Managing ventilation in the context of COVID-19: a HIS audience-led webinar

The next in the series of the HIS audience-led webinar on all-things ventilation in the management of COVID-19 went out recently. The panel consisted of:

  • Peter Hoffman – Consultant Clinical Scientist, London
  • Dr Chris Lynch – Graham Ayliffe Training Fellow, Sheffield Teaching Hospitals
  • Professor Catherine Noakes – Professor of Environmental Engineering for Buildings, University of Leeds
  • Karren Staniforth – Clinical Scientist, Nottingham University Hospitals NHS Trust
  • Dr James Price (chair) – Consultant in Infection Prevention & Control and Antimicrobial Stewardship, Imperial College Healthcare NHS Trust

The webinar video is below:

I’ve had a shot at summarising the Q&A if you don’t have time to view the webinar in full.

Why is there so much controversy about defining AGPs? Several reasons:

  • It’s technically difficult to determine whether an infectious aerosol is generated by a given procedure.
  • Also, it’s tricky to distinguish whether an aerosol is infectious (i.e. contains a sufficient quantity of virus to transmit it to another person).
  • Many infectious aerosols are transient – so longer term sampling can be required to capture them.
  • It varies by organism. An AGP for influenza may not necessarily be an AGP for SARS-CoV-2.
  • It’s important to define the terms used – what do we mean by “aerosol”? (Typically a droplet < 5 µM in diameter.)
  • Fear was a driver for some people making ‘unconvincing’ cases for some procedures being an infectious AGP!
  • HPS have produced a helpful review on AGPs.

What is the role of ventilation in AGP risk and control in dentistry? Dental drilling is an undisputed AGP. Dilution through air changes is the key control measure in managing AGPs. And extract-only ventilation may help.

When is it safe to clean a clinical area after an AGP? PHE guidance suggests 2 air changes before entering an area without an FFP respirator following an AGP, but the panel felt 5 air changes would be a better rule-of-thumb to follow. As to when an area should be cleaned after an AGP, the panel felt that after 5 air changes would be a pragmatic rule-of-thumb to follow, but the rate of deposition of microbes in droplets and aerosols is poorly understood so it’s difficult to judge (5 air changes is probably on the conservative side).

Do all AGPs need to be performed in an isolation room? If you have a negative pressure isolation room, and you can, then it should be used for an AGP. If you have a single room that isn’t an isolation room, then you should use a single room. If you don’t have a single room, then staff in the vicinity would need to wear PPE suitable for AGPs. And the risk to other patients would need to be considered and managed. Positive pressure rooms should not be used for AGPs.

Do open windows, fans, or air conditioning units impact on the ventilation on a COVID-19 cohort ward?

  • Open windows are a good way to dilute infectious droplets and aerosols and should be encouraged (review here).
  • Fans don’t introduce contamination and only recirculate air, so should be ok if positioned sensibly. (Although I would be concerned about the unknown impact of changing airflows in the ward.)
  • Air conditioning units don’t affect the microbial quality of air (provided they are serviced correctly), and have a limited impact on air flows, so are a better option than fans.

Should we adjust ventilation in theatres when managing COVID-19 patients? No, a fully functional and balanced theatre ventilation air handling system provides optimal air flows and dilution – and should not be tinkered with! If theatre ventilation needs to be adjusted, it will need to be adjusted through a planned process and not just for COVID-19.

Are there any novel solutions to improve ventilation? Nothing dramatic is on the horizon! Although there are some promising air disinfection systems that are being evaluated.


Finally, just a heads-up that the next HIS audience-led webinar is this Wednesday (24/06/2020) on ‘The role of the environment in COVID-19 transmission(I’ll be a panellist along with Dr Lena Ciric, Dr Stephanie Dancer, and Dr Manjula Meda).


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s