ABG’s, what do they mean?

Arterial blood gases… Chances are if you work in a progressive care or intensive care unit you have seen ABG results or you will.

If you’re like me in the beginning, you have no idea how to interpret the results. For the longest time I had no idea what I was looking at. I knew the pH was indicative of acidosis or alkalosis, and that was the end of it. Once I started working in an ICU I wanted to really understand what the results meant. I made one of our respiratory therapist teach me how to understand the results (he was awesome and was happy to help). It turns out ABG results are not too terribly difficult to interpret. You are trying to obtain three key pieces of information:

• Is the patient acidotic or alkalotic?
• Is this a respiratory or a metabolic issue?
• Is the body fully compensating, partially compensating?

While there is plenty of information on the ABG slip (or in the chart if your unit doesn’t have an ABG machine available) you can come up with the answer by looking at three key results: pH, paCO2, HCO3.

One of the ECCO learning modules I did had this handy little chart that made it easier to interpret the results. I thought I would share it with you all in case there is someone out there confused like I was, but may not have a quick resource available.

That’s it. This little handy chart has helped me a lot. It took what was, for me, a larger amount of overwhelming information and broke it down into something I could use. Here’s how to use it:

Look at the pH, is it <7.35 (you’re acidotic) or >7.45 (you’re alkalotic) or is it normal? Circle which side of the chart your value falls in. Then look at the PaCO2. We are looking at carbon dioxide in the blood here. Repeat the previous steps and circle where your value falls. Then look at your bicarb, HCO3. Circle where that value falls.

Remember pH tells you if they are acidotic or alkalotic. Now that you’ve figured that part out, it’s time to figure out if this is respiratory or metabolic. Look at your chart, is the CO2 circled on the same side as the pH? If yes, it’s respiratory. Is the bicarb circled on the same side as the pH? If yes, then it’s metabolic. Now, are we compensating? If you are partially compensating then you will have one value on the other side of the grid. If you are fully compensating then your pH will actually be normal.

I’m a person that needs to see something in action so let’s do a couple of examples:

Note let’s break out the chart:

pH is low so we know the patient is acidotic. The CO2 is on the same side as the pH. The bicarb is on the opposite side of the grid so the body is trying to compensate. We have respiratory acidosis, partially compensated.

Let’s do one more:

Bust out the handy dandy chart!

The pH is high so we know it’s alkalosis. The bicarb is on the same side of the chart as the pH but the CO2 is on the opposite side. Here we have metabolic alkalosis, the respiratory system is partially compensating, that’s why the CO2 is high.

I would like to mention one thing, if all your values are on the same side of the chart then it most likely means the one of the systems of the body aren’t compensating.

Hopefully this post is able to help someone out. If you have any other hints, tips, tricks let me know!