INF ECTION P R EVENTION
Calls to re-examine ventilation in hospitals
David Hartley supports a more critical appraisal of ventilation requirements in patient care areas, in light of the pandemic. He argues that air movement and clean-air flow pathways should be given the consideration they deserve in modular buildings increasingly used by health Trusts to more rapidly provide additional facilities.
New research has once again cast a spotlight on the dangers of infection faced by medical staff dealing with COVID-19 patients, and the changes which might be implemented to protect them. A research report Aerosol emission from the respiratory tract: an analysis of relative risks from oxygen delivery systems, published in February 2021,1 makes the case for more effective PPE for clinical staff, and more efficient ventilation to disperse and remove airborne particles. Dr. James Dodd, a consultant senior lecturer in respiratory medicine at North Bristol Lung Centre and the University of Bristol, led the study which suggests that coughing by COVID patients is putting staff at greater risk of catching the virus than had been previously thought. The study set out to quantify aerosol generation in both continuous positive airways pressure (CPAP) and high-flow nasal oxygen (HFNO) and compare it to breathing,
speaking and coughing without these supports. CPAP and HFNO are widely used modes of oxygen delivery and respiratory support for patients with severe COVID-19, and both are considered high-risk aerosol generating procedures. But there is limited high quality experimental data characterising aerosolisation during oxygen delivery and respiratory support. This is the first study to report on aerosol emission from patients with active COVID-19, with previous work on primates only.
In the recent study, CPAP (with exhalation
port filter) produced less aerosols than breathing, speaking and coughing (even with large >50L/m facemask leaks). HFNO was found to emit aerosols, but the majority of these particles were generated from the HFNO machine, not the patient. HFNO-generated particles were small (<1µm) passing from the machine through the patient and to the detector without coalescence with respiratory
aerosol, thereby unlikely to carry viral particles. Coughing was associated with the highest aerosol emissions with a peak concentration at least 10 times greater than the mean concentration generated from speaking or breathing.
As a consequence, the risk of SARSCoV-2 aerosolisation is likely to be high in all areas where patients diagnosed with or developing COVID-19 are coughing. The study suggests guidance on personal protective equipment policy should reflect these updated risks, and more effective ventilation of patient areas could also contribute to staff safety. The exact size range of aerosol particles responsible for airborne transmission (and the ability of virus to survive in these particles) continues to be debated, but it is clear that the dispersion of particles smaller than 5µm is largely determined by the room ventilation (air exchange) rate, thereby posing a potential risk to those even not in close contact, especially in poorly ventilated areas. Other research into Coronavirus has also highlighted the dangers of transmission via aerosol-based routes and droplets carried in exhaled breath, which means appropriately engineered ventilation and airflow management is increasingly critical. The most recent research published in
February has not yet been peer reviewed, but it has already led to new demands for better protective equipment – including FFP3 respirator masks – for staff caring for patients who are in the earlier stages of COVID-19. The report states: “Our data strongly
support an equal or even greater risk of SARS-CoV-2 infection via the aerosol route for healthcare workers providing care to patients with COVID-19 on acute medical units, general medical wards or in the emergency department rather than those on critical care wards, suggesting policy on PPE
APRIL 2021
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