We have a Vigio flo-trac machine in our ICU. It's meant to be put on an arterial line and will give two relevant numbers. The first is cardiac output, and the second is called stroke volume variation (SVV). SVV is a measure of the adequacy of fluid resuscitation. An SVV over 13 indicates hypovolemia.
The rub is that the manual says that it's only useful if the patient is ventilated without any spontaneous ventilations (in effect, control ventilation). I spoke with the Edwards rep today and he said that for SVV, that's true. The patient needs to be intubated without spontaneous ventilation.
But I learned today that the patient does not need to be intubated or can have spontaneous ventilation to measure cardiac output. So in those patients who are critically ill who you need to know the CO, you can use the flo-trac, regardless if the patient is intubated, has spontaneous ventilation (i.e. CPAP) or not.
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i had this same question. in fact, you asked two questions: SVV anc CO measurement. they are two different measurements. the SVV comes from a regularly varyng systolic BP. which can only be measured in a controlled, standard way, i.e, AC ventilation, or heavily sedated patient on SIMV, no spontaneous breaths which would affect systolic pressure variation. CO. however, is measured by analyzing the slopes of the arterial waveform. Edwards has a very helpful, tho a bit "math heavy" explanation of waveforem annalysis. It makes no mention of ventilation effect on shape of waveform, thus no effect on CO measurement, as it doesnt' use pressure variation, but wave shape variation to convert mmHg to ml/beat, thus, CO. So, you see, they are two different measurements, and both the answers you got were true.
Hope this helps.
Bob Rothwell, CNS, SICU, Seattle VA
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