Can some one remind me how to figure out Fick CO

getoverit, BSN, RN, EMT-P · Mar 31, 2009

The Fick principle states that total release or uptake of a substance by an organ equals the products of blood flow through that organ times the difference of arteriovenous concentrations of the substance. For these purposes, oxygen is the substance of interest and CO can be calculated as:

CO = oxygen consumption / (arterial oxygen content - venous oxygen content) = VO2 / (CaO2 - CvO2)

There are limitations to using the Fick formula in critically ill patients, as blood oxygen content and oxygen consumption may change significantly, even within minutes, making accurate calculations difficult. In addition, the Fick principle does not hold for patients with intracardiac shunts.

This is from the medscape page on pulmonary artery catheterization, hope it helps some. I remember being asked to explain the Fick principle and do the math during my orientation...quite awhile ago...but thermodilution is the best way to determine the CO. It's the only way I do it.

Gregron · Mar 31, 2009

Thanks for trying but there is some formula out there that uses constants and the patient weight. I am an Extern and about to graduate and work in the SICU and the nurse was using it. I wrote it down but can't find my damn paper!!!

allnurses Guide · Apr 1, 2009

I remember being asked to explain the Fick principle and do the math during my orientation...quite awhile ago...but thermodilution is the best way to determine the CO. It's the only way I do it.

I don't know that this is true. As far as I recall, the data show that all methods of calculating CO are equally inaccurate (+/- 30%).

I was taught to calculate Fick CO as: CO = VO2 (CaO2 - CvO2) x 100, where:

CaO2 (arterial oxygen content) = Hb x 1.36 x SaO2
CvO2 (venous oxygen content) = Hb x 1.36 x SvO2

So that shakes out to:

CO = VO2/[Hb x 1.36 x (SaO2 - SvO2)]

You do need to measure VO2 which is not easy. You do not need patient weight unless you are trying to figure out CI, when you divide by the BSA.

The formulae become more fun when you want to calculate O2 delivery/consumption !

getoverit, BSN, RN, EMT-P · Apr 3, 2009

I don't know that this is true. As far as I recall, the data show that all methods of calculating CO are equally inaccurate (+/- 30%).
I was taught to calculate Fick CO as: CO = VO2 (CaO2 - CvO2) x 100, where:
CaO2 (arterial oxygen content) = Hb x 1.36 x SaO2
CvO2 (venous oxygen content) = Hb x 1.36 x SvO2
So that shakes out to:
CO = VO2/[Hb x 1.36 x (SaO2 - SvO2)]
You do need to measure VO2 which is not easy. You do not need patient weight unless you are trying to figure out CI, when you divide by the BSA.
The formulae become more fun when you want to calculate O2 delivery/consumption !

You're probably right, I should have said that thermodilution is the easiest way to do it and they probably all are about the same accuracy. and after re-reading your post and thinking about all those numbers and values...I think my nose is starting to bleed!!

allnurses Guide · Apr 11, 2009

Ah come on now, ICU nurses love a few good hemodynamic numbers to play with!