Advanced Pathophysiology

Acid-Base Balance

Abdullah Al-Asaad: Okay. Hello everyone. My name is Abdullah Al-Asaad, I'm a medical student at [inaudible 00:00:16] University for Health Sciences. And today we're going to talk about acid base pathology. Now that we're done with physiology, it's time to talk about the diseases and pathologies that are associated with acid base. If you haven't seen the physiology video, a link to that will be provided down below in the description box. So, over here is a little bit of a table just to explain the kinds of pathologies related to acid base. So over here we have respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. So let's go one by one. So in respiratory acidosis, what's going to happen? Well, as you see in here, the arrows in red are the cause.

So in respiratory acidosis, we're going to have an increase in CO2 in our body, okay? That's the cause, okay? And since we have increase in CO2, what's going to happen? The equation's going to move to the right. So it's going to result in increase in hydrogen ions and increase in the bicarbonate, okay? However, the bicarbonate increase is not that significant in respiratory pathologists, okay? Remember that. Okay. As for respiratory alkalosis, we're going to have decrease in CO2. That's the cause, okay? Which will drive the whole equation to the left. So we're going to decrease the hydrogen ions and decrease the bicarbonate, as you said, it's not going to be that significant, okay? A very important example for this is when you hyperventilate. So when you hyperventilate, you flush out all of your CO2, okay? And as a result, the equation goes to the left and gives you respiratory alkalosis. So, it's a very important exam question.

They'll say a patient is hyperventilating, what will result? The answer is respiratory alkalosis. Why? You flush out the CO2, okay? Now, in metabolic acidosis, we have the cause could be either from hydrogen ions or the bicarb, okay? So it could be either increase in hydrogen and talk about metabolic acidosis, increase in hydrogen ions, or decrease in bicarb. Okay. Now let's say we have increase in hydrogen ions. The equation now is going to move to the left, which will decrease the bicarb, but in metabolic pathologies, the bicarb change is significant. Remember that. Okay. However, in metabolic alkalosis, we have decrease in hydrogen ions, okay? And as a result, the equation will move to the right, okay? So we have more bicarbonate, and as you said, metabolic, so it has to be significant, okay?

Over here I put the number 40, which is basically the normal or the regular level of carbon dioxide in our body. Now over here, the carbon dioxide, when it comes to metabolic acidosis or alkalosis, it differs. So basically if we have high or low, it will tell us if we have respiratory competition or not, okay? So, let's go one by one. So respiratory acidosis, we said caused by a decrease in alveolar ventilation, increase in CO2. So any pathology that will increase your carbon dioxide in your body, okay? The result will decrease in pH, okay? And a slight increase in bicarb, but not significant. The causes, as you can see here, respiratory depression, COPD, restrictive lung diseases, airway obstruction. So anything that will actually block the exchange of oxygen and carbon dioxide through ventilation, okay?

Now, respiratory alkalosis caused by an increase in alveolar ventilation relative to body CO2. So you decrease your CO2 in your body, okay? A result, a decrease in hydrogen ions, which will increase in pH, okay? Causes anxiety, why? Because people are having anxiety will start to hyperventilate, okay? And here are the rest of the causes. Now I put these two in red because many students have problems with pneumothorax and VQ mismatch. Well, basically a pneumothorax, it will result in atelectasis, okay? And atelectasis is basically when we'll have a pulmonary shunt, okay? So the rest of the lungs that are working are basically going to go into a hyperventilating state, which will flush out all of the CO2. Same thing happens with VQ mismatch. In VQ mismatch, we have both hypoxemia and hyperventilation.

Now, metabolic acidosis. The cause is going to be caused by a gain in hydrogen ions as fixed acid or loss of bicarbonate. And if you see fixed acid increase in hydrogen ions as fixed acids, you remember protein diets, okay? So a Western diet or a high protein diet, okay? Results decrease in pH and bicarbonate, okay? So here are some pathologies or causes of metabolic acidosis. So basically increase in acid production, okay? You have bicarbonate loss, for example, in renal tubular acidosis type two. Okay. Diarrhea, decrease ability of the nephron to excrete the fixed acid that you are generating or the fixed acid in your body. So renal tubular acidosis type one, as an example. Now in metabolic alkalosis, it's caused by a loss of hydrogen ions as fixed acid, okay? Or gain in bicarbonate. So the cause in metabolic processes either caused by hydrogen ion problems or bicarbonate. A result is increase in pH and bicarbonate. Causes vomiting.

Why put this in red? Because over here, vomiting will give us metabolic alkalosis. However, diarrhea will give us metabolic acidosis, put that in mind, okay? And here are the rest of the causes of metabolic alkalosis. Now, when you have a question about pH, acidosis, alkalosis, what's the cause? What's going on? Here are some steps so you can answer a question. First, you look at the pH. You see and determine if it's acidosis or alkalosis. The normal range, as we said, is seven point 35 to seven point 45. If it goes higher, that means alkalosis. If it goes lower, that means acidosis. Then you look at the carbon dioxide level. The normal is between 35 and 45, okay? So, and see if it explains the problem. And last, we check out the bicarb, okay? The normal is from 22 to 26. What I want you from this slide is to memorize the ranges. Okay.

Now over here, let's take an example. Let's say we check out the pH and it's 7.2. So over here below 7.4 that's acidosis, okay? So we determined that we're dealing with acidosis, okay? Next we check out the carbon dioxide, okay? If it's above 40, that supports acidosis, high carbon dioxide. So let's say we have a high carbon dioxide but a normal bicarbonate. In that case, we're dealing with a respiratory acidosis, okay? Then again, and if we check out the bicarb, okay? Let's say we have acidosis then we check out the bicarb and find the bicarb to be low and the CO2 to be normal. Okay. In that case, what do we have? We have metabolic acidosis. Okay. What if we have a high CO2 and a low bicarb? What does that tell us? Well, both of them, the CO2 and the bicarb are supporting the theory of acidosis. So what are we dealing with? Well, we call that a mix. So it's respiratory and metabolic acidosis, okay?

Now another thing I need you to know or memorize is basically over here. For example, let's say we have acidosis. Okay. And you have a CO2 of 60, which is high, okay? So we say, okay, the CO2 supports the theory of acidosis, okay? You check the bicarb. Okay. Why? Because when you check the bicarb, you can see if there's compensation or not, okay? So if the bicarb is high, what does that tell us? High bicarb basically supports the theory of alkalosis. So high bicarb is trying to make the blood more alkalotic, okay? Basically trying to bring the acidosis back to normal, okay? So that's renal compensation. And of course, the other way around. So let's say we have an acidosis caused by a low bicarbonate. If we check the respiratory system, which is the CO2, and we find out that the CO2 is low, let's say 20. That means the respiratory system is trying to compensate and bring the blood pH back to normal, okay?

Here's an easy way or some diagrams to show what's going on. So over here is the normal, let's say we have CO2 and bicarbonate, okay? Now let's just take a couple of examples, I'm not going to do all of them. So in respiratory acidosis, we're going to have what? Increase in CO2, right? Okay. So what is our kidney going to do so we can compensate? It's going to increase the bicarb, as you can see here. Okay. And of course, in respect to alkalosis the other way around, let's say we have a decrease in CO2. It went from one to 0.5. What's going to happen to the bicarb? It's also going to decrease. Okay. Here's a couple of examples you can read through the rest. Now, we're going to now explain something called an anion gap. Okay. This is very important when you're talking about metabolic acidosis, okay? Now what is an anion gap? Basically in our body we have the anions equal to the cations, okay? So in our body, we have major anions and major cations but in our equation, we're only going to deal with some of them, okay?

Which is sodium, is going to represent the cations, minus chloride and bicarbonate are going to represent the anions, okay? Now, if you go through this equation over here, as you can see, we have 140 minus 108 plus 24. This will give us the answer will be eight, okay? So a normal anion gap is basically from eight to 12, okay? In that range, okay? Now, as we said, it's important for metabolic acidosis. Now let's have this diagram to explain more of what's going on. So as you can see here, we have the sodium, okay? We have the potassium and we have the unmeasured cations, okay? Over here, we have the unmeasured anions, bicarbonate, and chloride, okay? Now, if we do this equation, we have 140 minus 104 plus 24. Okay. These two together will give us an anion gap of 12, okay? Which is normal. We said the normal's from eight to 12. That's the normal anion gap, okay? So we have two kinds of acidosis, okay?

We have a non-anion gap acidosis and an anion gap metabolic acidosis, okay? Now, if we have a normal gap metabolic acidosis or a non-anion gap metabolic acidosis, what does that mean? It's basically an acidosis coming from decrease in bicarbonate. Now, when we have decrease in bicarbonate, okay, you would think that the anion gap would get bigger. However, what happened to the chloride? It increased, okay? It increased. So over here, the bicarbonate decreased by 12 and the chloride increased by 12. So the anion gap stayed the same. Okay. However, if we have an elevated or an anion gap metabolic acidosis, what's going to happen? Basically it's caused by the anions that are unmeasured over here, okay? Are going to increase. So increase in anions, other than chloride, of course. Increase in anions, which is going to what? Are going to push down the bicarbonate. So the bicarbonate is going to get low, okay? So this will go to bring up the anion gap huge, okay? And as you can see, if you do the equation, you'll find a huge anion gap.

So if someone says, if you have an acidosis or an anion gap acidosis, what is the cause? You would say increase in the unmeasured anions, basically. Now, let's check out here. The non-anion gap metabolic acidosis, which we said the cause is loss of bicarbonate, okay? Two most important examples I need you to memorize is diarrhea and both renal tubular acidosis one and two, okay? We have also early renal failure, acetazolamide therapy, rapid intravenous hydration. As for the anion gap metabolic acidosis, the cause is increased in anions other than chloride, okay? Another frequent a mnemonic is KARMEL, okay? So we have ketoacidosis, aspirin, renal failure, methanol, ethylene glycol, and lactic acid. As you can see they all basically increase in acids in our body, which will increase the unmeasured anions, okay? Another thing I need you to remember here is over here, we have aspirin. As for the non-ion gap, we had what? We had acetazolamide. That will be the end of this video. Thank you very much.