Fick equation

Specialties CCU

Published

I would love to know a better version of the Fick equation than:

CO = O2 Uptake / ([Arterial O2] - [Venous O2])

Primarily, how to calculate O2 uptake. I have researched the internet and could not find an explanation - only the equation over and over. Our CVICU uses Baxter CCO/CCI monitors for the post open hearts and I would like another way to calculate CO (besides manual injections) as a back up in case of aberrant numbers in the presence of SVO2 recalibration (SVO2 75, CI 1.8, H/H 10/30, PaO2 95 on 50% FIO2). Thanks in advance!

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Sometimes we don't believe our thermodilution numbers - maybe the patient has wide-open TR. What we do is to draw simultaneous specs from a radial art-line and the distal port of the PA, sending them to the gas lab for sat numbers, which I assume gives you the O2 extraction, yes? The sat numbers get plugged into an equation that we keep on the in-house list of clinical calculators - it involves the current hemoglobin, body surface area, stuff like that. I can send you the equation from work if you like.

I would love to know a better version of the Fick equation than:

CO = O2 Uptake / ([Arterial O2] - [Venous O2])

Primarily, how to calculate O2 uptake. I have researched the internet and could not find an explanation - only the equation over and over. Our CVICU uses Baxter CCO/CCI monitors for the post open hearts and I would like another way to calculate CO (besides manual injections) as a back up in case of aberrant numbers in the presence of SVO2 recalibration (SVO2 75, CI 1.8, H/H 10/30, PaO2 95 on 50% FIO2). Thanks in advance!

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That would be great Mark. I also posted this question on the CRNA board and got a response that "O2 consumtion" equals 3ml/pt body weight in kg, or 125 x BSA. But I can always use more info if it makes the equation more succinct. Thanks for responding.

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Specializes in Critical care.

Here is an equation I learned...It is not as accurate as obtaining a true CO in cath lab with an oxygen consumption hood, but it is pretty close....

CO=kg x 3.3/Hgb x (Arterial sat - Venous sat) x 1.34 then multiply this number times 10 to move the decimal place.

You have to have paired gases...An ABG and VBG (from the PA port of the PA Cath), plus need current Hgb value and current weight....3.3 is a constant...1.34 is roughly the amount of oxygen that each Hgb molecule can carry in mls.....An example is below

CO = 85 x 3.3/15 x (98 - 75) x 1.34 =0.606

CO = 0.606 x 10 = 6.06 or 6.1 L/min

This is rough estimate of the CO to get the CI you just need to divide the CO by the BSA...Hope this helps....

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Kat - see if this link works - enter the numbers and hit the buttons...

http://is.partners.org/handbook/externalFrame.asp?pageId=350&ArticleTitle=CardiacIndex&OutputFICK

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