key: cord-1014409-0avcgu6w authors: Matsubayashi, R. N.; Harada, S.; Tominaga, M. title: Investigation of ventilation conditions associated with CO2 concentration changes in ultrasonographic exam room from the perspective of COVID-19 infection control date: 2021-03-02 journal: nan DOI: 10.1101/2021.03.01.21252598 sha: 8146e282f2bfff56ffd9f28eb7c0181419148293 doc_id: 1014409 cord_uid: 0avcgu6w Objectives Ventilation is an important factor in preventing COVID-19 infection. To clarify the state of ventilation in ultrasonic exam rooms, as an index of ventilation rate, the carbon dioxide (CO2) concentration in our exam rooms was measured. Methods We measured the CO2 concentration in each exam room before the examination and 0-15 minutes after end of the exam. The subjects were 70 cases (abdomen: 24, breast: 16, neck: 16, and musculoskeletal: 14). In infant cases, one parent accompanied the patient during the examination. Results The highest CO2 concentration was 2261 ppm, observed after the breast examination. In all cases, the CO2 concentration in the exam room was highest immediately after the examination or two minutes after. Almost all cases had recovered to within 120% of the pre-examination CO2 concentrations within 15 minutes after the examination. The average CO2 concentration after ultrasonography was significantly higher for breast examinations than others. Conclusions Even in a hospital with modern ventilation equipment, the CO2 concentration in the ultrasound room was high after the exam and it takes 15 minutes to recover to the pre-exam state. Care must be taken to ensure adequate ventilation in ultrasonographic facilities. The COVID-19 pandemic is ongoing worldwide, including in Japan. At the outbreak's beginning in Japan, many factors regarding the transmission route were unclear. However, since early March 2020, we have taken prompt measures in consideration of the probable airborne transmission route. Infection control within the Ultrasound Department is important to prevent hospital-related transmission of SARS-CoV-2. The environmental factors that increase the risk of spreading SARS-CoV-2 are now becoming clear, and knowledge about infection from asymptomatic individuals has been accumulated. Initially, close contact and respiratory droplets were suggested as the main transmission routes of SARS-CoV-2 [1] . Several studies have provided evidence for airborne transmission of viruses, showing that closed, crowded, and poorly ventilated environments contribute to viral transmission [2, 3, 4] . Recently, airborne transmission has been pointed out as an important pathway for the spread of SARS-CoV-2 [5, 6, 7, 8] . Many . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint 3 research results have indicated that environmental ventilation is an important factor in protection against the spread of COVID-19 [9, 10] . Although ventilation equipment is generally designed according to the standards of modern hospitals, complex arrangements and small exam rooms can result in inadequate ventilation in practice. Considering this situation, the air quality of indoor environments should be emphasized [10] . To prevent nosocomial infection, it is particularly important to understand the ventilation situation in hospitals and to implement countermeasures against the spread of COVID-19. Therefore, we measured carbon dioxide (CO2) concentrations in each exam room to assess the effect of subjects' respiration on room air quality. Because the examiner was present during the ultrasound examinations, the CO2 concentration in each room reflects the respiration of both the subject and the examiner. Thus, we also measured the CO2 concentration in the exam room when only the examiner was present for 10 minutes and compared the result to the situation when the subject was also present. Furthermore, in cases of infants and children aged less than 10 years, a single attendant was present during the examinations, and the observed concentration values are attributable to the respirations of all individuals present. In this study, we measured the CO2 concentration in the exam rooms in the absence of the patient. No information that identifies the individual patient was used. Therefore, the Institutional Review Board of the National Hospital Organization Kyushu Medical Center determined that no ethical review was necessary because the study did not involve human subjects. Our ultrasound center consists of 9 small exam rooms, which are separated by fixed partitions with little space above the partitions (Fig. 1) . . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) Each exam room is equipped with air intake and exhaust vents connected to the central ventilation system that was originally installed in each room, which meets the ventilation standards of the Japanese Building Code. All of these exam rooms and the hospital's facilities meet Japanese legal environmental standards; however, no evaluation of individual exam room air quality was conducted under actual clinical conditions. The subjects were 70 cases (abdomen: 24, breast: 16, neck: 16, and musculoskeletal (MSK): 14). In the cases of infants and children (abdomen: 6 and musculoskeletal: 6), one attendant accompanied the patient during the examination. In this study, we investigated the CO2 concentrations in each exam room before and after the ultrasound examinations. Changes in CO2 concentration over time were investigated at multiple time points after completion of the exams. Measurements were conducted using a multifunctional portable air quality tester (WYZXR Air Quality Monitor, Multifunctional Indoor Pollution Detector Meter). The air quality tester was positioned in the flat part of the ultrasound machine, just between the subject and the examiner (Fig. 2) . . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint The height of the air quality tester was 120 cm from the floor, the room temperature was 22-24°C and the humidity was 40%-45%. Each exam room had an area of 12-15 m 2 . All of the exam room doors were kept open and ventilated when ultrasound examinations were not being performed. After the CO2 concentration was measured before each examination, the ultrasound examination was performed with the door closed. After the examination, the CO2 concentration was measured at 0-15 minutes (0, 2, 4, 6, 10, and 15 minutes) after the end of the exam. One minute after the end of the examination, the door of the exam room was opened to allow air exchange with the aisle. For statistical analysis, Bonferroni/Dunn multiple comparison tests were used, with a significance level of p<0.005. The average duration of each examination was 10.3±5.6 minutes (3-26 minutes). There were no . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint 6 differences in examination time between body sites. The highest observed CO2 concentration was 2261 ppm, which was observed after breast examination. The CO2 concentration was significantly higher in breast examinations than other examinations at all time points after the examination ( Fig. 3) . . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. In half of breast examination cases, the highest CO2 value was shown 2 minutes after the examination. All six infant abdominal cases had the highest observed CO2 concentration 2 minutes after the examination. In other cases, the highest CO2 concentration was observed immediately or 2 minutes after the examination, and the value then decreased over time. A comparison of mean and maximum CO2 concentrations during post-test measurements among the sites showed that the breast had the highest values (p<0.0001) ( Table 1) (Fig. 4) . . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint 9 Except in the case of the single examiner alone in the exam room, the lowest mean and maximum CO2 concentrations were significantly lower in neck examinations. Both mean and maximum concentrations were significantly higher in the presence of an attendant than with the subject alone (mean concentration: p=0.0017, maximum concentration: p=0.007) (Fig. 5) . We compared the ratio of the CO2 concentration at each time point after the end of the test to the CO2 concentration before the start of the test. The mean CO2 concentration at all sites had recovered to within 120% of the pre-test CO2 concentration at 15 minutes after the end of the test, but the value was higher in . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint the case of the breast at all time points, and the concentration was still significantly higher 15 minutes after breast than neck examinations ( . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint (Fig.6 ). In the case of the examiner being alone in the room, CO2 concentrations were unchanged throughout all time phases, with a maximum of 103% of the pre-test value (immediately after the end of the test). In the present study, we measured the CO2 concentration in ultrasound exam rooms with the aim of evaluating the ventilation in ultrasound rooms under real clinical conditions. The results show that CO2 concentrations were elevated by breast examinations and the presence of an attendant in pediatric cases. In contrast, CO2 concentrations remained low during neck examinations compared with those of all other areas. A possible reason for the lack of elevated CO2 concentrations is that the subjects did not vocalize during the neck examinations. In contrast, in breast and pediatric cases, the examiner needs to talk to the patient or attendant to understand the lesion's location and symptoms, possibly influencing the increase in CO2 concentration. Examinations of the abdomen, which require repeated inhalation/exhalation during the test, showed lower CO2 concentrations than those of the mammary gland, suggesting that CO2 concentrations may be elevated by vocalization and speech. The observed changes in CO2 concentration over time suggest that air conditions would not recover to their pre-exam state for about 15 minutes in the absence of forced ventilation, suggesting that mechanical ventilation or a circulator to create air flow would be desirable. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint The current study has several limitations: it is a study of a single facility and a specific environment, and more precision-controlled methods are required for a rigorous assessment of air quality. We measured CO2 concentrations before and after testing in relatively small ultrasound rooms and examined the concentration ratios and changes over time. Even at a hospital with modern ventilation equipment, the CO2 concentration in the ultrasonic exam room rises immediately after the examination, and it takes at least 15 minutes to recover to the approximate concentration observed before the examination. In ultrasonographic facilities, care must be taken to ensure adequate ventilation. The data that support the findings of this study are available from the corresponding author, RM, upon reasonable request. Our ultrasound center consists of 9 small exam rooms, which are separated by fixed partitions with little space above the partitions. Each exam room had an area of 12-15 m 2 . The schematic diagram of CO2 measurement in each laboratory. The air quality tester was positioned in the flat part of the ultrasound machine, just between the subject and the examiner. The height of the air quality tester was 120 cm from the floor. Comparison of the ratio of the CO2 concentration at each time point after the end of the test to the CO2 concentration before the start of the test. The mean CO2 concentration at all sites had recovered to within ±20% of the pre-test CO2 concentration at 15 minutes after the end of the test, but the value was higher in the case of the breast at all time points, and the concentration was still significantly higher 15 minutes after breast than neck examinations. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted March 2, 2021. ; https://doi.org/10.1101/2021.03.01.21252598 doi: medRxiv preprint Airborne transmission of covid-19 Bioaerosol Sampling for Respiratory Viruses in Singapore's Mass Rapid Transit Network The risk of airborne influenza transmission in passenger cars Role of air distribution in SARS transmission during the largest nosocomial outbreak in Hong Kong. Indoor Air Aerosol and surface distribution of severe acute . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity respiratory syndrome coronavirus 2 in hospital wards Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1 Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals Indoor Air Quality: Rethinking Rules of Building Design Strategies in Post-pandemic Architecture How can airborne transmission of COVID-19 indoors be minimized?