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Volume Control Ventilation in Status Asthmatic
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I am curious to know if any other institutions are using Volume Control in Asthmatics. We have a couple of attendings that like to use volume control on asthmatics. I asked one of the attendings why he chooses volume control? He stated that when you have high resistance- in volume control- you will have a more even distribution of flow. He also atated that this leads to less turbulence. Lastly, he stated that the alveoli do not see the high pressures and that the trachea can handle these high pressures. I am talking high pressures. I saw pressures of 60 on a 10 year old asthmatic. My concern is that you do not know how much pressure the alveoli are seeing.
I was wanting to know if anyone else has used this practice and if so what study can you base this off of? The attendings that like to use this practice have both come from Philadelphia.
 
Posts: 4 | Registered: December 01, 2006Reply With QuoteReport This Post
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Picture of Renton
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Raw is still Raw, intrinsec or extrinsec; Yea, I do believe that what you see as 69 Pip might not be 69 P alv; there for, 69 should not upset you. A oesophagal ballon (such as on the avea Viasys or any bioCore tech) will enlighted you; but whou as that technology...

No mather the age...

ps: sorry about my writen English, an am French spocken...
 
Posts: 49 | Location: Ste-Agathe-Des-Monts, Québec, Canada | Registered: October 14, 2005Reply With QuoteReport This Post
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From memory..

There was an article a while back in Clinical Pulmonary Medicine journal (and these aren't in PDF so I can't email) there was a great wrap-up article about ventilation of intubated asthmatics by Dr. Pierson. He advocated using volume ventilation over pressure ventilation as one can maintain volume stability better that way.

If your PIP's are in the 60's what are the plateaue pressures and what are the auto-peep values?

I remember a conference lecture where Dr. Ravenscraft was describing how there is diminishing returns if one extends exp time past about 3.2 or 3.5 seconds. If one extends expiratory time any further the lungs don't empty that much more. But the converse is probably also true and we don't want to ever decrease exp time anymore than that. So if one takes a 3.5 second exp time and then figures on an insp time range of 0.5 to 1.5 (hey the Hamilton's Otis law calculation I've heard gives asthmatics longer I times) the max RR range is around 12-15. Everytime I've ever seen an asthmatic or severe COPDer being ventilated with higher rates there is usually auto-peep that is unknown (or the patient is paralyzed and the "raise the peep to meet the auto-peep" is used as a cop-out as opposed to reducing minute ventilatino and accepting a higher PaCO2. "We have come to bury auto-peep not to raise to it".

Assuming the patient has had their minute ventilation reduced and their exp time optimized then IF there is still any auto-peep it could be that adding Peep will help to empty OR will actually unveil auto-peep. Better still compare plateau pressuers both with initially optimized settings and then after a long exp time of up to a minute. If the plateaus pressure is way lower on the latter it could be that auto-peep is in regions which needs splinting open to even communicate.

Usually any asthmatic severe enough to truly need intubation also needs sedation/paralysis in order to get control (otherwise you're probably intubating patients based on something other than clincial need). I'm aware of the danger of steroids plus paralysis but for that initial stabilization I think it still is necessary.

The real severe asthmatics actually die of diffuse mucous plugging ("E tu Mucous?" to coninue the Ceasarean asides). I've seen good results from lavage/hand bagging/suciton using NS warmed to body temperature. This is especially true when after initial intubation and doing bag to tube ventilation one can't even get any air moving--even after a long exp time.

But to get back to PC vs VC. First I question if ARDSnet level VT's need to be adhered to. There is already so much deadspace that giving someone 6cc/kg predicted might mandate a RR so high as to worsen auto-peep a ton. Every cc increase above the deadspace threshold counts.

Anyway, so figure out what your VT target is and then start out in PC using a Ti of 1.0 to 1.5 and raise the pressure slowly, keeping rate 2 and hitting the manual breath while watching exp time and seeing what rate you get. If you start out with volume control and some arbritray settings there is usually PIP alarms gonig off and everyone gnashing teeth and wailing. Keep in mind that if flow doesn't come to a halt in PC (especially happens wiht short Ti's) you still don't have a plateau pressure. Anyway figure out what you want to do in PC (or let adjusting in PC show you what you can do) and then go do the same VT and Ti in volume control. Damn the PIP, it's the most meaningless number we ever document.

For good articles on this look up studies by Tuxen DV, the Pierson article I mentioned, Sue Ravenscraft and James Leatherman. (I'm probably forgetting some people).
 
Posts: 171 | Location: Palo Alto, CA USA | Registered: November 14, 2002Reply With QuoteReport This Post
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Wow Jeff you have given me a lot to ponder. Let me start here to answer your question- the patient had a plateau pressure of 32 and an auto peep of 25.
You said something interesting which is a situation that I can not answer. When I spokw with the physician about changing the patient to a Volume Targeted mode- He agreed. I placed the patient in PRVC/ SIMV with pressure Support. The patient was medically paralyzed. I set the Inspiratory time to the point where my inspiratory flow returned to baseline. I explained to the physician that when the flow became stagnant in a pressure driven mode- that teh PIP was basically the Plateau pressure. My PIP was 42 and my tidal volume was set at 7cc/kg. When I tried to prove my point- I held the patient in an inspiratory hold and the plateau returned to 32. AM I missing something here? Why was the plateau pressure not 42?
To address another point that you brought up- you talked about raising the PEEP- I want to make sure I understand you- I am used to raising the set PEEP to get closer to the auto PEEP and putting the patient in a support mode. I have used this routinely to help with inspiration and expiration. What I mean is that to allow the patient to trigger the ventilato- if they have to overcome the trapped gas in there lungs- they must overcome the difference between the set PEEP and the auto PEEP. Also when the patients goes from inspiration to expiration- my thought is that if you can "stint" the airways open, the patient would have less resistance thus decreasing the amount of expiratory force the patient has to use on exhalation. I agree with you on the point that once the patient is paralyzed you should decrease the PEEP and use lower tidal volumes.
 
Posts: 4 | Registered: December 01, 2006Reply With QuoteReport This Post
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It's really hard to speculate without being there. Get too esoteric and I'm probably speculating, or risk something more simple and risk insulting someone (not you necessarily, just in general).

As regards the PIP plateau difference, it could be that the rise time setting is causing a pressure blip? Looking at the pressure/time scalar is the pressure steadily 42 all the way across? Or does it decay to 32 as flow comes to a halt?

If the pressure is held a 42 but then drops to 32 with a prolonged hold it could be a leak/pneumo, or could be that with a breath hold you're unsticking airways and therefore the pressure drops?

When the auto-peep was 25 what were the specific vent settings? If the plateau pressure is 32 and the auto peep is 25 this means that to get 7cc/kg VT you are only needing 7cmH20 alveolar distending pressure. In a paralyzed and intubated asthmatic that seems WAY low. ?
 
Posts: 171 | Location: Palo Alto, CA USA | Registered: November 14, 2002Reply With QuoteReport This Post
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RTbeginner,

You are somewhat correct to believe that during PCV when the inspiratory time is long enough to cause the flow to be stagnant the PIP is basically the same as the Pplat. But the PIP will never actually equal the Pplat when a proper end inspiration pause applied.

If you put an end inspiratory pause on in PCV the pressure will decrease because of the dissipation of viscoelastic forces and the pendelluft phenomena.
 
Posts: 11 | Location: Saskatoon, Canada | Registered: November 28, 2006Reply With QuoteReport This Post
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