Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland

Transcription

1 Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland Paper ID 0081 ISBN: Effectiveness of an integrated air flow unit for an instrument table in an operating theatre Frank Behnke, Seyed H. Sagheby, Birgit Müller HTW Berlin, University of Applied Sciences, Berlin, Germany * Corresponding FrankBehnkeBerlin@gmail.com SUMMARY The objective of the study is a rethinking in the field of asepsis for surgical theatres regarding conventional ventilation engineering and their acceptance procedure. The focus of the study is on the efficiency of an instrument table with integrated local laminar airflow (LAF). Using air velocity measurements, a specially developed visual testing procedure and particle counts, the effectiveness of the instrument table was tested in different positions in a research surgery theatre. The study presents the possibility of the contamination of the instrument table s surface area through particles released in the head area of the surgical staff. In other cases, a positive effect of the local ventilation system on the table was observed. However, it became apparent that several factors have a significant impact on the effectiveness of an integrated local ventilation system. These factors need to be taken into account to actually achieve a contamination free table surface. The key factors are the length of the table, the position of the table relative to the protected area in the operating room, and the position of the contamination source. KEYWORDS Local ventilation concepts, asepsis in surgical theatres DIN , acceptance procedure for surgical theatres 1 INTRODUCTION The follow-up treatment of post-surgical wound infections leads to significant costs for health insurances every year. Post-surgical wound infections pose a serious threat for many different types of surgeries, and often lead to a lot of suffering by patients. One cause of such wound infections is the contamination through airborne dust particles or bacteria-carrying skin particles from the surgical team. Many local ventilation systems have been developed and tested with the aim of lowering the chance of infection so far. Instrument tables with an integrated local ventilation system are comparatively new in this area. These tables promise to create a sterile environment for surgical instruments, even in challenging areas with an increased contamination risk (e.g. outside the protected area) In this study, such an instrument table has been tested in the research surgery room of the HTW- Berlin with a low turbulence uni-direction ceiling airflow system (also called the Laminar Airflow unit from the ceiling: LAF-Ceiling) using realistic contamination release points. Several scenarios have been explored, mainly regarding the variations of the position of the instrument table in the surgical theatre.

2 In some already exiting studies with similar instrument tables with local ventilation concepts the air was supplied from the front side of the tables, (see e.g. Report [ Prüfbericht Nr.: HP Luzern, 2011] ) in each case the required protective effect was proven according to DIN (the German standard for ventilation in buildings of health care System). The study was based on the grade measurement as it is described in the DIN The study conducted measurements for different positions of the table in a research environment and reported dominantly positive effects of the instrument table with integrated local ventilation. In the present study, also, different positions for the instrument table in the surgical theatre were chosen. The source of contamination was, however, considered to be mainly a person near the instrument table. The source of contamination is actually not only on the floor - as normally carried out in the grade measurement - but also from the head area. This area as a source of contamination seems to be more realistic in some aspects than a contamination from floor area because the head and neck area of the surgical staff are often not sufficiently covered by surgical clothing. Assuming the main source of contamination in this area will also bring more challenges considering the laminar airflow from ceiling units above the surgery bed. This can also be the case for the instrument table when it is located inside the protected area. Furthermore, there can be turbulent flows caused by people moving during the surgery as well as by surgery lighting and other objects leading to a less effective removal of contaminated air. This all can lead to a higher risk of contaminations for instruments positioned on the table before they are used in the surgery. In a further publication about a similar instrument table with the title Possible contamination by instruments in surgery theatres during implantation of hip and knee joint endoprosthesis (U.Quint, 2016) the instrument table was positioned outside the protected area. With the growing number of medical equipment, surgery staff and instrument tables, the protected area of 3 3 m under the LAF-ceiling is not sufficient to accommodate all equipment. The instrument table is sometimes not only outside the protected area but more critically located on the borderline between the protected area and the remaining area in the surgery room (as will be shown here). The interaction of the outflowing air from the LAF-ceiling with the air outside the protected area results in an increased turbulence which could in turn increase the possibility of cross contamination on the table. Generally, it seems logical to keep only the areas contamination-free which are critical, e.g. the wound area and the instruments. This provides numerous advantages. The general ceiling-laf can then be used for the air-conditioning, pressure maintenance and the removal of heat and humidity loads and pollutants like anaesthetic gases. 2 MATERIALS/METHODS In this study the local ventilation concepts of the instrument table is studied using different methods. The following methods are used to find answers for the research questions: For the screening of the overall air velocity distribution on the instrument table an anemometer was used to measure the velocity in 343 points to create and visualize a quasi-3-dimentional air velocity field. This enabled us to find the causes of cross contamination on the table on the basis of air velocity magnitude and possible turbulences on different points on the table. The instrument table was also examined by a visual test procedure to find out its performance at different positions in the surgery theatre. This means that visible test aerosols were released near the table with minimal initial turbulence. The release points were alternatively the floor or the head area behind a dummy which was positioned near the table. The thermal properties of

3 the dummy used near the table matched that of a standing human. Using several cameras, the possible cross contamination on the table surface could be documented from different angles. Finally, a particle count was carried out on the table surface. This allows to clearly observe the difference between the contamination levels in case of particle release from the floor or from the head area. It also revealed where instruments on the table surface are best saved from contamination. 3 RESULTS The study has shown that the contamination avoidance on instrument table has different qualities. The most crucial factors thereby are the position of the table in the surgical theatre and the position of the source of contamination. Speed or the impulse of the local airflow protecting the table are additionally important. A contamination release from the head area had its most obvious negative effect when the instrument table was poisoned outside the protected area but close and parallel to the border of this area. The released test aerosol from the head area of the dummy was pressed down and sideward by the ceiling-laf to the ground (see Figure right) and therefore on the instrument table surface. This disturbs the horizontal less strong local airflow from the table ventilator significantly which results in an ineffectiveness of the local table airflow unit. Laminar ceiling airflow Figure 1. left: Position of the table: border line of the protected area, measurement points M1, M2 and M3 (particle count measurements). right: Disturbance at the border line of the protected area (purple coloured), the local LAF from the table is on, blue arrow: spreading direction of the aerosols. Figure 2 shows the relative amount of contamination (particle count) to the sum of all counted number particles in both experiment cases of contamination release from head and from floor area. This Figure shows the relative amount of particles during each test in percent. This is a special approach for rapid evaluation for this experiment. During these tests the table was poisoned outside the protected area, close and parallel to the border of this area (see Figure 1 left). The measurement points were positioned on the table surface starting with M1 close to the local air outlet, M2 in the middle and M3 a position at the end of the table. It is obvious that the contamination due to a release from the head area is much higher compared to the case in which the source of aerosol contamination is from the ground. It can be assumed that the grade measurement can be passed only much harder if the source of contaminations are generally in the head area.

4 C/C total % contamination area: floor contamination area: head M1 M2 M3 M1 M2 M3 Figure 2. Relative distribution of the measured aerosol concentration on the measurement points on the instrument table (number of particles in a measuring point divided by the total count of particles for all points in two cases). Contamination from the head area in comparison to the floor area, with a local LAF unit on the instrument table. It can be said that, in most cases aerosols crossed the table edge when they were supported by a sideward flow crossing the loner edge of the table (see Figure 3) especially in areas near the front part of the instrument table (between 0-15 cm from the local LAF unit) and near the end of the table. The position and angle of the LAF unit at the table and the table s length result in unnecessary problematic areas on the table surface :39 interface of the protected area, source of contamination: head area with local laminar airflow dummy direction of the local air supply direction of the contamination direction of the local air supply aerosols crossed the table edge Figure 3: Poison of the table: outside the protected area but close and parallel to the border of this area (see Figure 1). Left: top view of the table. Right: side view of the table, with local LAF turned on and source of contamination at the head area. table surface The observations above can be explained by the measured velocity field. Figure 4 shows the velocity measurements at different heights above the table surface. The manufacturer gives a protection air speed of about 0.4 m/s. As it can be seen at heights above 400 mm and lower than 100 mm this air speed cannot be maintained. Additionally, there were air turbulences measured in these areas resulting in an increase in the possibility of cross contamination, if contaminated sideward airflows reach the table edges.

5 direction of the air supply Figure 4: Air velocity field above the table area On the base of these findings it can be explained that the position of the instrument table clos and parallel to the border of the protected area is particularly unfavourable in case of contaminated air flowing (or being pushed) towards the table surface. The best visual results (the lowest contamination rate) was seen when the table was positioned outside the protected area and perpendicular to the wall of the operation theatre (see Figure 5). instrument table with integrated local laminar airflow (LAF) contamination source at the height of 1,75 m behind a heat dummy The protected area of the operation theatre Figure 5: The most effective positioning of the instrument table according to the visual test series. Also, tests inside the protected area have shown that the local LAF provides benefits over conventional instrument tables when moving the table near a source of contamination at the head area (see Figure 6).

6 Figure 6: Instrument table with local LAF moving through a contaminated area. 4 DISCUSSION The authors believe that the concept and the development of local ventilation methods for surgery rooms is generally a positive trend. They have significant advantages in many areas compared to conventional settings. Using local ventilation concepts can result in a higher efficiency of contamination suppression. Especially when a high number of medical equipment, operation staff and instrument tables are in the surgery room (which may also disturb the LAF from the ceiling), local ventilation concepts can help preventing particles and germs in critical areas. Operation costs could be decreased by a combination of ceiling LAF and local ventilation concepts through lowering the necessary volume flow rate of the ceiling LAF unit. The developments in this area should be followed in order to decrease the growing number of postoperative wound infections. Also, in order to reach positive effects, the use of local concepts should always be accompanied by user-friendly well-documented instructions for the medical staff. 5 CONCLUSIONS Besides giving valuable insights into the importance of the positioning of instrument tables with local LAF in the operation theatres, the results of this study show that the assumed position of the contamination source is of great influence for measuring the protective effect of a ventilation system in an operation theatre. The local ventilation unit on the table can lower the chance of contamination especially when the instrument table is located well outside of the protected area. Generally the areas close to the border of the protected area are not appropriate parking positions for instrument tables. The most favourable position was perpendicular to the protected area when the contamination source was standing at the longer edge of the table. Acknowledgements: We would like to thank Prof. Frank Reichert and Tobias Fries of the HTW-Berlin s research surgery theatre for their valuable support during the measurements. 7 REFERENCES DIN Deutsches Institut für Normung e.v., Raumlufttechnik Teil 4: Raumlufttechnische Anlagen in Gebäuden und Räumen des Gesundheitswesens, Berlin: Beuth Verlag. GT, Prüfstelle, Prüfbericht Nr.: HP Zwischenbericht, Luzern: s.n. U.Quint, Mögliche Instrumentenkontamination im Operationssaal während der Implatation von Hüpft- und Kniegelenkendoprothesen. Orthop Unfall, Issue 154, pp. 157 R. Oestenstad, L. Perkins,1992. An assessment of critical anthropometric dimensions for predicting the fit of a half-mask respirator, American Industrial Hygiene Association, pp.639