Stroke volume variance

Specialties MICU

Published

Hi, there,

New in the MICU, coming off a telemetry floor and trying to learn some of the hemodynamic parameters that we use. I'm okay with CO and such, but I am having trouble with stroke volume variance. We use presep catheters -- not swans in this icu -- and then are in a subclavian vein like a central line.

The problem I am having is this: I know now that SVV is higher when the patient is drier. Okay, fine. I can roll with that, but I was wondering the whys and hows of this -- the pathopysiology so to speak. I can get that stroke volume would be less with an "empty tank", but why would the stroke volume vary from beat to beat . . . or is it from some "normalized" stroke volume . . . I don't know. I know how to read the number, but I like to know why. Anybody out there have some helpful explanations -- or point me in the right direction.

Ionafey

Specializes in CCRN, MICU, CCU.

SV is contingent on preload. When a patient is dry, there is obviously less preload. LEss preload means that with each stroke there will be less afterload and altered filling. The altered and inconsistent filling will effect your SV and INCREASE your SVV. Out of curiosity, what type of hemodyn machine does your facility use?

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Hi! We have only recently begun to use the Vigileo and NEVER see swans. Do your docs actually use the numbers from the Vigileo? I swear, it feels like ours just have us record them and do nothing with them (no changes). That having been said, can anyone please explain to me what numbers your docs use, other than possibly the SVV? And how this correlates with your Swam numbers? I'm studying for the CCRN and trying to understand what I am studying and putting it together with what I am actually seeing in the unit. I would really appreciate it.

Thanks!!

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Specializes in CVICU.
Hi! We have only recently begun to use the Vigileo and NEVER see swans. Do your docs actually use the numbers from the Vigileo? I swear, it feels like ours just have us record them and do nothing with them (no changes). That having been said, can anyone please explain to me what numbers your docs use, other than possibly the SVV? And how this correlates with your Swam numbers? I'm studying for the CCRN and trying to understand what I am studying and putting it together with what I am actually seeing in the unit. I would really appreciate it.Thanks!!
Other than the SVV they should want to know things like the CO/CI (or SV/SVI same concept) and the SVR/SVRI. Just like with a swan the goal being try to figure out how to fix a hemodynamic problem (fluids, pressors, inotropes). As far as which numbers correllate: On a swan you have your CVP, PA, and PAOP pressures which are essentially measures of preload (volume). On a flowtrack you use SVV to determine your preload.Contractility is measured on a swan with CO/CI, both of these are available on the flow track vigileo system. Afterload is determined by numbers like SVR, this info is available with both swans and the flow track.
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Thank you so much aCRNAhopeful! That's much better than anything the docs like to say :bluecry1: I get how you can get an idea of preload from your SVV on the flotrac/Vigileo. And you can use your SVR to tell you if you need to relax the vessels if it's too high or give pressors if it's too low, right? Could you please explain to me how you can determine Contractility from your CO/CI? I would like to do an educational poster for my unit, but I want to be sure I can explain things in an understandable way (and that I fully understand them, too!) Also, it seems to me like the Vigileo only gives a "general" picture, where the Swan can give you a more specific picture, with your PA and wedge pressures - I feel like you can tell more easily where the problems are with the heart. I get that the Vigileo is more non-invasive, but does it truly help tell you the problem the way a Swan does? You guys are awesome!

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Specializes in CVICU.
Thank you so much aCRNAhopeful! That's much better than anything the docs like to say :bluecry1: I get how you can get an idea of preload from your SVV on the flotrac/Vigileo. And you can use your SVR to tell you if you need to relax the vessels if it's too high or give pressors if it's too low, right? Could you please explain to me how you can determine Contractility from your CO/CI? I would like to do an educational poster for my unit, but I want to be sure I can explain things in an understandable way (and that I fully understand them, too!) Also, it seems to me like the Vigileo only gives a "general" picture, where the Swan can give you a more specific picture, with your PA and wedge pressures - I feel like you can tell more easily where the problems are with the heart. I get that the Vigileo is more non-invasive, but does it truly help tell you the problem the way a Swan does? You guys are awesome!
Regarding SVR - you have the basic idea but just remember you're not treating the actual SVR number. You're treating the hypotension or low cardiac output state or whatever. So yes if pt is hypotensive and has a low svr (sepsis for example) then a pressor like norepi would be a good choice. If the SVR abnormal but the BP and CI are normal you would not be treating the number just to make it normal. Regarding CO/CI - cardiac output is the amt of blood pumped by the heart/min and the CI is CO divided by BSA to account for body size. CO/CI tell you how well the heart is pumping. If the CI is low and PA/CVP/PAOP pressures are high (or if the SVV is low indicating pt is not fluid responsive) then an inotrope would be used to get the weakened heart pumping adequately again. I suppose maybe the swan may provide a more specific picture in some ways but it can also muddy the waters and incorrect use of the data can be harmful to the patient. SVV may be a better way to determine fluid responsiveness than a clinician guessing what PA pressures are too low for that particular patient. Visit pacep.org for more info on hemodynamics, its free and a great resource for ICU nurses ESPECIALLY if you are studying for CCRN
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Specializes in ICU-my whole life!!.
Thanks for the replies, all. I think I am getting a better understanding of it. Still feel so lost in the unit right now, but it has only been two weeks. I'll likely be back with any other questions that frustrate my preceptors. :)

Ionafey

If your preceptors are getting frustrated bc of all your questions, then they should not be precepting !!!!

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