entire study period. Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 1. Overview of operating room (OR). Turbulent mixing ventilation Unidirectional displacement airflow System (TMV) (UDF) Name OR-1 OR-2 OR-3 OR-7 OR-8 Ceiling size [m ] – 3.2×3.2 3.2×3.2 Supply air [m /h] 2.200 2.200 1.600 9.000 9.000 Ambient volume [m ] 103 103 103 94 112 Number of surgeries 243 465 440 62 76 Mean value [min] 77 102 92 114 88 IC- Standard deviation 68 81 73 80 68 time Variation coefficient 88% 79% 80% 70% 78% TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time. Sedimentation ORs with their respective ventilation systems: short (<35 min), middle (36–75 min), and long (>75 min) IC time. Variance compar- Sterile sedimentation plates (ICR plates, item number: 03075e ison was verified by Levene test (F-test). Mean value discrepan - Heipha Dr. Müller GmbH Co., Eppelheim, Germany) were ex- cies were then tested for statistical signic fi ance by t test; p<0.05 posed on the instrument table. Scrub nurses positioned and was defined as significant and p<0.005 as highly significant. opened the plates in the sterile area. Plates were opened at the beginning of surgical incision and were closed at the To increase comparability of the situation before and after end of suturing (sedimentation period = incision-to-closure switching ORs, the last 138 surgeries in ORs 1–3 were com- time [IC time]) in accordance with the objectives of the stan- pared to the first 138 surgeries in ORs 7 and 8. Thereby, the dards DIN-1946-4 [9] and ISO-14698-1 [12]. The cover plates airborne bacterial burden in each OR and each surgery was were affixed with tape and labeled immediately after surgery. calculated and correlated to the IC time. Accompanying data sheets included the documentation of pa- tient information, duration of surgery (IC time), surgical pro- cedures, and plate numbers. Results For 48 h, ICR plates were incubated at a temperature of 37°C For the comparison of both ventilation systems, we performed (Incubator type B12, Heraeus Holding GmbH Co., Hanau, measurements in 5 ORs over a period of 6 years in the same Germany). The colonies grown were then counted numerical- hospital. A total of 1286 surgeries were performed and a cor- ly as colony-forming units (CFUs). responding number of sedimentation plates were used (1 plate for each surgery). The mean value of IC time was 94.6 min and Statistics varied between 77 min (OR 1) and 114 min (OR 7) (Table 1). The primary result parameter of the CFUs was matched to the Bacterial contamination analyzed ORs. The calculation of mean value, median, varia- tion coefficient, and standard deviation was completed. The Turbulent mixing ventilation (TMV) determination of the trimmed mean value (percentile range 85–95%) was used to eliminate outliers. IC time was harmo- In ORs 1, 2, and 3, we analyzed 243, 465, and 440 surgeries, nized to 60 min and the bacterial count was calculated (CFU/h) respectively. IC time ranged from 77 min (OR 1) to 102 min in accordance with the objective of the standard DIN-1946 (an- (OR 2) on average. Mean bacterial burdens were 6.5, 8.1, and nex F) to compare the airborne bacterial burden (in CFUs) be- 7.5 CFU in ORs 1, 2, and 3, respectively, and reached a maxi- tween the various ORs. The t test was used for pairwise com- mum of 121 CFU (OR 2). Trimmed mean values were 16.6, 18.5, parison of harmonized CFUs. and 17.1 CFU in ORs 1, 2, and 3, respectively. Detailed results are given in Table 2. Comparing ORs 1–3 with each other, no Three groups were created, based on different IC times and for statistically significant differences in airborne bacterial bur - comparison of the intraoperative bacterial transmission of the 5 den or harmonized bacterial burden were detectable (p>0.05). Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 2. System comparison of ventilation systems. Turbulent mixing ventilation Unidirectional displacement airflow system (TMV) (UDF) Name OR-1 OR-2 OR-3 OR-7 OR-8 Mean IC-time [min] 77 102 92 114 88 Mean value 6.5 8.1 7.5 0.3 0.4 Standard deviation 7.0 9.3 7.8 0.6 0.6 Median 4 5 5 0 0 CFU Minimum 0 0 0 0 0 Maximum 36 121 58 2 2 Trimmed SD (0.85–0.95) 16.6 18.5 17.1 1.0 1.0 Mean value 5.4 5.5 6.1 0.2 0.4 Standard deviation 4.3 6.3 9.2 0.4 0.9 Median 4 4 4 0 0 CFU/h Minimum 0 0 0 0 0 Maximum 23 101 96 1.7 6.7 Trimmed SD (0.85–0.95) 10.7 11.1 11.0 0.9 1.0 TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time; CFU – colony- forming units. Unidirectional displacement airflow (UDF) In OR 7, 62 surgeries were performed, with a mean IC time of 114 min. In OR 8, the 76 surgeries performed had an average IC time of 88 min. Therefore, mean airborne bacterial burdens were 0.3 and 0.4 CFU for OR 7 and 8, respectively, reaching a maximum of 2 CFU in both ORs 7 and 8. Trimmed mean value was 1 CFU for both ORs 7 and 8. Detailed results are shown in Table 2. In contrast, both OR 7 and OR 8 had no statistical- ly significant differences in airborne bacterial burden or har - monized bacterial burden (p>0.05). Comparison of ventilation systems OR-1 OR-2 OR-3 OR-7 OR-8 IC time was harmonized to 60 min and a calculation of the cor- responding bacterial count was performed to compare the 2 different ventilation systems. For turbulent mixing ventilation Figure 1. Comparison of bacterial burden in ORs 1–3 (turbulent mixing ventilation) with ORs 7 and 8 (unidirectional (TMV), bacterial burdens harmonized to 1 h were 5.4, 5.5, and displacement airflow). Brackets indicate statistical 6.1 CFU/h for ORs 1, 2, and 3, respectively, and reached maxima significance (p<0.05). of 23, 101, and 96 CFU/h, respectively. Trimmed mean values of harmonized airborne bacterial burden were 10.7, 11.1, and 11 CFU/h for ORs 1, 2, and 3, respectively. In contrast, airborne 1 CFU/h in ORs 7 and 8, respectively. Detailed results are pre- bacterial burden of ORs with unidirectional displacement air- sented in Table 2. Each OR with turbulent mixing ventilation flow (UDF) varied from 0.2 CFU/h in OR 7 to 0.4 CFU/h in OR 8, (ORs 1–3) demonstrated a statistically significant (p<0.005) and reached a maximum of 6.7 CFU/h in OR 8. Trimmed mean higher bacterial burden per hour compared to both ORs with values of harmonized airborne bacterial burden were 0.9 and unidirectional displacement airflow (ORs 7 and 8, Figure 1). Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU/h Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 3. Comparison of the last 138 surgeries in ORs 1–3 with the first 138 surgeries in OR 7 and 8. system Turbulent mixing ventilation (TMV) Unidirectional displacement airflow (UDF) Name OR1–3 OR7+8 Number of surgeries 138 138 Mean [min] 89 100 IC-time Standard deviation 74 75 Mean value 6.1 0.4 Standard deviation 5.7 0.6 Median 4.3 0 CFU Minimum 0 0 Maximum 26.3 2 Trimmed SD (0.85–0.95) 13.6 1 Mean value 5 0.3 Standard deviation 5.3 0.7 Median 3.8 0 CFU/h Minimum 0 0 Maximum 31.9 6.7 Trimmed SD (0.85–0.95) 10.8 1 TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time; CFU – colony-forming units; SD – standard deviation. Importantly, the large differences in maximum values of air - Last 138 vs. first 138 surgeries borne bacterial burden per h within the same study group were based on outliers. To increase reliability of comparing the 2 ventilation systems, the last 138 surgeries of ORs 1-3 (group A) were compared to the first 138 surgeries of ORs 7 and 8 (group B). Thereby, mean IC times were 89 min and 100 min for groups A and B, respectively. Mean airborne bacterial burden in group A was 6.1 CFU, ranging from 0 to 26.3 CFU and a trimmed value of 4 13.6 CFU. For group B, mean airborne bacterial burden was 0.35, with a minimum of 0 CFU and a maximum of 2 CFU, and a trimmed value of 1. Mean bacterial burden harmonized to 1 h was 5 CFU/h and 0.29 CFU/h for groups A and B, respec- OR1–3 OR7–8 tively. Detailed results are presented in Table 3. Comparing the 2 groups, group A had a significantly higher (p<0.005) air - borne bacterial burden than group B (Figure 2). Figure 2. Comparison of bacterial transmission of the last 138 surgeries in ORs 1–3 with the first 138 surgeries in ORs 7 and 8. Brackets indicate statistical significance Impact of surgical procedure duration (IC) on bacterial (p<0.05). burden The gathered data were analyzed. Surgical procedure duration to increased IC time, the bacterial burden constantly rose in (IC time) was divided into 3 groups: short (<35 min), middle ORs with turbulent mixing ventilation (ORs 1–3), whereas bac- (35–75 min), and long (>75 min) surgical procedures (Table 4). terial burden in ORs with unidirectional displacement airflow These groups were compared with the data collected. In relation (ORs 7 and 8) remained low over the study period (Figures 3, 4). Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU/h Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Table 4. System comparison with respect to surgery durations. Turbulent mixing ventilation Unidirectional displacement System (TMV) airflow (UDF) Name OR-1 OR-2 OR-3 OR-7 OR-8 Number of surgeries 61 73 88 7 13 Mean value IC-time [min] 26 26 25 21 21 Short IC-time Standard deviation IC-time 6 7 8 8 8 (<35 min.) Mean value CFU 2.5 2.8 3.5 0 0.3 Standard deviation CFU 1.9 2.2 5 0 0.6 Number of surgeries 115 160 149 17 26 Mean value IC-time [min] 56 56 55 54 52 Middle IC-time Standard deviation IC-time 11 12 12 9 11 (36 to 75 min.) Mean value CFU 4.9 5.7 4.7 0.4 0.3 Standard deviation CFU 4.4 10 3.9 0.6 0.5 Number of surgeries 66 220 191 38 37 Mean value IC-time [min] 143 162 151 159 137 Long IC-time Standard deviation IC-time 80 79 73 71 68 (>75 min.) Mean value CFU 12.9 11.8 11.8 0.4 0.4 Standard deviation CFU 9 8.9 9.2 0.6 0.6 TMV – turbulent mixing ventilation; UDF – unidirectional displacement airflow; IC-time – incision-to-closure time; CFU – colony- forming units. Discussion Turbulent mixing ventilation It is obvious that bacterial contamination of surgical wounds (TMV), ORs 1–3 Unidirectional displacement should be avoided as much as possible. As postulated by airflow (UDF), ORs 78 Soots et al. 30 years ago, 98% of bacteria found in wound in- fections originated directly or indirectly from airborne con- tamination [13]. In this context, Fitzgerald and Washington reported that the degree of airborne contamination depends on the number of persons and the physical activity of the OR team [14]. Strong physical activity during surgery leads to lib- eration of about 10 000 particles per min and 10% of these bacteria persist in the air longer than half an hour. According to Salvigni et al., presence of humans in the OR is without dis- 0 020406080100 120 140160 pute the biggest source of contamination [15]. Reducing the IC-time (min) number of medical personnel in the OR is difficult, so optimi - zation of ventilation systems is the best option to reduce bac- terial contamination in the OR. In our latest study we also used Figure 3. Comparison of turbulent mixing airflow systems (mean values of ORs 1–3) with unidirectional displacement sedimentation plates according to national and internation- airflow systems (mean values of ORs 7 and 8) in als standards [9,12] and demonstrated that unidirectional dis- correlation to surgery durations. IC-time – incision-to- placement airflow (UDF) significantly reduces bacterial burden closure time, CFU – colony-forming units. in the OR compared to other ventilation systems [10]. Besides having the lowest bacterial counts per h, the UDF system was Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Figure 4. Comparison of turbulent mixing airflow in ORs 1–3 with unidirectional displacement airflow in ORs 7 and 8, both in correlation to surgery durations. IC-time – incision-to-closure time, CFU – colony-forming units. 20 OR 7 OR 8 OR 1 OR 2 OR 3 04 1005 200 300 00 00 IC-time (min) able to constantly maintain airborne bacterial burden inde- the bacteria become airborne and induce drafts that are un- pendent of surgery duration. Furthermore, in agreement with comfortable for the OR team [17]. The dependence of TMV sys- the results of Thomas and Meierhans, we found the highest tems on the room volume is also disadvantageous because in- airborne bacterial burden in ORs equipped with a window- flow of sterile filtered air aims to reduce of bacterial burden, based ventilation system without filters or prevention of tur - not to replace contaminated air [18]. bulence [16]. Although our results showed the superiority of UDF, some limitations were seen retrospectively. Because in- To confirm compliance with the current standard for TMV vestigations were simultaneously performed in different ORs systems, a 99% reduction in airborne bacterial burden in ORs and, especially, with different OR teams, reduction of bacterial must be achieved within 25 min (recovery time). In contrast, burden cannot be attributed solely to the ventilation system. the same reduction is obtained by UDF systems in less than 8 s by a flow velocity of 25 cm/s out of the ceiling [19]. The aim of the present study was to determine the impact of ventilation system type on bacterial burden by comparison We demonstrated that UDF significantly reduces airborne bac - under similar conditions. Therefore, we performed investiga- terial contamination of the surgical site in comparison to TMV tions in the same institution involving the same OR team be- (0.29 vs. 4.98 CFU/h). Whereas TMV leads to linear increase fore and after switching from ORs with turbulent mixing ven- over time, UDF was able to maintain airborne bacterial burden tilation (TMV) to ORs with unidirectional displacement airflow at constantly low levels. Considering the conditions of mea- ventilation systems (UDF). Thereby, the surgical spectrum and surement (identical surgical spectrum, equipment, and staff), procedures remained identical and reduction of airborne con- this effect results mainly from the installation of the UDF ven - tamination was solely attributed to the ventilation system. tilation system. The main principle of UDF is to replace contaminated air by Limitations of this study include lack of specification regarding discharging sterile filtered air coming from the ceiling into the bacterial pathogenicity and relevance for the clinical outcome protection zone (PZ) [7]. The PZ is defined as the area beneath after surgery. The significant reduction of bacterial contami - the ceiling in which the surgical procedure is performed, in- nation might be clinically irrelevant because obvious wound cluding personnel and instrument table. Discharge occurs with infections probably do not depend on bacterial counts in the low velocity to avoid turbulence and to replace the potentially surgical field, but rather on concomitant diseases or the gen - contaminated air without mixture and without cross-contam- eral condition of the patient. OR wound infections only oc- ination. The latter is the main difference from turbulent mix - cur at a certain threshold of bacterial counts in the surgical ing ventilation systems (TMV), which have been the criterion field, which is not achieved by TMV or UDF ventilation sys - standard in ORs for several decades. Directly streaming ster- tems. Therefore, further studies are necessary to evaluate the ile filtered air via outlets into the surgical field (with different effect of ventilation systems on postoperative wound infec - types depending on the manufacturer, e.g., iron pipes) is the tions. Investigations in the literature have not accounted for only way to reduce bacterial burden by TMV [6]. A reduction co-morbidities, limiting the usefulness of results. of bacterial burden is thus required by mixing sterile filtered air with contaminated air. To provide the maximum mixture, Nevertheless, the results of the present study clearly show the TMV systems create turbulences by streaming with high ve- significant impact of ventilation systems on airborne bacteri - locity out of the supply air. High turbulences, however, make al burden during surgery. Indexed in: [Current Contents/Clinical Medicine] [SCI Expanded] [ISI Alerting System] This work is licensed under a Creative Commons [ISI Journals Master List] [Index Medicus/MEDLINE] [EMBASE/Excerpta Medica] Attribution-NonCommercial-NoDerivs 3.0 Unported License [Chemical Abstracts/CAS] [Index Copernicus] CFU Fischer S. et al.: UDF systems reduce intraoperative airborne bacterial burden MEDICAL TECHNOLOGY © Med Sci Monit, 2015; 21: 2367-2374 Conclusions postoperative wound infections, it is clear that microbiologi- cal contamination causes these infections. The unidirectional displacement airflow, which fulfills the re - quirements of standard DIN-1946-4 annex D of 2008, is an Conflict of interest effective ventilation system that reduces the airborne bac - terial burden under real clinical conditions by more than The authors state no conflict of interest. 90%. Although we did not specifically assess the incidence of References: 1. 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Medical Science Monitor : International Medical Journal of Experimental and Clinical ResearchPubmed Central

Published: Aug 13, 2015

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