Negative Paw

[EBME Tech]

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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[nimbus]

Scavenger relief set valve too low for given FGF.

 

[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.

 

[EBME Tech]

Scavenger relief valve wide open or too open for given FGF.

Active scavenging system, therefore no valves

 

[nimbus]

Active scavenging system, therefore no valves

There should still be a relief valve.

 

[EBME Tech]

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.

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....

 

[nimbus]

Yes, low flow was one of my thoughts too

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?

 

[EBME Tech]

There should still be a relief valve.

Sorry nimbus, I thought you where referring to the older scavenging systems. Negative relief valve functioning correctly (serviced by myself the previous week )

 

[EBME Tech]

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?

GE Avance CS2

 

[nimbus]

GE Avance CS2

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.

 

[EBME Tech]

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.

 

[anbuitachi]

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

 

[EBME Tech]

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...

 

[deleted875186]

Well that is interesting, an anaesthetist being unfamiliar with the workings of the anaesthetic machine...

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.

 

[anbuitachi]

Well that is interesting, an anaesthetist being unfamiliar with the workings of the anaesthetic machine...

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

 

[chocomorsel]

Well that is interesting, an anaesthetist being unfamiliar with the workings of the anaesthetic machine...

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.

 

[EBME Tech]

Thank you for everyone's input to this thread, and the honesty about equipment knowledge.

The answer, seems to be user error.

 

[MirrorTodd]

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.

 

[anaesthetic]

.

 

[chocomorsel]

I went from having excellent anesthesia techs who knew their stuff in residency to completely useless anesthesia techs in fellowship at a different institution. Made me really glad I asked a ton of questions and took the time to pick apart and really understand the mechanics of the different anesthesia machines (Drager, GE, etc.). One understated benefit of going to a huge residency with multiple hospital sites is that we were forced to get out of our comfort zone every month and deal with multiple variations of EMRs and anesthesia machines/setups as well as personnel.

Do that now. In my locums life.

 

[drmwvr]

Well that is interesting, an anaesthetist being unfamiliar with the workings of the anaesthetic machine...

Sounds like you were right there with him....surprising for an anaesthesia tech...wierd.