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<GJ,RRT>
posted
Forum,

This is the current information provided to the docs via "up-to-date. How does one convince an evidence based doc, that APRV has it's place?

GJ


AIRWAY PRESSURE RELEASE VENTILATION "” Continuous positive airway pressure is supplied to inflate the lungs during airway pressure release ventilation (APRV). The pressure is released cyclically, allowing the airway pressure to drop, gas to leave the lungs, and CO2 to be removed (show figure 3) [26,27]. In a paralyzed patient, APRV does not differ from PC-IRV. In spontaneously breathing patients, the cyclical release of airway pressure can be synchronized to occur after every few breaths, a modality termed intermittent mandatory airway pressure release ventilation (IMPRV) [28]. One advantage of this mode over PC-IRV is liberation from paralysis or heavy sedation and resumption of spontaneous breathing which in some animal models has been shown to improve V/Q matching [29].

Because intrathoracic pressure decreases with inspiration in spontaneously breathing patients, APRV tends to be well-tolerated hemodynamically. One trial switched patients with severe ARDS from IRV-PCV to APRV with an initial CPAP pressure of 75 percent of the prior peak airway pressure, and noted significant improvement in the cardiac index, O2 delivery, and vasopressor requirement [30]. Spontaneous breathing during APRV is associated with improved systemic hemodynamics and renal perfusion when compared to APRV without spontaneous breathing [31].

The presence of spontaneous respirations during APRV should favor distribution of ventilation to dependent, poorly aerated but perfused lung zones due to the "uncoupling" of spontaneous and ventilator-supported breaths. This view is supported by the observation that V/Q matching is enhanced when APRV is compared to mechanical ventilation utilizing PSV at the same airway pressure [32].

Since APRV involves the intermittent cyclical release of airway pressure from an upper (Phigh) to a lower (Plow) pressure level independent of spontaneous breaths, several studies have investigated the effects of different release times (duration of Plow) on gas exchange. In one study of 35 patients ventilated on APRV, various combinations of duration between upper (Phigh) and lower (Plow) pressure levels were applied. The study showed different release times were compensated by changes in spontaneous breaths, and did not effect oxygenation or ventilation [33].

The theoretical benefits of APRV are still being investigated:

One short-term study compared the use of VC-IRV and APRV in 18 patients with moderate to severe ARDS; each modality was used for 24 hours [7]. Decreased shunt and progressive alveolar recruitment, as evidenced by decreases in the alveolar-arterial gradient divided by FiO2, were seen after 16 hours of use with APRV but not with VC-IRV (show figure 4). Thus, patients receiving APRV had delayed gains in oxygenation without neuromuscular paralysis.
A randomized trial of 30 mechanically ventilated trauma patients at risk for ARDS compared APRV to pressure-controlled, time-cycled ventilation for 72 hours before crossing over to APRV [34]. During the initial 72 hour period PaO2/FiO2 ratio was higher and cardiac shunt was lower in the APRV group. As a result, fewer patients in the APRV group eventually met criteria for ARDS as opposed to acute lung injury. Spontaneous breathing was permitted in this trial, and less sedation was required in the APRV patients. The APRV also group had a shorter duration of ventilatory support, intubation, and ICU stay; however, mortality did not differ between groups.
A controlled trial randomly assigned 58 patients with ALI to either APRV or SIMV plus pressure support and found no difference in physiologic variables (PaO2/FIO2 ratio, PaCO2, pH, minute ventilation, mean arterial pressure, cardiac output) or outcomes (ventilator-free days and mortality) measured at day 28. They concluded that APRV did not differ from SIMV plus PS in clinically relevant outcomes [35].
At the present time, this modality remains experimental and has not been sufficiently evaluated in long-term clinical trials to recommend its use. APRV is relatively contraindicated in patients with severe obstructive airways disease or a high ventilatory requirement. In these circumstances, dynamic hyperinflation, high alveolar pressures, and barotrauma may result.

RECOMMENDATIONS "” Owing to the lack of controlled data demonstrating benefit, we do not consider using any of the above alternate ventilation modalities unless oxygenation goals cannot be met with conventional or open-lung ventilation, either with or without adjunctive prone positioning. In patients whose oxygenation fails to improve with these measures, we implement PC-IRV, with prone positioning if needed, and consider ECMO as a rescue modality.
 
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PC-IRV is really APRV without the "free breathing" exhalation valve. One could setup a paitent in APRV, look at the tidal volumes generated, then go and setup the patient in exactly the same I:E ratio in CMV with Autoflow on and flow assist off. It would then just be "volume targeted APRV". The oxygenation might not be as good because as soon as lung was recruited then the "P High"/Autoflow PC/VC PiP target would immediately ramp down.

Or one could setup the patient in the SIMV version of PC, no PS cept ATC, in exactly the same P High/P Low and I:E, other than the look of the screen and the adjustment interface, it would be the same as APRV.

I am not really a detractor nor a rabid advocate of APRV. I just think it's funny that a mode can thought of as experimental when exactly the same thing can be accomplished via other modes and settings not thought to be experimental (i.e. PC-IRV).
 
Posts: 171 | Location: Palo Alto, CA USA | Registered: November 14, 2002Reply With QuoteReport This Post
<brandx>
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This is a horrible study. Again APRV was used to target volumes of 6mls/kg and the tlow and Plow settings were not appropriate.
 
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Jeff,
Yes APRV and PC-IRV are clesly related and could be set up simulair, but most of the time when people are setting up PC-IRV the are using I:E's of 2:1 to wher APRV is using I:E's of 6:1. And to go along with that the benifits of free breathing that you mentioned, and the ease of manipulating the Tlow independantly of each of other parameters. To achieve this in PC-IRV you would have to play with your RR and IT setting. PC-IRV also uses PEEP to maintain FRC instead of looking at Tlow and flow waveforms.

Could some one set up a PC-IRV to look simulair to APRV yes, but why? APRV in principle is different in many areas than APRV, I can make something else look like, but it is still not APRV.

My kid can dress up like sperman on halloween, but that does not mean he is.


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Posts: 104 | Location: Springfield, MO | Registered: March 08, 2004Reply With QuoteReport This Post
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Was that a typo? Or do you really let your kid dress up like Sperm Man for Halloween, complete with the tail and all? And if he did dress up like Sperm Man, would you call it experimental? I better stop there!

Eek

The point I was trying to make is that I found it a bit silly that a place would embrace PC-IRV as OK and then view APRV as experimental. I agree with you in regards to the differences between APRV and PC-IRV, I just don't think that the difference is so great that someone could embrace PC-IRV yet view APRV as experimental. Also many of the Servo connected studies look at things like Open Lung Concept in which PC in high rates and purposeful auto-peep is done in a fashion of APRV, but clearly without augmenting spontaneous breathing. So it's almost like someone whom embraces MA-1 A/C mode but then looks at CMV/Autoflow or PRVC or VC+, better triggers, better response time, PC/VC hybrid, and would call it experimental. They are all just refinements of the basic strategy of A/C Volume targeted ventilation.

When using such strategies with modes/vents such as PC-IRV, oscillator, Open Lung Concept, whether or not the patient is spontaneously breathing, I think APRV mode provides an easy interface to set it up.
 
Posts: 171 | Location: Palo Alto, CA USA | Registered: November 14, 2002Reply With QuoteReport This Post
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We don't use PC-IRV or APRV. I want to use APRV but I would ask again.
How does one convince an evidence based doc, that APRV has it's place?


Chris Hanson RN, RRT-NPS, CPFT, AE-C
ER Registered Nurse
Grand Junction, Colorado
 
Posts: 66 | Location: Grand junction, colorado | Registered: August 21, 2006Reply With QuoteReport This Post
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Jeff,
Yes it was a typo, I have just had the opportunity to read what I wrote. Man I should really slow down I had MANY typo's in that last post and making my son a sperm was the worst (even though that would be funny to see peoples faces)
Sorry to have miss read your last post, I did not get what you were going for. But yes we do agree the importance of APRV and sometime the comedy behind getting it started over other modes. the lack of understanding is interesting. I have had doc that would not let me increase the PEEP to 15, but would allow me to go to APRV with my own settings (Phigh of 30).

GJ a evidence based doc should be the best to get to try APRV. There is a lot of evidence about its abilities. The hard ones are the ones stuck in their ways that do not want to look at the evidence.


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Posts: 104 | Location: Springfield, MO | Registered: March 08, 2004Reply With QuoteReport This Post
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The problem with evidence based docs and things like APRV is that there isn't solid evidence that it improves mortality or shortens ventilator days.

Sure there is evidence that APRV works, but there is also evidence that it doesn't make a difference. This same problem occurs with things like high frequency oscillator in adults and recruitment maneuvers.

People like Dr. Amato and Dr. Lachmann have been preaching for years about low tidal volumes and higher PEEP levels for ARDS patient (for them it made sense from a physiology point of view) but it wasn't till the huge ARDSnet study that people finally caught on.

I would recommend using things like APRV or HFOV when you can no longer provide lung protective ventilation with conventional ventilation. (This what DR. Neil McIntyre at Duke does when it comes to HFOV in adults).

Sorry, but until some large multicenter trials are done using APRV, you may be out of luck when it comes to convincing your doc about APRV. You could also try to make an argument from a physiology point but that's not always an easy task.

-- Jeffd

Also, I believe that modes don't really make a huge difference it how you use those modes that make a difference.
 
Posts: 11 | Location: Saskatoon, Canada | Registered: November 28, 2006Reply With QuoteReport This Post
<brandx>
posted
JeffD,

What is your definition of lung protective ventilation? I would also be curious to know from the forum how many patients being ventilated utilizing the the Low Tidal Volume approach do not require heavy sedation?

I am a firm believer in the "Open Lung Strategy"; recruit the lung early and keep it open...for me there is no better mode than APRV to achieve these goals.
 
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JeffD

quote:
I would recommend using things like APRV or HFOV when you can no longer provide lung protective ventilation with conventional ventilation. (This what DR. Neil McIntyre at Duke does when it comes to HFOV in adults).


1. Why? Though I unfortunately do not use APRV or HFOV, but am working towards APRV. Why use HFOV, different machine, circuit not as flexible. APRV appears that it would be better tolerated=less sedation. APRV uses ATC, not available with HFOV. Other than MRI you can transport(CT,OR,specials,etc.) on APRV, not so on HFOV. I've tried all the modes on our XL's via a mask and APRV did feel best to me=less sedation. How high can you get your MAP with ARDSnet vs. APRV? Why only use APRV in ARDS?
2. Just because Dr.Mcintyre does it doesn't mean it's the best or only choice.

There needs to be a multicenter study comparing APRV to ARDSnet, since all newer ventilators offer APRV or their(840,AVEA,etc) version.

GJ

This message has been edited. Last edited by: GJ,RRT,


Chris Hanson RN, RRT-NPS, CPFT, AE-C
ER Registered Nurse
Grand Junction, Colorado
 
Posts: 66 | Location: Grand junction, colorado | Registered: August 21, 2006Reply With QuoteReport This Post
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