MEDICAL GAS PIPELINE SYSTEMS
Oxygen concentrator helps meet surge in demand
Like many large acute hospitals, London’s Charing Cross Hospital in west London has seen increased oxygen demand over the past six months, and in March, with the coronavirus pandemic beginning to ramp up, its Estates team found the site’s existing oxygen VIE (Vacuum Insulated Evaporator) was already beginning to struggle to meet demand, and would not be capable of meeting the predicted COVID-19 surge demand. As HEJ reports, when two already overstretched oxygen suppliers were unable to help upgrade the VIE, Imperial College Healthcare NHS Trust’s long-standing medical gas pipeline supplier, SHJ Medical Gas Specialists, stepped in to help with an oxygen concentrator-based solution.
In March this year – when the effects of the COVID-19 pandemic were beginning to hit the UK – the Estates Department at Charing Cross Hospital (part of the Imperial College Healthcare NHS Trust) started to prepare for the first influx of patients. While the oxygen infrastructure pipework at the hospital was good, the site’s Vacuum Insulated Evaporator (VIE) was struggling to supply the predicted surge requirements. Although technically capable of delivering 3,000 litres per minute, the vaporisers created a pinch point, bringing the supply down to just 1,833 L/min. The Trust contacted two major oxygen suppliers to request assistance with upgrading the VIE, or providing additional VIE plant, but, with their resources stretched nationwide, and directed primarily to new field hospitals, neither was able to help. Charing Cross Hospital was then facing the prospect of having to turn patients away.
Oxygen concentrator solution The Trust’s long-standing medical gas pipeline supplier, SHJ Medical Gas Specialists, suggested using an oxygen concentrator. Although common overseas, concentrators had rarely been used in a UK mainland hospital before, where the ‘tradition’ has generally been to rely on liquid oxygen stored in a Vacuum Insulated Evaporator. Rather than relying on stored liquid oxygen, a concentrator uses a compressor and a refrigerant dryer on the ambient air to generate a tank of air compressed to 7.5 bar. This air is then filtered and passed through a PSA (Pressure Swing Adsorber), which sieves and retains the oxygen, while discharging the waste nitrogen. The oxygen is stored in a buffer vessel and then used as normal. The concentrator supplied to Charing Cross had a theoretical maximum oxygen flow of 850 L/min.
The hospital decided to allocate the concentrator to one of its blocks, the Riverside Wing, which houses the hospital’s Acute Medical Admissions
The oxygen concentrator connection and distribution manifold, and emergency standby manifold, arrangement.
Unit, Day Surgery Ward, theatres, and Recovery, and in which new COVID beds had hurriedly been placed. Pipework was laid to enable the concentrator to supply the block independently, while retaining the connection to the main VIE to allow maximum flexibility. It also allowed generated oxygen to be supplied to the entire hospital site via a ring main in the event of total failure of the VIE.
The engineering challenges Plant space
As at most hospitals, space is at a premium, and there are not many plant rooms lying empty waiting to accommodate an oxygen concentrator. Charing Cross Hospital is no different, and so to overcome the problem, SHJ suggested a technique it had used before – housing the concentrators in two 40 ft metal shipping containers installed in the hospital car park. In an ideal world, the containers would have been pre-fitted out and placed in position already up and running. In this instance, however, given the urgency, the empty containers were craned into position and fitted out on site. Figure 1 shows the layout of the concentrator plant within the container: In addition to the new plant, an external wraparound ring main was created to increase oxygen carrying capacity to key wards. Figure 2 shows the configuration of the new plant within the hospital.
Oxygen purity Oxygen generator vessels.
While oxygen from a VIE will produce a nominal 99.6% purity, an oxygen concentrator produces at 93% +/–3% (i.e. the purity will range from 90% to 96%). With a lighter load a high purity is
October 2020 Health Estate Journal 39
©Estates and Facilities Management Dept, Imperial College Healthcare NHS Trust
©Estates and Facilities Management Dept, Imperial College Healthcare NHS Trust
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