A Quantitative Study of Particle Dispersion Due to Respiratory Support Modalities in Pre-Hospital and In-Hospital Critical Care Environments

Abstract

RATIONALE: Patients with COVID-19 may require supplemental oxygen and non-invasive respiratory support devices during pre-hospital aeromedical transport as well as in-hospital intensive care units. It is unclear whether these therapies increase the dispersion of potentially infectious bioaerosols and placing health workers at increased risk. METHODS: The studies were conducted in two environments: (1) fixed-wing air ambulance cruising at 25,000 ft;(2) a simulated critical care unit in hospital. A breathing patient simulator consisting of a medical mannequin exhaling nebulized particles from the lower respiratory tract was connected to a ventilator to simulate a patient with mild-moderate respiratory distress. Aerosolized saline and DNA bacteriophage φX174 were used to model aerosol dispersion in the aeromedical and simulated intensive care unit, respectively. Dispersion of 1.0 μm particles were measured in key locations, due to the three respiratory support modalities including;non-invasive bilevel positive pressure ventilation (BiPAP);high-flow nasal oxygen (HFNO);and nasal prongs. In the simulated intensive care unit study, viability of aerosolized bacteriophage φX174 was quantified using plaque assays (Fig. 1) RESULTS: In both environments, particle concentrations were highest close to the simulator's mouth and declined with distance from the mouth. In the aeromedical environment, nasal prongs (with a surgical mask) were associated with the highest particle concentrations and BiPAP the lowest. In that environment, at a location near the mouth, particle concentrations associated with HFNO with a surgical mask (5.5 × 104 particles/L of sampled air) and BiPAP (7.5 × 103 particles/L) were significantly lower when compared to nasal prongs with a surgical mask (1.2 × 105 particles/L) (each P < 0.05). In the simulated intensive care unit, HFNO was associated with the highest particle concentrations and BiPAP the lowest. In this environment, at a location near the mouth, particle concentrations as well as bacteriophage viability associated with nasal prongs (7.4 × 104 particles/L and 1.6 × 104 PFU/L) and BiPAP (1.1 × 104 particles/L and 1.9 × 102 PFU/L) were significantly lower when compared to HFNO (5.3 × 105 particles/L and 2.6 × 104 PFU/L) (each P < 0.05). CONCLUSIONS: These findings highlight the comparable risk of dispersing particles among respiratory support devices and the importance of appropriate infection prevention and control practices and personal protective equipment for healthcare workers when caring for patients with transmissible respiratory viral infections such as COVID-19. These findings also suggest a comparable risk associated with use of nasal prongs and HFNO in both environments.