Exploring the significance of desats

dsm · Post by **dsm** » Fri Feb 16, 2007 4:04 pm

Last week in another thread the topic of what constituted a desat came up (desat = desaturation which it turns out is when someone's SpO2 % drops by 4 points).

As this was something I had not registered previously (I had thought a desat was going below 88%), it naturally triggerd off a lot of questions in my mind & am hoping some of our medical members can clarify some of the questions ...

Q1 is the mention of dropping 4 points in 30 seconds relevant ?

Q2 if someone's SpO2 drops from say 96 to 92 (a desat) & goes back up within say 20 seconds, does this matter ?

Q3 are desats that occur above 90% less relevant than similar timed desats crossing below 90% & 88%

Q3 is the real importance of desats the actual number that occur on say a per hour basis ?

Tks

DSM

NightHawkeye · Post by **NightHawkeye** » Fri Feb 16, 2007 6:10 pm

DSM,

I'm certainly no clinician, but am certainly willing to offer an opinion relevant to your question. Although I've read that there is no standard definition for desaturation, the value of 4% apparently has some history. Here is a screen-shot for the SCORE oximeter software (with default settings loaded). Either of two conditions trigger a desaturation event; a desaturation below 89%, or a drop in SpO2 of at least 4%. Note, however, that the 4% drop can be from either the previous peak value or the average of previous highest events (at clinician's choosing), and that its duration must be at least 10 seconds (presumably to eliminate most motion induced drops).

So, in answer to your questions, the SCORE software behaves in the following manner:

Q1: Yes, 30 second events are scored.
Q2: Yes, the event is scored, even if SpO2 quickly returns to baseline.
Q3: SCORE software scores both as desats, and summarizes the total time spent below 89% as shown in the screenshot below:

Q4: The SCORE software doesn't involve itself with the number of desaturations per hour, although it's clear that the software could easily have been programmed to do so had it been deemed important.

It also needs to be stated that either desats below 89% or desat drops of 4% alone can be selected at the whim of the clinician. The clinician can also program the software to use a different desat value, 2% perhaps, as you indicated.

Hope this is the sort of info you were looking for.

Regards,
Bill

dsm · Post by **dsm** » Sat Feb 17, 2007 1:52 am

Bill,

That is very helpful info - it basically says that the clinician can go by a base set of values or can set their own.

The base info makes sense.

What I had been wondering in particular was if the drops from 96 to 92 were mildyrelevant or significantly relevant.

I have some software that analyses the output from my Ohmeda & the info you have provided looks like very useful param to set in for producing some stats.

Thanks muchly

DSM

lvwildcat · Post by **lvwildcat** » Sat Feb 17, 2007 7:58 am

I am a Critical Care RN and heres the general consensus of the pulmonologists- most are happy with an O2 sat >92%. But of course there are exceptions to every rule- in people with COPD(chronic obstructive pulmonary disease) it is not unusual for their O2 sat to stay at around 88%-let's just say some of these people"live there at 88%", In COPD pts it is actually harmful to try to achieve a saturation higher then their usual because it lowers their CO2 level and in these patients that is their drive to breathe. Us RNs often joke about these people in the 50-50 club;their O2 and CO2 levels are about equal but thats their norm.
I was quite shocked when I read results of my own sleep study. Even though it was a brief period-my O2 sat dropped to 57% YIKES!!!!!

StillAnotherGuest · Post by **StillAnotherGuest** » Sat Feb 17, 2007 9:03 am

lvwildcat wrote:In COPD pts it is actually harmful to try to achieve a saturation higher then their usual because it lowers their CO2 level...

It raises their CO2 level.
SAG

Slinky · Post by **Slinky** » Sat Feb 17, 2007 9:48 am

Good to see you posting again, SAG.

Aren't there two schools of thought for COPD patients on its being harmful to try to achieve a saturation higher then their usual?

Or am I just mixed up because in Pulmonary Rehab I was told to up my 02 to whatever level it took to maintain 95% 02 sats whilst exercising.

StillAnotherGuest · Post by **StillAnotherGuest** » Sun Feb 18, 2007 5:36 am

Slinky wrote:Good to see you posting again, SAG.

I've been basking in my BLT.

Aren't there two schools of thought for COPD patients on its being harmful to try to achieve a saturation higher then their usual?

Which two schools are you referrig to?

Or am I just mixed up because in Pulmonary Rehab I was told to up my 02 to whatever level it took to maintain 95% 02 sats whilst exercising.

Must get pretty breezy once you get up to 60-70 LPM.
SAG

Slinky · Post by **Slinky** » Sun Feb 18, 2007 7:46 am

Giggle. I don't exercise THAT hard in PR!!! They've set a target HR of 122 so I'm supposed to keep my 02 sats at 95% but not go over a HR of 122. I "was" doing 26 minutes on the treadmill at 2, 26 minutes on the AirDyne cycle at 6-7 and 26 minutes on the arm ergometer. The bike was the toughest and I "loved" the arm ergometer.

At EFFORTS an RT there also supports this opinion of however much 02 is needed to maintain 95% sats and says there are those who are changing their opinion about "too much" 02 under most conditions and do not support the theory that it raises their CO2 levels any more than it does their 02 levels. In other words, the balance remains the same.

I'm just parroting what I've read and been told. What do I know? That is why I asked you about two schools of thought.

Slinky · Post by **Slinky** » Sun Feb 18, 2007 7:54 am

LVWildCat, I remember when I was in the hospital a nurse cautioning another nurse about giving me oxygen to bring me up to a saturation higher then my usual. She said that since my body was used to working at my usual sats, bringing it artifically higher would upset that balance and my body would begin to require the higher sats and supplemental 02. Or something similar. I was hospitalized for a blood clot caused by improperly administered medication via IV in ER.

StillAnotherGuest · Post by **StillAnotherGuest** » Sun Feb 18, 2007 10:17 am

Slinky wrote:At EFFORTS an RT there also supports this opinion of however much 02 is needed to maintain 95% sats and says there are those who are changing their opinion about "too much" 02 under most conditions...

When he comes up with a treatment plan that relates to "all" conditions, have him call me.

Speaking of treatment plan, oxygen therapy should be based on a number of variables:

Whether you retain CO2 or not.
If you're at rest or at exercise.
If you're awake or asleep.
If you're stable or acutely ill.

LVWildCat, I remember when I was in the hospital a nurse cautioning another nurse about giving me oxygen to bring me up to a saturation higher then my usual. She said that since my body was used to working at my usual sats, bringing it artifically higher would upset that balance and my body would begin to require the higher sats and supplemental 02. Or something similar.

It was probably something like

nurse wrote:"Retain progressively more CO2 until she has a respiratory arrest."

Slinky · Post by **Slinky** » Sun Feb 18, 2007 10:31 am

Giggle. No she didn't mention anything that drastic. Even "I" would recognize that! But I'll grant you that you know a LOT more about all this than I do!!! That's why I was asking. I wasn't trying to be argumentative, just trying to gain some understanding. W/o a full background it is easy for a patient to interpret something said in a somewhat different light and it sounds like that is what I might have done.

StillAnotherGuest · Post by **StillAnotherGuest** » Mon Feb 19, 2007 6:54 am

Slinky wrote:No she didn't mention anything that drastic.

OK, how about

nurse wrote:"Alter ventilation/perfusion ratio to require an ever-increasing need for higher oxygen flows?"

Slinky · Post by **Slinky** » Mon Feb 19, 2007 8:53 am

Uh, uh. Nothing technical. Just to not mess w/the level of 02 my bod was used to functioning with.

lvwildcat · Post by **lvwildcat** » Mon Feb 19, 2007 9:54 am

SAG- your statement about high O2 increasing CO2 in COPD patients was correct. What was I thinking? Perfect example of why I(personally) should not do more than 1 thing at a time. I was typing response;talking with DH on phone;and getting dog ready for her weekly class all at same time.

Exploring the significance of desats

Exploring the significance of desats

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