The HILLSIDE:Reference desk for COVID-19 Infrastructure
ICU Ventilation for COVID-19:
Assuming the virus is a low risk from an aerosolization point of view is it worth investigating the use of HEPA filters to purify the air in the room where we accommodate the COVID-19 patients? The same question can be asked with regards to the use of UV.
Is it not better to try and reduce the virus within the room, rather than filtering the air through a HEPA filter.
- The existing HVAC places our ICU is under positive pressure. For risk management when housing COVID patients, we wish to convert it to negative pressure. Any advice/ pointers?
- Please provide advice on recirculating air in an ICU, under COVID-19?
"It became clear to me that the spread of COVId-19 is directly connected to the spread of the active virus. Having been Hospital engineer at a 1200 bed local hospital, I am acutely aware that virus longevity depends on, inter alia.:
- actual time that virus is inside its transmission-carrier fluid,
- actual temperature during its transmission, and
- concentration of the virus in carrying fluid (as fluid may evaporate).
Could you consider providing a guideline on these time/temperature characteristics of the virus?
Only thereafter could architects, engineers etc. identify effective risk-reducing protocols. This could lead to more financially-justifiable 'anti-Corona' measures
Discussion
These questions are mostly unanswerable at the moment but I can try to help you understand what is known, and what a prudent response would be. In all likelihood, we will be able to look back and say we overreacted in the name of patient safety, but we should be wary of being criticised in hindsight of not having the best interests of our staff and patient at heart.
SARS-COV-2 is understood to preferentially droplet spread. Some evidence exists that it might be contact spread but there is no convincing evidence that it is long-range airborne in the sense of droplet nucleation such as with TB. Evidence of short-range airborne transmission has been reported, but this should be seen in the context of droplet spread. Laboratory studies have shown that the virus can remain viable in air for extended periods[1], but no support for this outside of lab settings have been found. Correlations between culture viability, particle size and the infectious quantum were not made in this study. This makes its application to real-world settings premature.
Studies which have found the virus in air, ducting and on extraction fans have so far failed to prove that the virus found was still viable. Making that assertion is like assuming that the bacon in my freezer means that pigs live there. It has been suggested that high temperature and humidity would reduce the spread of the virus. The temperature ranges suggested (>30°C) are beyond what we could endure in an ICU but the humidity ranges of between 40-60% are achievable. The high humidity slows the nucleation of the viral droplet and increases its settling speed, thereby reducing its range.
Much of the work being done to understand the transmission mechanism of COVID-19 is focussed on community transmission. It is important to remember that transmission in an ICU will not be the same as in homes and workplaces. The conditions and procedures in ICUs could promote transmission. Firstly, in a COVID ICU unit, the contamination source strength is much higher than other spaces since infected patients are congregated there and these are presumably very ill patients with high viral shedding. Secondly, procedures like intubation are release high quantities of aerosolised particles, unlike general talking or coughing. Additionally, viral shedding through talking and coughing can be more readily mitigated than from intubation.
Until viability studies have been conducted of viral particles found in ventilation systems, no firm guidance can be offered regarding the reduction of viability or radially spread particles. Until that time I think it would be prudent to assume that the virus should be considered as airborne within the ICU only. This would affect how we treat the ventilation in the COVID-ICU but not the pressurisation of the ICU. I believe that air recirculated within an ICU should always be (H13) HEPA filtered for reasons beyond just COVID, so assuming your systems are designed in accordance with the IUSS BES guide, There should be no reason to change
--Tobyvan (talk) 11:16, 19 May 2020 (SAST)
- ↑ Neeltje van Doremalen, Trenton Bushmaker, Dylan H. Morris, Myndi G. Holbrook, Amandine Gamble, Brandi N. Williamson, Azaibi Tamin, Jennifer L. Harcourt, Natalie J. Thornburg, Susan I. Gerber, James O. LloydSmith, Emmie de Wit, and Vincent J. Munster, “Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1,” The New England Journal of Medicine (2020), DOI: 10.1056/NEJMc2004973 [1]
- ↑ Po Ying Chia et al, 2020 (Preprint) “Detection of Air and Surface Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Hospital Rooms of Infective Patients,” medRxiv preprint (2020), https://doi.org/10.1101/2020.03.29.20046557 [2]
