March 23, 2014 at 5:50 PM #12531
Several people have asked, so here it is … enjoy 🙂
The Monster Method of ABG Interpretation
The Monster Method of ABG Interpretation
Arterial blood gas (ABG) interpretation can be a scary thing to learn. What worries people the most about ABGs is that the patients that have them drawn are usually pretty sick. This can dramatically increase the stress level. You then have to think back to what the normal ranges are and whether the results show an acidosis or an alkalosis, whether it is compensated or not, and if so, by how much. All of this can be overwhelming. I remember the first few ABG results I got back as a nurse. I looked at them as if they were some type of monster. What were these numbers trying to tell me? I still look at ABG results as if they were monsters, but not the scary kind. I look at them as the nice, soft, furry, colorful monsters you will find in a children’s toy store. To use this method of ABG interpretation, you have to visualize each ABG as if it were a furry monster, and based on the color of his fur and clothing, you can figure out everything you need to know about his acid/base balance. Good luck.
Hello everybody! I’m an ABG monster. Many people are afraid of ABG monsters, but I will show you that there is no reason to be afraid.
All ABG monsters can give you information about their pH, PaCO2, and bicarb levels. I’ll show you how easy it is to understand all of this data.
The first piece of information you can get from an ABG monster is his pH. The pH is a measurement of how much acid and base is in a fluid. The lower the number is, the more acidic the fluid. The higher the number is, the more basic, or alkalotic, the fluid. The normal range for pH in arterial blood is 7.35-7.45. If you work swing shift in a busy unit, this will be an easy range to remember because it represents the 10 minutes you take to eat your lunch and visit the restroom, 7:35-7:45.
The color of fur on an ABG monster depends on his pH. My pH is perfect at 7.40, so my fur is white. ABG monsters with pH levels less than 7.35 are acidic and will have red fur. Monsters with pH levels greater than 7.45 are alkalotic and will have blue fur. This is easy to remember if you think back to your chemistry class. Litmus paper turns red in an acid solution and blue in a basic, or alkalotic, solution.
Let us practice. If an ABG monster has a pH of 7.2, what is the color of his fur? A pH of 7.2 is more acidic than the normal range of 7.35-7.45, so his fur is red.
If an ABG monster has a pH of 7.5, what is the color of his fur? A pH of 7.5 is more alkalotic than normal, so his fur is blue.
The next piece of information you should look at on your ABG is the PaCO2 level. The PaCO2 level is the partial pressure of Carbon Dioxide, CO2, in the arterial blood. CO2 can be considered an acid when looking at your ABG results. The more CO2 in the blood, the more acidic the blood will be, and accordingly, the lower the pH. The lower the CO2 level is, the higher the pH.
CO2 is a waste product of cellular metabolism and is carried from the cells to the lungs by the blood. The amount of CO2 in the blood is regulated by the respiratory system. The capillaries and alveoli in the lungs exchange CO2 and Oxygen, O2. As you breathe, you increase the amount of O2 in your blood and decrease the amount of CO2. This process is commonly called “blowing off” CO2, since the CO2 leaves your body as you exhale.
The normal value for PaCO2 in arterial blood is 35-45. This is an easy range to remember because it is the same numbers found in the normal pH, 7.35-7.45, without the 7.
To remind you that PaCO2 is regulated by the respiratory system, all ABG monsters will wear color coordinated shirts, depending on their PaCO2 level.
Monsters with a normal PaCO2, 35-45, will wear white shirts, since their PaCO2 levels are not making the blood more acidic nor alkalotic. Monsters with PaCO2 levels above 45 will wear red shirts to show that their CO2 levels are making the blood more acidic, and monsters with PaCO2 levels below 35 will wear blue shirts to show that their lack of CO2 is making the blood more alkalotic.
Let’s practice this once. What color shirt is an ABG monster wearing if his PaCO2 level is 49? Since his PaCO2 level is above normal, he has more CO2, an acid, in his blood. Therefore, he is wearing a red shirt to indicate that his respiratory system is making his blood more acidic.
The third piece of information to look at on your ABG is the HCO3, (bicarbonate) (bicarb) level. Bicarb is a base that makes the blood more alkalotic. The higher the bicarb level is, the higher the pH. The normal range for the bicarb level may vary slightly from one lab to another, but we will use the values of 22-26 for the standard range. This range for bicarb is also easy to remember because it is the ages you wish you were, when you are no longer that age.
The kidneys regulate the amount of bicarb in the blood. For ABG interpretation, this is called the metabolic system. To help you remember that the kidneys, or metabolic system, regulate the amount of bicarb, ABG monsters will wear color coordinated pants based on their bicarb levels.
Monsters with bicarb levels of 22-26 will wear white pants, since their bicarb levels are not making the blood more acidic or alkalotic. Monsters with bicarb levels of less than 22 will wear red pants, since their lack of bicarb will allow the blood to be more acidic. Monsters with bicarb levels of more than 26 will wear blue pants since their extra bicarb will tend to make the blood more alkalotic.
Let’s practice this once. What color of pants would an ABG monster wear if his bicarb level were 20? This bicarb level would show that the kidneys, or metabolic system, were excreting too much bicarb into the urine. The loss of this extra base would make the blood more acidic, so this ABG monster would wear red pants, to indicate the decrease in pH.
This is all of the data you need to interpret ABG values. Look at the fur color, the shirt color, and the pants color, and the rest will fall into place.
Take a look at my friend here. His pH is 7.30, which is more acidic than the normal range of 7.35-7.45. That is why his fur is red. Now look at his PaCO2, which is 51. He has more CO2, which is an acid, than the normal range of 35-45, so his respiratory system is making him more acidic. That is why he wears a red shirt. Lastly, let’s look at his bicarb level. His bicarb is 26. The normal range of bicarb is 22.26, so he wears white pants, since his bicarb level is normal. Have you figured out what type of ABG monster he is yet? His fur is red, so you know he is some type of acidosis. Now we need to figure out if he is a respiratory or metabolic acidosis. To do this, find the piece of clothing that matches his fur color and this will tell you which system is causing the problem. In this case, it is his red shirt that matches his red fur. The shirt covers the respiratory system, so he is a respiratory acidosis.
Let’s try another ABG monster. This monster’s values are: pH 7.5, PaCO2 39, and bicarb 35. The pH is higher than the 7.35-7.45 normal range, so he has the blue fur of alkalosis. His PaCO2 is in the normal range of 35-45, so he has on a white shirt to indicate that his respiratory system is not making him acidic or alkalotic. His bicarb level is higher than the normal range of 22-26, so he has on blue pants to show his metabolic system is raising his pH, making him more alkalotic. Now we find which clothes match his fur color, which is blue. We see that it is his blue pants, which cover the metabolic system, which matches his blue, alkalotic fur. This is how we know that he is a metabolic alkalosis.
Let’s try one more, but be careful not to jump to conclusions because this one is a little bit different. This ABG monster has a pH of 7.29, a PaCO2 of 52, and a bicarb level of 21. What type of monster is he? We can see by his pH that he is acidic, so we know we will call him some type of acidosis, but which type? Let’s see if either his pants or shirt match his red, acidic fur. His PaCO2 level is high at 52, so we know his respiratory system is not blowing off enough acid, so he will wear a red shirt, indicating that it is his respiratory system that is making his blood more acidic. Don’t stop here though! You have to look at his bicarb level too. His bicarb level is only 21, which means that his kidneys are dumping out too much base. For this reason he will also have on red pants, to show that his metabolic system is also making his blood more acidic. Lastly, we look to see which articles of clothing match his fur, and we see that both his pants and shirt match his red fur color. In this case we will have a respiratory and metabolic acidosis. Both systems are making his blood more acidic.
In the last case, both the metabolic system and the respiratory system were each working, or not working, as the case may be, to make the blood too acidic. Normally though, if one system is making the pH too high or too low, the other system will try to counteract it, so that the pH will stay within the normal range. For this reason, you can have ABG monsters that have all of their values out of the normal range, but only one system is causing the problem. The other system is out of the normal range to compensate for the problem. As a rule, the respiratory system can change the pH very quickly by holding onto or blowing off CO2. It takes the metabolic system a longer time to affect the pH by holding onto or excreting bicarb. How do you know what to call these ABG monsters that have one system raising the pH and the other system lowering the pH?
Let’s take a look at another ABG monster. His pH is 7.49, his PaCO2 is 42, and his bicarb level is 32. What should we call him? His pH is high, so he has the characteristic blue fur of alkalosis. His PaCO2 is also high, but this would tend to make him more acidic, so he has on a red shirt. His bicarb level is high also, which gives him blue pants to indicate his metabolic system is making him alkalotic. His fur tells us he is alkalotic and it is his pants that match his fur, so we know that he is some type of metabolic alkalosis. What about his red shirt? In this case, his lungs are trying to hang onto more CO2 in an effort to make his pH come back down into the normal range. His pH would be even higher than 7.49 if it weren’t for the increase in the PaCO2 level. For this reason we will call this ABG a partially compensated metabolic alkalosis. If his PaCO2 level were normal, and he was wearing a white shirt like in our other examples, he would be called a non-compensated metabolic alkalosis, since the respiratory system wouldn’t have been working to bring the pH back into the normal range.
What if one system was able to compensate the other system enough to bring the pH back into the normal range of 7.35-7.45? This is often the case, so let’s take a look at another example. An ABG monster has a pH of 7.36, PaCO2 of 48, and bicarb of 29. His PaCO2 is higher than normal, making his blood more acidic, so he will be wearing a red shirt. His bicarb is also high, making his blood more alkalotic, so he will be wearing blue pants. His pH, however, is normal at 7.36, so what is going on? Is it a fully compensated respiratory acidosis or a fully compensated metabolic alkalosis? To decide, we need to look more closely at the pH. Normal pH is 7.35-7.45. A pH that is in this range, but closer to 7.35, can be considered to be on the acidic side of normal. A pH that is closer to the 7.45 can be considered to be on the alkalotic side of normal. The pH in our example, 7.36, is in the normal range, but on the acidic side. Therefore, we are dealing with a fully compensated acidosis. Now we need to look at the system that would be causing the acidosis. In this case, it would be the respiratory system that is causing the acidosis, so we have a fully compensate respiratory acidosis. Even though the metabolic system was able to bring the pH back up into the normal range, it will never be able to over compensate and bring the pH over 7.40. In fact, when compensating for an acidic system, it would be difficult, if not impossible, for the other system to bring the pH above 3.38. It would be equally hard for a system to compensate an alkalotic system enough to bring the pH down below 7.42. What color fur do you think this ABG monster ought to have? To make things simple, and to give a little more color to our red, white, and blue world. We will say that the fur of an ABG monster that has a pH between 7.35 and 7.39 will be light red, or pink. This will indicate that it is in the normal range, but tending to be more acidic. We will also say that a pH between 7.41 and 7.45 will be a light blue, to indicate that it is in the normal range, but tending to be more alkalotic.
Let’s practice this new bit of information a few times. What color would the ABG monster be if he had a pH of 7.2? The correct answer would be red, since 7.2 is lower than the normal range, making him acidic.
What color would an ABG monster be if he had a pH of 7.42? In this case, the fur color would be a light blue. Not dark blue fur like in an alkalotic ABG monster, but a light blue, indicating that he was on the basic side of normal.
What color would a monster be if he had a pH of 7.37? Since the normal range is 7.35-7.45, this monster would be pink, or light red, to indicate that he was on the acidic side of normal.
In order to keep all of this straight, just remember that if one system is causing the change in the pH and the other system is normal, then it is an uncompensated change, based on the color of fur and which article of clothing matches it. If both systems are outside the normal range, one being red, the other being blue, and the pH is outside the normal range, then it is a partially compensated problem, based on the monster’s pH and which system is causing that change. If both systems are outside normal, one acidic and the other alkalotic, and the pH is within the normal range, then we have a fully compensated state, and will base the name on the fact that the pH will either be on the acidic or basic side of normal, and on which system is causing that deviation.
Just remember, if both systems are making the blood more acidic or basic, then it is not compensated, even though both are outside the normal range. In these cases it would be a respiratory and metabolic acidosis or a respiratory and metabolic alkalosis.
Let’s try a few more, now that we have all of the facts. A monster has a pH of 7.36, a PaCO2 of 50, and a bicarb level of 30. To use a systematic method, let’s first look at the pH. In this case, the pH is on the acidic side of normal, so his fur color will be pink, or light red. Next, his PaCO2 is too high, making the blood more acidic, so his shirt will be red, matching the reddish tint of his fur. Lastly, his bicarb level is also too high, but this is a base, so his pants will be blue, since his metabolic system is making his blood more alkalotic. Since it is his shirt that matches his acidic fur, we can call this a respiratory acidosis. Since his metabolic system is going in the opposite direction, trying to fix the problem, and in fact, has brought the pH back into the normal range, we can call this a fully compensated respiratory acidosis. If the bicarb and the PaCO2 levels stayed the same and the pH was lower than 7.35, such as 7.32, then he would have red fur, instead of pink, and we would call him a partially compensated respiratory acidosis.
What would you call an ABG monster with a pH of 7.48, a PaCO2 of 48, and a bicarb level of 31? The pH is higher than normal, so his fur will be a dark blue, indicating some type of alkalosis. The PaCO2 is high, making the blood more acidic, so his shirt will be red. The bicarb level is high, making the blood more alkalotic, so his pants will be blue. His fur is blue, his shirt is red, and his pants are blue. It is the pants that match the blue fur, so we have a metabolic alkalosis. His shirt clashes with his pants, so there is some type of compensation going on, but not enough to bring the pH back into the normal range, so we have a partially compensated metabolic alkalosis. If the pH had come back into the high end of normal and the other values remained the same, then we would have had a fully compensated metabolic alkalosis and light blue fur.
Let’s try one more example, pH of 7.29, PaCO2 of 50, and a bicarb level of 31. The fur will be red, since the pH is below normal. The shirt will be red, since the PaCO2 is above normal, and the pants will be blue, since the bicarb is above normal. Red fur and red shirt makes this a respiratory acidosis. Since the pants clash with the shirt, we will call it a partially compensated respiratory acidosis. Had the kidneys been able to bring the pH back into the normal range, we would have had a fully compensated respiratory acidosis and pink fur.
You should be able to work some of these on your own now. Here are a few ABG monsters for you to name yourself. The correct answers will follow if you get stuck.
1. pH = 7.50, PaCO2 = 20, bicarb = 26.
2. pH = 7.21, PaCO2 = 30, bicarb = 19.
3. pH = 7.36, PaCO2 = 51, bicarb = 31.
4. pH = 7.49, PaCO2 = 33, bicarb = 30.
1. Blue fur, blue shirt, white pants. This gives us a respiratory alkalosis with no compensation. A non-compensated respiratory alkalosis.
2. Red fur, blue shirt, red pants. This gives us a metabolic acidosis, with some respiratory compensation. A partially compensated metabolic acidosis.
3. Pink fur, red shirt, and blue pants. This gives us a respiratory acidosis that is fully compensated by the metabolic system. A fully compensated respiratory acidosis.
4. Blue fur, blue shirt, and blue pants. This gives us an alkalosis that is caused by both the respiratory and metabolic systems. A combination respiratory/metabolic alkalosis.
How did you do? If you still need work, you can make up your own ABG values and use this system to figure out what to call your monsters. Just remember to look at the fur color first, and then the shirt color, and lastly the pants color, to find which ones match. You can use the attached color coded reference sheet to check your results.
But wait a minute! I told you that my color was white because my pH was 7.40. What should you do if you come across an ABG monster with a pH of 7.40? You should be happy, because your ABG would be normal. There is very little chance that you will ever see an ABG with a perfect pH like mine, and even less of a chance if one or more of the other levels are not normal.
There is one last piece of information given on the ABG lab report, but don’t worry; this one is even easier than the rest. This piece of datum is the pO2 or the partial pressure of Oxygen in the arterial blood. The normal value for this is 80-100. If your ABG has a normal pO2 level, you call it whatever you would have called it based on the other ABG values. If the pO2 is less than 80, then you call it whatever the fur and clothes dictate, but you add the words, “with hypoxemia,” to indicate that the blood does not have as much Oxygen as it should. If the pO2 is greater than 100, you add the words, “with hyperoxemia” to your ABG name.
You now know everything you need to fully interpret any ABG monster. They may look scary, but they are really there to help you figure out what is wrong with the patient and which system is causing the problem. Good luck!March 23, 2014 at 5:54 PM #12532
A while back I had a catastrophic computer meltdown. This was not the final copy of this document, but it is the most recent one I could easily find.
EDIT: you can download the Word file for the lecture and the excel cheat sheet here: [Facebook group disbanded, see below for mighty nurse link]
RE-EDIT: Mighty Nurse has made a page for this. You can get the excel spreadsheet there, and then “click here” for the above lecture. http://www.mightynurse.com/monster-method-of-abg-interpretation/#sthash.Mr1BCaM5.dpufMarch 24, 2014 at 7:37 AM #12533
lellie1031MemberMarch 24, 2014 at 3:45 PM #12541
Lelie: spreadsheet mailed to both addresses. Enjoy.
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