ABGs and Compensation

this is my method of teaching abg analysis and is from my published and lectured material.

blood gas analysis

® oxygenation—always look at oxygenation first!

® pao2 80-100 mm/hg—o2 below 80 hypoxia >100 too much o2

® sao2 95-100%

® acid / base balance

® ph 7.35 - 7.45 lower acidic higher alkaline, if its in normal range and the other things are out of range it is compensated

® paco2 35-45 mm/hg respiratory component(also an acidic component) lower co2 = alkaline, higher the co2 = acidic

® hco3 24-28 meq/l metabolic component ( also a basic component) higher the bicarb more alkaline, lower more acidic

acidic

normal

basic

ph

co2

hco3

whichever component is with the ph is the kind of problem it is, if it is compensated draw a line down the center of the normal which ever way the ph is leaning is the direction (acidic or acidosis) and which ever component is in that direction is the kind (resp or metabolic)

questions to ask to determine situation

compensated or uncompensated? (ph in normal range and other items are out of normal range it is compensated if ph is out of normal range it is uncompensated) this is an important question because if it is compensated it likely occured over a long period of time--the body can compensate for slowly occurring changes--not usually an emergency opposed to uncompensated which is an acute situation and may likely be an emergency!

resp or metabolic? (which component is with the ph)

acidosis or alkolosis? ( is it in the acid or alkaline direction)

hope it helps,

karen

That middle section of my post was a chart with acidic, normal, and alkaline across the top and ph, co2, and hco3 down the left side.

pH 7.35

pco2--55

hco3--30

So, your metabolic and respiratory component are both out of line right? Here's how I learned it:

for the values up there--pH-is normal (but closer to acid than base)

CO2- there are a lot of acids, so it is acid

HCO3- there are a lot of bases, so this is base

So look at it like this :

pH---acid

CO2 -- acid

HCO3---base

Which component matches the pH? The respiratory component matches. (Resp acidosis) But, since the pH is actually normal and the metabolic is elevated, we know that the pH is normal because the bicarb is elevated-or compensating.

Resp acidosis w/complete compensation.

If the pH was still below 7.35 and all the other numbers are the same, then we would call it a partial compensation.

HTH!

The way I do it is like this

Write down all 3 values.

Determine if they are acidic or alkaline

Start w/ the PaCo2. Is it acidic or alkaline? Let's say it's acidic

Now look at the Ph. Is it acidic? If so...you have respiratory acidosis.

Now look at the HCO3-. Is it alkaline? If so, you have compensation.

Look back at the Ph. It was acidic, right? Therefore the HCO3- has only PARTIALLY compensated....because if it had fully compensated the Ph would be in the normal range.

Few examples:

Ph 7.24

PaCo2 50

HCO3- 22

Well here we have an acidic Ph, an acidic PaCo2 and a "normal" HCo3-. Therefore we have respiratory acidosis with NO compensation.

But if it was like this:

Ph 7.24

PaCo2 50

HCO3- 32

Now the HCO3- is alkaline....showing compensation. Now we would have respiratory acidosis w/ partial compensation ( because the Ph is 7.24 which is acidic).

Last one..same scenario....say you had the ABG above and then it was redrawn and you saw this

Ph 7.4

PaCo2 50

HCO3- 38

Now the PH is NORMAL...so the HCO3- has FULLY compensated. This would be respiratory acidosis w/ full compensation ( using scenarios above as the prior values)

http://realnurseed.com/abg.htm this is really good, the way abg's are explained, in very plain words. just go to the middle of the page where it says ''land of abg's''

That website was great! I'm on my 13 day semester break and here I am still trying to figure out ABG's! Thanks to you, I have a better grasp on it! Thank you!!!