Expiratory filter sets substantially reduce exhaled small bioaerosol particles and potential COVID-19 virus load

ABSTRACT

Aim/Introduction: Airborne infections are particularly challenging for in-patient care units. In general, hospitals take more precautions to prevent airborne spread of diseases and several guidelines recommend expiratory filters during nebulizer therapies to reduce exhaled bioaerosols. However, a substantial reduction of virusloaded aerosols depend on a high filter performance for particles 100 -500nm in size. This study aimed to test the effectiveness of filter pads in the reduction of exhaled aerosols by applying 99mTclabeled graphite aerosol. Material(s) and Method(s) In 37 patients with suspected pulmonary embolism or CTEPH an inhalation scintigraphy was performed with 99mTc-labeled graphite aerosol (Technegas ©, particle size 30 -60nm ). The exhalate was filtered by a PARI filter/valve set equipped with a PARI filter pad and then collected in a plastic bag reservoir. Count rates of the filter pads and reservoirs were estimated by planar imaging within a SPECT/ CT. In addition, the individual volumes of the exhaled air were determined. The percentage filter efficacy of the filter pads was calculated. Finally, correlational statistics (Spearman's correlation) addressing the following interactions were performed (1) exhalate volume and count rates of the filter pads, (2) filter pads' count rates and filter retention efficacy, and (3) exhaled breath volume and filter retention efficacy. Result(s) Mean count rates of the filter pads and the reservoirs containing the filtered exhalate were 26023 +/- 8327 cts/s and 169 +/- 153 cts/s, respectively. The efficacy of the PARI filter/ valve set with PARI filter pad was 98.5 +/- 0.9% (range 96.2 -99.7%). The mean exhaled volume was 9.5 +/- 4.6 l (range 2.4 -21.0 l). The exhalate volumes positively correlate with the filter pad count rates (p=0.006) which, in turn, negatively correlate with the filter pad efficacy (p=0.04). However, an inter-relation of exhaled breath volume and filter pad efficacy failed to reach significance (p=0.07). Conclusion(s) The filter pad of the PARI filter/valve set demonstrated a high retention rate of aerosol particles < 100nm in size. Therefore, in patients suffering from respiratory infections these filter pads used in expiratory filters are suitable to substantially reduce airborne virus load, e.g. COVID-19 SARS CoV2, in their exhalates. Additionally, we found evidence that the filter retention efficacy decreased with increased filter particle load indicating a need for regular filter changes.