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+--- Thread: Importance of flow limits when titrating ASV (/Thread-Importance-of-flow-limits-when-titrating-ASV)
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Importance of flow limits when titrating ASV - raylock1 - 04-07-2023
I have been using an AVS for about 3 years. The EPAP has been set at 9. After reading some old posts, it occurred to me that this may be too high. So I have reduced the EPAP from 9 to 8 and then to 7. At the level of 7, I am still seeing zero obstructive apneas. I find that I am sleeping well (better?) at the lower rate. However, I have not given any consideration to the number of flow limitations some of which reach a level of 1. How and/or how much should the level of Flow Limitations enter into the titration process? Thanks.
RE: Importance of flow limits when titrating AVS - Sleeprider - 04-08-2023
I assume you meant ASV rather than AVS so I'm going change the title to reflect that. It would really help to see some Oscar charts. EPAP is the setting used to keep the airway patent against OA (will flag as UA on your machine), and we try to keep the EPAP low on the ASV, and perhaps use ASV auto in a range that allows adjustment. Flow limitation is often seen in ASV when a lack of spontaneous effort results in a machine generated breath. These typically look flow-limited, however, if a lot of low-level flow limitation is present, we may want to look at PS min as well. I think this would be easier to answer with a chart that includes your settings, respiratory statistics, Events, Flow, Mask pressure, Flow limitation, etc.
RE: Importance of flow limits when titrating AVS - raylock1 - 04-08-2023
[attachment=49644 Wrote:Sleeprider pid='472344' dateline='1680963519'][attachment=49644]I assume you meant ASV rather than AVS so I'm going change the title to reflect that.
Yes, Sleeprider, thanks for that. It seems my dyslexia was on display.
I was just looking for general information but I agree that it's more helpful to look at specific cases. I will post an Oscar page (if I can remember how)
RE: Importance of flow limits when titrating AVS - Sleeprider - 04-09-2023
My impression is that flow limits are generally very low as indicated by the 0.0 95th percentile flow limit statistic. Individual breaths show high flow limitation, and as I suggested above, these are likely breaths where there is a lack of spontaneous effort rather than obstructive or restrictive flow limitation. Note all of your flow limits are individual vertical lines, rather than a period of elevated flow limitation. I think the difference is important for people using ASV to understand. With central apnea, some breaths are delivered by the machine pressure support, and as this type of inspiration proceeds resistance or back-pressure increases as the chest is not expanding to cause the movement of air. This flattens the peak of the inspiratory wave as the machine pushes to achieve target vent. With obstructive or restrictive flow limitation, the resistance is in the upper airway. With spontaneous effort the chest rises and creates negative pressure to cause airflow. Any constriction, or obstruction by tissue in the upper airway can limit the peak flow rate. The mechanisms are very different, so this is why we are not concerned with the appearance of flow limits with ASV.
RE: Importance of flow limits when titrating AVS - raylock1 - 04-09-2023
Here are a couple screen shots from last night. I reduced the EPAP to 6
RE: Importance of flow limits when titrating ASV - raylock1 - 04-09-2023
Thanks for the explanation. I think I was posting the last reply at the same time you were posting.
RE: Importance of flow limits when titrating ASV - Sleeprider - 04-09-2023
Still looks good. Note the individual flow limits are quite spaced out in the zoomed graph, and I think if you zoom in even more, you will see the flow limits align with individual breaths where a higher mask pressure is being delivered during an "under-performing" breath that is typical of central and complex apnea. If you can line up flow rate, mask pressure and flow limitation, and zoom in fairly tightly, I'm sure you will see a pattern emerge as you scroll across these flow limit occurrences.
RE: Importance of flow limits when titrating ASV - raylock1 - 04-14-2023
Here is a 10 minute period when there was a cluster of flow limits. The flow graph is strange. Possibly the ASV was doing its job during this period as evidenced by the pressure in the mask?
I am confused by the pressure settings. The original prescription was for Ps Min 0, Min EPAP 9: while I have been using Ps Min 3 and EPAP min 6. Both result in a min IPAP of 9. Aren't they basically the same setting?
RE: Importance of flow limits when titrating ASV - Sleeprider - 04-14-2023
I'm seeing brief periods of flow limitation where pressure support is relatively low, and these reductions in flow are followed by larger breaths or recovery breathing. These appear to be RERA events. These may be reduced respiratory effort, but since the inspiration peaks appear flattened (a bit closer zoom is needed) they may be obstructive. An area this is prominent is 03:00:45 to 03:02:15. Your screenshot covers about 13 minutes, and a more useful resolution is closer to 3-4 minutes so we can better interpret the flow.
RE: Importance of flow limits when titrating ASV - Rich66 - 04-15-2023
raylock1 Both result in a min IPAP of 9. Aren't they basically the same setting?
They are the same for the IPAP minimum AT 9 -- BUT the treatments are different because of the differences in EPAP settings -- and Pressure Support settings. And then factor in how they relate to the EPAP maximum and Pressure Support maximum. When trying to figure out how to set and adjust settings, think of the EPAP as separate from the IPAP. Question if you should turn the EPAP higher or lower for your needs. Then question if you should turn the IPAP higher or lower for your needs == and yes, you change the PS settings to set the IPAP. Also, keep in mind, the ACTUAL EPAP at every particular moment is in charge -- the Pressure Support follows the lead of the EPAP.
If your EPAP min is 5, and max is 9 -- and PS min is 3, and max is 12 == at the point where your EPAP is at 7.2, then the max you'll get for IPAP is 19.2. If you follow that very moveable vertical green line and then look at the graph figures you can see the actual readings at any particular time.
As for IPAP, are you having headaches, bloating, or burping issues -- then turn the pressure support down. Do you feel like you're having to pull in the air to get enough air, then turn it up. As for EPAP, try to figure out where you get the best sleep with fewest apneas. An AHI score of 0.00 is great, but not if you still feel sleepy all day. The important question is "how do you feel". Also, in my opinion, try to keep leaking to a very minimum so you get true scores from the graphs to help you.