ABSTRACT
<Background> With the global epidemic of COVID-19, there has been a growing concern about the risk of exposure to the virus among healthcare workers. Gastrointestinal (GI) endoscopy has been considered as one of the high infectious procedures because of the high risk of aerosol exposure. However, that caution is mainly directed at secretions and aerosols from the patient's mouth, and less attention is currently paid to air leaks from the endoscopic system itself. Although a few reports have been published on air leaks from GI endoscopic systems, no systematic and quantitative studies of air leaks have been conducted. Schlieren system is an optical device for visualizing minute changes in airflow that are invisible to the naked eye, by using differences in the refractive index of the medium, and has been mainly used in the field of engineering. We aimed to systematically evaluate air leaks from GI endoscopic systems using Schlieren system, and to determine the relationship between the amount of leakage and insufflation conditions including the types of biopsy valves. <Methods> The following experiments were performed on explanted swine stomachs while maintaining an intra-gastric pressure at each preset value. We attempted to visualize air leaks using System Schlieren (SS100, Kato Koken, Kanagawa, Japan). In all experiments, biopsy forceps were inserted and withdrawn 3 cm per 3 seconds. This action was repeated five times in each experiment. Experiment 1: Examined the feasibility of the Schlieren device in visualizing air leaks from biopsy valves. Experiment 2: The intragastric pressure was varied in the range of 4 to 15 mmHg and the air leaks were quantified and compared in each pressure. Experiment 2: Compared the air leaks between the types of biopsy valves, e.g. reusable, disposable, universal, deteriorated reusable valves after more than 10 times of uses. Image J (National Institute of Health, US) was used to measure the initial velocity and area of the leak on obtained images. The average values of initial velocity and leakage area over five sessions were calculated. For the leak area analysis, image analysis was performed for both forceps insertion and withdrawal. <Results> Experiment 1: Air leaks were seen at the moment of forceps insertion and withdrawal (Fig 1). Experiment 2: There was a linear relationship between intragastric pressure and initial velocity/diffusion range of the leak (Fig2A). Experiment 3: Disposable and deteriorated reusable biopsy valves had larger initial velocity/diffusion range of the leak (Fig2B). <Conclusions> We successfully visualized air leaks from GI endoscopic systems using the Schlieren system. We herein recommend the use of lower intragastric pressure at the times of insertion/withdrawal of forceps, and avoidance of using disposable/deteriorated biopsy valves, for less gas leakage and possibly less aerosol exposure.(Figure presented)Figure1. Visualization of air leak from biopsy valve(Figure presented)Figure 2. Results of analysis on air leakage from biopsy valve