How to calculate A-a gradient from ABG? - gudiyaa

[ArchivalUser]

How do you calculate the A-a gradient for PCP (which is a steroid treatment indication) using the ABG?

[ArchivalUser]

A=Arterial oxygen in ABG

a=Alveolar, so I am assuming that would be room air.

So difference btw the two will be the gradient! Just my guess!!

[ArchivalUser]

Hi,

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[ArchivalUser]

A-a gradient

i measure as (150-5/4 Pco2 )-Pao2


This is easy to remember .

Normal value is around 10 mm Hg

[ArchivalUser]

jeez..this is serious! I thought it would be some thing simple!

[ArchivalUser]

Hi,

If interested in research positions, contact me at MariaRez2010. We have positions in different states and specialties. Some are in the top 5 universities in the US. Provide some brief info about yourself, your visa status, your USMLE scores, what (sub)specialty, which state, when you want to start and for how long. In the subject, please mention what you’re looking for. For example: “Endocrine research in Chicago.”

We do have paid positions too, but you need to have had a prior experience in lab research. Otherwise, it's unlikely you can get a paid position. Also remember the visa limitation (you can't get paid on all visas). Some positions are non-paid initially, but may become paid with time as you gain experience and prove yourself to be productive.

We can provide a list of customers that you can contact for feedback about the service. These customers approved to be references, otherwise, we don't disclose any private information of any of our old customers without their knowledge and consent.

Thank you.

[ArchivalUser]

yes, krithikanan's formula is the most simplest one. i remembered it this way: [150-1.2(pco2)]-pao2 which is pretty much the same!

[ArchivalUser]

pco2 + po2 -150 + 1/3 pco2


i find this very easy

[ArchivalUser]

here is a good discussion on this http://www.usmleforum.com/showthread.php?tid=603279-5

[ArchivalUser]

previous post

* Re:about CCS
#2441290
hays - 08/01/11 12:47

You calculate A-a O2 gradient after you order ABG you click OXY on primum software you will have so many options oxygen, pulse ox, ABG choose ABG after you advance the clock for result you calculate

http://en.wikipedia.org/wiki/Alveolar-arterial_gradient

If A-a gradient more than 35 or pO2 less than 70 you give steroid review your note it's difficult for me to remember number for the exam any tips
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* Re:about CCS
#2441295
gunny - 08/01/11 12:59

oh..thanks!

i ordered ABG from the options....only thing I was confused about was..how to order/calculate Alveolar o2..

so instead of this claculation can we just go ahead with pao2..and less than 70..admit/steroids.
* Re:about CCS
#2441308
hays - 08/01/11 13:21

I think so
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* Re:about CCS
#2441309
hays - 08/01/11 13:21

I think the a-a gradient is for MCQs not for CCS

* Re:about CCS
#2441326
gunny - 08/01/11 14:02

ok..may b that makes sense and thank u so much for providing info...

* Re:about CCS
#2441542
misshyd - 08/01/11 22:06

A-a gradient in PCP will help you classify whether PCP is severe enough to require steroids. So it is important in MCQ and also in CCS cases like PCP , PE etc.

there is a simple way to calculate A-a gradient ( this is in dr.red pulmonology)

Remember A-a gradient = alveolar 02 - arterial 02

Now, alveolar 02 = [ 713 (FIO2) - 1.25 (PCO2) ] . Remember at room air, fio2 = 21% = 0.21

so, alveolar o2 at ROOM AIR = 150-1.25( PCO2) REMEMBER THIS IS AT ROOM AIR ONLY.

arterial o2 (po2) and PC02 are obtained from ordering Arterial bLood gases ( ABG)

When patient comes, do an ABG on room air so that you will get to calculate the A-a gradient at room air. A-a gradient in PCP will help you decide to give steroid or not . In respiratory failure cases, A-a gradient will help us to know the cause of resp failure. A-a gradient is huge in pulmonary embolism where as in hypercapnic resp failure like copd exacerbation, opiod overdose; A-a gradient is either normal or only slightly elevated.

So, easy formula for A-a gradient at Room air = 150-1.25 (pco2) - p02

roughly, even if you skip that 1.25; the even simpler formula is 150-pCo2 - pO2

Get ABG at room air and supplement values in above formula.

good luck


* Re:about CCS
#2441548
gunny - 08/01/11 22:15

thank you so much!!!!!!!

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