01.04 ABG (Arterial Blood Gas) Interpretation-Tic Tac Toe

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  1. The Tic Tac Toe method uses visual placement of values for evaluation.

Nursing Points


  1. Setup
    1. Three columns:
      1. Acidosis
      2. Normal
      3. Alkalosis
    2. Two rows under the headers
      1. Left blank
  2. Process
    1. For each value, determine if it represents acidosis, alkalosis, or a normal value.
    2. Write “pH”, “pCO2” and HCO3” under their correct columns
    3. Whichever value is in the same column with pH is the source:
      1. pCO2 = Respiratory
      2. HCO3 = Metabolic
    4. Mixed Conditions
      1. All 3 values will be in the same column
        1. The extra one will be “off the charts”
  3. Determining Compensation
    1. Fully Compensated
      1. If you have a normal pH and both pCO2 and HCO3 are abnormal under different columns, you will have ‘tic tac toe’ straight across
        1. Will NOT have any in the same column
    2. Partial Compensation
      1. If you have two in the same column (pH and one other), AND the other value is in the opposite column (NOT normal)
        1. The Normal column will be empty

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Video Transcript

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!!

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  • Question 1 of 4

A nurse is caring for a client who is recovering from a chest injury. The provider orders arterial blood gases for the client. The results are pH 7.26, pCO2 52 mmHg, HCO3 25 mmHg, and oxygen saturation 92 percent. Which of the following best describes this client’s condition?

  • Question 2 of 4

A nurse is caring for a client who requires a mechanical ventilator for breathing assistance. The nurse checks the client’s routine ABG values and notes: pH 7.51, pCO2 32 mmHg, HCO3 24 mEq/L. These laboratory values best represent which of the following?

  • Question 3 of 4

A nurse is caring for a client who is receiving a test of arterial blood gases after being admitted as an inpatient to the hospital. The client has the following ABG results: pH 7.26, PaO2 46mmHg, pCO2 50mmHg, HCO3 24mmHg. Which response from the nurse is most appropriate?

  • Question 4 of 4

A nurse is caring for a client with ARDS and views the ABG results seen in the diagram. Based on the ABG results, which of the following findings would the nurse be most likely find in this client?