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Measuring output - how do you do it?

Todd Fraser on 10-06-2012

One of the interesting by-lines from the recent CICM Annual Scientific Meeting in Melbourne was the regional difference in trend to monitor cardiac output. While the contingent of European presenters seemed to favour its use broadly, their Australasian counterparts appear far more selective. With the fall of the Swan-Ganz catheter, it appears few intensivists in the Southern Hemisphere have replaced it with an alternative. Perhaps driving this is the sparsity of evidence supporting any other modality, or in fact, the lack of evidence that titrating therapy to a benchmark cardiac output makes any difference to long term outcomes. So what do you do at your shop?


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Todd Fraser wrote 06-21-2012 10:53:48 am
Thanks all, good comments.

I can't help feeling that I need something to work with too - particularly in a septic patient with a dicky ticker. Its nice to know that the cardiac output is at least in an acceptable range. I target Cardiac index of at least 2.3, but there isn't decent evidence for this, I know.

I suspect its a horses for courses deal - agree, the PiCCO has some appeal with the lung water issue. I'm sure we overdo the fluids and this may assist in convincing people not to give more if they can avoid it. ScvO2 also has some intuitive appeal - it would be nice to see more outcome studies to support this.



veerendra jagarlamudi wrote 07-05-2012 10:15:02 pm
The scvO2 has a lot of interpretation issues, especially in sepsis and phase of sepsis, high value can indicate established sepsis and i don't think we can do anything about it, low value in sepsis may mean many things though, like low cardiac index or low blood pressure or low flux of oxygen due to other reason, i would still use Cardaic index and SVRI, along with lactate, peripheral perfusion as my monitors of circulation



Jean Bridie wrote 06-13-2012 10:31:55 am
I guess there is still no good measure of tissue perfusion, either global or regional. The best we can do is either lactate or central venous oxygen saturations, which provide some measure of global perfusion. Even then, there are still no firm goals around ScvO2.

Measuring regional perfusion is even worse. Gut tonometry has gone, and there is very little available for any other body region.

Until we can establish that, none of the other monitors will make any difference because they are simply surrogate markers.



Todd Fraser wrote 06-13-2012 10:36:29 am
Good points Jean,

Even when we do have a hard endpoint, whatever that may be, it too is still a surrogate marker for what we actually want which is survival in a good functional state. Perhaps there is a "permissive hypo perfusion" state that we'll eventually be targeting! Or it may be that even if we have a benchmark, we won't know the best way to achieve it - more fluids? More inotrope? More blood? Cooling? Peripherally acting vasodilators?

There is still much to learn



Jo Butler wrote 06-13-2012 12:32:10 pm
I must say I can't help but want to know what the cardiac output is. While I know that there is little evidence to support one particular number, its reassuring to either know its okay, or to be able to treat it if its not.

I used to use the PAC a lot, and did so until recently despite the evidence against it (and still believe there are reasons to doubt this), but it seems "uncool" to do so now, so have been using the Vigileo pulse contour analysis monitor.



James O'Connor wrote 06-15-2012 07:56:43 pm
I wonder whether the PiCCO is the most useful of the available monitors. The thing that I think sets this apart is the extravascular lung water measurement. I find this more useful than just about anything else - once the patient is stable, its good to target this to dry the patient out. This ties in well with the FACTT trial which suggests that this strategy is helpful in ARDS.

As for the CO measure itself, I'm not sure its all that helpful.



veerendra jagarlamudi wrote 07-05-2012 10:15:02 pm
The scvO2 has a lot of interpretation issues, especially in sepsis and phase of sepsis, high value can indicate established sepsis and i don't think we can do anything about it, low value in sepsis may mean many things though, like low cardiac index or low blood pressure or low flux of oxygen due to other reason, i would still use Cardaic index and SVRI, along with lactate, peripheral perfusion as my monitors of circulation



Yang Yang wrote 07-15-2012 05:54:18 pm
Time for ECHO. Non invasive and obtain most of the clinical information: CO/CI/PA systolic/diastolic/volume status/SAM...In combination of the non invasive tissue perfusion probe (use in research now), I think the difficult point is not to obtain the information using various ways but what is normal is hard to define.



Jackson Bird wrote 07-18-2012 01:48:39 pm
The problem with tissue monitoring is that it is still not reflective of the total circulation, or of individual organ perfusion. Nor is there a validated benchmark normal value. And even if there was, there is no evidence that achieving this value helps. And if there was, there is no agreement on the best way to achieve it.

Too many unknowns to be dogmatic.

Echo is also limited by lack of ability to be performed continuously, and inter-observer (and intra-observer) variability.



Chris Poynter wrote 09-20-2012 09:03:30 am
The more I learn about haemodynamic monitoring the more confusing it becomes. I yearn for the simple days as a house surgeon where the "fluid challenge for all!" mantra seemed like the perfect simple solution. Now I drag patients up to the unit after 10L of fluid have unsurprisingly failed to cure their septic shock on the wards and realise the error of my former ways.

I don't think that any given monitor provides all the answers and I worry about those who concentrate too heavily on the numbers produced by the bedside monitor. Those numbers all have their limitations, are often surrogates for what we think that we are measuring and as stated above, even the numbers we want don't actually translate to meaningful endpoints reliably. It is important to remember that any monitor/number that we have for a patient constitutes just one pice of the jigsaw puzzle and the whole picture cannot be reliably be determined from that piece alone.

For what it is worth, we still use PACs and SvO2s when we really feel we need guidance and have recently been discussing the limitations of pulse contour analysis due to an aggressive campaign for introduction here without clear evidence for benefit. That discussion has centred around the fact that Vigileo/EV1000 monitors are uncalibrated monitors of the most peripheral part of an arterial tree which is often influenced by vasoactive drugs used as a surrogate for cardiac output which is used as a surrogate for adequacy of tissue perfusion.



 

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