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  1. #11
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    How do you make oxygen?


    Sent from my iPhone using Tapatalk

  2. #12
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    Further to Tims post,

    The reason for this issue arising (and we are going through the exact same thing in NZ) is that there are attempts to adapt the many ventilators on anaesthetic machines usually used only in the operating rooms for longer term care of covid patients. These operating room systems are set up to operate with very little gas flowing into them (more or less just replacing the oxygen and anaesthetic gas consumed); very much like our closed circuit diving rebreathers which replace only oxygen consumed. Operating room ventilator systems require CO2 scrubber to work in this mode, just like our diving rebreathers. Tim is right in saying that you can operate one of these systems without a CO2 scrubber just by having so much fresh gas flowing into the loop (like a constant diluent flush in rebreather diving terms) that it washes out any CO2 and prevents accumulation in the loop. There are two problems with this though: one that Tim mentioned is gas supply; and the other is humidification of the inspired gas. High flow gas into the circuit would be too dry for long term ventilation, so if we are going to use operating room ventilator systems, we either need to use them with low fresh gas flows and CO2 scrubber (so that moisture is not washed out of the circuit) or high fresh gas flows and no CO2 scrubber with a humidifier incorporated in the circuit. The humidifiers are also a scarce resource, so there are no easy options. We are looking at both modes of use.

    Simon M
    Last edited by simon mitchell; 28-03-2020 at 07:43 PM.

  3. #13
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    Quote Originally Posted by simon mitchell View Post
    Further to Tims post,

    The reason for this issue arising (and we are going through the exact same thing in NZ) is that there are attempts to adapt the many ventilators on anaesthetic machines usually used only in the operating rooms for longer term care of covid patients. These operating room systems are set up to operate with very little gas flowing into them (more or less just replacing the oxygen and anaesthetic gas consumed); very much like our closed circuit diving rebreathers which replace only oxygen consumed. Operating room ventilator systems require CO2 scrubber to work in this mode, just like our diving rebreathers. Tim is right in saying that you can operate one of these systems without a CO2 scrubber just by having so much fresh gas flowing into the loop (like a constant diluent flush in rebreather diving terms) that it washes out any CO2 and prevents accumulation in the loop. There are two problems with this though: one that Tim mentioned is gas supply; and the other is humidification of the inspired gas. High flow gas into the circuit would be too dry for long term ventilation, so if we are going to use operating room ventilator systems, we either need to use them with low fresh gas flows and CO2 scrubber (so that moisture is not washed out of the circuit) or high fresh gas flows and no CO2 scrubber with a humidifier incorporated in the circuit. The humidifiers are also a scarce resource, so there are no easy options. We are looking at both modes of use.

    Simon M
    Thanks for the clarification

  4. #14
    Prior Member Tim Digger's Avatar
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    Surely one of the high quality condenser humidifier filters at the patient y conector would be adequate to the task? But I suppose they are in short supply as well and many of the bacterial/viral filters that claimed to be humidifiers were inadequate to the task of humidifying gases. I remember it was a while before we found one that functioned reasonably well and that was inferior to a proper warm high flow humidifier.
    Evolution is great at solving problems. It's the methods that concern me.
    Tim Digger

  5. #15
    Last of the Mohicans gobfish1's Avatar
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    Quote Originally Posted by simon mitchell View Post
    Further to Tims post,

    The reason for this issue arising (and we are going through the exact same thing in NZ) is that there are attempts to adapt the many ventilators on anaesthetic machines usually used only in the operating rooms for longer term care of covid patients. These operating room systems are set up to operate with very little gas flowing into them (more or less just replacing the oxygen and anaesthetic gas consumed); very much like our closed circuit diving rebreathers which replace only oxygen consumed. Operating room ventilator systems require CO2 scrubber to work in this mode, just like our diving rebreathers. Tim is right in saying that you can operate one of these systems without a CO2 scrubber just by having so much fresh gas flowing into the loop (like a constant diluent flush in rebreather diving terms) that it washes out any CO2 and prevents accumulation in the loop. There are two problems with this though: one that Tim mentioned is gas supply; and the other is humidification of the inspired gas. High flow gas into the circuit would be too dry for long term ventilation, so if we are going to use operating room ventilator systems, we either need to use them with low fresh gas flows and CO2 scrubber (so that moisture is not washed out of the circuit) or high fresh gas flows and no CO2 scrubber with a humidifier incorporated in the circuit. The humidifiers are also a scarce resource, so there are no easy options. We are looking at both modes of use.

    Simon M
    Hi Simon
    Just wanted to ask what sort of volume o2 wise
    Would be required to keep someone ventilated for
    Say 24 hour s * 14 days
    None diver as of 2018.

  6. #16
    Prior Member Tim Digger's Avatar
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    Very dependent on ventilator design and settings. ITU ventilators are profligate with gases. Maybe 1200 litres an hour possibly more. Theatre ventilators in order to conserve expensive anaesthetic agents and prevent pollution are much less so, much like your rebreather but then they use CO2 absorbers which is back to the start of the thread.
    Evolution is great at solving problems. It's the methods that concern me.
    Tim Digger

  7. #17
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    Hi gobfish,

    Yep, as Tim says. Just to put a harder number on the anaesthesia machine option, with an anaesthetic machine ventilator on a closed anaesthetic circuit with CO2 scrubber and a sedated patient the oxygen consumption would be about 300 - 400 ml per minute.

    Simon

  8. #18
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    One thing I have being considering was using a membrane oxygen generator.
    Would depend on if up to 40% O2 was suitable for providing a suitable breathing gas for a patient, one of the other products that leaves with the O2 is moisture that is usually removed prior to going to a high pressure compressor.

  9. #19
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    Quote Originally Posted by Scubacoach View Post
    One thing I have being considering was using a membrane oxygen generator.
    Would depend on if up to 40% O2 was suitable for providing a suitable breathing gas for a patient, one of the other products that leaves with the O2 is moisture that is usually removed prior to going to a high pressure compressor.
    The membrane system is more of an oxygen concentrator than an oxygen generator and so the other gases and contaminants in the atmosphere are contained and concentrated in the produced product.

    At present the product produced from a membrane would fail to meet current medical standards for medical breathing gas.

    Even the latest generation of oxygen generators fail to meet the current requirements with only one company currently in Europe that meets the exacting standard and is certified to produce breathing oxygen to a medical breathing gas standard. It is a membrane system using a non carcinogenic zeolite.
    The rest use imported zeolite from China heavy in carcinogen material more suited for industrial gas uses.

    The NHS would need to lower its medical standard for breathing gases or take liability for using an inferior carcinogenic product, the only time I am aware of this hapening was when a UK hyperbaric centre used industrial carcinogenic zeolite as it was cheaper from an industrial supplier of imported zeolite used mainly for industrial gas process fish farms etc and by doing so broke the manufacturers and installers service and support agreements for the hyperbaric equipment on site.
    I think I still have the HSE report on it although it may break Simons time frame reference for this forum. What you dont know you dont miss so to speak. Iain M
    Last edited by iain/hsm; 29-03-2020 at 11:08 PM.

  10. #20
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    Quote Originally Posted by iain/hsm View Post
    The membrane system is more of an oxygen concentrator than an oxygen generator and so the other gases and contaminants in the atmosphere are contained and concentrated in the produced product.

    At present the product produced from a membrane would fail to meet current medical standards for medical breathing gas.

    Even the latest generation of oxygen generators fail to meet the current requirements with only one company currently in Europe that meets the exacting standard and is certified to produce breathing oxygen to a medical breathing gas standard. It is a membrane system using a non carcinogenic zeolite.
    The rest use imported zeolite from China heavy in carcinogen material more suited for industrial gas uses.
    A load of the concentrators commonly issued to people who've been on the capstan full strength for the last 50 years are made in USA. Don't know where they get their zeolite but they've told the medical mob to stop changing the zeolite before the interval needs it as otherwise they can't have the new units.

    UK wanted to buy a bunch of them tother week and were apparently quite prepared to get them delivered by crab air.


 
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