Little Larissa - please read

Well, there's BiLevel with SV mode turned on and there's BiLevel with SV mode turned off. So I think Dr. Vergara is correct in saying that he is using BiLevel: a separate expiratory pressure and a separate inspiratory pressure.

And Banned is correct in saying that Dr. Vergara has BiLevel SV mode turned on and not BiLevel ST mode. And yet the machine behaves as if it were set up in ST mode. It behaves that way since IPAP peak just about always reaches the set value of IPAP max. The IPAP peak line is literally superimposed or overlain directly on top of the IPAP max line. You could literally set IPAP min at the same value as IPAP max and achieve those same results.

Essentially, here is what I think is happening with Laryssa's IPAP delivery: 1) she's late for almost every breath, so the machine initiates virtually each breath, then 2) she invariably approaches the left reference curve of inspiration so slowly that IPAP max is algorithmically extrapolated as compensation for every breath.



Off the top of my head:

The similarities between Auto SV and AVAPS:
1) both directly target and deliver pressure support (neither machine directly delivers flow),

2) both have an IPAP max and IPAP min as well as having an EPAP,

3) both use flow as secondary targeting variables, and

4) both AVAPS and SV algorithms were modeled using adult respiratory curves (unlike BiLevel ST modality which is often used for children).


The differences between Auto SV and AVAPS:
1) AVAPS allows an assured tidal volume (a constant or fixed value) that is directly keyed-in by the clinician, whereas SV does not (hence no volume assurance with SV),

2) AVAPS will slowly increase IPAP pressure on a gradual as-needed basis, whereas SV will very quickly increase IPAP pressure on a per-breath basis (not to confuse AVAPS with older VAPS)

3) AVAPS works with tidal volumes whereas SV works with peak flow

4) SV will analyze peak flow to recognize four states: a) high respiratory drive, b) acceptable respiratory drive, c) low respiratory drive, and d) an oscillating respiratory drive typical of CSR (oscillating between states A and C); AVAPS does not attempt to perform any "drive state" recognition for its IPAP pressure response.

Hope this helps!

Thanks SWS,

I could follow that ok.

The bottom line of your post is that

1) AUTOSV tracks peak flow (4 min window) & uses pressure support breath-by-breath to achieve its min Peak Flow target averaged from the 4 min tracking.

2) AVAPS tracks tidal flow and uses slowly adjusted pressure support to try to keep the user's tidal flow on target.

If we compare 1) to the Vpap AdaptSV, the VpapSV tracks volume & rate in a 3 min window & adjusts pressure precisely and within a breath to keep to its target and inspiration waveform.

DSM

Also re setup of the Bipap SV - this is what I think it does (haven't tried, am just going from memory of the manual)


I think that ...
Epap = Ipap sets it up as Cpap but if IpapMAX is set higher than IpapMIN & Epap then the machine activates SV and will adjust IpapMAX to meet a tidal flow target. Thus it operates a bit the way I am seeing in Laryssa's chart. And the printouts will probably refer to Av Peak Ipap.


If Epap < IpapMIN and IpapMAX = IpapMIN than it is in Bipap S mode. Then if BPM is set to a number (3-30 I think) it is in Bipap S/T mode.

As a general rule ...
When IpapMAX is set above IpapMIN, SV mode is always activated.


Re the printed data charts, I am in agreement with SWS saying perhaps the orange line is overlaying the black line, but I am sure I have seen in my own charts where it is clear to see when one line overlays another. The confusion for me in Laryssa's chart is that it refers to Av Peak Ipap which I don't believe it should if the machine is in S or S/T mode. In those modes surely it should just be referring to Epap and Ipap (not Av Peak Ipap).

Am wondering if the machine is in CPAP SV mode ?.

DSM

_________________

CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, CPAP

_________________

CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, CPAP

dsm wrote:Thanks SWS,

I could follow that ok.

The bottom line of your post is that

1) AUTOSV tracks peak flow (4 min window) & uses pressure support breath-by-breath to achieve its min Peak Flow target averaged from the 4 min tracking.

2) AVAPS tracks tidal flow and uses slowly adjusted pressure support to try to keep the user's tidal flow on target.

If we compare 1) to the Vpap AdaptSV, the VpapSV tracks volume & rate in a 3 min window & adjusts pressure precisely and within a breath to keep to its target and inspiration waveform.

DSM

Sounds good! Here's another in-a-nutshell summary:

1) Assured tidal volumes and gradual pressure changes with AVAPS (for conditions like obesity hypoventilation, neuromuscular disease, and certain COPD cases), and

2) Averaged peak flows and quick per-breath pressure changes with Auto SV to compensate respiratory controller states (for conditions like CSA, CHF/CSR, CompSA)


There are some key differences between Resmed's Adaptive SV algorithm and Respironics' Auto SV algorithm that are probably beyond the scope of this thread.

dsm wrote:Am wondering if the machine is in CPAP SV mode ?

No it's currently set in BiLevel SV mode. To achieve CPAP SV mode you would set EPAP=IPAP min and then select an appropriate albeit higher IPAP max.

SWS,

Again that makes good sense to me. I do believe that I have stumbled upon uses for SV (in my use) that perhaps Respironics hadn't thought of. I still think of this machine as an amazing advance over cpap & apap & have a lot of reasons I can put forward to explain why. But that too is for a different thread.

DSM

brazilian wrote:DSM, in fact, the machine is set as bilevel, as I was told today by Dr. Vergara.

Since the machine is the only one in Brazil, they still have some doubts and are trying to figure out how it works, so they set it like that.

Hi Brazilian,

You may want to suggest to Dr. Vergara that the medical team adjust Laryssa's BiPAP from IPAP MIn 12 to IPAP Min 16, in order to bring the machine into Bi-level ST configuration.

In the current mode of operation (SV, if IPAP Min has not been changed since Laryssa's Aug. 5th, 2008 report) there is no known benefit for Laryssa. As SAG suggested earlier, the machine is simply 'Auto Winging' her therapy, and may not be making best use of the device.

There is only so much the machine can do and it is unlikely that SV is what she needs. It would probably be more beneficial for Laryssa to be utilizing the device as a Bi-level ST.

Banned

Well, I would preface my comments by saying that continuing to use the Servo Option is pointless (however, I don't think it's "dangerous", or even "harmful", it's providing therapy in spite of mode selection rather than because of it).

Back when the back-up rate was set at 20, which generally allowed about 15% of patient generated breaths to occur, I believe that the Apnea Controller was taking precedence, and the IPAP floated within Min and Max.

When the rate was increased to 25, virtually all patient effort is suppressed. By prediction, as well as the available reports, Peak Flow is generally in the 12.5 LPM range. The patent suggests that a default minumum Target Flow is set at 15 LPM, so now essentially every breath needs support and pressure stays buried at IPAPMax (although I don't believe that's actually the case, I think there is some breath-to-breath variability, that level of detail is just not seen in the coarse overview of the graph).

Now I have a question. Why are we at 16/12 cmH2O IPAP 7 cmH2O EPAP when the original parameters were supposed to be 15/5?

Syn......chro......ny......

SAG

StillAnotherGuest wrote: When the rate was increased to 25, virtually all patient effort is suppressed.

That was my thought, unless it is the intent to ensure all breathes are machine initiated. They may still be chasing O2 desat levels. I'm not sure how much fun Laryssa is having breathing with the machine, but she looks peaceful.

StillAnotherGuest wrote:Now I have a question. Why are we at 16/12 cmH2O IPAP 7 cmH2O EPAP when the original parameters were supposed to be 15/5?

This may be a result of dsm's observation that the BiPAP Auto SV looses 1cmH2O at the mask end of the hose (e.g. no proximal tube). I have no guess where the additional 1cmH2O EPAP (lose) came from.

StillAnotherGuest wrote:Syn......chro......ny......

Good point!

Banned

Banned wrote:

StillAnotherGuest wrote:Now I have a question. Why are we at 16/12 cmH2O IPAP 7 cmH2O EPAP when the original parameters were supposed to be 15/5?

This may be a result of dsm's observation that the BiPAP Auto SV looses 1cmH2O at the mask end of the hose (e.g. no proximal tube).I have no guess where the additional 1cmH2O EPAP came from.

Banned, I realize you meant "where the additional 1cm IPAP came from". And I realize that we're all wondering where that additional 7cm EPAP came from. I know I sure am.

However, I doubt that additional 7cm EPAP (for a total of 12cm) directly or indirectly came from dsm's emphasis about how surprisingly low 5cm EPAP was (coupled with mouse-breathing analogies---not to be confused with popular mouth-breathing concerns). DSM correctly and very considerately emphasized that he is not a health professional or biomedical engineer of any kind. And I believe DSM had specifically mentioned an EPAP setting arund 6cm much earlier in this thread.

Regardless, I think that Dr. Vergara realizes patients on this message board generally have considerably more expertise with CPAP machinery than diseased physiology. And I suspect most of us realize that you can't effectively integrate diseased physiology with advanced biomedical machinery without adequately understanding both complex halves of that biomechanical systems-related merger. In Laryssa's case the physiologic and machine-related considerations are not a simple matter of differentiating central-apnea/obstructive-apnea or full-block/no-block.

Laryssa may have neuromuscular related CSA. Nelson had mentioned much earlier in this thread that neuromuscular related disease is one of Dr. Vergara's areas of expertise. In cases of neuromuscular disease (cases that are most often unaccompanied by classic OSA-type airway obstruction) EPAP is often appropriately set as low as 4cm or 5cm. My understanding is that the wider PS and lower EPAP often help with mechanical unloading, which in turn can help mediate CO2 exchange. Additionally, lesser diaphragmatic muscular effort typical of any three-year-old child may require more mechanical unloading (via lowered EPAP) than muscular effort typically sourced by an adult with a healthy and fully functional diaphragm.

The fact that Laryssa initially achieved her best results during a PSG at 15/5 makes me also wonder why EPAP is all the way up at 12cm.

-SWS wrote: The fact that Laryssa initially achieved her best results during a PSG at 15/5 makes me also wonder why EPAP is all the way up at 12cm.

Min PS is at 12, EPAP is still at 7.


Banned

banned wrote:Min PS is at 12, EPAP is still at 7.

And who says apnea adversely affects memory or cognition? As a side note I had to take a pass on cutting sheet metal today because my "visual jitters" are not at all behaving. Memory and general cognition are not far behind on those days. Thanks very much for kindly straightening that out, Banned!

To summarize, the current SV setting of IPAP max=16 and IPAP min =12 with EPAP=7 algorithmically malfunctions very similar to a functional ST setting of 16/7 in this potential misapplication of SV.


And to further summarize, the above results and settings beg these two questions:

1) Why not just set up in ST mode at 16/7, since SV mode can't function as designed in this pediatric case?

and

2) How did the initial PSG recommendation of 15/5 migrate into the currently employed BiLevel values, which happen to function as near-equivalents of ST 16/7 (despite SV modality being turned on simply by setting IPAP min and IPAP max at different values)?


Again, thanks for straightening that out, Banned.

2) How did the initial PSG recommendation of 15/5 migrate into the currently employed BiLevel values, which happen to function as near-equivalents of ST 16/7 (despite SV modality being turned on simply by setting IPAP min and IPAP max at different values)?

Laryssa migrated from 2 year old to 3 year old during that time. Couldn't that be the reason?


O.

ozij wrote:Laryssa migrated from 2 year old to 3 year old during that time. Couldn't that be the reason?

Sure sounds like one reasonable possibility to me, O. There's not a vast difference between genuine ST of 15/5 and SV modality behaving like an ST machine set at 16/7. The PS values are 10 and 9 respectively.

Depending on her condition, PS may get smaller and EPAP may get higher as she physically matures. That hypothetical pressure trend would approach what we are most familiar with as adult BiLevel/CPAP users with healthy diaphragmatic breathing effort (pulmonary effort requiring less neuromuscular mechanical unloading).

SAG wrote:I think there is some breath-to-breath variability, that level of detail is just not seen in the coarse overview of the graph

I agree. There are roughly 1,500 pediatric breaths packed into each hour-long epoch. Tough to pick out any hundred-breath segment on that summary graph, let alone any two or three consecutive breaths.

-SWS wrote:
<snip>

dsm wrote:Am wondering if the machine is in CPAP SV mode ?

No it's currently set in BiLevel SV mode. To achieve CPAP SV mode you would set EPAP=IPAP min and then select an appropriate albeit higher IPAP max.

Agreed, Doug. Anytime IPAP max is not equal to IPAP min, then the SV algorithm is enabled. Conversely anytime IPAP max is equal to IPAP min, then the SV algorithm is disabled.

In Laryssa's case, the SV algorithm is peaking out at IPAP max on just about every breath. And that's why it looks almost identical to having her machine set up at BiLevel ST of 16/7.



Some example Respironics BiPAP AutoSV settings with SV turned on and SV turned off:

EPAP=7, IPAP min=12, & IPAP max=16: BiLevel SV mode (12/7 during min and as much as 16/7 on an as-needed basis) (Laryssa's current setting, although 16/7 is almost always delivered)

EPAP=7, IPAP min=16, & IPAP max=16: BiLevel ST mode (BiLevel 16/7 at all times)

EPAP=7, IPAP min=7, & IPAP max=16: CPAP w/ SV mode (CPAP=7 during non-SV moments, and SV ranging as high as 16/7 on an as-needed basis)

EPAP=7, IPAP min=7, & IPAP max=7: ordinary CPAP mode (CPAP=7 at all times)