ABG interpretation

Your pH is within normal range though it is on the alkaline side. Your C02 is low which would be alkalotic and the HCO3 is alkaline. The best way to look at it is if you drew and arrow and your pH and CO2 had arrows moving the opposite direction it would be a respiratory issue and if they are pointing the same direction it is a metabolic issue. So in this case you have Respiratory Alkalosis that is fully compensated because your pH is within the normal range. Hope this helps!

Your pH is normal high (above 7.41) so it is alkalosis - your pco2 is 30 (normal 35-45) so it's low and your Hc03 is high at 29 (normal 22-26)

Think of Rome (Resp opposite metabolic equal). If the ph and hco3 are both high then YES IT IS METABOLIC ALKALOSIS!!!!

Hello Everyone! I have a question and I am hopeful someone here can help me interpret this ABG: pH, 7.45; PCO2, 30; HCO3, 29; O2 Sat, 94% I think it is metabolic alkalosis, but would like to get some feed back to ensure I am in the right direction with this. Thanks in advance for your help in guiding me in the right direction!

It looks like Resp and Met Allalosis to me????

pH 7.45 is within normal range although on the edge to alkaline

PaCO2 also within normal range

O2 sat is within normal range as well

HCO3- is high.

Looks like Metabolic alkalosis not compensated

Correction: PaCO2 30 is not within normal range...This patient is hypocapneic to begin with. HCO3- level should be below 22 but if patient stays hypocapneic for long enough bicarb secretion increase (maybe to 29)

pH 7.45 is within normal range although on the edge to alkaline

PaCO2 also within normal range

O2 sat is within normal range as well

HCO3- is high.

Looks like Metabolic alkalosis not compensated

How do you see that the CO2 is within normal range? 35-45 is normal for CO2. Below 35 is alkalosis and above 45 is acidosis. Also, 02 sat does not really matter when interpreting ABG's because the hemoglobin could be saturated with CO2 instead of O2 so you could get a false reading. Your paO2 is what is important.

Sorry about that, you fixed it before my reply was posted.

This patient has respiratory alkalosis to begin with..the pH should be above 7.45 or Bicarb beliw 22 because the body strive for homeostasis. Low CO2 means less carbonic acid pxn. if hypocapnia last for long enough, more bicarb is produced by the kidneys to pull the H+ out of the cells and form an acid (H+HCO3>H2CO3). It seems to me that this is why this patient has high bicarb levels. I don't know if this is a real or hypothetic case but it may help to check the potassium level to get an idea of what's happening.

This is really interesting and I sure want to know what is the Dx..please keep us updated.:)

This patient has respiratory alkalosis to begin with..the pH should be above 7.45 or Bicarb beliw 22 because the body strive for homeostasis. Low CO2 means less carbonic acid pxn. if hypocapnia last for long enough, more bicarb is produced by the kidneys to pull the H+ out of the cells and form an acid (H+HCO3>H2CO3). It seems to me that this is why this patient has high bicarb levels. I don't know if this is a real or hypothetic case but it may help to check the potassium level to get an idea of what's happening.

This is really interesting and I sure want to know what is the Dx..please keep us updated.:)

This is a case study I am working on for Pharm. So it is hypothetical, but the potassium levels are normal (4.0). The patient in this study had aspergillosis pneumonia.

Thank you everyone for your helpful advice! :)

Thank you Esme12!! Appreciate the worksheets!!! :)

This is a tutorial I wrote to teach ABGs. It's been out on the net for years now and I guess I should be flattered to see other people take credit. I just want to give you a tool to figure out ABGs wherever you are, whether or not you have materials at hand.

ABGs Made Simple

You want simple ABGs? Piece o' cake. People who have seen this before, well, just scroll on by. Newbies who want a brief ABG's refresher, take out your pencils and a piece of paper, cuz you'll need to do a bit of drawing :).

I taught ABG interpretation for yrs in a way that made it pretty foolproof. You will make your own key to interpret ABG's, and will be able to reproduce it from memory any time you need to with very little trouble if you learn a very few **key concepts**, labeled **thus**..

Take a piece of paper. Make a big box on it, then draw vertical and horizontal lines on it so you have four boxes. I will try to make this come out, but...you should have

AB

CD

where the four boxes a,b,c,d are such that a is above c and b is above d. You don't need to label the boxes a,b,c,d, just get them in the right alignment. (This is WAY easier with a whiteboard; bear with me).

*Inside* each of the 4 boxes write the following, down the left edge:

pH

CO2

Bic

Now, OUTSIDE the big box do the following: above the "A" box write "resp"; above the "B" box write "metabolic"

To the left of the "A" box write "acidosis" and to the left of the "C" box write "alkalosis"

Now you have a "resp" column and a "metabolic" column, an "acidosis" row and an "alkalosis" row. So you have respiratory acidosis and alkalosis boxes, metabolic acidosis and alkalosis boxes.

With me so far?

Now, you're going to label the PRIMARY DERANGEMENTS, so later you can tell what's the derangement and what's the compensation. OK? In the respiratory column, underline CO2's. In the metabolic column, underline the Bicarb's. That's because in **respiratory disorders, the CO2 gets messed up**, and in **metabolic disorders, the Bicarb is messed up**. You knew that, or could figure it out pretty quick if you thought about it, right? Thought so. Yes, it really is that simple.

Now. You are going to put upward-pointing and downward-pointing arrows next to the pH, CO2, and Bicarb labels inside every box. Ready?

pH first. In the "alkalosis" row, make up arrows next to pH, because **pH is elevated in alkalosis (by definition)**. Put down arrows in the acidosis row's pHs, because **acidosis means a lower that nl pH**.

Remember that **CO2 is (for purposes of this discussion and general clinical use) ACID** and **Bicarb is ALKALINE** (this is the end of the key concepts. Not too bad, huh?). (oops, I forgot: **nls are generally accepted as pH 7.35-7.45, CO2 35-45 (nice symmetry there), bic 19-26**)

Now go to the box that is in the respiratory column and the acidosis row. Figured out that CO2 must be elevated? Good. Put an up arrow next to that CO2. Go to the respiratory alkalosis box. Figures that CO2 must be low to cause this, right? Put a down arrow next to that CO2.

OK, now go to the next column, the metabolic one. I think you can figure out what happens here: in the metabolic alkalosis box, put an up arrow next to the Bic, because high bicarb makes for metabolic alkalosis. Put a down arrow next to the Bic in the metabolic acidosis box, because in metabolic acidosis the bicarb is consumed by the acids (like, oh, ASA) and is low.

You are now going to put arrows next to the blank spots in your boxes that show compensatory movements. Ready? OK, what does your body want to do if it has too much acid? Right, retain base. Yes, of course if your body has too much acid it would like to get rid of it...but if it can't do that, then retaining bicarb is the compensation. So for every elevated CO2 you see, put an up arrow with its bicarb.( Chronic CO2 retainers always have elevated bicarbs, and this is why.) You will find an up arrow next to the CO2 in the resp/acidosis box.

So if your body is short on acids, what does it do? Right, excrete base. So put a down arrow next to the bicarb in the resp/alkalosis box, because chronic low CO2 makes the body want to get back into balance by getting rid of bicarb. However, remember that it takes a day or two for the kidney to do this job, and if you have nonfunctioning kidneys they won't do it at all.

Likewise in the metabolic/alkalosis box, a high bicarb makes your body want to retain acid, increasing CO2 being the fastest way to do that because all you have to do is hypoventilate, to bring your pH back towards nl. Put an up arrow next to the CO2 in the met/alk box. See the pattern here? Put a down arrow next to the CO2 in the met/acidosis box, because if your body has too much acid in it (think : ASA overdose? DKA?) it will want to get rid of CO2 to compensate, and the fastest way to do that is to hyperventilate. This is why patients in metabolic acidosis are doing that deep, rapid breathing thing (Kussmaul's respirations).

OK, I hear you wailing: but how do I know whether that elevated or decreased CO2 or Bicarb in my ABG report is primary or compensatory?

Well, now you have your key. So take your ABG reports and look at them. Say, try these. (Notice that O2 levels have nothing to do with acid-base balance ABG interpretation) (OK, if you are VERY hypoxic you can get acidotic...but you see that in the metabolic component, not the O2 measurement, because it's lactic ACID your body is making if it's working in an anaerobic way)

1) pH = 7.20, CO2 = 60, Bic = 40.

First thing to look at is the pH. 1) is acidosis, with a low pH. Look at your acidosis choices (you have two). Find the acidosis where both CO2 and Bicarb are elevated, and you find your answer: respiratory acidosis with metabolic compensation. This is what you see in chronic lungers who have had high CO2's for so long their kidneys have adapted to things by retaining bicarb. (It takes about 24 hrs for your kidneys to make this compensatory effort, so you can tell if your resp acidosis is acute (no or little change in bicarb) or chronic)). (Remember, your lungs' first and most important job is not getting oxygen in, it's getting CO2 out, and when chronic lungers have CO2 retention, they're really getting bad. People with acute bad lungs will often have low oxygens and low CO2's , because their ability to gain O2 goes first, and while they're trying to deep breathe their way back to a decent PaO2, they hyperventilate away their CO2. ....but I digress....)

2) pH = 7.54, CO2 = 60, Bic = 40

pH here? This is alkalosis, with a high pH.

The only box where pH is high and CO2 & Bic are both elevated is metabolic alkalosis with respiratory compensation. Sometimes you'll see this in people who have a bigtime antacid habit. Really. (You can get a short-term metabolic alkalosis with rapid severe vomiting, because the body's nl balance between acid and base has been disrupted due to a sudden loss of acid. Things will equilibrate pretty quickly, though, all things considered.)

So even though you have identical abnormal CO2's and Bicarbs, you can look in your boxes, find the match, and see what you have. Remember you underlined the primary disorder in each box?

Wanna try another one?

3) pH = 7.19, CO2 = 24, Bic = 12. Bingo, you found it: an acidosis where the CO2 and the Bic are both abnormally low. Only fits in the metabolic acidosis box, so you have a metabolic acidosis with a respiratory compensation effort. Incidentally, this is what you see in diabetic ketoACIDOSIS, when they come in huffing and puffing to blow out that CO2 because their ketosis is so high. Also you see this picture in ASA OD's, because this is acetylsalicylic ACID they ate, and the fastest way to get rid of acid is to blow it off via hyperventilation. Increasing your bicarb takes 24-48 hrs. Another quick way to get a metabolic acidosis is to poop out a lot of diarrhea, because you lose a lot of bicarb that way. Another classic place for this is in mesenteric artery thrombosis, in which you have a lot of ischemic bowel sitting in there screaming for oxygen and making lactic acid when it can't have any.

I know this is LONG, but trust me, you'll never go wrong with it, and you can recreate it anytime. It doesn't really even matter how you set up your boxes, so long as you have a metabolic and a respiratory axis and an acid/alkaline axis. Rotate your paper and you'll see what I mean.

Why don't I care about PaO2 here? Well, because ABG's mostly tell you about A/B balance and CO2 and Bicarb, that's why. Probs with them can be serious probs without any abnormality in oxygenation at all.

Remember that PaO2 (arterial oxygen, measured in torr or mmHg) is not the same as SpO2,( hemoglobin saturation, a percentage of red cells carrying oxygen). if you think they are, your pt could be in serious trouble before you do anything. There is a nomogram that shows you the relationship between arterial oxygen and saturation, which I regret I cannot reproduce here. But you can sketch out a basic version...

Draw a graph where sats are on the vertical (left) axis and PaO2's are on the horizontal (bottom) axis. Draw little shaded band across the top at the 95%-100% sat areas. That's your normal saturation. Draw a few dots there indicating a line of PaO2's of 80-100, because those are normal PaO2's.

Now draw a dot for SpO2 of 90 and PaO2 of about 75. Now, another dot showing SpO2 of 85 and PaO2 of about 60. Another dot: SpO2 of about 80 and PaO2 of about 55. Connecting all these dots should give you a sort of S curve, indicating that while the top is pretty flat in the PaO2 80-100, SpO2 95-100 range, PaO2 drops off like a shot at decreasing SpO2 levels.

Your pt with a sat of 85 is not doing OK, he's in big trouble. While a PaO2 of 75 torr isn't too bad at all, a SAT of 75% is heading for the undertaker unless dealt with.

Here's my very favorite ABG of all time: pH = 7.11, PaO2 = 136, PaCO2 = 96, bicarb = 36.

What happened to this lady? What will happen next?

"Call" if you have any questions...