Photoplethysmography

[Cup of Joe]

Maybe its just a fancy word that makes me look smart.

All of our units have cardiac monitors with pulse ox and blood pressure cuffs, and it shows the photoplethysmogram from the pulse ox. I've been doing some reading on it, and have read it can change based on certain cardiac dysrhythmias (v-fib, v-tach, a-fib, etc.), shock, and hypovolemia, but does it have any practical application in the world of EMS?

Obviously as a basic, it won't do too much for me, but I'm kind of curious to see what you all think about it.

 

[VFlutter]

As a basic you can still learn what a normal pleth looks like so you can determine if the Sp02 you are looking at is accurate or not. And to simply answer your other questions, yes the pleth waveform corresponds to the cardiac rhythm.

Good wikipedia picutre

 

[Brandon O]

The best use of the pleth waveform is to evaluate the quality of the signal. The sat number is just a number; watching the waveform will help you understand if it's registering strong and clear or is "listening to noise" the same way you'd be struggling to hear a blood pressure while your partner bangs you down the worst road in Detroit.

It's also, for all intents and purposes, a rough and ghetto measure of distal perfusion -- call it a poor man's Doppler. It probably won't add much to a diagnosis of hypovolemia, but it can help locate a distal pulse if you're unable to palpate one, or confirm its absence. The information it's giving you (pulse rate, rhythm, and strength) is essentially the same information you obtain when palpating the pulse, but it's a different and perhaps more sensitive way of measuring and displaying it, which can be handy. (I once tried to "palpate" a blood pressure using the pulse ox... it was not successful, but my hopes remain high.)

Some more thoughts here http://emsbasics.com/2011/08/07/pulse-oximetry-application/

 

[systemet]

As a basic you can still learn what a normal pleth looks like so you can determine if the Sp02 you are looking at is accurate or not.

I think this is a good answer. While the area under the pleth should theoretically relate to cardiac output, I don't think it's really very useful for that.

And to simply answer your other questions, yes the pleth waveform corresponds to the cardiac rhythm.

Good wikipedia picutre

I just wanted to point out something interesting here. I've never looked to see if this happens in real traces, but if you look at the pleth, the complex following the PVC is much larger. This is a combination of two phenomena:

(1) This PVC is associated with a compensatory pause, allowing a longer time for passive filling, and possibly resulting in fuller atria prior to atrial systole, increasing preload for the next beat.

(2) Facilitation. The PVC results in a large influx of calcium into the ventricular myocytes. When the next sinus complex occurs, the calcium concentration reaches a higher peak level, resulting in more activation of the contractile filaments, e.g. inotropy.

 

[Brandon O]

I just wanted to point out something interesting here. I've never looked to see if this happens in real traces, but if you look at the pleth, the complex following the PVC is much larger. This is a combination of two phenomena:

(1) This PVC is associated with a compensatory pause, allowing a longer time for passive filling, and possibly resulting in fuller atria prior to atrial systole, increasing preload for the next beat.

(2) Facilitation. The PVC results in a large influx of calcium into the ventricular myocytes. When the next sinus complex occurs, the calcium concentration reaches a higher peak level, resulting in more activation of the contractile filaments, e.g. inotropy.

Pulsus alternans may also be an example of this.