ABG's

**SKM-NURSIEPOOH, BSN, RN** · Nov 11, 2005

lab values or something like that.

i hope this is what you're looking for ~ cheers,

moe

suebird3 · Nov 11, 2005

sounds good......and helpful. thanks for the post! :)

suebird

papawjohn · Nov 11, 2005

Hey DayRay!!! (that's kinda alliterative, eh?)

I don't know 'zactly the 'tool' your instructor used of course, but I've found a way of dealing with the ABG numbers so that they make a picture of your Pt's breathing. And that's really what your focus should be: How's the pt breathing. (Try not to think of the results as a jumble of strange numbers and deal with them by memorizing formulas---unless you're much smarter than me. Cause I can't do that worth a toot.)

When I was a youngster I was a lifeguard. This was before we did CPR. (Can you believe it? There was no CPR?!) We were supposed to rhythmically lift and stretch a drowning victims elbows and arms around--hopefully using the shoulder blades as levers to force air in and out of his lungs. (You have to wonder--did anyone actually get 'resuscitated' that way?) The point is, the chant we were taught went: "IN goes the good air, OUT goes the bad air." And THAT is still what our job is all about.

So we'll look at ABGs from the point of view of "IN goes the good air, OUT goes the bad air". But lets reverse the order; start with the 'bad air' part:

BAD AIR--the body has to get rid of CO2. If the lungs are doing good, thats how it does it. We measure this as pH and as pCO2.

(You remember--CO2 turns into a weak acid in the blood. The weak acid is measured on a 'teeter-totter' with bases in the blood to give you the pH--which is a way of measuring the strength of the acid in the blood. The exact chemistry isn't so important as you stand there at the bedside--but you have to know those two things. So if you need to review that--check out a book or the web or ask me to 'splain it; but remember--CO2 equals acid--and acid is balanced by bases to give a number called pH. OK?)

GOOD AIR--the lungs take oxygen in and load it up onto the RBCs (imagine little pick-up trucks having oxygen molecules piled up in them). This changes the color of the RBC!!! The venous blood with low O2 levels is a dark burgondy color; arterial blood full of O2 is crimson. Thats how the pulse oximeter works--it reads the color of the blood and gives you a SATURATION number. (Which--btw--is a percentage. If your Pts 'sat' is 98, you've learned that the RBC have 98% of all the oxygen that they can carry.) As they travel thru the blood stream, these little pickup trucks are constantly spilling oxygen into the plasma of the blood so that the cells along the highway can splurp it up. That gives the plasma a kind of a 'force' of oxygen that 'pushes' it toward the cells. Does that give you a picture of your Pts blood as a fluid with energy--forcing oxygen into the cells along the banks of the stream? That's the picture you need to have of respiration. So think for a minute about it--the SATURATION of the RBCs give the blood a FORCE of oxygen to feed the cells. OK?

Now we're looking at this Pt's ABGs and we're thinking, 'is the BAD AIR getting out and is the GOOD AIR getting in? That's all we're worried about.

So lets arrange the numbers to help us think about it. What I do is make a little 'form' and then plug the numbers into it. On the left side I put the pH. In the middle I make a cross so that I have 4 corners. On the right side I put the Sat %. Like:

7.30 + 94%

What do we have here? We've got one half of the BAD AIR side of the ABG and one half of the GOOD AIR side. (Usually when I'm going over this with a 'baby-nurse' at work, we pause and think about that for a minute and I go-on and go-on about "pH" shows the "acid CO2" is getting a little farther advanced--right? So if the lungs are going to be getting rid of it--they need to work a little harder. You see that? Yes? And the little pickup trucks aren't loaded with quite as much oxygen as they could be, now are they? But we think for a minute about what we've learned ABOUT THE PATIENT from these numbers.)

Then I 'fill in' the + this way: upper left-pCO2, upper right-BICARB. So we might have this:

7.30......46.5....22......94%

We have filled in the BAD AIR side of the equation. Since the pCO2 is a little high (making a bit more acid that we want) and the BICARB is lowish but normal (showing the kidneys aren't balancing their half of the 'teeter-totter' that makes the pH)--we can see that our Pt's lungs are making him slightly acid--and that the Kidneys haven't ''compensated".

WOW!!! YOU HAVE JUST FIGURED OUT THAT YOUR PATIENT HAS UNCOMPENSATED RESPIRATORY ACIDOSIS-----WOOH HOOO!!! I am so pleased to have a smart character like you to teach! It makes my job so easy!

Now what if your Pt was in Renal failure? And the numbers looked like this:

7.30.......35....16......94%

Well, a smart character like you would think about that 'teeter-totter' and say "why, the kidneys aren't providing enough BICARB." And I'd say: "How do you know?" and you'd say--"Look, Papaw--the bicarb is low and the lungs are trying to make up for that by getting rid of all the CO2 they can--but the lungs can't keep up."

WOOOH HOOOO!!! You've just realized that your pt has UNCOMPENSATED METABOLIC ACIDOSIS. Damn. You make my job so easy.

All that from just 4 numbers!!! Cool. What else cal we learn, Papaw? you ask. So we fill in the two lower sections with the pO2 and the Base Excess. Like this:

7.30.....46.5....22.....94%

..........88.5.....+2.........

And the pO2 confirms that the amount of oxygen being spilled into the plasma by our fleet of little red pickup trucks is....well, enough--but sort of marginal. And the BE (which I don't learn that much from--but in really bad ABGs or Dialysis Pts or severe shock goes WAAAAY off one way or the other. As long a it's between +3 and -3--you're pt's not TOOO messed up.)

Now what does a nurse do for the Pt whose ABGs are like this? Lets say you put a BIG load of oxygen---a non-rebreather mask---on him. Well, if he is a chronic emphysema Pt, his SAT looks great (100%) and you're proud you helped him. But he breaths slower and slower and slower---and his BAD AIR accumulates and accumulates until he finally has a ph of 6.9--and either dies or gets intubated and sent to the ICU.

How'd that happen?! Well, OUR body 'senses' it needs to take a breath when the pH is low (because the CO2 is high)---but Mr Smith here has spent part of our life smoking cigarettes and teaching HIS body that it doesn't need to breath just because of some silly pH. (He just needs another cigarette.)

So the 'back-up' system that our ancestors evolved is "breath when the Oxygen is low". That's what keeps Mr Smith breathing, his pO2 is low. Well--our non-rebreather kept our his oxygen high, and his body ignored the pH getting lower and lower (because the BAD AIR wasn't getting OUT). Until he was CTD (Circling The Drain.)

No, we need our COPD pts breathing better with just a little oxygen. So, you put a little nasal cannula on our guy, and you call the Dr and give her the ABGs (proudly saying---"Mr Smith has UNCOMPENSATED RESPIRATORY ACIDOSIS, ma'am. And his sat was kind of low. So I put N/C at 2liters on him. And do you think we can start nebulizers on him?)

And THAT is how experienced and accomplished nurses take great care of their pts. And you can do it too.

Wow---that was kind of long. But its kinda complicated. Takes ol' Papaw a

long time to go thru it. But you're so darn clever--you picked it right up.

Good Goin'

Papaw John

Havin' A Party!, ASN, RN · Nov 11, 2005

Hey Papa. Love the way you teach, Daddy-O!

Great post... and so much creativity and style!

MarySunshine · Nov 11, 2005

Thanks Papaw -- I'm a new nurse and that was a great review for me!

Momto3andNurse2B · Nov 11, 2005

papawjohn,

Wow, what a great post for me, a nursing student, who has a test on acid-base balance in 10 days!

I'm going to print your post, add it to my notes, and share it with my classmates, if you don't mind.

Thanks!

JAHJF · Nov 11, 2005

---------------------ACID-------NORMAL RANGE-------BASE

pH____________________________7.35-7.45_____________

PCO2 (resp)______________________45-35______________

HCO3 (metabolic)__________________22-26______________

PO2_____________________________80-100_____________

BE______________________________+2/-2_______________

O2 SAT__________________________95-100______________

-----------------N=normal

Example: Pt in respiratory acidosis

--------------------ACID-------NORMAL RANGE-------BASE

pH_______________7.306_______7.35-7.45______________

PCO2_____________51.0__________45-35_______________

HCO3_____________N(24.9)_______22-26_______________

This is what I used in nursing school. Hope it helps.

Dayray, RN · Nov 14, 2005

Thanks for all the replies. I just got home from work so I'm not coherient enough to undrestand them but I'll read them later

thanks!

suebird3 · Nov 14, 2005

thanks! i could use this....

suebird

hrtprncss · Nov 14, 2005

I always end up posting this for some reason, guess I have an obsession about this site. http://realnurseed.com/abg.htm Go to Land of ABG's by the middle section, provided by Vonfrolio. ABG's in one of it's most simplified form.