Vent Scalars

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Hernandez

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Just curious. Did your fellowship teach them, and do you use them?

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Kind of. Some do. Some don't. And the guy that understands it best has a hard time explaining it well to anyone else.
 
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My attending's don't teach it very well. I took it upon myself to read the above book because in our department the terrorists can be overwhelming when I'm on call. I have found it to be moderately helpful.
 
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Whatca think?



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Its a machine breath because there is no decrease in flow immediately prior to the increase in flow and is volume-targeted. There has to be a leak because the volume scalar doesn't return to the baseline at the end of exhalation.
 
Its a machine breath because there is no decrease in flow immediately prior to the increase in flow and is volume-targeted. There has to be a leak because the volume scalar doesn't return to the baseline at the end of exhalation.

I came to same conclusion but it was a very consistent abnormality, so I doubted it was in the pt. I couldn't find a circuit leak and ultimately changed the vent out. Unfortunately they never answered me as to what was broken in the bent but it was supposedly "repaired"

I like that waveform as it's bizarre looking
 
Its a machine breath because there is no decrease in flow immediately prior to the increase in flow and is volume-targeted. There has to be a leak because the volume scalar doesn't return to the baseline at the end of exhalation.

Isnt that a pressure control breath? Decelerating flow. If it was volume control, flow would be constant ( a square shaped flow curve) and peak pressure would be increasing. Did you mean something like "pressure regulated volume control"- Machine tries to achieve a pre-set volume but does so in a decelerating flow so that it never passes a pre-set peak pressure.
 
Isnt that a pressure control breath? Decelerating flow. If it was volume control, flow would be constant ( a square shaped flow curve) and peak pressure would be increasing. Did you mean something like "pressure regulated volume control"- Machine tries to achieve a pre-set volume but does so in a decelerating flow so that it never passes a pre-set peak pressure.


No, decelerating flow is also used in VACV. VACV can be sine, square, decel, and rarely exponential decay (so I've read, never seem a machine that can do that) PACV is only decelerating flow. Look at how constant the volume peak is, VACV.

A least with the PB840s, I used decel mostly, as for some reason most patients did not like the square waveform.
 
No, decelerating flow is also used in VACV. VACV can be sine, square, decel, and rarely exponential decay (so I've read, never seem a machine that can do that) PACV is only decelerating flow. Look at how constant the volume peak is, VACV.

A least with the PB840s, I used decel mostly, as for some reason most patients did not like the square waveform.

VACV = volume control?

Maybe Im confused. In Volume control, you tell the machine to give a preset volume, ie 400cc. Then you set a respiratory rate, ie 12. and an I:E ratio that will dictate how long you have to delivery that 400cc breath. The length of time the machine has based on I:E + Respiratory rate + the resistance of airway/Compliance will dictate the peak pressure achieved during that inspiratory effort. In pure volume control, machine is dumb and just deliveres 400cc in whatever time period it has regardless of pressure it is causing, thereby resulting in an up-slanting pressure curve. In pure volume control, that flow is not decelerating and the flow curve should be flat.

In "pressure-regulated volume control" which is called other stuff as well, such as "Volume Control-Auto Flow", you set a desired TV, ie 40oc. But the difference is that you tell the machine that it can not go beyond a certain pressure in delivering that volume. When it is trying to push air in, the flow decreases as the machine meets more resistance. The volume you can achieve in this mode is based on the respiratory rate and I:E ratio-> If you are breathing at 30 the machine has very little time to try and get 400cc of air in. To try and push all that air in would require a high pressure which limits the volume delivered.

So are you saying in the other "volume control" modes that you set a volume, but then instead of setting a desired pressure limit + desired volume (i.e. Pressure regulated volume control) that you just set an inspiratory flow pattern?

I think most of this is semantics. To me, any time you are regulating your flow based on pressure and not volume, its a pressure control breath.

What are the names of the other modes?

Thanks
 
VACV = volume assist control ventilation. PACV = pressure assist control ventilation.

Why couldn't one control the pattern of flow in a Volume control ventilation?

If you don't trust me, crack open tobins. Chapter 3. Page 55-58. Or go to a vent and adjust the flow pattern yourself.
 
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VACV = volume control?

Maybe Im confused. In Volume control, you tell the machine to give a preset volume, ie 400cc. Then you set a respiratory rate, ie 12. and an I:E ratio that will dictate how long you have to delivery that 400cc breath. The length of time the machine has based on I:E + Respiratory rate + the resistance of airway/Compliance will dictate the peak pressure achieved during that inspiratory effort. In pure volume control, machine is dumb and just deliveres 400cc in whatever time period it has regardless of pressure it is causing, thereby resulting in an up-slanting pressure curve. In pure volume control, that flow is not decelerating and the flow curve should be flat.

In "pressure-regulated volume control" which is called other stuff as well, such as "Volume Control-Auto Flow", you set a desired TV, ie 40oc. But the difference is that you tell the machine that it can not go beyond a certain pressure in delivering that volume. When it is trying to push air in, the flow decreases as the machine meets more resistance. The volume you can achieve in this mode is based on the respiratory rate and I:E ratio-> If you are breathing at 30 the machine has very little time to try and get 400cc of air in. To try and push all that air in would require a high pressure which limits the volume delivered.

So are you saying in the other "volume control" modes that you set a volume, but then instead of setting a desired pressure limit + desired volume (i.e. Pressure regulated volume control) that you just set an inspiratory flow pattern?

I think most of this is semantics. To me, any time you are regulating your flow based on pressure and not volume, its a pressure control breath.

What are the names of the other modes?

Thanks


in a volume controlled breath you pick the tidal volume and the pressure is determined by the patients compliance. The RR determines you cycle time, (RR 10 = cycle time of 6 seconds). The flow or I:E time determines the percentage inspiration and expiration. For example say the patient is getting a 1L TV breath and the flow is set at 60 LPM, it therefore takes 1 second to deliver the 1000cc TV breath, leaving 5 seconds for exhalation.

You cn however change he flow to whatever you want it to be, decelerating, ramp etc...

In a PACV the volume will vary slightly and not be the exact same as it is in the above scalar (since the compliance might change slightly breath to breath i.e; IN PRVC the scalar would look similar to above, EXCEPT that with the above leak (TV never returns to baseline) or whatever the hell was wrong with the vent the scalar might look different since its actually a pressure controlled breath and you might lose some TV with the leak
 
in a volume controlled breath you pick the tidal volume and the pressure is determined by the patients compliance. The RR determines you cycle time, (RR 10 = cycle time of 6 seconds). The flow or I:E time determines the percentage inspiration and expiration. For example say the patient is getting a 1L TV breath and the flow is set at 60 LPM, it therefore takes 1 second to deliver the 1000cc TV breath, leaving 5 seconds for exhalation.

You cn however change he flow to whatever you want it to be, decelerating, ramp etc...

In a PACV the volume will vary slightly and not be the exact same as it is in the above scalar (since the compliance might change slightly breath to breath i.e; IN PRVC the scalar would look similar to above, EXCEPT that with the above leak (TV never returns to baseline) or whatever the hell was wrong with the vent the scalar might look different since its actually a pressure controlled breath and you might lose some TV with the leak

I see. I haven't played with the inspiratory flow pattern on a volume control setting yet. Thats interesting. So you can set a decelerating flow pattern with a fixed Tidal volume. In that situation you may get various different peak pressures but a constant delivered tidal volume. I feel like in most situations I would rather have variability in my delivered TV but assurance that I am not going over a preset peak pressure.

Good stuff. Ill be sure to mess around with the Puritan Bennett next time Im around one.

Thanks
 
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