Fundamentals - Practice & Skills, part 17: Acid/Base Imbalances

August 06, 2021 6 min read

Full Transcript

Hi, I'm Meris. And in this video, we're going to be talking about acid-base imbalances. I'm going to be following along using our Fundamentals of Nursing flash cards. These are available on our website, And if you already have a set for yourself, I'm going to be starting on card number 99. Let's get started.

Now, before we even get started, I want to do a very brief review of expected lab values for acid-base balance. And if you want to get a little bit more in-depth with this, we do have an arterial blood gas deck that can help you understand how to interpret ABGs and the normal values. And then we also have our lab values deck, which covers normal values and a lot of other considerations for most of the labs you're going to need to know in nursing school. So important things that we're going to be looking at to diagnose a respiratory or metabolic imbalance. We're going to be looking at the pH, which should be between 7.35 and 7.45. Anything less than 7.35 is acidosis. Anything greater than 7.45 is alkalosis. The other thing we're going to look at is carbon dioxide. The partial pressure of carbon dioxide in arterial blood should be between 35 and 45. The higher it is, the more acidic. The lower it is, the more basic. So it's the opposite of pH, and it's the opposite of bicarbonate. Bicarbonate or HCO3 is going to be the metabolic buffer for the acid-base system. The normal values of this are going to be 21 to 28. If I have less than 21, we are on the acidic side. If I have more than 28, we're getting into alkalosis. So just wanted to review that very quickly before we actually get into each specific imbalance.

Okay. Now let's talk about the respiratory imbalances for acid base. So first on this card is respiratory alkalosis. And this is going to be marked by a pH greater than 7.45 alkalosis and a PaCO2, a partial pressure of carbon dioxide less than 35. So that's going to be respiratory alkalosis. This is the more infrequently seen disorder of respiratory imbalances. The big cause here is going to be hyperventilation. So this can be from anxiety, from pain, or from some sort of a neurological disorder or injury that's causing hyperventilation. But I'm blowing off too much CO2, so it's dropping in my blood, and then that's going to cause me to be on the alkalosis side of the scale. So you will see that this is going to be less frequent than the other, which is respiratory acidosis.

Now, respiratory acidosis means that I'm going to have a pH less than 7.35, but I'm going to have partial pressure of carbon dioxide that is greater than 45. Very important to understand that, that opposite relationship between pH and CO2. Now, why am I having this? Well, this is because for some reason or another, I'm holding on to too much carbon dioxide. A big one here is going to be air trapping for diseases and disorders like COPD, if I have an air-trapping disorder like that. But another big cause is going to be oversedation. For instance, if I have a patient who's coming out of anesthesia and they're not fully awake, they're not breathing enough, it's going to have them hold on to more oxygen, hold on to more carbon dioxide, and then we're going to end up having the acidosis. By that same token, it doesn't have to be sedation like anesthesia. It could be something like an overdose - an overdose on an opioid or benzodiazepine can cause this - or even if I have a patient who's being mechanically ventilated, and the settings are having them breathe too infrequently.

So how do I treat each disorder? Well, respiratory alkalosis, it's more infrequent, but the big thing is going to be calming your patient down. But I can also have them breathe into their cupped hands or into a paper bag, for instance, to help them to rebreathe some of that carbon dioxide to increase the amount in their blood. Now, for respiratory acidosis, on the other hand, I'm going to want to encourage them to breathe more frequently. So maybe this is adjusting ventilator settings. Maybe this is a sternal rub to wake up my patient, or maybe this is administering the antidote for a medication that they are too heavily sedated or overdosed on, such as naloxone or flumazenil. The other thing, though, is that if I do have a patient with COPD, they're just always going to be trapping air, so they are always going to have respiratory acidosis. Very important to understand that. Now, they can have worse respiratory acidosis than usual, but there will always be some kind of acidotic state because they are always holding on to too much air.

Okay. Let's move on to metabolic. Now, when we're looking to see about metabolic disorders, the two key lab values we need to be paying attention to are, again, pH, but also bicarbonate or HCO3. So HCO3's excreted by the kidneys. It's one of our buffers. So this is going to be something that would be out of whack if the problem is with the metabolic system. Remember, respiratory system, I'm going to have an imbalance with the carbon dioxide because it's coming from my lungs. Metabolic, I'm going to have an imbalance from my kidneys, from something that isn't my respiratory system. Now, metabolic alkalosis, this means a pH greater than 7.45 and a bicarb greater than 28. Remember, they have a directly proportional relationship, so they go in the same direction.

So big cause here is going to be antacid overdose. If you take too many antacids, you're going to obliterate the acid in your stomach and end up with alkalosis. And then also, you can remember that metabolic alkalosis can also be caused by vomiting or excessive GI suctioning, for instance, through an NG tube. I'm removing the acid from the stomach, so now we're getting more alkalotic. Here's how I remember that. It's not a cool chicken hint on here because it's kind of hard to write down. But I think that vomiting can cause metabolic alkalosis because vomiting is metabolic alkalosis. Okay. So kind of that's how I remember it.

Now, moving on to metabolic acidosis. This one is going to be very, very common in your patients who have DKA, diabetic ketoacidosis. It's in the name, so that helps you to remember. And then kidney failure. If my kidneys are failing and I can't put out enough bicarbonate, I'm going to end up with acidosis. So remember that the lab values here for metabolic acidosis are going to be a pH less than 7.35 and bicarbonate less than 21. So the treatments are going to depend on what the cause is, right? If I'm vomiting, then I'm going to need to give them an antiemetic. If I'm having an overdose of antacids, then I'm going to need to stop that. If I have DKA, we need insulin. So the treatment's going to depend on what the actual cause is. But just very important to understand why sometimes we have too much or too little bicarbonate. So I also want to point out here just one more quick thing. With metabolic acidosis, you can also end up in this state from excessive diarrhea. Now, I told you my hint, metabolic alkalosis. I would like for you to try and fill in the blanks and think of what my hint might be, if it were not a little PG-13, for how you can remember that diarrhea causes metabolic acidosis. All right?

So I hope that review was helpful for you. When you get more in-depth with ABGs in med-surg or wherever, that is for you in your curriculum, I would very much recommend getting the ABG interpretation deck, the med-surg deck, and the lab values deck, all of which are available on If you liked this video and you found it helpful, I would love it if you could give it a like. And if you have a really great way to remember one of these things, I want to hear about it, please leave me a comment. I know other people want to see it too. Be sure to subscribe to the channel because up next, we're going to be talking about macronutrients, micronutrients, and BMI, so you want to be the first to know when that drops. All right. Thanks so much and happy studying.

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