SpO2 "lag"

[abckidsmom]

*Peers through tired eyes*...I can tell if you're agreeing with me, disagreeing or saying something different altogether :wacko:

Sometimes I really don't make any sense. I agree with you. I think.

 

[Brandon O]

Pulse ox never promised to be the lone ranger, then answer to the question of oxygen delivery, but it clearly has its uses. Its not completely useless just because you dont have a gas and a Hb/Hct.

No, course not. Just trying to point out that regardless of questions of accuracy, these variables are going to interact anyway...

 

[Melclin]

Man I must have been in some kind of snippy mood last night. I even got involved in an argument in the comments section of a news web site. How embarassmentingly.

Drinks all round.

My shout.

 

[Brandon O]

Man I must have been in some kind of snippy mood last night. I even got involved in an argument in the comments section of a news web site. How embarassmentingly.

Drinks all round.

My shout.

Your punishment will be drinking Foster's.

 

[Melclin]

Your punishment will be drinking Foster's.

Jeeze man. Its not like I murdered your mum. Harsh.

You know I've never actually seen fosters on tap anywhere but in countries that aren't Australia. Not a single soul here drinks it on account of it being, you know, horrible.

 

[hogwiley]

The thing that confuses me when I hear about this lag time is that when I get a reading on someone thats a little low, sometimes If I have them cough and deep breath a bit, or take some drags on an incentive spirometer, Ill usually see their sats increase fairly quickly. I dont really see a lag time. Likewise if I put them on o2 or increase the flow rate.

 

[Brandon O]

The thing that confuses me when I hear about this lag time is that when I get a reading on someone thats a little low, sometimes If I have them cough and deep breath a bit, or take some drags on an incentive spirometer, Ill usually see their sats increase fairly quickly. I dont really see a lag time. Likewise if I put them on o2 or increase the flow rate.

Well, think about the mechanisms we've been discussing. The two main factors in lag are signal averaging and venous/pulmonary oxygen reserves. You can't escape the former, although the exact duration may vary depending on the device, but it's short enough that it won't necessarily be striking. What about the latter? It should make sense that the effect is more profound for creating delay between LOW alveolar oxygen states and a DECREASE in sat. If you suddenly stop breathing or if I decrease your FiO2, you still need to burn through the oxygen in your blood and particularly the oxygen in your lungs before your sat starts to drop. Conversely, if I increase your FiO2 or you increase your minute volume, the effects should be faster; you'll be increasing your blood-borne oxygen content almost immediately. The only delay should be the time for O2 to cross into the circulation in quantity and reach the probe site. In people with poor cardiac output or peripheral perfusion, this can actually be significant, which is why it's a good idea to assume 1-1.5 minutes of lag in all sick people, but in most cases it should be appreciably less.

Make sense? That's why the situations you're describing are on the "increase" side of the fence.

 

[hogwiley]

Well, think about the mechanisms we've been discussing. The two main factors in lag are signal averaging and venous/pulmonary oxygen reserves. You can't escape the former, although the exact duration may vary depending on the device, but it's short enough that it won't necessarily be striking. What about the latter? It should make sense that the effect is more profound for creating delay between LOW alveolar oxygen states and a DECREASE in sat. If you suddenly stop breathing or if I decrease your FiO2, you still need to burn through the oxygen in your blood and particularly the oxygen in your lungs before your sat starts to drop. Conversely, if I increase your FiO2 or you increase your minute volume, the effects should be faster; you'll be increasing your blood-borne oxygen content almost immediately. The only delay should be the time for O2 to cross into the circulation in quantity and reach the probe site. In people with poor cardiac output or peripheral perfusion, this can actually be significant, which is why it's a good idea to assume 1-1.5 minutes of lag in all sick people, but in most cases it should be appreciably less.

Make sense? That's why the situations you're describing are on the "increase" side of the fence.

Yeah makes sense. I kind of had a vague notion of what you said and figured because of that its quicker for them to show a sat increase than a decrease on the pulse ox. I just havent had an opportunity to see this in person, since its not like I take away someones o2 or allow their airway to close to see how long it takes for their sat to drop. Thanks for the good explanation though.

 

[hogwiley]

Jeeze man. Its not like I murdered your mum. Harsh.

You know I've never actually seen fosters on tap anywhere but in countries that aren't Australia. Not a single soul here drinks it on account of it being, you know, horrible.

What would happen if an Australian walked into a pub and ordered a Fosters out loud, would the whole place go silent or everyone laugh assuming your joking?

 

[Melclin]

What would happen if an Australian walked into a pub and ordered a Fosters out loud, would the whole place go silent or everyone laugh assuming your joking?

The later I suspect. Quickly followed by the publican asking what part of the UK you were visiting from.

 

[BLS Systems Limited]

Yeah makes sense. I kind of had a vague notion of what you said and figured because of that its quicker for them to show a sat increase than a decrease on the pulse ox. I just havent had an opportunity to see this in person, since its not like I take away someones o2 or allow their airway to close to see how long it takes for their sat to drop. Thanks for the good explanation though.

For a quick example, try it out on yourself. Put on the oximeter and hold your breath. See how long it takes for the sat's to drop and compare it to how fast it takes to return (if you're still awake). While this isn't the exact same as the CO2 will build as well, it does give an appreciation to those experiencing hypoxia.

 

[Brandon O]

For a quick example, try it out on yourself. Put on the oximeter and hold your breath. See how long it takes for the sat's to drop and compare it to how fast it takes to return (if you're still awake). While this isn't the exact same as the CO2 will build as well, it does give an appreciation to those experiencing hypoxia.

Don't think I've ever seen a healthy person successfully drop their sat by holding their breath. Will to live and all that...

 

[BLS Systems Limited]

Don't think I've ever seen a healthy person successfully drop their sat by holding their breath. Will to live and all that...

I got mine down to 78%. The secret is to hyperventilate to blow off as much CO2 as possible (drive to breathe and all that). Don't bear down as the vasovagal stimulation could cause a drop in BP. As you approach the cusp of the desaturation curve, the SpO2 will start to drop faster and faster.

Fun stuff when its slow on a night shift...

 

[Brandon O]

I got mine down to 78%. The secret is to hyperventilate to blow off as much CO2 as possible (drive to breathe and all that). Don't bear down as the vasovagal stimulation could cause a drop in BP. As you approach the cusp of the desaturation curve, the SpO2 will start to drop faster and faster.

Fun stuff when its slow on a night shift...

:lol: Clearly we must all try this.

 

[abckidsmom]

:lol: Clearly we must all try this.

Where's the no legal advice warning?

Kids, don't try this at home and if you do don't say you heard it here. But if you happen to have done it, make sure and post pics of your skin and the monitor so we will believe you.

 

[Anjel]

Where's the no legal advice warning?

Kids, don't try this at home and if you do don't say you heard it here. But if you happen to have done it, make sure and post pics of your skin and the monitor so we will believe you.

No legal advice allowed lol