Does anyone have experience on
1. Using APRV on patients that have been paralyzed (i know in general we try not to do it).
2. Complete mechanical ventilation isn`t good. Is APRV prticularly more harmful in paralyzed patients as a mode compared to other modes in paralyzed patients? Even if u achieve an ok pH/pCO2
3. If the patient isn`t paralyzed and the spontaneous breaths are clearly dead space volumes is it really helping the patient?
4. When u do APRV and PS for the spontaneous breaths how do one really know what transalveolar pressures one is dealing with?

Does anyone have experience on
1. Using APRV on patients that have been paralyzed (i know in general we try not to do it).

Actually I don't have much experience using APRV---but when I have it has often been during severe "rescue" situations and the patient was paralyzed. It was used as a kind of "poor man's oscillator". Rate 60 Ti 0.6 Te 0.4 Phigh 45 Plow zero. Patient had severe mostly unilateral lung disease. I was called in from home to help ventilate a patient in a big teaching hospital ICU. I could have just as easily use PC inverted, same free exh valve, etc. BUT using APRV was akin to a smoke grenade--under cover of which I could use settings they would have blown gaskets over had I used a mode they had default dogma built up over (PC). Despite the inherent simplicity of settings "APRV" invokes a mysterious aura like I'm using some recipe for fried monkey brains. Stand back and let the chef cook. Had they been familar with APRV dogma they might have been bellowing about how APRV is only for spontaneous breathing and he was paralyzed, etc.

2. Complete mechanical ventilation isn`t good. Is APRV prticularly more harmful in paralyzed patients as a mode compared to other modes in paralyzed patients? Even if u achieve an ok pH/pCO2

Well if the patient is paralyzed then complete ventilation is "what's for dinner". I don't see why it would be more harmful because a patient is paralyzed. You don't have Minute ventilation stability the same as if in Volume modes (PRVC or flow controlled). On the other hand there is the ability to distribute the ventilation better----imagine the most and least compliant lung units--if you keep the focus of of the ventilation "up high" then the most compliant won't over distend and the least compliant won't collapse. Of course one might set up the patient in APRV, optimize. Then go over to CMV/Autoflow and set exactly the same rate and I:E ratio (inverted). Peep zero. Now the Phigh will go up or down to maintain a VT. Beware the dogma if ye go there!

3. If the patient isn`t paralyzed and the spontaneous breaths are clearly dead space volumes is it really helping the patient?

Depends. If the patient is already getting adequately ventilated by the set APRV settings then ineffective patient breaths----provided that they aren't leading to fatigue or a waste of badly needed reserves--would tend to keep some diaphragmatic action going.


4. When u do APRV and PS for the spontaneous breaths how do one really know what transalveolar pressures one is dealing with?

This is one bone of contention. The Servo Vent has PS and the Drager APRV expert (Dr. Habashi) says something to the effect that it "contaminates" APRV. Of course in APRV on Drager one can set ATC and still get some minimal PS---why such a minimal setting would be of untoward concern eludes me. But setting a high PS atop a robust Phigh might lead to overdistension.

1) APRV in a paralyzed - yes you can use APRV in a paralyzed patient you will just have to alter the settings. I traditionally will start with a Phigh of 4 seconds, Phigh either at my Ppl or 5 above my mean, Plow zero and Tlow at 50% of my PEFR. After those settings I would get a gas and see where I am at after an hour or so. The paralyzed patient just means you are not getting any help from the patient. As far as Jeff's occilator method, I'm not sure you need APRV to recreate those settings and I don't know if I would go with them (we have VDR's that I would choose first).
2) APRV harmful - don't know if I would say it is any more harmful than anyother mode of ventilation.
3) Deadspace volume - the patients spontaneous movement of volume during APRV is helpfull in that it will help move up CO2 so that during the release phase you get a larger amount of CO2 removal. We see this when we put in a EtCO2 monitor in line and it is reading higher than the actual PaCO2 (only reason I could come up with and is apart of the Habashi "dogma")
4) PS in APRV - you don't know exactly what the transalveolar pressure is, but what is it in normal PS ventilation. I use common sense and a study that we did a few years ago. The pressure will decrease across a ETT so the pressure you are reading at the vent is not what the patients lungs are seeing. Low levels of PS can be used 5-8 cmH2O without any or much being shown at the carina. Now if you go with Habashi's "dogma" then no PS because it is pushing the breath into the patients lungs vs the patient pulling it. This pushing of the breath causes the breath to go anterior (assuming patient line supine) due to less resistance vs pulling the breath in will pull it more posterior (where you are wanting it).