Need help with acid-base case study please!

Have you read about acid-base in your text? Try to google it because sometimes it's easier to comprehend. Lungs and kidneys control the ph. Also, any other abnormalities in Theseus?

Sorry, typo. These labs

http://www.orlandoregional.org/pdf folder/Inter of Arterial Blood Gas.pdf

Your new best friend^ This helped me, since I just got done doing acid-base balance myself in Patho.

Good luck!

Ok, let's start with interpreting the lab values.

Arterial blood gases: pH 7.25; PaO2 60 mmHg; PaCO2 78 mmHg; HCO3- 34 mEq/l

• Serum sodium (Na+) 140 mEq/L
  
• Serum potassium (K+) 2.0 mEq/L
  
• Serum chloride (Cl-) 105 mEq/L
  

Ignore the ABGs for a second since your first question asks about electrolyte imbalances. You have 3 electrolyte levels here. Which one is out of range? If you have studied the normal ranges for serum electrolytes, this one should stick out to you like a sore thumb.

Serum sodium is 140. Normal range is what? 135-145 (varies slightly depending on the lab) so he's good there.

Serum chloride is 105. Do you know the normal range for this? High normals are usually around 106-107 so no problem here either.

Serum potassium is 2.0. This is what we call a critical lab value. What's the normal range? Is this higher or lower than normal? What do we call it when there is an electrolyte imbalance involving potassium? What are the important things to monitor with an out-of-range potassium level?

Now, let's look at the ABGs:

pH 7.25. What's normal? If you said 7.35-7.45, you're right. So your pH is lower than normal which tells you that you have some kind of acidosis going on. How do you tell where it's coming from? Based on your PaCO2 and HCO3 values, right?

PaCO2 is 78 mmHg. What is the normal range for this? 35-45. CO2 is an acid and your level is elevated so you have more acid than normal and, voila, you have the cause of your acidosis. So what does this mean? CO2 is the respiratory piece of the puzzle right? So you're dealing with a respiratory acidosis (which should make sense with a patient with a respiratory pathophysiology).

HCO3 is 34 which means that this, too, is elevated. Normal range is 22-26. HCO3 is a base. You have an acidotic state, so why is the base level elevated as well? Have you learned about compensation yet? Unless the underlying problem is corrected, your HCO3 will continue to rise until it's able to get the pH within range. The kidneys are working here to correct the acidosis by excreting more carbonic acid and reabsorbing more bicarbonate to bring the serum level up.

EVERYTHING is out of range here. What does it mean when all values are out of range? It means you're dealing with a partially compensated state. In an uncompensated state of respiratory acidosis, the HCO3 would still be normal. It's elevated because the body is trying to compensate but you know that it's only partially compensated because your pH is still profoundly abnormal. A fully compensated state would give you a normal pH.

Try the tic tac toe exercise. It really helped me. And I would also recommend youtube videos.

Thank you everyone! Everything you posted helped me understand this topic. I feel way more confident now in solving these case studies :)

This is the system I derived to teach ABGs in the early 80s, although I put it up on the net and I see it almost verbatim in other places now. Happy to help. I find this even simpler than the nine-box "tic-tac-toe" earlier. But it really doesn't matter-- read 'em all and find the one that works the best for YOU. Bonus material: Oxygen: PaO2 versus SpO2, and why you need to know the difference.

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 blackboard :) so 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 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 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.

Likewise in the metabolic/alkalosis box, a high bicarb makes your body want to retain acid, increasing CO2 being the fastest cuz 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? DK**A**?) it will want to get rid of CO2 to compensate, and the fastest way to do that is to hyperventilate.

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 betwreen 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 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 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.

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?

Electrolyte imbalance: HYPOKALMEMIA (serum K+ is 2.0 meq where normal range is 3.5-5.0) like someone mentioned (critical finding)

Acid/base imbalance: Uncompensated respiratory acidosis--to understand acid/balance questions... focus on the pH, PaCO2 and HCO3 levels; PaO2 is not necessary for ABGs but they are when you are considering oxygenation status and effectiveness of MVS (mechanical ventilation)

Remember: CO2=acid and HCO3=base

Step 1: Look at the pH and ask if it is normal, acidosis, alkalosis

Normal pH=7.35-7.45

7.45=alkalosis

Step 2: Look at the CO2 and Bicarb to see which one is causing the imbalance

The causative factor will be in the same direction as the out of range pH in terms of acidity or alkalinity (for example, a pH of 7.30 is acidic so the CO2 will be in the acidic direction or ELEVATED [more CO2 means more acid] while the HCO3 in an acidic direction will be DECREASED [less HCO3 means less base and therefore more acid]) and visa versa for alkalosis

Step 3: is there any compensation? To determine this look to see if the pH is within normal range...if it is not then there is no compensation; if it is then there is compensation

The non-causative factor will be compensating and should be out of range as well and in the OPPOSITE direction in terms of acidity and alkalinity. So if pH was more on the acidic side the compensating factor will look basic and vice versa...for example, pH=7.35, PaCO2= 55 and HCO3= 30 1)the pH is within range but on the acidic side 2) the CO2 is elevated and therefore the causative factor since it is an acid and 3) the HCO3 is in the opposite direction of the pH because it is elevated and therefore more basic in order to compensate for the high acid-Respiratory acidosis with metabolic compensation

***in your case even though the bicarb is elevated in an effort to compensate it isn't because the pH is still really low