Hospital ventilation as a form of control over the spread of airborne viruses

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Researchers from University Hospitals of Leicester NHS Trust in the UK and Turku University of Applied Sciences in Finland have examined the risks posed to healthcare workers treating patients with viruses that can be transmitted through the air and how different forms of ventilation can protect those treating patients.

The study, called Reducing aerosol infection risk in hospital patient care, was commissioned and published by the Institution of Occupational Safety and Health (IOSH) as the risks to frontline healthcare workers when caring for patients with viruses are well known – yet less known is the optimal design of mechanical ventilation systems.

Under different ventilation, distance and PPE settings, laboratory experiments were carried out using a breathing thermal manikin as the patient and computer simulation to assess contaminated and supply airflow.

It found that if the healthcare worker is leaning over a patient lying on a bed in an isolation room – for example, to check blood pressure, pulse rate of temperature – the air the patient breathes out flows directly towards them. In a room with mixing ventilation, this means their exposure level rises by up to six times, significantly increasing their chance of infection.

The researchers found that local downward ventilation can reduce this exposure to one third of the exposure found with a general mixing ventilation. However, consideration has to be given into how this is designed and where it is placed to minimise discomfort for patients, for example from draughts such a system creates.

The report adds that the position of the exhaust plays a role in healthcare worker protection, in addition to supply air distribution. In this study, the most effective exhaust positions were in the wall behind the patient bed or in the lighting panel above and behind the patient.

It is hoped the findings can lead to more informed and evidence-based environmental control methods such as well-positioned ventilation, which is considered more effective than the use of personal protective equipment.

Mary Ogungbeje, Occupational Safety and Health Research Manager at IOSH, says: “This important research highlights the risks that healthcare workers face when they are treating patients infected with airborne viruses as well as how these risks can be managed.

“No one should have their safety and health put at risk by the work they do. Many people working in healthcare have to come into contact with patients who are infected with contagious viruses, so it is crucial that effective systems are in place to protect them.

“Our study suggests that some forms of ventilation, particularly local downward ventilation, can be efficient in managing the risks together with the use of personal protective equipment. We hope, therefore, that further research will be conducted to build on these findings and help protect many healthcare workers from being exposed to viruses and potentially becoming ill.”

The research also found that the use of nebulisers and oxygen masks with side vents by patients may pose additional risks to healthcare workers. Ideally, they should not enter the room while such therapy is ongoing for a patient with a confirmed respiratory infection – except to turn on or turn off such treatment. If they do have to enter the room during such treatment, they should regard this as an exposure to a potential virus and wear an FFP2 or FFP3 mask.

Dr Julian Tang, Consultant Virologist at the University Hospitals of Leicester NHS Trust and Honorary Associate Professor at the University of Leicester, says: “The most effective form of control is the ventilation engineering level of control. That means that we have to try and improve the amount of clean air in the environment compared to the amount of contaminated air.

“The research has shown that there are certain types of ventilation – beyond just different speed and volume of ventilation – that can benefit healthcare workers better without being detrimental to the patient. This report has tried to highlight those particular designs to show that if you are going to build a new hospital with new isolation rooms, these sorts of design are what you might want to follow.

“Obviously it’s difficult to modify existing isolation rooms to these new findings and some existing facilities will be easier to modify than others, but if you know what the optimal ventilation design and strategy is, you can work towards it.”

Fiona Potter, Vice-Chair of IOSH’s Health and Social Care Group, says: “The research evidences what many people would instinctively understand; that the closer you are to an infected patient and the less ventilation available, the higher the risk factors. Hence why there is a requirement for healthcare staff to wear FFP3 and FFP2 masks and full PPE, when undertaking Aerosol Generating Procedures (AGPs).

“The research could provide a valued input into future design and location of ventilation systems in isolation wards and may provide a steer if the Heath and Technical Memorandums on Specialised Ventilation for healthcare premises, are revised.”

Download the full report here.



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