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With the increased use of ventilators during the Covid-19 pandemic, there have been fears that some hospitals are at risk of running out of oxygen

https://www.theguardian.com/society...-oxygen-coronavirus-patients#maincontent

Consequently, work is being done to estimate or calculate oxygen usage by such devices.

In its guidance on rapid conversion of existing wards into facilities for intubating COVID-19 patients (https://www.england.nhs.uk/coronavirus/publication/covid-19-standard-operating-procedure-estates/), NHS England uses an oxygen flow rate of 10 l/min when calculating the expected total flow during simultaneous demand. It is noted in this guidance that this should be offset against the original design and other departments that will still require the HTM 02-01 recommended diversified flow for areas such as: operating theatres, theatre recovery, critical care, ED resuscitation, etc (http://www.bcga.co.uk/assets/HTM_02-01_Part_A.pdf - page 23).

We can also attempt to determine oxygen requirements on an equipment model basis. For this, reference can be made to technical manuals (which may give guide values for oxygen flow directly or provide limits for oxygen concentration and flow rates) or to the literature. Care should perhaps be taken to appreciate that requirements of Covid-19 patients with regards to oxygen consumption may be different then considered in these technical documents and studies

List of some studies into oxygen consumption of ventilators:

https://www.ncbi.nlm.nih.gov/pubmed/19020137
https://academic.oup.com/milmed/article/179/12/1465/4159921
https://www.ncbi.nlm.nih.gov/pubmed/15920201
https://ccforum.biomedcentral.com/articles/10.1186/cc4410



Given the importance of maintaining a sufficient oxygen supply, work is also being done to try and reduce the oxygen consumption of the devices themselves. This may include the prioritised use of more efficient devices and the conversion of existing device to be driven by air rather than oxygen.


A couple of points to discuss:

• What is the best way of estimating the oxygen consumption by existing equipment?
• What steps can be taken to reduce the oxygen consumption of existing equipment?

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Savant
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Try driving as much as possible on medical air such as anaesthetic machines. Speak to your manufacturers and see if they have any suggestions or guidance.

Last edited by Dustcap; 08/04/20 11:41 AM.

30 years since the Chernobyl disaster and yet we still have no super heroes or zombies.
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Super Hero
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If PMG systems have been properly designed in the first place, with a correctly sized VIE etc. ... and have not simply been added to in an ad-hoc fashion over the years .... and proper maintenance has been carried out, then there should not be a problem.

Also, don't hospitals keep a reserve in cylinders these days?

The Guardian piece is misleading (what a surprise); there are lots of "almost" and "could have" there. Also, unless there has been more than one such case, I would not myself consider the hospital concerned as a "major London hospital".

Regarding the questions:-

1) The best way ... refer to the manual
2) Use less ... see Dustcap's post about entraining air

And the letter? Stating the obvious, I would have thought (or maybe just CYA).


If you don't inspect ... don't expect.
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If push comes to shove and pressure drop becomes an issue, it is also possible to "back feed" gas into the system.

If, for example you are using recovery as a temporary ICU then the shut off valves to that area can be closed, cutting it off from the main gas supply. Two 15 bottle O2 cylinder packs are then attached to a manifold and the output from the manifold fed into the wall O2 supply by a standard pipe/medical gas outlet fitting. Generally this would take up one bed space but such is life.

This will work as long as you can keep the area you are trying to supply fairly small otherwise the wardies are going to be shuffling bottle packs in and out all the time! This will reduce the demand on the main system hopefully restoring the necessary pressure. It also has the advantage that, if your shut off valves are leaking a little across themselves, well it's all O2 so it does not really matter.

Not in the rule book this one but necessity is the mother of invention (and also the really good band that played with Frank Zappa)!!

Dave


Thoughts and information provided on this forum are mine and mine alone and do not necessarily reflect the policy of NSW Health. They may also be complete bollocks!!
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Super Hero
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In one (sandy) place I worked, there was requirement to have (and practice) a "siege plan". We had two specially constructed four-wheeled trailers full of large (J-size) oxygen cylinders, towed by four-wheel drive trucks. Backed up by many full cylinders in a secure shed. The trailer itself was interesting; the design resembling bottles in a wine rack (that is, with cylinders near horizontal, for "ease of replenishment"). I wish I had a photo.

I have also seen "cubes" of cylinders of the type you mention, Dave ... able to be carted about by fork-lift (or, if necessary, "cranes" of the Hiab type).

Meanwhile, regarding the Guardian piece - even other press reports have not given details about the exact nature of the problem. But the Trust chief executive has said:- "We didn’t run out of oxygen but our system was running at maximum capacity and so we needed to reduce the demand and make some adjustments to ensure it could continue to run safely". So yes, we could speculate about pressure drop.

Although, to be honest, I was wondering if a delivery of liquid oxygen was over-due! We will probably never know.

But anyway (and apparently), the hospital engineers had things sorted out very quickly.

Naturally (sadly), this hasn't prevented the usual "point scoring" ... with the mayor spouting that the situation was "shocking" ... and has called for the Government to upgrade the system "now".

In passing, it may be worth mentioning that there has been talk for years about the need for a new hospital. The area it serves has been over-developed, with the usual lack of increase in infrastructure that many of us have become used to. Hopefully funds will be found once the present crisis passes. Who knows.


If you don't inspect ... don't expect.
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Master
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I would have thought any system is belt and braces; ie main system running on liquid O2 from a central tank with a number of ramps with numerous bottles connected via manifolds, which effect an auto change over when the pressure drops.

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Super Hero
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Yes indeed, Malcolm ... but all depending upon proper maintenance, and regular deliveries, of course.

I was at a place where there was a mysterious high consumption of oxygen. We ultimately tracked it down to an open Tee on a pipe (up in the false ceiling of course); a "test point" that must have been there since the hospital was first commissioned!

"Check and test", Mate ... check and test.


If you don't inspect ... don't expect.
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Master
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Hopefully some enterprising bod was using the room below the leak for Micheal Jackson type oxygen therapy !!

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Super Hero
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It was just a small orifice, Malcolm (and certainly not noisy enough to hear the leak) ... a small diameter spigot for a pressure gauge, or some such thing. Still basically an open circuit, though.

Jacko used a Sechrist 2500-B Hyperbaric Chamber, by the way.


If you don't inspect ... don't expect.

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