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.