HOSPITAL OXYGEN SYSTEMS
Hospital supply analysed in response to the pandemic
Carl-Magnus von Behr, a PhD student at the Institute for Manufacturing (IfM) at the University of Cambridge, Oliver Lambson, co-founder of a carbon fibre electric guitar start-up, Rubato Guitars, Moritz Meyer zu Köcker, Logistics project manager at MAN Trucks and Bus and a recent MPhil graduate in Industrial Systems, Manufacture, and Management from the University of Cambridge, and Tom Ridgman, who formerly delivered the latter MPhil course at the IfM, discuss a collaborative project to determine whether the hospital oxygen (O2
) infrastructure in the UK had sufficient capacity to supply the rapidly rising number of COVID-19 patients.
At the start of the COVID-19 pandemic, the Cambridge University Hospitals (CUH) NHS Foundation Trust contacted the Institute for Manufacturing, (part of the University of Cambridge Department of Engineering) for help in setting up PPE supply chains. This led to a much wider collaboration, including three teams of postgraduate volunteers stepping forward. One of the projects identified was to determine whether the hospital oxygen (O2
) infrastructure had sufficient
capacity. During the build-up to the UK’s first COVID-19 peak in April 2020, several NHS Trusts experienced challenges with their O2
supply by
exceeding the infrastructure’s designed maximum flow rate.1
NHS England
responded with an Estates and Facilities Alert on the 31 March,2 monitoring of the O2
suggesting close supply system to
prevent potentially catastrophic system failures due to capacity overloads. Prior to the pandemic, the largest CUH hospital, Addenbrooke’s, had 1,000 inpatient beds, including 45 for intensive care. The base case planning for the pandemic required a maximum of 44 ICU and 125 non-ICU beds. With many patients requiring oxygen treatment, the reasonable worst case admission plan would have been at least four times greater.
Identifying the key issues To meet the clinical requirements for gases such as O2
capacity to supply the rapidly rising number of COVID-19 patients. At the early stages of the pandemic, there was a strong focus on the need for extra ventilator capacity, but much less on whether hospitals had sufficient infrastructure to supply the additional O2
Liquid 2-phase Gaseous
A schematic diagram of the duplex VIE system and storage tanks at Addenbrooke’s Hospital in Cambridge.
for the local people of Cambridge, and specialist services for a regional, national, and international population with rare or complex conditions. Since then, the site has expanded continually, and is now part of one of the largest biomedical campuses in Europe. As a result of 60 years of continual expansion, the delivery capacity of the medical gas pipeline system (MGPS) at ward level was unclear. From a monitoring and control viewpoint, the only available data was the level in the supply tanks, the pipeline pressures, and the usage recorded by nurses on the wards. The team identified three key issues to comply with the NHS Alert: assessing and verifying the infrastructure, establishing accurate system monitoring, and determining the maximum number of treatable patients.
Assessing and verifying the infrastructure Bulk supply system
, medical gas pipeline
However, the first CUH estate was opened in 1962, with Addenbrooke’s Hospital - which provided both healthcare
systems (MGPS) are installed in hospitals. Their design principles are well documented in the HTM 02-01 A&B guidelines by the UK Department of Health.3,4
In March 2020, CUH had a duplex Vacuum Insulated Evaporator (VIE) system (one primary and one secondary VIE). The storage tanks had a capacity of 52 million litres [free air], which is sufficient to sustain normal O2
usage for over three
weeks. After independent research and consultation with the O2
supplier, the risk
for disruption of external supply was found to be small. Both VIEs have a spare set of vaporisers. While a single vaporiser would barely achieve 2000 L/min, both sets operating simultaneously reach a design capacity of nearly 4000 L/min. This capacity is reduced by icing, acting as insulation, and lower ambient temperatures. Technical specifications of the vaporisers surveyed suggest a potential throughput drop of 20% when reducing ambient temperature from 20˚C to 0˚C. Due to this dependency on the ambient temperature, the true capacity of a vaporiser will vary day by day depending on weather.
Control panel
Both VIEs have their own control panel, with a flow capacity of 3000 L/min each. The panels contain a pressure-regulating valve which is set to the standard design setting of 4.2 bar. Depending on the pipe sizes and valve types used, the control panel may be the bottleneck for the maximum system flow rate. A common distinction in installed hardware is between ‘standard’ panels, allowing a maximum of 3000 L/min, and ‘high-flow’ panels, allowing up to 5000-6000 L/min. With ample vaporiser capacity and two control panels it was initially proposed to run both the primary and the secondary
January 2021 Health Estate Journal 45
Gaseous (slow
evaporation in the tank)
Vaporiser Liquid Storage tank
~–160˚C ~12 bar
~20˚C ~12 bar
Control panel
Distribution ~20˚C
~4.2 bar
Heat exchange with ambient air
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