Today one of our anaesthetists reported an anaesthetic machine showing repeated negative Paw, with a spontaneously breathing patient (vent in bag mode) The patient was not in any respiratory distress. The machine in question is within calibration spec. I would therefore like to know, under what circumstances a repeated negative paw could be caused by the patient?
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Negative Paw
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deleted87051
Scavenger relief set valve too low for given FGF.
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deleted162650
Can see it at low flows or not enough air in the bag so that it completely collapses during inspiration and negative pressure (vacuum) is created in the circuit.
Active scavenging system, therefore no valves
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deleted87051
There should still be a relief valve.
Yes, low flow was one of my thoughts too. Though having said that, I would have thought this experienced anaesthetist would have known low flows could cause neg pres....
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deleted87051
Yep. Scavenging system is sucking too much gas out of the breathing circuit. Set correctly, you can operate at low flows. Which machine is it?
Sorry nimbus, I thought you where referring to the older scavenging systems. Negative relief valve functioning correctly (serviced by myself the previous week 😉 )
GE Avance CS2
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deleted87051
You should be able to run low flow and spontaneous ventilation with that machine....if the circuit pressure becomes negative, you can either increase the FGF or partially close the pop off valve so less gas within the circuit gets scavenged.
Yes, APL can be adjusted to suit. Again, I'm assuming this is something any anaesthetist would know., hence why I'm trying to find how the patient would cause negative paw.
Only other explanation would be moisture in flow sensors.
i would disagree. i can see several people i work with not know this
Well that is interesting, an anaesthetist being unfamiliar with the workings of the anaesthetic machine...
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deleted875186
I’ll second this. Graduated resident here. Feels like a lot of my co residents even read the chapter on the anesthesia circuit and machine in depth. A lot of people simply push the vent button and call it a day.
the ideal situation is definitely to know it. but there are so many different machines these days so it's not too surprising. also thats why there are techs.
not hard to imagine this for other people as well. a phd in biology may not know the internal mechanics of a flow cytometer
Learned it in residency for exams then promptly dumped it out when I needed room for physiology and pathology knowledge. I know the basics. Like how to turn it on. Switch modes. Trouble shoot many things. But plenty I don't know. I have always relied on the expertise of the anesthesia technicians. I call for help when I can't figure it out. Like the whole scavenging system being too open or closed, I don't even remember learning about that honestly. I think I learned about it being closed when I worked at a facility that turns off the system every night.
I bet people who supervise CRNAs full time are even worse than I.
Ya let's not get all Holier than thou here people. The times of anesthesiologists owning their own machines and being able to take them apart and put em back together is way long gone.
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deleted641888
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Do that now. In my locums life.
Sounds like you were right there with him....surprising for an anaesthesia tech...wierd.
