Tic Tac Toe Method Arterial Blood Gas (ABG) Interpretation for Nurses & Nursing Students

Video blood gas tic tac toe

Don’t you love ABG problems in nursing school? Well, I didn’t until my professor taught us the TIC TAC TOE Method for ABGs and then solving ABG problems actually started to be somewhat fun. Below I show you how to solve ABG problems using the Tic Tac Toe method. There is also another method called the ROME method that you can use to solve ABG problems.

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After you read and watch the video on using the Tic Tac Toe Method, don’t forget to that the ABG’s practice quiz to test your knowledge.

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In addition, you may be interested in:

Dosage & Calculation Problems in Nursing School
Respiratory Acidosis vs Respiratory Alkalosis

Nurse Sarah’s Notes and Merch

Just released is “ABG Interpretation Notes, Mnemonics, and Workbook by Nurse Sarah“. These notes contain 64 pages of Nurse Sarah’s illustrated, fun notes with mnemonics, and worksheets that include over 90 ABG practice problems and 60 test review questions covering ABG concepts.

You can get an eBook version here or a physical copy of the book here.

Why Learn How to Interpret Arterial Blood Gases as Nurse?

Being able to interpret Arterial Blood Gases (ABGs) as a nurse is very important. Many new nurses feel they are not comfortable with interpreting ABGs after they graduate. Some of these nurses feel they will never use it in their job and feel it is the respiratory therapist’s job or find it’s too confusing to understand.

However, as the nurse taking care of the patient with abnormal Arterial Blood Gases (ABGs) it is your responsibility to know what to report to the doctor and how to properly oxygenate your patient based on their ABGs.

Luckily there is a super easy way to help you interpret ABGs and I want to share it with you below.

First, we need to lay the foundation and talk about what three lab values you need to look at when trying to figure out ABGs, how to determine if that value is consider normal, an acid, or basic (alkalotic), and what fancy terms are used once the ABG is figured out.

Watch this video I made on how to use the TIC TAC TOE Method for solving Arterial Blood Gases. Don’t forget to subscribe to my YouTube channel for more teaching videos.

Explanation & Examples on Solving ABGs Problems

Below are the terms used to label abnormal ABG results:

Respiratory Acidosis (uncompensated, partially compensated, or fully compensated)
Respiratory Alkalosis (uncompensated, partially compensated, or fully compensated)
Metabolic Acidosis (uncompensated, partially compensated, or fully compensated)
Metabolic Alkalosis (uncompensated, partially compensated, or fully compensated)

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When you are analyzing ABG results there are three things to look for when trying to find out if your patient is in respiratory or metabolic acidosis or alkalosis. Here they are and their normal numeric values (commit them to memory):

pH: 7.35-7.45
CO2: 35-45 (CO2 lab value ALWAYS indicates a RESPIRATORY issue)
HCO3: 22-26 (HCO3 lab value ALWAYS indicates a METABOLIC issue)

Now to determine when these values are considered an acid or base. For pH anything less than 7.35 is an acid and anything greater than 7.45 is a base. For CO2 (NOTE: it is the opposite) anything less than 35 is a base and anything greater than 45 is an acid. For HCO3 anything less than 22 is an acid and anything greater than 26 is a base. Here is a guide to help you understand it:

Let’s talk about blood pH for a moment because if FULL compensation presents there will NOT be a tic tac toe and you will have to look closely at the blood pH to determine which system is causing the issue and which system is trying to “fix” the issue (hence compensate).

A normal blood pH is 7.35-7.45. The absolute normal is 7.40. Any normal blood pH that falls between 7.35-7.40 is NORMAL but on the “acidotic” side and any normal blood pH that falls between 7.40-7.45 is on the “alkalotic” side. This is illustrated below:

In order to use the tic tac toe method you must first get a sheet of paper and set up a “tic tac toe” grid. Then label each “column” as “acid”, “pH”, and “base”. It should look like this:

Now lets solve a problem using the tic tac toe method: ABG results are the following…..pH 7.24, PCO2 75, HCO3 28

Draw your tic tac toe lay out.
Analyze your pH. Ask yourself is it normal, basic, or acidic? Since the pH is less than 7.35 making it an acid, place it under the acid column.
Analyze your PCO2. Ask yourself is it normal, basic, or acidic? Since the PCO2 is greater than 45 making it an acid, place it under the acid column along with pH. Remember PCO2 is the opposite and the normal is 35-45.
Analyze your HCO3. Ask yourself is it normal, basic, or acidic? Since HCO3 is greater than 26 making it basic, place it under the base column because the value is considered basic.
Your tic tac toe lay out should look like this:

Now that you have your tic tac toe grid set up. You need to figured out what you have. Since your pH is acidic you know that you have acidosis going on but is it respiratory or metabolic acidosis? Since CO2 represent respiratory and it is under the acid column with your pH you have respiratory acidosis going on.

But is it fully compensated, partially compensated, or uncompensated respiratory acidosis? Look at your HCO3! Since your HCO3 is under basic, the metabolic system is trying to balance the body’s system out by becoming basic so it is partially compensating. So the answer is Partially Compensated Respiratory Acidosis. Note: If HCO3 was under the normal column it would not be trying to compensated and therefore it would be considered uncompensated respiratory acidosis.

Let’s try another one: ABG results are: pH 7.50, PCO2 36, HCO3 32. Here is what your tic tac toe grid should look like:

Analyze your pH. Ask yourself is it normal, basic, or acidic? Since the pH is greater than 7.45 making it a basic, place it under the base column.
Analyze your PCO2. Ask yourself is it normal, basic, or acidic? Since the PCO2 is between 35-45 it is normal, place it under the normal column.
Analyze your HCO3. Ask yourself is it normal, basic, or acidic? Since HCO3 is greater than 26 making it basic, place it under the base column because the value is considered basic.
Since your pH is basic you know you have some alkalosis going on. But is it respiratory or metabolic? Since the HCO3 (which represents metabolic) is under you basic column with pH it is a metabolic issue. So your patient is in: Metabolic Alkalosis.
Now is it fully compensated, partially compensated, or uncompensated metabolic alkalosis? Look at the CO2! Since it is under the normal column that means the CO2 has NOT tried to help out the body’s system by making itself acidic. So the body is not compensating.
Answer: Uncompensated Metabolic Alkalosis

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Let’s try another problem: blood pH 7.37, PaCO2 33, and HCO3 17….tic tac toe should look like this:

Pull again for your memory bank to analyze the values. You should determine this:

pH: 7.37 (falls within 7.35-7.45) = NORMAL but it’s on the acidotic side

PaCO2: 33 (less than 35) = ALKALOTIC

HCO3: 17 (less than 22) = ACIDIC

So, we don’t have a tic tac toe, therefore, the values are representing compensation (is it partial or full?).

To determine the type of compensation look at the pH…is it normal or abnormal? It’s NORMAL! Therefore, we have full compensation.

BUT is this a respiratory or metabolic problem?

To determine this, look at the blood pH:

The blood pH is normal, but it falls on the acidotic side. Our metabolic system is also acidotic but our respiratory system is alkalotic. The problem is with the metabolic system and the respiratory system is trying to balance out the blood’s acidotic state by decreasing the carbon dioxide level (PaCO2) to make things more alkaline, which will help increase the blood’s pH from it’s acidotic state….which is has and this is why we have full compensation rather than partial. Note: If the pH was not normal and the HCO3 was still acidotic, it would be partial compensation. On the flip side, if the pH was not normal but the HCO3 was normal, it would be uncompensated.

Our answer is: metabolic acidosis, fully compensated by the means of respiratory alkalosis

Do you want to see how well you know how to interpret ABGs? Here is a free ABG practice test.