Arup has developed a CFD (Computational Flow Dynamics) model to optimise the flow field and the concentration/residual time of particles inside an operational shield developed by the MTC, Rolls-Royce and supported by Innovate UK, based on an idea developed by Dr Ian Renfrew, a leading interventional radiologist and Dr Paolo Perella, anaesthetic registrar at the Royal London Hospital, Barts Health NHS Trust.
Intubation and extubation
The transparent shield will be used when carrying out procedures that generate aerosols such as intubation and extubation on patients with COVID-19 or other infectious diseases transmitted in respiratory secretions and aerosols.
At the height of the pandemic in the UK in early April, the Arup team formed of Edith Blennerhassett, Dr Mohammad Tabarra, Dr Ertan Hataysal and Amir Pournasr were asked to lend their industrial aerodynamics expertise and assess the performance of the box in containing the spread of airborne viral particles.
Once the airpaths of the particles were visualised, the clear benefits of the shield could be demonstrated to all, leading to wider applications of the box in protecting the safety of the frontline medical staff.
Arup focused on simulations of the airflow patterns and the trajectories of a range of different size particles emitted from a typical COVID-19 patient during coughing and normal breathing cycles.
The aim was to optimise the location and extract rate of the suction inside the box, maximise the capture of the airborne particles and minimise the dispersion to the larger room, where other staff are present.
Various simulations have been carried out to investigate the particle behaviour within the shield compared to within the room without the shield.
The CFD simulations showed that the AGP shield traps more than 90% of all particles; about 97% of the larger particles (≥20 µm) adhere to the inner surfaces of the shield, and about 80% of the smaller particles (≤8 µm) are extracted from the box.
The effectiveness of the small particle removal enhances with the location of the internal suction tube and its extraction rate. All these findings have been collated and submitted to the 'British Journal of Anaesthesia' and are being published in other fora.
The results show the positive impact of multi-disciplinary collaboration between industry (Rolls-Royce and MTC), clinical teams (Dr Ian Renfrew and Dr Paolo Perella, and colleagues) and Arup engineers in honing the design of the AGP Shield.
a. Covid-19 particle distribution in the room with the presence of the AGP shield
b. Covid-19 particle distribution in the room without the presence of the AGP shield
The AGP shield box brings many benefits during the intubation/extubation procedures. The shield not only prevents the spread of particles that carry and transmit the virus, but also has the potential to speed up the number of patients that can be attended to.
With the shield box applied, far less of the pathogenic particles are dispersed in the large ITU room or operating theatre, so a much shorter ventilation purge time is required before the next patient can be attended to.
Analysing air circulation and particle removal has many applications in a COVID-19 world, expanding beyond hospitals and care settings to public transport, aircrafts, hotels, shops and many other businesses.
Find out more about Arup’s work supporting governments, public authorities and businesses to adapt, helping with the transition from crisis to recovery: https://www.arup.com/covid-19.