Impact of Operating Room Ventilation on Particle Elimination in Proximity under Realistic Settings

MUCHUAN NIU, Haoxuan Chen, Jonathan Liu, Chi-hong Tseng, John Shin, Nir Hoftman, Yifang Zhu, University of California, Los Angeles

     Abstract Number: 218
     Working Group: Indoor Aerosols

Abstract
During the COVID-19 pandemic viral particle transmission via pulmonary aerosol has created enormous risks for healthcare workers (HCWs) in the operating room (OR). The ventilation system in the OR is one of the main means of reducing particle contamination and preventing surgical site infection (SSI). Published studies on the effectiveness of OR ventilation systems were generally conducted in experimental conditions and the particle number concentration (PNC) at different distances from the source has yet to be characterized.

To assess the function of the OR ventilation in a real-world setting, we recruited 40 patients going into elective surgery and sampled particles generated from a saline nebulizer at three different locations during induction of general endotracheal anesthesia. The nebulizer source was placed at the head area of the surgical table. The first sampling location was 0.6 m from the nebulizer laterally on the opposite side of the table. The other two sampling locations were 0.8 and 1.0 m apart from the nebulizer, representing the locations of the anesthesiologist’s and medical assistant’s faces, respectively. For each patient, a total of five sampling sessions were designed to compare the PNCs under different patient and physician activities. Results showed that at 1 m from the source, significantly lower PNC levels (~ 300 particles/cm3) were observed compared to the other two locations. The decay rate at 0.8 m from the nebulizer was significantly higher than the other two locations when the nebulizer was turned off, suggesting greater ventilation efficacy at the anesthesiologist’s location. Modelling results of factors that affect decay rate are to be reported. Our results under realistic OR settings suggest relatively smaller particle exposure risk at further distances from the particle source; while particles were removed more rapidly at the anesthesiologist location, which is likely dependent upon the ventilation system’s airflow.