Distinguishing between different acid-base disorders—a simple rule
Learn how to apply a simple rule to identify whether your patient's primary acid-base disorder is metabolic or respiratory.
Acid-base problems can occur isolated or in combination. Even when they are combined, there's usually one problem that causes more problems than the others. In this video, you'll learn the relationship between pH, HCO3, and pCO2, and a simple rule which will help you decide whether the primary problem is respiratory or metabolic in nature.
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Transcript
How to identify the primary acid-base disorder
[0:00]
Acid-based problems can occur isolated or in combination. But even if they're combined, there's usually a primary problem that's most pronounced. In this lesson, you'll learn a simple rule of how you can tell if the primary problem is metabolic or respiratory in nature. So, let's recap the different types of acid-based disorders real quick. For simplicity's sake, I've not separated out acute and chronic respiratory problems.
Respiratory acidosis and respiratory alkalosis
[0:30]
As we said, in respiratory acidosis, pCO₂ is elevated, which causes pH to fall. As a reaction to that, bicarb will also be elevated. In respiratory alkalosis, on the other hand, pCO₂ falls, pH rises, which will then also cause the bicarb to fall. So, you can see that in respiratory problems, the pH and pCO₂ change in two different directions.
Metabolic acidosis and metabolic alkalosis
[0:58]
Let's see what the situation is in metabolic problems. In metabolic acidosis, we said bicarb falls and pH falls, which causes the pCO₂ to also fall. How about metabolic alkalosis? Here, the bicarb rises, which causes a rise in pH, which then also causes a compensatory rise in pCO₂. So, as you can see, in metabolic problems, the change in pH and pCO₂ are in the same direction, and that constitutes a simple rule for identifying the primary acid-base problem in our cases.