PT  - JOURNAL ARTICLE
AU  - Brochu, Vincent
AU  - Bouchard, Pierre-Alexandre
AU  - Veillette, Marc
AU  - Turgeon, Nathalie
AU  - Lellouche, François
AU  - Duchaine, Caroline
TI  - Evaluation of the Impact of Gas Humidity on Expiratory Filtration During Invasive Mechanical Ventilation
DP  - 2023 Oct 01
TA  - Respiratory Care
PG  - 3950870
VI  - 68
IP  - Suppl 10
4099  - http://rc.rcjournal.com/content/68/Suppl_10/3950870.short
4100  - http://rc.rcjournal.com/content/68/Suppl_10/3950870.full
AB  - Background: Expiratory filtration are required to avoid contamination of the air in ICU rooms of patients under invasive mechanical ventilation. Usual filtration tests are conducted for large particles (3,000 nm), while smaller particles may carry several viruses. SARS-CoV-2 virus size is about 100 nm and may be carried with particles of any size, including particles smaller than 1,000 nm. The impact of gas humidity to evaluate the filtration efficiency for different particle size is unknown. Methods: On a test bench simulating dispersion of aerosols with particles ranging from 29 to 5000 nm, we evaluated the filtration efficiency of an HMEF, a HEPA filter, and an HME: DAR Hygrobac S, Draeger Twinstar HEPA and HumidStar 55. Devices were placed one at the time in the test bench. Aerosols were generated from a buffer suspension containing two model viruses: φX174 and MS2. Viral aerosols passed through the filter at a dry and humid air flow of 60 L/min. Absolute humidity of dry and humid gases were approx. 7 and 30 mg H2O/L. Particle counters and air samplers were placed upwind and downwind of the filter. Particles were counted and infectious viruses were quantified upwind and downwind to calculate the filtration efficiency for both particles and viruses. The maximal filtration efficiency sensitivity in this test bench is 99.99%. Results: Main preliminary results are shown in the figure. The filtration efficiency is reduced for small particles below 1,000 nm. With dry gases, filtration is reduced for particles below 1,000 nm, while with humid gases, filtration is reduced for particles below 500 nm. For particles of 300 nm, filtration efficiency was below 95%. The filtration efficiency is significantly higher with HEPA filter in comparison with HMEF. The HEPA filter filtration was 99.99%/99.99% with dry air, while the HMEF filtration was 99.09%/98.87% with dry air and 99.48%/99.56% with humid air for PhiX174 and MS2 respectively. HME filtered less than 60% for particles and viruses, which may be related to high flow used. Conclusions: Gas humidity has an impact on filtration efficiency. Particles under 300nm are not entirely filtered with the tested HMEF. However, the infectious viruses are present in smaller quantities reflecting that many unfiltered particles do not contain viruses. However, with HMEF, the filtration efficiency based on cultivable viruses do not attain expected results (above 99.999%). The clinical impact of this reduced filtration is unknown. Figure A shows the filtration efficiency regarding the size distribution of particles at different relative humidity. This graph shows particles only. Figure B shows the filtration efficiency for infectious viruses and for particles ranging from 29nm to 5000nm. Filtration efficiency means are shown for each triplicate.