POP-off valve closed

[apma77]

---

Members do not see this ad.

If the pop-off valve is left closed during pre-oxygenation are you still delivering O2 to help preoxygenate the patient??

any thoughts?

 

[badgas]

Yeah, I have some thoughts....

How about Brett Favre throwing for SIX TDs last week! Will Carson Palmer play this week?

Oops, is this off topic??

 

[DrDre']

iF the pop-off is totally closed, you will not be able to functionally provide ventilation. THe patient will be trying to exhale against 70 mmHg of pressure. A little is great for cpap but fully closed will not work. That and you may cx a PTX!

If the pop-off valve is left closed during pre-oxygenation are you still delivering O2 to help preoxygenate the patient??

any thoughts?

 

[apma77]

I would think with a mask on for pre-O2 the patient would still be able to breathe in fresh O2 just not be able to exhale it out therefore...rebreathing??

 

[Planktonmd]

I would think with a mask on for pre-O2 the patient would still be able to breathe in fresh O2 just not be able to exhale it out therefore...rebreathing??

Assuming you have a perfect seal with your mask, the patient will be rebreathing if your fresh gas flow is equal to oxygen consumption (closed circuit anesthesia), if your gas flow is more than that (250cc/min) then for a short period of time he will rebreath until the bag becomes inflated like a big balloon and then there are 2 possibilities:
1- The bag pops
2- The patient's lung pops

 

[LongSnow]

Try this sometime during your morning machine check - close the pop-off, obstruct the circuit, and hit the flush valve. Keep doing it. The bag does not pop - you can inflate it to a ridiculous size! Also, you will notice that the pressure will not get much above the 40's, especially after it gets really big.

Do not recommend doing this with a patient however!

 

[Planktonmd]

Try this sometime during your morning machine check - close the pop-off, obstruct the circuit, and hit the flush valve. Keep doing it. The bag does not pop - you can inflate it to a ridiculous size! Also, you will notice that the pressure will not get much above the 40's, especially after it gets really big.

Do not recommend doing this with a patient however!

Those bags are great aren't they? 😀

 

[apma77]

so are we saying then you can still adequately preoxygenate with the pop-off clsoed but make the patient hypercarbic from rebreathing??

 

[Planktonmd]

so are we saying then you can still adequately preoxygenate with the pop-off clsoed but make the patient hypercarbic from rebreathing??

No, You will not make the patient hypercarbic because you have a CO2 absorber in the circuit, You will preoxygenate and produce barotrauma in the process unless you keep your fresh gas flow under the oxygen demand.
Why do you want to preoxygenate with a closed Pop off valve?

 

[Planktonmd]

By the way, patients always re breath unless you are using an open circuit system, but they don't get hypercarbic because there is a CO2 absorber.

 

[numbmd]

Actually with a circle circuit it is either semi open, semi closed or closed. It all has to do with flow rates. Patients will always rebreathe whatever is in their dead space/reservoir (oropharynx, mask, everything proximal to Y piece. Typical phraseology however refers to rebreathing exhaled gas from within the circuit. Temporarily forget the mapleson circuits and forget malfunctioning one way valves. Your circuit will not have any rebreathing if the fresh gas flows are higher than the peak inspiratory flow. All exhaled gas will go out the scavenging system. Once your peak inspiratory flow exceeds your fresh gas flows, gas will be drawn from the co2 absorbers. All a matter of flows.

What's really cool is going closed circuit. The bellows never reach the top of the canister nor the bottom. You can inject liquid anesthetic into the circuit and not crack the vaporizer. Only provide enough oxygen flow for O2 consumption and gas analysis.

 

[numbmd]

An open system actually has no circuit at all. Just a few masks, and some cheesecloth.

Great question: How many masks do you use when you do open drop ether?

 

[Planktonmd]

What's really cool is going closed circuit. The bellows never reach the top of the canister nor the bottom. You can inject liquid anesthetic into the circuit and not crack the vaporizer. Only provide enough oxygen flow for O2 consumption and gas analysis.

It is difficult to do closed circuit anesthesia with mechanical ventilation because the ventilator will not work properly at such low flows.
I do closed circuit always with spontaneous ventilation.
It's a nice technique but I think that the residents are not taught how to do it anymore.

 

[numbmd]

The old machines can do it with a bellows, the bellows just don't go up all the way to the top.

 

[dfk]

Try this sometime during your morning machine check - close the pop-off, obstruct the circuit, and hit the flush valve. Keep doing it. The bag does not pop - you can inflate it to a ridiculous size! Also, you will notice that the pressure will not get much above the 40's, especially after it gets really big.

Do not recommend doing this with a patient however!

actually, untrue. i put a peds FM with plastic seal still on and occluded circuit to prime as i went to get kid. (forgot pop off was closed). OR nurse comes into pre-op and said bag fell off machine. when i questioned what he meant, he couldn't tell me. we get back to the OR, put the kid on the table and i go to grab mask, only to notice the rez bag was shredded from pressure. crazy stuff. perhaps it was because it was a peds bag, but shredded none the less. so, these rez bags are not that infalliable.

 

[SleepIsGood]

It is difficult to do closed circuit anesthesia with mechanical ventilation because the ventilator will not work properly at such low flows.
I do closed circuit always with spontaneous ventilation.
It's a nice technique but I think that the residents are not taught how to do it anymore.

it saves $$$ too doesnt it?

plus can you really do it with sevo at such low flows? yah yah i know the studies saying you need atleast 2 lpm were done on rats, but I thought it's still what's on the package insert?

 

[Planktonmd]

it saves $$$ too doesnt it?

plus can you really do it with sevo at such low flows? yah yah i know the studies saying you need atleast 2 lpm were done on rats, but I thought it's still what's on the package insert?

It saves money, conserves patient's temperature and when used with spontaneous ventilation allows a very nice way to end an anesthetic, try sometimes to get the patient to breath spontaneously at the end of the case and switch to closed circuit (close the pop off valve and turn everything off except 250cc/min O2), they will cruise like that and when you are ready just turn the flow up and open the valve.
The need for flow > 2L/min with Sevo has never been shown to have any clinical significance.

 

[periopdoc]

I routinely do minimal flow and closed circuit desflurane anesthesia with 125-150 ml/min fresh gas flow. If you do the molar calculations, it is pretty easy to get minimal flow desflurane to be much cheaper than sevoflurane at 2 Liter per minute flow rate. The cheapest and coolest is low to minimal flow isoflurane for marathon cases, but this is a little harder to do.

There is no need to close the pop-off valve for closed circuit anesthesia unless the disc in the pop-off valve is malfunctioning or your scavenging system suction is set too high. As long as the bag is not pressurized, no gas should escape the system.

I like to figure out VO2 for my patients by ensuring that all exhaled gasses are returned to the circle system then adjusting my O2 flow until the bag neither decreases or increases in size over time. Voila a rough estimation of VO2. There is a trick to doing this and there is a hint about that trick included in this paragraph.


If you have never done minimal flow anesthesia, let me give you three warnings.

1st - Pay attention to your CO2 absorbent and your inspired CO2 level as you will exhaust your CO2 absorbent much more quickly than with "normal" flows.

2nd - The majority of ventilation is re-breathed gas. Fresh gas flow is only a small contribution to your overall ventilation. Therefore, you will have to dial in a higher concentration on your vaporizer than you want to have as an inspired concentration. Pay attention to your inspired and end tidal volatile agent levels and adjust your dial up and down accordingly. Don't forget to reduce your vaporizer settings when you increase fresh gas flow.

3rd - Thoroughly question anyone who gives you a break as to their comfort with low flow anesthesia and abandon it for the duration of your break if they aren't completely on board. I have tried to teach several or our CRNAs, but I always come back from break to find things FUBARed. There are a couple of attendings who I would not trust either.

-pod

 

[LongSnow]

actually, untrue. i put a peds FM with plastic seal still on and occluded circuit to prime as i went to get kid. (forgot pop off was closed). OR nurse comes into pre-op and said bag fell off machine. when i questioned what he meant, he couldn't tell me. we get back to the OR, put the kid on the table and i go to grab mask, only to notice the rez bag was shredded from pressure. crazy stuff. perhaps it was because it was a peds bag, but shredded none the less. so, these rez bags are not that infalliable.

I do admit that i have never tried this with a peds bag; maybe if I get too board on call tonight i'll try it! I've gotten the adult bag so big that it touched the floor! Pretty cool that the pressure was only mid thirties at that size. Wonder how big the peds bag got before it popped....

 

[dhb]

It saves money

You can do cases with less than 5ml of sevo

 

[Planktonmd]

2nd - The majority of ventilation is re-breathed gas. Fresh gas flow is only a small contribution to your overall ventilation. Therefore, you will have to dial in a higher concentration on your vaporizer than you want to have as an inspired concentration. Pay attention to your inspired and end tidal volatile agent levels and adjust your dial up and down accordingly. Don't forget to reduce your vaporizer settings when you increase fresh gas flow.


-pod

The time to reach a certain concentration is longer but you can increase the flow and increase the vaporizer's output until you reach the concentration you need then you go back to closed circuit and shut the vaporizer off, the vapor concentration will stay constant for a long time.
This is equivalent to injecting liquid agent in the circuit.
For a true closed circuit you have to close the pop off valve.

 

[Duane E]

1st - Pay attention to your CO2 absorbent and your inspired CO2 level as you will exhaust your CO2 absorbent much more quickly than with "normal" flows.

Why is this? Does some of the expired CO2 not go through the scavenger at normal flow rates?

I would think at higher flow rates you would exhaust it quicker because of the CO2 in the 'air'.

 

[bogatyr]

If you have never done minimal flow anesthesia, let me give you three warnings.

1st - Pay attention to your CO2 absorbent and your inspired CO2 level as you will exhaust your CO2 absorbent much more quickly than with "normal" flows.

2nd - The majority of ventilation is re-breathed gas. Fresh gas flow is only a small contribution to your overall ventilation. Therefore, you will have to dial in a higher concentration on your vaporizer than you want to have as an inspired concentration. Pay attention to your inspired and end tidal volatile agent levels and adjust your dial up and down accordingly. Don't forget to reduce your vaporizer settings when you increase fresh gas flow.

3rd - Thoroughly question anyone who gives you a break as to their comfort with low flow anesthesia and abandon it for the duration of your break if they aren't completely on board. I have tried to teach several or our CRNAs, but I always come back from break to find things FUBARed. There are a couple of attendings who I would not trust either.

-pod

The Narkomed 6400 has a feature called the "Low-flow Wizard" which has a fancy display that you adjust your fresh gas flow to keep it in the green. You don't have to do any of the fancy math stuff.

 

[apma77]

so are we effectively preoxygenating a patient even if the popoff is closed??

 

[Planktonmd]

so are we effectively preoxygenating a patient even if the popoff is closed??

You can't effectively preoxygenate a patient with increasing continuous airway pressure that will rapidly reach dangerous levels, the first couple of breath will be OK but then the tidal volume will decrease and the airway pressure will increase rapidly until you cause a pneumothorax.
The answer to your question is no, you can't.

 

[apma77]

many a times ive seen residents forget to open the popoff valve when preoxygenating a patient with the mask on prior to going to sleep. obviously the patient is awake and therefore there will be a leak (patient messing with the mask) so patient will get uncomfortable sometimes but not always.

Another attending argued with me that the patient was still being oxygenated because the O2 was still coming thru...this did not make any sense to me...No ETCO2...the sat not increasing...i begged to differ

 

[Planktonmd]

many a times ive seen residents forget to open the popoff valve when preoxygenating a patient with the mask on prior to going to sleep. obviously the patient is awake and therefore there will be a leak (patient messing with the mask) so patient will get uncomfortable sometimes but not always.

Another attending argued with me that the patient was still being oxygenated because the O2 was still coming thru...this did not make any sense to me...No ETCO2...the sat not increasing...i begged to differ

Preoxygenation ideally means good seal of the face mask and giving 100% O2 for a while to replace nitrogen in the lungs and this can't be done if the pop off valve is closed because the airway pressure will rise rapidly and prevent any effective exchange then cause barotrauma.
If what you mean by preoxygenation is blowing some oxygen near the patient's airway then yes, you can give oxygen even if the pop off valve is closed but this is not real pre oxygenation.

 

[MTGas2B]

To pre-oxygenate you need to ventilate. With the pop-off closed, the patient can't exhale for all the reasons mentioned. Now, if the pop-off is just at 10 say, most patients can probably exhale against 10 cmH20. In a short time with the flows up, they'll also be inhaling with 10 cmH20. It becomes CPAP as someone previously mentioned. Its not comfortable, and they might keep complaining to you that it feels like they can't breath, but you could technically pre-oxygenate adequately.

Now, if the pop-off is closed, and your counting on a mask leak for adequate exhalation, that probably won't work either. If its leaking one way, it probably leaks the other way. Maybe some skilled folks can use their hand and a mask to make a one way valve, I haven't mastered that one. You can probably get close that way, but as long as air (nitrogen) is leaking in you haven't really achieved the real goal of pre-oxygenation, denitrogenation.

 

[periopdoc]

I believe that you actually would/ could pre-oxygenate/ de-nitrogenate adequately with the popoff valve completely closed as long as your flow is reasonably high and your mask seal is a little loose.

On inhalation, you will draw from the area of greatest positive pressure, in this case from the anesthesia machine/ bag, as long as there is adequate flow to ensure a leak around the mask, to the atmosphere, even during inhalation. On exhalation, CO2, Nitrogen etc will exhaust to the atmosphere around the mask and will be further flushed by the O2 coming from the machine.

On the Fire Department, we used a similar arrangement of continuous positive pressure to ensure that we were only breathing fresh air and not the toxic fumes that we were exposed to.

So, as long as you had an appropriately loose seal, say 10 cm H2O, you could theoretically preoxygenate and denitrogenate with little discomfort to the patient. Of course, it is easier to just have a complete seal and an appropriately adjusted pop-off valve.

Of course if your sats aren't increasing, you do not have the correct mask fit, and you would not be adequately preoxygenating, or the patient has a bad shunt.


- pod