Overnight Pulse Ox Test - Updated Sat Night

[Madalot]

I have been doing nightly pulse ox tests using my monitor, the 50F wrist monitor. Last night's test has me a tad perplexed (report to follow). The report is indicating NO desaturation events, yet it lists my lowest level at 83 and the graph shows about 4 desats below 88%. Does that mean that they weren't long enough to warrant being an "event" or is something wrong with my monitor/software?


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[echo]

Sounds preplexing to me too, madalot. I would guess that either the drops were less than 4% and/or less than 10 seconds.

Tou can play around with the graphs: magnify the graph so that you can see the events down to the minute, from there you can probably see how quickly the pulse-ox is changing. Second, you can try a different setting in the thresholds/parameters, so instead of 4% set it to for example 2% or 5 seconds rather than 10 seconds. Although you had a lot of events, you probably recovered from each one quickly. On the other hand, can the SPO2 change so quickly, in both directions? I don't know. Your pulse ox does not report any "artifacts" though I would probably expect it (limb movements, fo example). What happens when you move around your arm or fingers with the pulse-ox connected (when awake)? Does the reading bounce around? Your pulse graph on the other hand is pretty stable.

As for the verdict, is it broken or not? Probably not I would say, just from the other info listed. But maybe someone else has some more professional advice!

[Madalot]

Thanks for the input, Echo.

I think what's got me confused is that previous tests HAVE shown similar drops, but the report indicates them as events and lists the average event duration in seconds -- mine have been anywhere from 25-45 seconds average. From the looks of this report (and keeping previous tests in mind) the logical conclusion is that while I did have those desaturations, they didn't last more than the 10 seconds required to log them as an event.

Based on previous tests, I have a very hard time believing that this is accurate.

As to your question about movement, I have tested that and regular movements don't cause any issues or artifacts. I HAVE had artifacts before and depending on how many and the severity, I discount the entire test because of it. In recent weeks, artifacts haven't been much of an issue.

I'm just confused all the way around.

[-SWS]

either the drops were less than 4% and/or less than 10 seconds.

Well, looking at that definition of "Desaturation Event" on your above chart, Madalot, I think echo probably got it right.

Did you per chance save that file? If so, view it again using your "SpO2 Review" software. At the bottom of the screen you'll see soft buttons for 1, 10, 60, and M. Select the 1 minute intervals instead. Then use the scroll-right and scroll-left buttons to position that one-minute epoch right where your worst desaturations occurred. You'll notice the horizontal axis is now comprised of 10-second increments or divisions. You should be able to see whether those desats were at least 10 seconds long. You will also be able to see if the downward slope was either steep or gradual. An overly-gradual drop, for instance, might not meet the software's "Desaturation Event" scoring criteria. That definition is not clear about the maximum time window allowed for the 4% drop against recent baseline.

[echo]

An overly-gradual drop, for instance, might not meet the software's "Desaturation Event" scoring criteria. That definition is not clear about the maximum time window allowed for the 4% drop against recent baseline.

Correct, I've often wondered about that too. What exactly is the time window used to conclude a "drop". On my father-in-law's recent pulse ox he also did not have too many events even though there were drops into the high 80%s (but he had 60% "artifacts".

[-SWS]

That definition is not clear about the maximum time window allowed for the 4% drop against recent baseline.

What exactly is the time window used to conclude a "drop".

I'm thinking that if a patient spends sustained time at say 80%, that sustained SpO2 drop would be probably be considered "hypoventilation" by the software rather than a short, discrete "Desaturation Event". I think the 10-second criterion is a clue that the software scoring probably attempts to correlate those events with apneas and hypopneas---both of those latter also requiring 10-second durations.

he had 60% "artifacts".

I bet archeologists and anthropologists are just clamoring to see him... <Vaudeville rimshot>

[Madalot]

either the drops were less than 4% and/or less than 10 seconds.

Well, looking at that definition of "Desaturation Event" on your above chart, Madalot, I think echo probably got it right.

Did you per chance save that file? If so, view it again using your "SpO2 Review" software. At the bottom of the screen you'll see soft buttons for 1, 10, 60, and M. Select the 1 minute intervals instead. Then use the scroll-right and scroll-left buttons to position that one-minute epoch right where your worst desaturations occurred. You'll notice the horizontal axis is now comprised of 10-second increments or divisions. You should be able to see whether those desats were at least 10 seconds long. You will also be able to see if the downward slope was either steep or gradual. An overly-gradual drop, for instance, might not meet the software's "Desaturation Event" scoring criteria. That definition is not clear about the maximum time window allowed for the 4% drop against recent baseline.

Even if it isn't saved, I can download it again from the monitor if necessary. I will try to do that sometime today and let you know what the results are. I'm in the midst of a few crises right now, but hopefully things will settle down this afternoon and I can try this.

Thank you! I appreciate that input.

[M.D.Hosehead]

I'm also perplexed by Madalot's tracing. I think Echo and SWS are right that It would make a big difference if the "window" were 30 seconds, or 1,3, or 5 minutes, but we don't know what it is.

I also agree with the need to look at the expanded time scale (Echo clued me into that on a previous post; thanks). Perhaps, as SWS suggests, a too gradual change doesn't get flagged. I also suspect that a too-rapid change is probably a movement artifact. For example, if the O2 % drops from 95% to 86% in a few seconds, I'd disregard it. You can't make it drop anywhere near that fast by holding your breath.

OTOH, on the large scale (the report you posted), the long periods of low and fluctuating saturation, e.g. from hours 2.4 to 3, are accompanied by a generally increased pulse rate. Since that is a known physiologic response to low O2 saturation, it seems something undesirable must be happening to your SaO2. And yet as you say, the column, "SpO2" records zero events and zero % artifacts. I can't understand that.

Does review of your machine's printout enlighten this question? You have a servo machine? I'm totally in the dark about what kind of oximeter records those can cause.

[Madalot]

Thanks for the help everyone. I appreciate the fast input on this.

All my crises are in holding patterns right now, so I did what was suggested and looked at the information in smaller time increments. I looked at the 3 more significant desats (the first one looked like it was around 87% so I didn't do that one).

Here's what I found:

2:37:40 -- I was at 90% and noticed a step-like downward trend. It went to a low of 84% and went back up into the middle 90's at 2:38:10. The upward back to middle 90's was sharp, NOT step like. The entire "trip" took 20 seconds.

4:17:50 -- Started at 93% and did the step thing again down to 83%, then went back up to 99% at 4:18:25. This trip took 35 seconds.

4:29:10 -- Started at 97% and stepped down to 84%. The upward was sharp and I was back up at 98% at 4:29:50. This trip took 40 seconds.

M.D.Hosehead -- I am on a ventilator, running in S/T AVAPS mode, with a target tidal volume of 400 and a pressure range of 14 - 23. I don't have access to software for this machine. My pulse ox monitor is the CMS-50F wrist monitor.

[echo]

I would say, based on this, that a larger time window of eg 20 seconds would pick up those "events. What that means physiologically, I would leave to MD and SWS to answer! (IMHO they are probably significant, and do not represent artifacts).

BTW good point with the pulse reading - that alone was one of the reasons that I did not suspect artifact or misreadings (thank you MD for explaining it clearly).

[Madalot]

I would say, based on this, that a larger time window of eg 20 seconds would pick up those "events. What that means physiologically, I would leave to MD and SWS to answer! (IMHO they are probably significant, and do not represent artifacts).

BTW good point with the pulse reading - that alone was one of the reasons that I did not suspect artifact or misreadings (thank you MD for explaining it clearly).

Thanks Echo. I'm a little confused again -- but that's not unusual these days. LOL

The program is set to indicate an event: a drop in sp02 by at least 4% for a minimum duration of 10 seconds. The way my brain is thinking is that because each of the drops (steps) lasted LESS than 10 seconds, it didn't record them as events. Setting the window HIGHER would make it even less likely to pick it up as an event.

Or is my brain not looking at this right???

[-SWS]

2:37:40 -- I was at 90% and noticed a step-like downward trend. It went to a low of 84% and went back up into the middle 90's at 2:38:10. The upward back to middle 90's was sharp, NOT step like. The entire "trip" took 20 seconds.

4:17:50 -- Started at 93% and did the step thing again down to 83%, then went back up to 99% at 4:18:25. This trip took 35 seconds.

4:29:10 -- Started at 97% and stepped down to 84%. The upward was sharp and I was back up at 98% at 4:29:50. This trip took 40 seconds.

Well, all the upward trends and their contributing durations in seconds don't actually matter---since "desaturation event" scoring by the software only focuses on: 1) downward trends, and 2) whether THEIR durations happen to drop 4% for 10 seconds.

In light of those above two points, I would attempt to note the SpO2 numeric value (short-trend average??) immediately prior to the drop. Then I would mentally create a 10-second sliding window (sliding left-to-right), and see if a 4% comparative drop is ever sustained for at least 10 seconds.

Here's an arbitrary example of what I think would qualify as a 4% desaturation event:
SPo2 starting at 93%, then at any near-subsequent point SUSTAINING at least 10 seconds at 89% or lower.

Thus briefly dipping 4% or more for less than 10 seconds would not qualify.

[echo]

Well, I was thinking that you need to widen the window (so 20 seconds for example) because your SPO2 is dropping too slowly for it to flag it as an event. For example, maybe during those "steps" you mention, it only drops by 2% in 10 seconds, rather than 4%. Increasing the window would pick those up too. Like SWS says, check the detailed graph to see whether you can determine how many seconds it takes for the SPO2 to drop by 4%. Is that more clear?

[Madalot]

I went and looked at one of the three desats and clocked it by seconds where it was obvious there was a change:

4:17:20 -- 98%
4:17:30 -- 97%
4:17:40 -- 94%
4:17:50 -- 92%
4:18:00 -- 88%
4:18:10 -- 86%
4:18:12 -- 84% -- it stayed here until
4:18:25 -- Started back up and peaked
4:18:33 -- at 99%

I would think that when it stayed at 84% for 13 seconds, it should have indicated that as an event???

[echo]

Oh, I think I understand the misunderstanding. The pulse ox could be flagging two things:
1) A drop in the SPO2 of minimum 4% and stays at the low SPO2 for 10 seconds before it starts to increase again. But then what is the time window of that "drop" to occur?
or
2) A drop of 4% during a window of 10 seconds, after which it increases (or not).

My thinking is that it's the second case. In the case of the first case, then you are right, and the 10 second window would be too large in your case since your low SPO2 doesn't last for minimum of 10 seconds.

Ugh, now *I* am confused!