Any major problems?

Just trialing the vent at our site now. Im wondering about the Rise %. It doesnt seem to make a lot of change. Recently had a patient with cholangeohepatic failure. This patient became increasingly flow starved on PSV perhaps due to rising levels of ammonia. Upon manipulating this mode it was discovered the Rise % made very little change in patient status or in Pisnp or V waveforms. Autopeep did not appear to be an issue.

The patient was changed to PRVC and again the pressure waveforms on insp seemed to flucuate greatly indicating a situation where the flow may not have been great enough to meet the patients needs so in attempt to curtail this we tried to increase Rise % and no dice. No change. Interestingly we sedated the patient more causing a bit of an improvement. Many other manipulations were attempted resulting in switching out the vent for our old faithful.

In lab my collegue and I tried to sim this on ourselves. Fun though sick and difficult we found also that the Peak flow seemed to cycle before the peak pressure was obtained. Again manipulating the rise % one would have expected a sharp quicker rise to peak pressure however this was not the case. Contrary to this neither did we find that decreasing Rise % made any real change in how these pressures were reached.

Has any other site encountered issues with rise time % not being overly responsive with this ventilator.

My other question is regarding A/C modes. A total rate of 22 is set. The patient is triggering and assisting the vent. Typically A/C is not overly patient friendly however on newer gen mcvents im noticing that patients seem to be able to make efforts trig the vent and get a breath without the same level of adverse effects such as stacking. Furthermore the patient overriding the set rate didnt seem to change the total breaths from set breaths. Does the vent provide a window similar to SIMV which allows for better synchrony or is this my imagination?

I appologize if these questions seem unclear but any constructive input is appreciated.

thankyou

Did the switch to "Old Faithful" fix the problem? If so what was the vent and mode?

I haven't worked with the Vela, but can't imagine that maxing out rise time wouldn't make the rise the target pressure ordinarily too sluggish.

The "clue" for me was that your patient was becoming flow starved on PS. The patient who wants their breath yesterday (desperate attempt to compensate) wants both resistive and elastic loads taken care of. PS doesn't guarantee any elastic unloading, and shortening rise time might take with one hand as it gives with another (the breath may then terminate earlier if the pressure is reached sooner).

PRVC is really a form of Pressure Control which adjusts for the dialed in VT. If the VT is set lower than what a desperately breathing patient wants (in this era of low VT's) then the patient will continue to draw more volume and the vent will continue to reduce target PC Pi as a vicous cycle ensues----the more the patient desperately draws the less the vent gives. In this situation shortening rise time won't solve the problem.

You either have to go to straight PC with a target Pi enough to unload the patient, or switch to "old fashioned" VC with a flow enough to overshoot what the patient demands.

And yes A/C would be what I would use (eihter PC A/C, PRVC A/C provided VT and or sedation fixed, or VC A/C). If the VT and flow are both set high enough such that the necessary unloading occurs why then muck it up with SIMV and trying to find some PSV to intersperse?

Is this what "Old Faithful" accomplished?

You are right in that modern A/C has solved many of the original technical problems (along with Propofol) which all caused us to go down the ole IMV/SIMV/SIMV + PS pathway. Partly I think SIMV and PS was created because older A/C was so asynchronous for the patient (and maybe longer vent hours to charge instead of quicker intubation?).

Thank you very much Jeff for your response. Firstly in response to your question did old faithful help. Yes. It would seem that the Seimens 300 did have a positive affect on patient comfort. However this may be purely anectodotal in that by this time the patient was further along the sepsis cascade also further into the anagesia. One thing which was evident however was the obivous difference in fuctionality of the rise time %. Graphically a huge difference in rise vs the Avea. Numberically a faster flow and a more definate rise to peak pressure. What we observed was that the Avea rises much more passively to peak pressure and as a matter of fact peak pressure was not yet reached at the end of peak flow but rather later in the insp phase. it was a bit bizzare therefore difficult to explain im finding.

I appreciate many of your comments regarding Time constant during PSV mode and their effects of course on the patients comfort and ability to inspire fully. I would argue however that given enough PSV niether Compliance nor Resistance are a problem. Patients in general when sedation is an issue display greater comfort and compliance with therapy on a PSV mode. I have I had three wishes I would have loved to have a PAV mode available as it not only defines but more accurately addresses these issues. Of benefit to the AVEA is the esophageal pressure monitoring capability, however it is little more than monitoring capability. Combine this data on a patients WOB with a mode such as PAV and I think we've found something truely revolutionary however the powers that be arent will to tear down these proverbial wall just yet.

So we did try VC which because of the inclimate situation to do solely with a lack of appropriate sedation. VC despite a square wave and obvious sharper rise did little more than demonstrate increased discomfort. This is where some of the questions I have posted began to arise such as Rise time why so sluggish, and AC is it really smarter or is it just my imagination.

Having failed a kick at the can in VC, we attempted SIMV with PRVC and with you know normal SIMV. Somewhat there was a greater degree of comfort as the patient was able to acheive some PSV breaths but still there remained the issue of sluggish rise to peak. Another collegue attempted PCV which did seem to make some headway however by this time the issue of sedation was more adequately addressed on a PRN basis. They settled on PRVC as generally speaking we like the dual modes.

As I mentioned what we then found was as the patient rode the rate there was no issue surrounding an adequate enough rise. The graphics were text book the sats were good, we were acheiving a safe tidal volume consistently and the patient was comfortable. The moment the patient began to override the Pinsp again began with the funkiness.

What we have learned is that the Rise % between 1 and 9 varies between only about +/- 10 lpm accoring to a rep. I havent found this yet in lit review but I havent looked either. This still doesnt adequately explain the variable rise to our peak pressure understanding that C lung and Raw will play an obvious role esp. in PSV and PRVC mode well in anymode for that matter but with an adequately comfortable patient it made little sense.

So we switched to the 300 and voila fin de la problem. Nice rise good peak comfy patient so huh? I dunno. Seemed to us to be a vent issue. Anyway I thought it was interesting and I appreciate your response.

Thanks again

It would be interesting to lineup both the Servo and the Avea and do a Risetime comparison. I did a Risetime peek at a PB 840 I turned around tonight. Problem is that I was using a big Hudson RCI bag. With this big bag the Risetime effect you see on a patient wasn't evident. But at PC with Pi 20 Peep 5. 10% Risetime yielded a PIP of 28 (3 overshoot) and risetime of 100% gave a PIP of 30. Risetime on the 840 goes by a & (0-100). Whereas the Evita (and I believe Servo's) have a definite time to rise pressure (0 to 2 seconds on Drager) the PB reps only told me that the risetime is a bit of like an "adrenaline" index. Anyway on a patient (whom is sedated) one can change from 10 to 100% risetime and I show the students the big difference. 100% on the 840 seems chock full of epi.

If the Avea has a risetime which adjusts flow by a certain amount, it would seem to me that rabid patient flow demand would totally overwhelm it. ?

My experience with using PSV as the default mode (stable support plus weaning off, plus an SBT) is that once a patient gets fatigued and dyspneic it is alot harder to just increase PS level as opposed to switching to a PRVC version of A/C. But maybe with risetime, exp flow termination adjustments it would work as well (raise Pi, back off a bit on risetime and exp flow termination to guarantee a VT ...or just set directly?).

So you have PAV? I would be interested in hearing tales of it's use in clinical practice.

In my humble opinion the Avea rise time is akin to a wrinkle old man summiting everest as opposed to your 840 shirpa. Adrenaline scale be damned this sucker seems to take all day. Well maybe thats a bit harsh but I am not convinced it is as sharp an attack as either the 840, Evita 4, or Seimens 300 not having tried the "I". There are however many many things that I like about the Avea. Excellent new modes like PRVC with SIMV albeit I agree with you not entirely neccessary, esophageal pressure monitoring, inspiratory and expiratory
flow manipulations though it doesnt have active exhalation it is similar, P flex which can sim a large volume syringe technique to acquire P inflection and deflection points to assist with safe ventilation in protection against VILI, Heliox ventilation, and well it has that barney colour which makes it so gosh darn inviting. Another cool thing that a collegue pointed out to me is that not only can you obtain

Once again we have it on another patient so I am as yet unable to attempt the lab you suggested. I thought that was a great idea by the way and the minute I can switch it out and give it a whirl I let you know how they compare. Because we're trialing the AVEA we have to have in on as many PTs as poss.

This particular case again a hepatic failure due to chronic ETOH, obese, chronic gases, seizures, difficult to intubate was actually lots of fun but then Im like that. Until tonight has been on PRVC and was very "comfortable". After having a short stint on PRVC/SIMV we made the switch to PSV. The patient has had low ventilating pressures despite very small lungs on CXR and obvious pickwickian features. While on PRVC in this situation I did not find there to be any noticable flucuation rising to Peak insp press. I recieve the PT on a rise of 5% and did manipulate it some to see if there would be an obvious change in the flow or rate of attack. Noticably and in defense of earlier comments I certainly could hear the vent pushing more. I did see a slight increase in Pinsp with higher rise, and the graphic demonstrated less of a sinusoidal wave than when on a lower rise. The variance between high and low were not overly dramatic having only +- 3lpm between 1 to 9 rise %. It is interesting also to look at the picture the graphic demonstrates. The Peak insp doesnt arrive until the later 2-5% of the breath while peak flow has long since occurred. I would have expected a quick ramp to that peak pressure and then a decelartion like one would expect with decelarting modes. Its almost like it uses an accelarating wave pattern? What we found on the 300 on the previous patient seemed consistent with your PB 840 in that it demonstrated an obviously more genuine attack which was measurable. On PSV the same flucuations in Pinsp have come back to haunt us I have turned on AAC which seems to have helped a bit. The more uncomfortable the patient becomes the more previlent this flucuation. With some breathes the Pinsp has to or three dips on the way to peak. Somewhat this is a characteristic of PSV I believe however on other vents it seems less dramatic. Anyway Im sure Ive beat this to death now but I am still very curious about it. I hold that the patients so far seem to easily be outstripping the vent. Maybe we got a wimpy loaner Im thinking.


PAV - My experience clinically thus far with PAV has been with non invasive ventilation. We have been running Visions here for about a year with PAV. I find it a useful tool but most of my collegues save a few find it cumbersome. I liken it to IPAP which you can fine tune. It requires you ask more questions of the patient to get to the right level of Vassist and Fassist but once you're there you can wean very easily. So with the Vision it is totally arbitrary you sort of guess with some feed back from the patient where the best levels are to overcome compliance and resistance and you know when you see decreased WOB. A handy little quick and dirty tool. Many of my collegues still hold they can't see the point because ST BiPAP allows them to get the same effects and less buttons. Plus none of us fully understand how the vent is capable of distinguishing Vast and Fast within the IPAP. I mean to say what is it that it is doing we see it making a change but how?

On the 840 I have only had one opportunity during our vent trials to try PAV. The patient was in PSV well on the way to weaning so it wasnt much to go on about. The neat thing is that this sucker calculates and shows you all the data and sets accordingly.

Well Jeff thanks again for the ideas. Hope you havent found this too long winded but eh.. we are RTs

Just a thought, but it sounds to me like there may have been a problem with the trigering mechanism resulting in a delay between the patients attempt to get more air and the ventilator finally pushing hard enough for the patient to sense the air flow. This was a big problem with some of the old ventilators which had response times of 250 msec as in the MA 2+2. While most new generation ventilators start to deliver air within single digit time frames, simple issues like excessive resistance in an HME, water in the tubing or a skinny/kinked ET tube can create a significant lag between the drop in intrathoracic presure and a positive flow of air finally traversing through the ventilator tubing and into the patient's lungs. Neal Macintyre described this really well when he was encouraging us to use PSV more. As I understand his comments, a hyperpneac/tachypneac patient has the greatest demand for air during the initial phase of inspiration. When ventilator manufacturers started to put rise time adjustments on their machines to avoid the overshoot and premature termination of inspiratory flow you get in a high resistance system, most of them did it by slowing the rise to peak pressure right from the onset of inspiration. Bird was the only manufacturer who tempered the flow on the VIP as circuit pressure got close to peak pressure e.g if the pressure support level was set to 20 and the inspiratory percent rise was set at 20%, the ventilator would begin slowing the air flow when the circuit pressure reached 80% of the set pressure support level. Because of the way current manufacturers manipulate rise to pressure right from the onset of inspiration, a patient with air hunger and high airways resistance would be flow starved during the beginning of inspiration while setting the rise time to its shortest would result in overshoot and premature termination of inspiration in PS. For a bottom line (if there's nothing wrong with the inspiratory trigger) I agree with Jeff's comment that you may be better off in Volume AC with a sufficiently high flow rate untill you can resolve the cause of the patient's air hunger. Incidently I believe Robert Kaczmarek wrote a paper in RC some 10 months ago where they compared the affect of manipulating % rise time on several ventilators and found there was a much greater affect on some ventilators vs others. The 840 vs the Servo-i is one example I recall where there was a substantially greater affect between minimum and maximum on the 840 vs the Servo-i.

sure enough this was a particular error to the trigger on this particular vent. In otherwords it turned out to be a mechanical error with that particular machine.

Fin,

Maybe a stupid question, but are you from Europe? We have been waiting to see PAV from PB here and I did not think they released it in the US?

Nope Im Canadian.

We are looking at the PB 840 now and they just programmed it into the demo they are showing us here in GA

quote:

Originally posted by R. Sabella:
Fin,

Maybe a stupid question, but are you from Europe? We have been waiting to see PAV from PB here and I did not think they released it in the US?