MEDICAL GAS SYSTEMS
at each outlet point for CPAP patients, down to 15 L/min for ‘step-down’ patients. As treatment techniques became more refined, flow rate requirements reduced down to a maximum of 30 L/min for each outlet. However, we continue to test for a worst case scenario of 60 L/min. Using digital test gauges and metered leaks capable of adapting to different ports, we monitor and record the pressure as the flow increases. We also take into account the fact that some wards and ICUs will be occupied and unavailable for testing. With the cooperation of the AP and department managers, we ascertain the actual flow rates in use within those departments, and include them in our calculations.
The NHSI guidance also suggests using MEC flow and pressure drop testers to use as a ‘dial up’ variable orifice for loading the oxygen system. We do not believe that this is the optimal method for site-wide testing. Instead, we use sets of calibrated Amal jets and carriers to match the design flows and test flows required. This way, we can build a detailed picture of which wards and areas can deliver the best support to COVID patients. For some hospitals, the results add an additional layer of confidence in their system design and contingency plans.
Choosing the right COVID ward locations
It is also common, however, for hospitals to need to relocate patients to areas where pressure remains consistently high while the system is experiencing a high load. For example, we found that many designated areas would have been able to pass the 60 L/min standard when initially designed, but as we simulated patients
Inserting a test gauge into an oxygen valve for accurate flow measurement.
overflowing to other areas, the pressure would drop. This is not a problem of wards running out of oxygen – the VIEs generally hold up very well. It’s the system itself that was not designed to pass that flow.
When designating wards for COVID-19 patients, we recommend that hospitals avoid using departments or wards on radial branch lines towards the end of the run. Instead, we recommend ensuring that patients are located in proximity to larger diameter mains. Part of our work involves not just helping hospitals identify a ward capable of passing such high flow rates, but also helping them understand how many patients it can realistically supply without being overwhelmed. If we established that a ward was capable of drawing a total of 300 L/min, then it
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followed that its maximum occupancy would have been five patients requiring the highest volumes of oxygen.
Establishing the difference between capacity and demand
If relocating overflow patients is at one end of the scale of response to effective flow capacity testing, then at the other end are significant modifications to the oxygen pipeline’s infrastructure. We conducted a test at one hospital which had a system designed to deliver 2,500 L/min of oxygen. As part of our flow test, we calculated the flow rates for individual wards across the entire hospital, as well as meeting with the site’s engineers to outline the hospital’s COVID- 19 strategy. After referencing the existing site record drawings, we developed a
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