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The next method for ABG interpretation is the Tic Tac Toe method. Now, I’ll be honest, this is my preferred method. But, make sure you’re trying all of the methods to figure out what makes sense to you and what works. Everyone has a different learning style, so these each cater to different types of learners.
This method, specifically, is very visual – it relies on visual placement of each value as acidosis, alkalosis, or normal.
So – I call this version 1. This is actually what I use personally, and you’ll even find a blank version in our ScrubCheats. Essentially you would put a star or a heart or a smiley face on the chart based on your results and see which ones match up. But as I was putting this lesson together, I realized that it’s not as easy to see compensation and it’s not as clear – and honestly, it’s really more like the physiology version – so I’m going to show you Tic Tac Toe version 2 and show you how quick and easy it is, and I think you’re going to love it!!
So in version 2, you will set up a little table that looks like this – three columns, acidosis, normal, and alkalosis. And you’ll have 2 rows. This is super easy to just jot at the top of a test paper or on your brain sheet in clinicals. As you do step 1 of interpretation, you’ll place each value in the box it corresponds to. So if your pH is acidotic, your PaCO2 is acidotic, and your bicarb is normal, you just write them in. Then, if you have two that match in a column, you automatically know that’s your source just by looking at it. So, step 2 basically takes no thought. This is a respiratory acidosis. Let’s work through some examples and we’ll look at compensation as we go.
Step 1 – pH is high, so it’s alkalosis – I’ll write pH in this box. PaCO2 is low, so it’s alkalosis – I’ll write PaCO2 in this box. Bicarb of 22, that’s normal, so I’ll write it under normal. Immediately, Step 2 is done – I see my source is the CO2 and therefore this is a Respiratory Alkalosis. Now, for step 3 – the first sign is that both the CO2 and bicarb are abnormal, right – but we can see that bicarb is normal, so there’s NO compensation. So this is an uncompensated respiratory alkalosis.
Let’s do another – step 1. pH 7.29 is acidotic, so put pH here. CO2 37 is normal, put CO2 here. Bicarb 16 is low, which is acidotic, put HCO3 here. So, right away we see that we have a metabolic acidosis. Step 3 – are both bicarb and CO2 abnormal? No, so this is an uncompensated metabolic acidosis. Now, one thing I want to show you is that you could also have a MIXED condition. Let’s say the CO2 was 47 – it would ALSO be acidosis, right? So I always say, you know you have a mixed condition if you have a level that’s off the charts – you basically have a double-whammy issue here.
Okay, let’s do another one. Step 1 – pH 7.32 is acidotic, CO2 55 is acidotic, bicarb 29 is alkalotic, because it’s high. So step 2 – we can see that we have a respiratory acidosis. Now, step 3 – is there compensation? Are both bicarb and CO2 abnormal? YES. pH is still abnormal so it’s only partially compensated. Here’s the trick – we know it’s a partially compensated condition if the normal column is completely empty. See it? So that’s the partial compensation trick.
Let’s look at our last one – you can probably guess what this one’s gonna be. Step 1 – pH 7.44 is normal. CO2 52 is acidosis. HCO3 35 is alkalosis. This is the one time I’ll skip to step 3 – here’s our trick – if you see a straight line ALL the way across, with a normal pH – you KNOW it’s fully compensated! So you just go back to that critical thinking to determine the source. Again, we just need to know which side of normal our pH is on – in this case, it’s leaning towards alkalosis, so it would be a fully compensated metabolic alkalosis.
So, again, this trick is very visual, but it makes it very quick and that’s why it’s my favorite. Grab the ABG fill in the blank again and use this trick to go through those problems. See if this is the best one for you! We even have some ABG-specific flashcards that you can check out. Some of them ask about the physiology, but there are also about a dozen interpretation cards in there! So make sure you check that out. Now, go out and be your best selves today. And, as always, happy nursing!!