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)

now i'm getting confused between acids and bases and acids and alkaline!

i know acid is decreased

and base is increased with ph

with pco2, increased is an acid

decreased is alkaline?

hco3, increased is alkaline

and decreased is a base right?

so then with this ....

ph 7.35

pco2--55

hco3--30

ph is acid

pco2 is acid

and hco3 is alkaline?

but cardiacrn2006 vbmenu_register("postmenu_1634429", true); , wrote that it was base.

to me that looks like respiratory acidosis

is alkaline and based used interchangeably??

:confused:

I'm getting so confused trying to actually learn this... should I just memorize this chart of blood parameters that we received?

It has all the H+ imbalances: uncompensated and then parially compensated for metabolic acidosis, metabolic alkalosis, uncompensated & compensated respiratory acidosis and respiratory alkalosis....

Then it has the PH, PCO2 and HCO3 and whether it would be Increased, normal, or decreased with each imbalance.

I'm thinking I might be better off if I memorized it since I'm just not comprehending it.

WHat do ya think?

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!!!

Im going to check out that website!!

But here is what I don't get:

We were taught that if the ph is low and bicarb is low then its metabolic, and if ph is los but CO 2 is increased or vice versa its a respiratory problem.

So then when I'm looking at this problem,

PH 7.55

PCO2 30

HCO3 40

According to the rules that we were taught up above ^^ that would be metabolic alkalosis because the ph and HCO3 are equal... but no its respitaroy alkalosis w/ compensation... ***?!

and then heres anotehr

ph 7.50

PCO2 50

HCO3 42

The ph and HCO3 are both increased ... so that should indicated metabolic alkalosis but nooo... its metabolic alkalosis with comepensation. I dont understand where this compensation comes in!!

okay that first website was really helpful but i don't get this part:

c. the middle name

now that you know your patient’s first and last name, you would like to know

her middle name.

(name alert: these people are all related and you have many patients with the

same first and last name. a middle name will give you more information to go

on.)

1. first you need to look at the co2 and hco3.

(remember: normal co2 = 35-45. normal hco3 = 22-26)

2. the middle name will either be respiratory or metabolic.

3. if the co2 is 45--her middle name is respiratory.

4. if the hco3 is 26--her middle name is metabolic.

what if the co2 is 45 and the hco3 26...

how do you choose between respiratory and metabolic?

Normal Ph range is 7.35-7.45 with 7.4 being the absolute value

Normal PaCo2 is 35-45. Below 35 is alkaline ( base) and above 45 is acidic

Normal HCO3- is 22- 26. Below 22 is acidic and above 26 is alkaline ( base)