Distinguishing between different acid-base disorders—a simple rule

Learn a simple rule to identify the primary acid-base problem occurring in your patient.

Rainer Oberbauer, MD MSc
Rainer Oberbauer, MD MSc
14th Mar 2018 • 2m read

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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Video Transcript

[00:00:00] 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. As we said,

[00:00:30] 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 into different directions. Let's see what the situation is

[00:01:00] 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

[00:01:30] are in the same direction and that constitutes a simple rule for identifying the primary acid-base problem in our cases. Let's check out a couple of these cases. It's your turn now to use your new found skills in order to identify the primary problem underlying the following quiz questions. Please use the simple rule you've learned in the previous lessons.