Why is the answer to this question Metabolic Alkalosis?

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Normal values:

pH (7.35-7.45)

pO2(90-100)

pCO2 (35-45)

HCO3(24-32)

Question:

What is this clients disorder?

--> Client with an NG Tube has a pH of 7.50 (Alkalosis), pO2 90 (normal), PCO2 of 42 (normal) and HCO3 25 (normal)

Answer: Metabolic Alkalosis.

.

... I understand why it is alkalosis, but why is it metabolic if the HCO3 is in the normal range???

Thanks.

In response to ladyfree28:

I understand what you're saying about the compensation but I thought the body can never over compensate. Meaning, it will never compensate so much that the pH will cross over to the opposite abnormal range..

Specializes in Emergency.
The pH rises because of the loss of bicarbonate, hence the compensation, making the imbalance alkalotic.

For more information; a great link that one of my nursing instructors utilized in helping us understand ABGs when I was in nursing school:

Interactive Online Continuing Education for Nurse Professionals

As tryingtohaveitall said, loss of bicarbonate = low pH. Loss of PaCO2 = alkaline. I'm sure it was just a little mistake though.

I understand what you're saying about the compensation but I thought the body can never over compensate. Meaning, it will never compensate so much that the pH will cross over to the opposite abnormal range..

I can't say for sure. But, the normal range for bicarbonate is 22-26. In the case of the original study, patient's bicarbonate was on the high end. We can suspect that it was above 26 based on the pH. However, we can also suspect it is decreasing due to the lower PaCO2 and thereby the renal system is excreting some extra bicarbonate.

It's confusing because the values are normal for all but the pH. No sign that there's any respiratory or metabolic issues aside from the alkalotic pH.

It's really not confusing if you take out the NG tube. Yeah, if you look at the NG tube, you can start to bring in hypokalemia and hypernatremia (IIRC?). But, we're not looking at this. This is strictly acid-base. Look at the lab values. That's all you need.

Specializes in Pedi.
The professor's answer is that the condition is metabolic alkalosis secondary to gastric acid loss. It's confusing because the values are normal for all but the pH. No sign that there's any respiratory or metabolic issues aside from the alkalotic pH.

The bicarb is on the lower end at 25, so low bicarb, How is that not nearing being acidic?

The normal range of bicarb on an arterial blood gas is 22-26 (look it up), so 25 is on the higher end which points to alkalosis. Your pH is alkalotic and your CO2 is within range but on the higher end so pointing more towards acid. Metabolic alkalosis is the only scenario that fits.

Specializes in Pediatrics, Emergency, Trauma.

It's late and I'm tired, but loss of bicarbonate, your buffer, makes you more acidic. Normally your body compensates by normalizing your pH, not going alkalotic unless I'm misunderstanding what you're saying.

As Kel215 pointed out, the normal range for bicarbonate...I actually had to double check. :yes:

My point was more when the bicarbonate is affected, and all other values are normal; the imbalance is metabolic; the pH is alkalotic.

I actually found the tool I used through nursing school that my nursing instructor gave us, and it is a great way to help clear confusion on interpreting acid-base values:

http://realnurseed.com/abg.htm

My $0.02 cents. It's metabolic because the cause of the increased pH has nothing to do with the respiratory system. Also, a major clue is: one of the most common causes of metabolic alkalosis is NG suctioning.

With suctioning, gastric acids (acid) decrease and bicarb (base) is retained. HCO3- or bicarb is a base and........... bases are alkaline.

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

This is how I learned it...

ROME:

Respiratory= Opposite:

- pH is high, PCO2 is down (Alkalosis).

- pH is low, PCO2 is up (Acidosis).

Metabolic= Equal:

- pH is high, HCO3 is high (Alkalosis).

- pH is low, HCO3 is low (Acidosis).

Or this.......by VickyRN The Orange Grove ABG Tic Tac Toe

Mays, D. A. (1995). Turn ABGs into Child’s Play. RN, 58(1), 36-40. paperclip.png Attached Files

Specializes in Med Surg.
BTW, Nursing2102, remember that metabolic syndromes act together whereas respiratory act inversely. ^HCO3 and ^pH = Metabolic whereas ^pH and decreased PaCO2 = Respiratory.

(or I guess you can use sarakjp's method...)

I cannot stress enough that remembering only this "act together or act inversely" will not help you in real life. You need to be able to think about and understand the situation, not look for numbers "going together or apart."

So, take a look at the labs. A long look. What do we know about metabolic syndromes -- be it alkalosis or acidosis? Is that it first goes through respiratory alkalosis/acidosis and is then advanced to metabolic syndrome. COMPENSATORY. The renal system is trying to fix the system by doing what it does best.

You have a pH that is 7.50 -- this is high, KIND of near normal. You then have a PaCO2 that is nearing ABOVE normal levels. Then, you have the bicarbonate that is high but seems to be lowering. Your kidneys are excreting bicarbonate and your system is retaining the carbonic acid to try and normalize it.

Look at the PO2...what does this look like? Hypoventilation. This patient is not breathing enough and is retaining CO2 -- ACID! However, hypoventilation is COMPENSATORY and will actually stimulate the action to breathe.

Think to yourself when you look at the labs, "Ok. I know several of these labs are normal; however, many of the labs are nearing the high range or low range." What does this mean? Again! COMPENSATORY. The kidneys are long term compensatory systems.

Somewhat confused explanation; doesn't hang together with physiology of A/B balance.

1) Yes, it's an alkalosis. The body will regulate CO2 to regulate pH in metabolic disorders preferentially, because it's really fast ( you can blow off CO2 to decrease a metabolic acidosis rapidly, or retain CO2 to compensate for a metabolic alkalosis with ease). You can also blow off CO2 easily (assuming nl lung function) when you make more CO2, as with exercise-- this is the main reason you huff and puff when you exercise; getting more O2 in is secondary to getting the CO2 out.

2) Normal bicarb range is 22-26.

3) Compensation never quite makes it into the normal range. Thus, a respiratory acidosis with increased bicarb for metabolic compensation will still have a slightly acidotic endpoint. A metabolic alkalosis with CO2 retention as respiratory compensation will still be on the alkalotic side.

Therefore, it is my contention that this question has a major typo in it, and the faculty who presented it meant the bicarb to be 35. That would square with a metabolic alkalosis with respiratory compensation (CO2 retention) and still being in the (slightly) alkalotic range. There is no other explanation for this.

ABGs Made Simple. Note: I have been posting this on the Net for decades, and someone has appropriated vast swaths of it for a thing called something like ABG Bingo. I would have been happy to give permission to use it, but would have appreciated credit where due.:)

Ahem.

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.

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 to 22-26**)

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...

Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

The ABG bingo is from The Orange Grove ABG Tic Tac Toe

Mays, D. A. (1995). Turn ABGs into Child’s Play. RN, 58(1), 36-40.http://florida.theorangegrove.org/og/file/cd19d63a-cd33-0eab-b7d2-bb7195970a4d/1/ABG.swf

The ABG bingo is from The Orange Grove ABG Tic Tac Toe

Mays, D. A. (1995). Turn ABGs into Child’s Play. RN, 58(1), 36-40.http://florida.theorangegrove.org/og/file/cd19d63a-cd33-0eab-b7d2-bb7195970a4d/1/ABG.swf

The second one didn't open and the first one isn't the ABG TIcTacToe posted here that I saw (And it's more confusing than it has to be by far). I wrote mine in the late 80s. :)

Just wanted to let everyone know, my classmate e-mailed the professor about this question and she confirmed that it was a mistake and the bicarb should have been a 35, not 25.

Thanks to everyone who attempted to explain!

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