What Is An Arterial Blood Gas (ABG)?
“Hi, I’m John from respiratory. I have to draw some of your blood.” This is how I usually introduce myself when I come to draw an arterial blood gas (ABG).
Since people with COPD often receive an ABG, I thought I would answer some of the most common questions I get.
“I already had my blood drawn. Can you just use that blood?”
No. The type of blood the laboratory tech drew was venous blood. What I need is arterial blood.
“Why can’t you just use venous blood?”
Usually, when a person from the laboratory draws your blood, it’s venous blood (from the veins). Veins contain deoxygenated blood that is returning to your heart and lungs to pick up oxygen. There are many veins in your body, some of which can be seen by looking at the surface of your skin. Some of these are relatively easy to draw blood from, such as the veins on the back of your hand or antecubital space (the opposite side of your elbow). By looking at these areas of your body, for instance, you might see some veins.
Deoxygenated blood tends to be darker in color, thereby giving veins that bluish tint. Most tests run in the lab can be run by using venous blood. An ABG is different in that it requires arterial blood.
“What is arterial blood?”
Once deoxygenated blood is returned to your heart through your venous system, it is then pumped to your lungs where it picks up oxygen. This freshly oxygenated blood returns to your heart, which in turn pumps it through your entire body through a series of arteries. This is how all the tissue of your body, including your heart and lungs, are oxygenated. This is the type of blood I want: freshly oxygenated.
“Why do you need freshly oxygenated blood?”
This allows us to determine how well your lungs are oxygenating all the tissues of your body.
“Is arterial blood harder to get?”
Yes – in a way. Arteries tend to be deeper under the skin than veins, and there aren’t nearly as many arteries as veins. However, the neat thing about arteries is that when you place your finger directly over them you can feel a pulse, so this kind of helps us locate your arteries.
“Where do you draw ABGs. I mean, where on my body?”
The best place to draw an ABG is from the radial artery. This is where they are drawn from, say, about 80% of the time. It is usually close enough to the surface so you can easily feel a pulse.
It’s located on the palm/wrist area, about a finger lengths in from your thumb side. If you want to you can try feeling it with your other hand. It’s best if you use your middle and index fingers. If you can’t feel it that’s fine, it just means it’s deeper. But most of the time it’s easy to feel.
“Do ABGs hurt?”
Let me put it this way. I had severe asthma as a kid. The first time I had an ABG drawn was when I was only 12-years-old. Yes, it was a little uncomfortable, but I handled it just fine. Of course, to be fair, I was pretty used to needles by this time in my life.
So, it can be uncomfortable, but I find that most patients handle it just fine. In fact, sometimes, I even have patients say things like, “That wasn’t nearly as bad as I thought.”
“But, my doctor said it will hurt. Is this true?”
The radial artery runs alongside the radial nerve. This is what makes the back of your wrist a sensitive area. Whether or not it will hurt sort of depends on the skill of the person drawing your blood and your own body. So, it can feel uncomfortable, but my job is to make is as comfortable as I can.
‘What does an ABG tell you?”
It measures the gases in your arteries.
- Arterial Oxygen Level. This will let us know if you need more oxygen than what is provided in the air around you. If needed, we can offer supplemental oxygen by using a nasal cannula or a variety of masks.
- Arterial Carbon Dioxide (CO2) Level. This will let us know how effective your lungs are at blowing off this waste product of cellular respiration. An elevated CO2 can indicate the severity of your disease, although it can also be used to help determine how best to treat you.
- Arterial Acid/ Base Level (pH). Your body is very good at maintaining a normal pH. However, severe COPD flare-ups can diminish your lung’s ability to blow off CO2. When this happens, CO2 can cause your arterial blood to become acidic. So, this can help determine how bad your COPD flare-up is and how best to treat you.
So, what does this mean?
The bottom line here is that an ABG can offer your doctor some valuable information as to how effective your lungs are at oxygenating your body and blowing off CO2. Normal ABG results will show your doctor you are doing all the right things and you should continue the course you are already on. Abnormal ABG results can help your doctor determine what adjustments to make in the course of your treatment regimen to get you feeling better.