A Simple Screening Test of Filtration Efficiency for Protecting the Gas Sampling Line from CoronavirusUsing Fluorescent Microspheres

Brustowicz, Robert M.; Yuki, Koichi

BACKGROUND: During the corona virus pandemic, preventing contamination of the anesthesia machine, critical to avoid cross‐contamination between patients, has proven challenging when treating premature infants and neonates. While attaching a HEPA filter to the endotracheal tube will protect the anesthesia machine and the gas sampling line from contamination, this contributionto the dead space makes ventilation of these small patients challenging. Direct filtration of the gas sampling line eliminates this problem;however, appropriate filters are not readily available. AIMS: Identify a small filter capable of filtering outparticles of a size similar to the SARS‐CoV‐2 virus for the gas sampling line. METHODS: We used fluorescence microspheres suspended in a solution for a challenge test to determine the filtration efficiency of various filters. The microspheres varied in diameter (0.02 µm, 0.042 µm, 0.109 µm and 0.989 µm). A fluorescence plate reader was used to evaluate the degree of fluorescence intensity in the flow‐through from various filters and referenced to the fluorescence intensity of the input. RESULTS: AHEPA filter,as recommended as an anti‐viral filter, effectively filtered all the particles tested. The B. Braun PERIFIX Flat Epidural Filter was the second most effective filter, filtering particleslarger than 0.042 µm.Other filters tested did not filter fluorescence microspheres equivalent in size to a single coronavirus particle (0.07 µm). CONCLUSIONS: Although the Food and Drug Administration (FDA) has not approved the Flat Epidural Filter for use as an anesthesia machine gas filter, our simple challenge test suggests that it could be used to effectively filter the anesthesia gas sampling line.